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# SPDX-License-Identifier: GPL-2.0+
#
# (C) Copyright 2000 - 2013
# Wolfgang Denk, DENX Software Engineering, wd@denx.de.

Summary:
========

This directory contains the source code for U-Boot, a boot loader for
Embedded boards based on PowerPC, ARM, MIPS and several other
processors, which can be installed in a boot ROM and used to
code.

The development of U-Boot is closely related to Linux: some parts of
the source code originate in the Linux source tree, we have some
support booting of Linux images.

Some attention has been paid to make this software easily
configurable and extendable. For instance, all monitor commands are
implemented with the same call interface, so that it's very easy to
code (for instance hardware test utilities) to the monitor, you can

Status:
=======

In general, all boards for which a configuration option exists in the
Makefile have been tested to some extent and can be considered
"working". In fact, many of them are used in production systems.

In case of problems see the CHANGELOG file to find out who contributed
the specific port. In addition, there are various MAINTAINERS files
scattered throughout the U-Boot source identifying the people or
companies responsible for various boards and subsystems.

Note: As of August, 2010, there is no longer a CHANGELOG file in the
actual U-Boot source tree; however, it can be created dynamically
from the Git log using:

make CHANGELOG

Where to get help:
==================

In case you have questions about, problems with or contributions for
U-Boot, you should send a message to the U-Boot mailing list at
<u-boot@lists.denx.de>. There is also an archive of previous traffic
on the mailing list - please search the archive before asking FAQ's.

Where to get source code:
=========================

The U-Boot source code is maintained in the Git repository at
git://www.denx.de/git/u-boot.git ; you can browse it online at
http://www.denx.de/cgi-bin/gitweb.cgi?p=u-boot.git;a=summary

any version you might be interested in. Official releases are also
directory.

Pre-built (and tested) images are available from
ftp://ftp.denx.de/pub/u-boot/images/

Where we come from:
===================

- start from 8xxrom sources
- create PPCBoot project (http://sourceforge.net/projects/ppcboot)
- clean up code
- make it easier to add custom boards
- make it possible to add other [PowerPC] CPUs
- extend functions, especially:
* Provide extended interface to Linux boot loader
* network boot
* ATA disk / SCSI ... boot
- create ARMBoot project (http://sourceforge.net/projects/armboot)
- add other CPU families (starting with ARM)
- create U-Boot project (http://sourceforge.net/projects/u-boot)
- current project page: see http://www.denx.de/wiki/U-Boot

Names and Spelling:
===================

The "official" name of this project is "Das U-Boot". The spelling
"U-Boot" shall be used in all written text (documentation, comments
in source files etc.). Example:

This is the README file for the U-Boot project.

File names etc. shall be based on the string "u-boot". Examples:

include/asm-ppc/u-boot.h

#include <asm/u-boot.h>

Variable names, preprocessor constants etc. shall be either based on
the string "u_boot" or on "U_BOOT". Example:

U_BOOT_VERSION		u_boot_logo
IH_OS_U_BOOT		u_boot_hush_start

Versioning:
===========

Starting with the release in October 2008, the names of the releases
were changed from numerical release numbers without deeper meaning
into a time stamp based numbering. Regular releases are identified by
names consisting of the calendar year and month of the release date.
Additional fields (if present) indicate release candidates or bug fix
releases in "stable" maintenance trees.

Examples:
U-Boot v2009.11	    - Release November 2009
U-Boot v2009.11.1   - Release 1 in version November 2009 stable tree
U-Boot v2010.09-rc1 - Release candidate 1 for September 2010 release

Directory Hierarchy:
====================

/arch			Architecture specific files
/arc			Files generic to ARC architecture
/arm			Files generic to ARM architecture
/m68k			Files generic to m68k architecture
/microblaze		Files generic to microblaze architecture
/mips			Files generic to MIPS architecture
/nds32		Files generic to NDS32 architecture
/nios2		Files generic to Altera NIOS2 architecture
/openrisc		Files generic to OpenRISC architecture
/powerpc		Files generic to PowerPC architecture
/riscv		Files generic to RISC-V architecture
/sandbox		Files generic to HW-independent "sandbox"
/sh			Files generic to SH architecture
/x86			Files generic to x86 architecture
/api			Machine/arch independent API for external apps
/board			Board dependent files
/cmd			U-Boot commands functions
/common			Misc architecture independent functions
/configs		Board default configuration files
/disk			Code for disk drive partition handling
/doc			Documentation (don't expect too much)
/drivers		Commonly used device drivers
/dts			Contains Makefile for building internal U-Boot fdt.
/examples		Example code for standalone applications, etc.
/fs			Filesystem code (cramfs, ext2, jffs2, etc.)
/lib			Library routines generic to all architectures
/net			Networking code
/post			Power On Self Test
/scripts		Various build scripts and Makefiles
/test			Various unit test files
/tools			Tools to build S-Record or U-Boot images, etc.

Software Configuration:
=======================

Configuration is usually done using C preprocessor defines; the
rationale behind that is to avoid dead code whenever possible.

There are two classes of configuration variables:

* Configuration _OPTIONS_:
These are selectable by the user and have names beginning with
"CONFIG_".

* Configuration _SETTINGS_:
These depend on the hardware etc. and should not be meddled with if
you don't know what you're doing; they have names beginning with
"CONFIG_SYS_".

Previously, all configuration was done by hand, which involved creating
symbolic links and editing configuration files manually. More recently,
U-Boot has added the Kbuild infrastructure used by the Linux kernel,
allowing you to use the "make menuconfig" command to configure your
build.

Selection of Processor Architecture and Board Type:
---------------------------------------------------

For all supported boards there are ready-to-use default
configurations available; just type "make <board_name>_defconfig".

Example: For a TQM823L module type:

cd u-boot
make TQM823L_defconfig

Note: If you're looking for the default configuration file for a board
you're sure used to be there but is now missing, check the file
doc/README.scrapyard for a list of no longer supported boards.

Sandbox Environment:
--------------------

U-Boot can be built natively to run on a Linux host using the 'sandbox'
board. This allows feature development which is not board- or architecture-
specific to be undertaken on a native platform. The sandbox is also used to
run some of U-Boot's tests.

See doc/arch/index.rst for more details.

Board Initialisation Flow:
--------------------------

This is the intended start-up flow for boards. This should apply for both
SPL and U-Boot proper (i.e. they both follow the same rules).

Note: "SPL" stands for "Secondary Program Loader," which is explained in
more detail later in this file.

At present, SPL mostly uses a separate code path, but the function names
and roles of each function are the same. Some boards or architectures
may not conform to this.  At least most ARM boards which use
CONFIG_SPL_FRAMEWORK conform to this.

Execution typically starts with an architecture-specific (and possibly
CPU-specific) start.S file, such as:

- arch/arm/cpu/armv7/start.S
- arch/powerpc/cpu/mpc83xx/start.S
- arch/mips/cpu/start.S

and so on. From there, three functions are called; the purpose and
limitations of each of these functions are described below.

lowlevel_init():
- purpose: essential init to permit execution to reach board_init_f()
- no global_data or BSS
- there is no stack (ARMv7 may have one but it will soon be removed)
- must not set up SDRAM or use console
- must only do the bare minimum to allow execution to continue to
board_init_f()
- this is almost never needed
- return normally from this function

board_init_f():
- purpose: set up the machine ready for running board_init_r():
i.e. SDRAM and serial UART
- global_data is available
- stack is in SRAM
- BSS is not available, so you cannot use global/static variables,
only stack variables and global_data

Non-SPL-specific notes:
- dram_init() is called to set up DRAM. If already done in SPL this
can do nothing

SPL-specific notes:
- you can override the entire board_init_f() function with your own
version as needed.
- preloader_console_init() can be called here in extremis
- should set up SDRAM, and anything needed to make the UART work
- these is no need to clear BSS, it will be done by crt0.S
- for specific scenarios on certain architectures an early BSS *can*
be made available (via CONFIG_SPL_EARLY_BSS by moving the clearing
of BSS prior to entering board_init_f()) but doing so is discouraged.
Instead it is strongly recommended to architect any code changes
or additions such to not depend on the availability of BSS during
board_init_f() as indicated in other sections of this README to
maintain compatibility and consistency across the entire code base.
- must return normally from this function (don't call board_init_r()
directly)

Here the BSS is cleared. For SPL, if CONFIG_SPL_STACK_R is defined, then at
this point the stack and global_data are relocated to below
CONFIG_SPL_STACK_R_ADDR. For non-SPL, U-Boot is relocated to run at the top of
memory.

board_init_r():
- purpose: main execution, common code
- global_data is available
- SDRAM is available
- BSS is available, all static/global variables can be used
- execution eventually continues to main_loop()

Non-SPL-specific notes:
- U-Boot is relocated to the top of memory and is now running from
there.

SPL-specific notes:
- stack is optionally in SDRAM, if CONFIG_SPL_STACK_R is defined and
- preloader_console_init() can be called here - typically this is
done by selecting CONFIG_SPL_BOARD_INIT and then supplying a
spl_board_init() function containing this call
- loads U-Boot or (in falcon mode) Linux

Configuration Options:
----------------------

Configuration depends on the combination of board and CPU type; all
such information is kept in a configuration file
"include/configs/<board_name>.h".

Example: For a TQM823L module, all configuration settings are in
"include/configs/TQM823L.h".

Many of the options are named exactly as the corresponding Linux
kernel configuration options. The intention is to make it easier to
build a config tool - later.

- ARM Platform Bus Type(CCI):
CoreLink Cache Coherent Interconnect (CCI) is ARM BUS which
provides full cache coherency between two clusters of multi-core
CPUs and I/O coherency for devices and I/O masters

CONFIG_SYS_FSL_HAS_CCI400

Defined For SoC that has cache coherent interconnect
CCN-400

CONFIG_SYS_FSL_HAS_CCN504

Defined for SoC that has cache coherent interconnect CCN-504

The following options need to be configured:

- CPU Type:	Define exactly one, e.g. CONFIG_MPC85XX.

- Board Type:	Define exactly one, e.g. CONFIG_MPC8540ADS.

- 85xx CPU Options:
CONFIG_SYS_PPC64

Specifies that the core is a 64-bit PowerPC implementation (implements
the "64" category of the Power ISA). This is necessary for ePAPR
compliance, among other possible reasons.

CONFIG_SYS_FSL_TBCLK_DIV

Defines the core time base clock divider ratio compared to the
system clock.  On most PQ3 devices this is 8, on newer QorIQ
devices it can be 16 or 32.  The ratio varies from SoC to Soc.

CONFIG_SYS_FSL_PCIE_COMPAT

Defines the string to utilize when trying to match PCIe device
tree nodes for the given platform.

CONFIG_SYS_FSL_ERRATUM_A004510

Enables a workaround for erratum A004510.  If set,
then CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV and
CONFIG_SYS_FSL_CORENET_SNOOPVEC_COREONLY must be set.

CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV
CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV2 (optional)

Defines one or two SoC revisions (low 8 bits of SVR)
for which the A004510 workaround should be applied.

The rest of SVR is either not relevant to the decision
of whether the erratum is present (e.g. p2040 versus
p2041) or is implied by the build target, which controls
whether CONFIG_SYS_FSL_ERRATUM_A004510 is set.

this erratum.

CONFIG_A003399_NOR_WORKAROUND
Enables a workaround for IFC erratum A003399. It is only
required during NOR boot.

CONFIG_A008044_WORKAROUND
Enables a workaround for T1040/T1042 erratum A008044. It is only
required during NAND boot and valid for Rev 1.0 SoC revision

CONFIG_SYS_FSL_CORENET_SNOOPVEC_COREONLY

This is the value to write into CCSR offset 0x18600
according to the A004510 workaround.

This value denotes start offset of DDR memory which is
connected exclusively to the DSP cores.

This value denotes start offset of M2 memory
which is directly connected to the DSP core.

This value denotes start offset of M3 memory which is directly
connected to the DSP core.

CONFIG_SYS_FSL_DSP_CCSRBAR_DEFAULT
This value denotes start offset of DSP CCSR space.

CONFIG_SYS_FSL_SINGLE_SOURCE_CLK
Single Source Clock is clocking mode present in some of FSL SoC's.
In this mode, a single differential clock is used to supply
clocks to the sysclock, ddrclock and usbclock.

CONFIG_SYS_CPC_REINIT_F
This CONFIG is defined when the CPC is configured as SRAM at the
time of U-Boot entry and is required to be re-initialized.

CONFIG_DEEP_SLEEP
Indicates this SoC supports deep sleep feature. If deep sleep is
supported, core will start to execute uboot when wakes up.

- Generic CPU options:
CONFIG_SYS_BIG_ENDIAN, CONFIG_SYS_LITTLE_ENDIAN

Defines the endianess of the CPU. Implementation of those
values is arch specific.

CONFIG_SYS_FSL_DDR
Freescale DDR driver in use. This type of DDR controller is
found in mpc83xx, mpc85xx, mpc86xx as well as some ARM core
SoCs.

Freescale DDR memory-mapped register base.

CONFIG_SYS_FSL_DDR_EMU
Specify emulator support for DDR. Some DDR features such as
deskew training are not available.

CONFIG_SYS_FSL_DDRC_GEN1
Freescale DDR1 controller.

CONFIG_SYS_FSL_DDRC_GEN2
Freescale DDR2 controller.

CONFIG_SYS_FSL_DDRC_GEN3
Freescale DDR3 controller.

CONFIG_SYS_FSL_DDRC_GEN4
Freescale DDR4 controller.

CONFIG_SYS_FSL_DDRC_ARM_GEN3
Freescale DDR3 controller for ARM-based SoCs.

CONFIG_SYS_FSL_DDR1
Board config to use DDR1. It can be enabled for SoCs with
Freescale DDR1 or DDR2 controllers, depending on the board
implemetation.

CONFIG_SYS_FSL_DDR2
Board config to use DDR2. It can be enabled for SoCs with
Freescale DDR2 or DDR3 controllers, depending on the board
implementation.

CONFIG_SYS_FSL_DDR3
Board config to use DDR3. It can be enabled for SoCs with
Freescale DDR3 or DDR3L controllers.

CONFIG_SYS_FSL_DDR3L
Board config to use DDR3L. It can be enabled for SoCs with
DDR3L controllers.

CONFIG_SYS_FSL_DDR4
Board config to use DDR4. It can be enabled for SoCs with
DDR4 controllers.

CONFIG_SYS_FSL_IFC_BE
Defines the IFC controller register space as Big Endian

CONFIG_SYS_FSL_IFC_LE
Defines the IFC controller register space as Little Endian

CONFIG_SYS_FSL_IFC_CLK_DIV
Defines divider of platform clock(clock input to IFC controller).

CONFIG_SYS_FSL_LBC_CLK_DIV
Defines divider of platform clock(clock input to eLBC controller).

CONFIG_SYS_FSL_PBL_PBI
It enables addition of RCW (Power on reset configuration) in built image.

CONFIG_SYS_FSL_PBL_RCW
It adds PBI(pre-boot instructions) commands in u-boot build image.
PBI commands can be used to configure SoC before it starts the execution.

CONFIG_SYS_FSL_DDR_BE
Defines the DDR controller register space as Big Endian

CONFIG_SYS_FSL_DDR_LE
Defines the DDR controller register space as Little Endian

CONFIG_SYS_FSL_DDR_SDRAM_BASE_PHY
Physical address from the view of DDR controllers. It is the
same as CONFIG_SYS_DDR_SDRAM_BASE for  all Power SoCs. But
it could be different for ARM SoCs.

CONFIG_SYS_FSL_DDR_INTLV_256B
DDR controller interleaving on 256-byte. This is a special
SoCs with ARM core.

CONFIG_SYS_FSL_DDR_MAIN_NUM_CTRLS
Number of controllers used as main memory.

CONFIG_SYS_FSL_OTHER_DDR_NUM_CTRLS
Number of controllers used for other than main memory.

CONFIG_SYS_FSL_HAS_DP_DDR
Defines the SoC has DP-DDR used for DPAA.

CONFIG_SYS_FSL_SEC_BE
Defines the SEC controller register space as Big Endian

CONFIG_SYS_FSL_SEC_LE
Defines the SEC controller register space as Little Endian

- MIPS CPU options:
CONFIG_SYS_INIT_SP_OFFSET

Offset relative to CONFIG_SYS_SDRAM_BASE for initial stack
pointer. This is needed for the temporary stack before
relocation.

CONFIG_XWAY_SWAP_BYTES

Enable compilation of tools/xway-swap-bytes needed for Lantiq
XWAY SoCs for booting from NOR flash. The U-Boot image needs to
be swapped if a flash programmer is used.

- ARM options:
CONFIG_SYS_EXCEPTION_VECTORS_HIGH

Select high exception vectors of the ARM core, e.g., do not
clear the V bit of the c1 register of CP15.

COUNTER_FREQUENCY
Generic timer clock source frequency.

COUNTER_FREQUENCY_REAL
Generic timer clock source frequency if the real clock is
different from COUNTER_FREQUENCY, and can only be determined
at run time.

- Tegra SoC options:
CONFIG_TEGRA_SUPPORT_NON_SECURE

Support executing U-Boot in non-secure (NS) mode. Certain
impossible actions will be skipped if the CPU is in NS mode,
such as ARM architectural timer initialization.

- Linux Kernel Interface:
CONFIG_CLOCKS_IN_MHZ

U-Boot stores all clock information in Hz
internally. For binary compatibility with older Linux
kernels (which expect the clocks passed in the
bd_info data to be in MHz) the environment variable
"clocks_in_mhz" can be defined so that U-Boot
converts clock data to MHZ before passing it to the
Linux kernel.
When CONFIG_CLOCKS_IN_MHZ is defined, a definition of
"clocks_in_mhz=1" is automatically included in the
default environment.

CONFIG_MEMSIZE_IN_BYTES		[relevant for MIPS only]

When transferring memsize parameter to Linux, some versions
expect it to be in bytes, others in MB.
Define CONFIG_MEMSIZE_IN_BYTES to make it in bytes.

CONFIG_OF_LIBFDT

New kernel versions are expecting firmware settings to be
passed using flattened device trees (based on open firmware
concepts).

CONFIG_OF_LIBFDT
* New libfdt-based support
* The bootm command automatically updates the fdt

OF_TBCLK - The timebase frequency.
OF_STDOUT_PATH - The path to the console device

boards with QUICC Engines require OF_QE to set UCC MAC

CONFIG_OF_BOARD_SETUP

Board code has addition modification that it wants to make
to the flat device tree before handing it off to the kernel

CONFIG_OF_SYSTEM_SETUP

Other code has addition modification that it wants to make
to the flat device tree before handing it off to the kernel.
This causes ft_system_setup() to be called before booting
the kernel.

CONFIG_OF_IDE_FIXUP

U-Boot can detect if an IDE device is present or not.
If not, and this new config option is activated, U-Boot
removes the ATA node from the DTS before booting Linux,
so the Linux IDE driver does not probe the device and
crash. This is needed for buggy hardware (uc101) where
no pull down resistor is connected to the signal IDE5V_DD7.

CONFIG_MACH_TYPE	[relevant for ARM only][mandatory]

This setting is mandatory for all boards that have only one
machine type and must be used to specify the machine type
number as it appears in the ARM machine registry
(see http://www.arm.linux.org.uk/developer/machines/).
Only boards that have multiple machine types supported
in a single configuration file and the machine type is
runtime discoverable, do not have to use this setting.

- vxWorks boot parameters:

bootvx constructs a valid bootline using the following
serverip, gatewayip, hostname, othbootargs.
It loads the vxWorks image pointed bootfile.

Note: If a "bootargs" environment is defined, it will overwride
the defaults discussed just above.

- Cache Configuration:
CONFIG_SYS_L2CACHE_OFF- Do not enable L2 cache in U-Boot

- Cache Configuration for ARM:
CONFIG_SYS_L2_PL310 - Enable support for ARM PL310 L2 cache
controller
CONFIG_SYS_PL310_BASE - Physical base address of PL310
controller register space

- Serial Ports:
CONFIG_PL010_SERIAL

Define this if you want support for Amba PrimeCell PL010 UARTs.

CONFIG_PL011_SERIAL

Define this if you want support for Amba PrimeCell PL011 UARTs.

CONFIG_PL011_CLOCK

If you have Amba PrimeCell PL011 UARTs, set this variable to
the clock speed of the UARTs.

CONFIG_PL01x_PORTS

If you have Amba PrimeCell PL010 or PL011 UARTs on your board,
define this to a list of base addresses for each (supported)
port. See e.g. include/configs/versatile.h

CONFIG_SERIAL_HW_FLOW_CONTROL

Define this variable to enable hw flow control in serial driver.
Current user of this option is drivers/serial/nsl16550.c driver

- Console Baudrate:
CONFIG_BAUDRATE - in bps
Select one of the baudrates listed in
CONFIG_SYS_BAUDRATE_TABLE, see below.

- Autoboot Command:
CONFIG_BOOTCOMMAND
Only needed when CONFIG_BOOTDELAY is enabled;
define a command string that is automatically executed
when no character is read on the console interface
within "Boot Delay" after reset.

CONFIG_RAMBOOT and CONFIG_NFSBOOT
The value of these goes into the environment as
"ramboot" and "nfsboot" respectively, and can be used
as a convenience, when switching between booting from
RAM and NFS.

If defined to 1, all characters received during a
echoed back. This might be needed by some terminal
emulations (like "cu"), but may as well just take
time on others. This setting #define's the initial
value of the "loads_echo" environment variable.

- Kgdb Serial Baudrate: (if CONFIG_CMD_KGDB is defined)
CONFIG_KGDB_BAUDRATE
Select one of the baudrates listed in
CONFIG_SYS_BAUDRATE_TABLE, see below.

- Removal of commands
If no commands are needed to boot, you can disable
CONFIG_CMDLINE to remove them. In this case, the command line
will not be available, and when U-Boot wants to execute the
boot command (on start-up) it will call board_run_command()
instead. This can reduce image size significantly for very
simple boot procedures.

- Regular expression support:
CONFIG_REGEX
If this variable is defined, U-Boot is linked against
the SLRE (Super Light Regular Expression) library,
which adds regex support to some commands, as for
example "env grep" and "setexpr".

- Device tree:
CONFIG_OF_CONTROL
If this variable is defined, U-Boot will use a device tree
to configure its devices, instead of relying on statically
compiled #defines in the board file. This option is
experimental and only available on a few boards. The device
tree is available in the global data as gd->fdt_blob.

U-Boot needs to get its device tree from somewhere. This can
be done using one of the three options below:

CONFIG_OF_EMBED
If this variable is defined, U-Boot will embed a device tree
binary in its image. This device tree file should be in the
board directory and called <soc>-<board>.dts. The binary file
is then picked up in board_init_f() and made available through
the global data structure as gd->fdt_blob.

CONFIG_OF_SEPARATE
If this variable is defined, U-Boot will build a device tree
binary. It will be called u-boot.dtb. Architecture-specific
code will locate it at run-time. Generally this works by:

cat u-boot.bin u-boot.dtb >image.bin

and in fact, U-Boot does this for you, creating a file called
u-boot-dtb.bin which is useful in the common case. You can
still use the individual files if you need something more
exotic.

CONFIG_OF_BOARD
If this variable is defined, U-Boot will use the device tree
provided by the board at runtime instead of embedding one with
the image. Only boards defining board_fdt_blob_setup() support
this option (see include/fdtdec.h file).

- Watchdog:
CONFIG_WATCHDOG
If this variable is defined, it enables watchdog
support for the SoC. There must be support in the SoC
specific code for a watchdog. For the 8xx
CPUs, the SIU Watchdog feature is enabled in the SYPCR
register.  When supported for a specific SoC is
available, then no further board specific code should
be needed to use it.

CONFIG_HW_WATCHDOG
When using a watchdog circuitry external to the used
SoC, then define this variable and provide board
specific code for the "hw_watchdog_reset" function.

- Real-Time Clock:

When CONFIG_CMD_DATE is selected, the type of the RTC
has to be selected, too. Define exactly one of the
following options:

CONFIG_RTC_PCF8563	- use Philips PCF8563 RTC
CONFIG_RTC_MC13XXX	- use MC13783 or MC13892 RTC
CONFIG_RTC_MC146818	- use MC146818 RTC
CONFIG_RTC_DS1307	- use Maxim, Inc. DS1307 RTC
CONFIG_RTC_DS1337	- use Maxim, Inc. DS1337 RTC
CONFIG_RTC_DS1338	- use Maxim, Inc. DS1338 RTC
CONFIG_RTC_DS1339	- use Maxim, Inc. DS1339 RTC
CONFIG_RTC_DS164x	- use Dallas DS164x RTC
CONFIG_RTC_ISL1208	- use Intersil ISL1208 RTC
CONFIG_RTC_MAX6900	- use Maxim, Inc. MAX6900 RTC
CONFIG_RTC_DS1337_NOOSC	- Turn off the OSC output for DS1337
CONFIG_SYS_RV3029_TCR	- enable trickle charger on
RV3029 RTC.

Note that if the RTC uses I2C, then the I2C interface
must also be configured. See I2C Support, below.

- GPIO Support:
CONFIG_PCA953X		- use NXP's PCA953X series I2C GPIO

The CONFIG_SYS_I2C_PCA953X_WIDTH option specifies a list of
chip-ngpio pairs that tell the PCA953X driver the number of
pins supported by a particular chip.

Note that if the GPIO device uses I2C, then the I2C interface
must also be configured. See I2C Support, below.

- I/O tracing:
When CONFIG_IO_TRACE is selected, U-Boot intercepts all I/O
accesses and can checksum them or write a list of them out
to memory. See the 'iotrace' command for details. This is
useful for testing device drivers since it can confirm that
the driver behaves the same way before and after a code
change. Currently this is supported on sandbox and arm. To
to the bottom of arch/<arch>/include/asm/io.h and test.

Example output from the 'iotrace stats' command is below.
Note that if the trace buffer is exhausted, the checksum will
still continue to operate.

iotrace is enabled
Size:   00010000	(buffer size)
Offset: 00000120	(current buffer offset)
Output: 10000120	(start + offset)
Count:  00000018	(number of trace records)
CRC32:  9526fb66	(CRC32 of all trace records)

- Timestamp Support:

When CONFIG_TIMESTAMP is selected, the timestamp
(date and time) of an image is printed by image
commands like bootm or iminfo. This option is
automatically enabled when you select CONFIG_CMD_DATE .

- Partition Labels (disklabels) Supported:
Zero or more of the following:
CONFIG_MAC_PARTITION   Apple's MacOS partition table.
CONFIG_ISO_PARTITION   ISO partition table, used on CDROM etc.
CONFIG_EFI_PARTITION   GPT partition table, common when EFI is the
bootloader.  Note 2TB partition limit; see
disk/part_efi.c
CONFIG_SCSI) you must configure support for at
least one non-MTD partition type as well.

- IDE Reset method:
CONFIG_IDE_RESET_ROUTINE - this is defined in several
board configurations files but used nowhere!

CONFIG_IDE_RESET - is this is defined, IDE Reset will
be performed by calling the function
ide_set_reset(int reset)
which has to be defined in a board specific file

- ATAPI Support:
CONFIG_ATAPI

Set this to enable ATAPI support.

- LBA48 Support
CONFIG_LBA48

Set this to enable support for disks larger than 137GB
Also look at CONFIG_SYS_64BIT_LBA.
Whithout these , LBA48 support uses 32bit variables and will 'only'
support disks up to 2.1TB.

CONFIG_SYS_64BIT_LBA:
When enabled, makes the IDE subsystem use 64bit sector addresses.
Default is 32bit.

- SCSI Support:
CONFIG_SYS_SCSI_MAX_LUN [8], CONFIG_SYS_SCSI_MAX_SCSI_ID [7] and
CONFIG_SYS_SCSI_MAX_DEVICE [CONFIG_SYS_SCSI_MAX_SCSI_ID *
CONFIG_SYS_SCSI_MAX_LUN] can be adjusted to define the
maximum numbers of LUNs, SCSI ID's and target
devices.

The environment variable 'scsidevs' is set to the number of
SCSI devices found during the last scan.

- NETWORK Support (PCI):
CONFIG_E1000
Support for Intel 8254x/8257x gigabit chips.

CONFIG_E1000_SPI
Utility code for direct access to the SPI bus on Intel 8257x.
This does not do anything useful unless you set at least one
of CONFIG_CMD_E1000 or CONFIG_E1000_SPI_GENERIC.

CONFIG_E1000_SPI_GENERIC
Allow generic access to the SPI bus on the Intel 8257x, for
example with the "sspi" command.

CONFIG_EEPRO100
Support for Intel 82557/82559/82559ER chips.
Optional CONFIG_EEPRO100_SROM_WRITE enables EEPROM
write routine for first time initialisation.

CONFIG_TULIP
Support for Digital 2114x chips.
Optional CONFIG_TULIP_SELECT_MEDIA for board specific
modem chip initialisation (KS8761/QS6611).

CONFIG_NATSEMI
Support for National dp83815 chips.

CONFIG_NS8382X
Support for National dp8382[01] gigabit chips.

- NETWORK Support (other):

CONFIG_DRIVER_AT91EMAC
Support for AT91RM9200 EMAC.

CONFIG_RMII
Define this to use reduced MII inteface

CONFIG_DRIVER_AT91EMAC_QUIET
If this defined, the driver is quiet.
The driver doen't show link status messages.

CONFIG_CALXEDA_XGMAC
Support for the Calxeda XGMAC device

CONFIG_LAN91C96
Support for SMSC's LAN91C96 chips.

CONFIG_LAN91C96_USE_32_BIT
Define this to enable 32 bit addressing

CONFIG_SMC91111
Support for SMSC's LAN91C111 chip

CONFIG_SMC91111_BASE
Define this to hold the physical address
of the device (I/O space)

CONFIG_SMC_USE_32_BIT
Define this if data bus is 32 bits

CONFIG_SMC_USE_IOFUNCS
Define this to use i/o functions instead of macros
(some hardware wont work with macros)

CONFIG_SYS_DAVINCI_EMAC_PHY_COUNT
Define this if you have more then 3 PHYs.

CONFIG_FTGMAC100
Support for Faraday's FTGMAC100 Gigabit SoC Ethernet

CONFIG_FTGMAC100_EGIGA
Define this to use GE link update with gigabit PHY.
Define this if FTGMAC100 is connected to gigabit PHY.
If your system has 10/100 PHY only, it might not occur
wrong behavior. Because PHY usually return timeout or
useless data when polling gigabit status and gigabit
control registers. This behavior won't affect the

CONFIG_SH_ETHER
Support for Renesas on-chip Ethernet controller

CONFIG_SH_ETHER_USE_PORT
Define the number of ports to be used

CONFIG_SH_ETHER_CACHE_WRITEBACK
If this option is set, the driver enables cache flush.

- TPM Support:
CONFIG_TPM
Support TPM devices.

CONFIG_TPM_TIS_INFINEON
Support for Infineon i2c bus TPM devices. Only one device
per system is supported at this time.

CONFIG_TPM_TIS_I2C_BURST_LIMITATION
Define the burst count bytes upper limit

CONFIG_TPM_ST33ZP24
Support for STMicroelectronics TPM devices. Requires DM_TPM support.

CONFIG_TPM_ST33ZP24_I2C
Support for STMicroelectronics ST33ZP24 I2C devices.
Requires TPM_ST33ZP24 and I2C.

CONFIG_TPM_ST33ZP24_SPI
Support for STMicroelectronics ST33ZP24 SPI devices.
Requires TPM_ST33ZP24 and SPI.

CONFIG_TPM_ATMEL_TWI
Support for Atmel TWI TPM device. Requires I2C support.

CONFIG_TPM_TIS_LPC
Support for generic parallel port TPM devices. Only one device
per system is supported at this time.

Base address where the generic TPM device is mapped
to. Contemporary x86 systems usually map it at
0xfed40000.

CONFIG_TPM
Define this to enable the TPM support library which provides
functional interfaces to some TPM commands.
Requires support for a TPM device.

CONFIG_TPM_AUTH_SESSIONS
Define this to enable authorized functions in the TPM library.
Requires CONFIG_TPM and CONFIG_SHA1.

- USB Support:
At the moment only the UHCI host controller is
supported (PIP405, MIP405); define
CONFIG_USB_UHCI to enable it.
define CONFIG_USB_KEYBOARD to enable the USB Keyboard
and define CONFIG_USB_STORAGE to enable the USB
storage devices.
Note:
Supported are USB Keyboards and USB Floppy drives
(TEAC FD-05PUB).

CONFIG_USB_EHCI_TXFIFO_THRESH enables setting of the
txfilltuning field in the EHCI controller on reset.

HW module registers.

- USB Device:
Define the below if you wish to use the USB console.
Once firmware is rebuilt from a serial console issue the
command "setenv stdin usbtty; setenv stdout usbtty" and
attach your USB cable. The Unix command "dmesg" should print
it has found a new device. The environment variable usbtty
can be set to gserial or cdc_acm to enable your device to
appear to a USB host as a Linux gserial device or a
Common Device Class Abstract Control Model serial device.
If you select usbtty = gserial you should be able to enumerate
a Linux host by
# modprobe usbserial vendor=0xVendorID product=0xProductID
else if using cdc_acm, simply setting the environment
variable usbtty to be cdc_acm should suffice. The following
might be defined in YourBoardName.h

CONFIG_USB_DEVICE
Define this to build a UDC device

CONFIG_USB_TTY
Define this to have a tty type of device available to
talk to the UDC device

CONFIG_USBD_HS
Define this to enable the high speed support for usb
device and usbtty. If this feature is enabled, a routine
int is_usbd_high_speed(void)
also needs to be defined by the driver to dynamically poll
whether the enumeration has succeded at high speed or full
speed.

CONFIG_SYS_CONSOLE_IS_IN_ENV
Define this if you want stdin, stdout &/or stderr to
be set to usbtty.

If you have a USB-IF assigned VendorID then you may wish to
define your own vendor specific values either in BoardName.h
or directly in usbd_vendor_info.h. If you don't define
CONFIG_USBD_MANUFACTURER, CONFIG_USBD_PRODUCT_NAME,
CONFIG_USBD_VENDORID and CONFIG_USBD_PRODUCTID, then U-Boot
should pretend to be a Linux device to it's target host.

CONFIG_USBD_MANUFACTURER
Define this string as the name of your company for
- CONFIG_USBD_MANUFACTURER "my company"

CONFIG_USBD_PRODUCT_NAME
Define this string as the name of your product
- CONFIG_USBD_PRODUCT_NAME "acme usb device"

CONFIG_USBD_VENDORID
Define this as your assigned Vendor ID from the USB
Implementors Forum. This *must* be a genuine Vendor ID
to avoid polluting the USB namespace.
- CONFIG_USBD_VENDORID 0xFFFF

CONFIG_USBD_PRODUCTID
Define this as the unique Product ID
- CONFIG_USBD_PRODUCTID 0xFFFF

- ULPI Layer Support:
The ULPI (UTMI Low Pin (count) Interface) PHYs are supported via
the generic ULPI layer. The generic layer accesses the ULPI PHY
via the platform viewport, so you need both the genric layer and
the viewport enabled. Currently only Chipidea/ARC based
viewport is supported.
To enable the ULPI layer support, define CONFIG_USB_ULPI and
CONFIG_USB_ULPI_VIEWPORT in your board configuration file.
If your ULPI phy needs a different reference clock than the
standard 24 MHz then you have to define CONFIG_ULPI_REF_CLK to
the appropriate value in Hz.

- MMC Support:
The MMC controller on the Intel PXA is supported. To
enable this define CONFIG_MMC. The MMC can be
accessed from the boot prompt by mapping the device
to physical memory similar to flash. Command line is
enabled with CONFIG_CMD_MMC. The MMC driver also works with
the FAT fs. This is enabled with CONFIG_CMD_FAT.

CONFIG_SH_MMCIF
Support for Renesas on-chip MMCIF controller

Define the base address of MMCIF registers

CONFIG_SH_MMCIF_CLK
Define the clock frequency for MMCIF

- USB Device Firmware Update (DFU) class support:
CONFIG_DFU_OVER_USB
This enables the USB portion of the DFU USB class

CONFIG_DFU_NAND
This enables support for exposing NAND devices via DFU.

CONFIG_DFU_RAM
This enables support for exposing RAM via DFU.
Note: DFU spec refer to non-volatile memory usage, but
allow usages beyond the scope of spec - here RAM usage,
one that would help mostly the developer.

CONFIG_SYS_DFU_DATA_BUF_SIZE
Dfu transfer uses a buffer before writing data to the
raw storage device. Make the size (in bytes) of this buffer
configurable. The size of this buffer is also configurable
through the "dfu_bufsiz" environment variable.

CONFIG_SYS_DFU_MAX_FILE_SIZE
When updating files rather than the raw storage device,
we use a static buffer to copy the file into and then write
the buffer once we've been given the whole file.  Define
this to the maximum filesize (in bytes) for the buffer.
Default is 4 MiB if undefined.

DFU_DEFAULT_POLL_TIMEOUT
Poll timeout [ms], is the timeout a device can send to the
host. The host must wait for this timeout before sending
a subsequent DFU_GET_STATUS request to the device.

DFU_MANIFEST_POLL_TIMEOUT
Poll timeout [ms], which the device sends to the host when
entering dfuMANIFEST state. Host waits this timeout, before
sending again an USB request to the device.

- Journaling Flash filesystem support:
CONFIG_JFFS2_NAND
Define these for a default partition on a NAND device

CONFIG_SYS_JFFS2_FIRST_SECTOR,
CONFIG_SYS_JFFS2_FIRST_BANK, CONFIG_SYS_JFFS2_NUM_BANKS
Define these for a default partition on a NOR device

- Keyboard Support:
See Kconfig help for available keyboard drivers.

CONFIG_KEYBOARD

Define this to enable a custom keyboard support.
This simply calls drv_keyboard_init() which must be
defined in your board-specific files. This option is deprecated
and is only used by novena. For new boards, use driver model

- Video support:
CONFIG_FSL_DIU_FB
Enable the Freescale DIU video driver.	Reference boards for
SOCs that have a DIU should define this macro to enable DIU
support, and should also define these other macros:

CONFIG_VIDEO
CONFIG_CFB_CONSOLE
CONFIG_VIDEO_SW_CURSOR
CONFIG_VGA_AS_SINGLE_DEVICE
CONFIG_VIDEO_LOGO
CONFIG_VIDEO_BMP_LOGO

The DIU driver will look for the 'video-mode' environment
variable, and if defined, enable the DIU as a console during
boot.  See the documentation file doc/README.video for a
description of this variable.

- LCD Support:	CONFIG_LCD

Define this to enable LCD support (for output to LCD
display); also select one of the supported displays
by defining one of these:

CONFIG_ATMEL_LCD:

HITACHI TX09D70VM1CCA, 3.5", 240x320.

CONFIG_NEC_NL6448AC33:

NEC NL6448AC33-18. Active, color, single scan.

CONFIG_NEC_NL6448BC20

NEC NL6448BC20-08. 6.5", 640x480.
Active, color, single scan.

CONFIG_NEC_NL6448BC33_54

NEC NL6448BC33-54. 10.4", 640x480.
Active, color, single scan.

CONFIG_SHARP_16x9

Sharp 320x240. Active, color, single scan.
It isn't 16x9, and I am not sure what it is.

CONFIG_SHARP_LQ64D341

Sharp LQ64D341 display, 640x480.
Active, color, single scan.

CONFIG_HLD1045

HLD1045 display, 640x480.
Active, color, single scan.

CONFIG_OPTREX_BW

Optrex	 CBL50840-2 NF-FW 99 22 M5
or
Hitachi	 LMG6912RPFC-00T
or
Hitachi	 SP14Q002

320x240. Black & white.

CONFIG_LCD_ALIGNMENT

Normally the LCD is page-aligned (typically 4KB). If this is
defined then the LCD will be aligned to this value instead.
For ARM it is sometimes useful to use MMU_SECTION_SIZE
here, since it is cheaper to change data cache settings on
a per-section basis.

CONFIG_LCD_ROTATION

Sometimes, for example if the display is mounted in portrait
mode or even if it's mounted landscape but rotated by 180degree,
we need to rotate our content of the display relative to the
framebuffer, so that user can read the messages which are
printed out.
Once CONFIG_LCD_ROTATION is defined, the lcd_console will be
initialized with a given rotation from "vl_rot" out of
"vidinfo_t" which is provided by the board specific code.
The value for vl_rot is coded as following (matching to
fbcon=rotate:<n> linux-kernel commandline):
0 = no rotation respectively 0 degree
1 = 90 degree rotation
2 = 180 degree rotation
3 = 270 degree rotation

If CONFIG_LCD_ROTATION is not defined, the console will be
initialized with 0degree rotation.

CONFIG_LCD_BMP_RLE8

Support drawing of RLE8-compressed bitmaps on the LCD.

CONFIG_I2C_EDID

Enables an 'i2c edid' command which can read EDID
information over I2C from an attached LCD display.

- Splash Screen Support: CONFIG_SPLASH_SCREEN

If this option is set, the environment is checked for
a variable "splashimage". If found, the usual display
of logo, copyright and system information on the LCD
is suppressed and the BMP image at the address
console is redirected to the "nulldev", too. This
allows for a "silent" boot where a splash screen is

CONFIG_SPLASHIMAGE_GUARD

If this option is set, then U-Boot will prevent the environment
variable "splashimage" from being set to a problematic address
This option is useful for targets where, due to alignment
restrictions, an improperly aligned BMP image will cause a data
abort. If you think you will not have problems with unaligned
accesses (for example because your toolchain prevents them)
there is no need to set this option.

CONFIG_SPLASH_SCREEN_ALIGN

If this option is set the splash image can be freely positioned
on the screen. Environment variable "splashpos" specifies the
position as "x,y". If a positive number is given it is used as
number of pixel from left/top. If a negative number is given it
is used as number of pixel from right/bottom. You can also
specify 'm' for centering the image.

Example:
setenv splashpos m,m
=> image at center of screen

setenv splashpos 30,20
=> image at x = 30 and y = 20

setenv splashpos -10,m
=> vertically centered image
at x = dspWidth - bmpWidth - 9

- Gzip compressed BMP image support: CONFIG_VIDEO_BMP_GZIP

If this option is set, additionally to standard BMP
images, gzipped BMP images can be displayed via the
splashscreen support or the bmp command.

- Run length encoded BMP image (RLE8) support: CONFIG_VIDEO_BMP_RLE8

If this option is set, 8-bit RLE compressed BMP images
can be displayed via the splashscreen support or the
bmp command.

- Compression support:
CONFIG_GZIP

Enabled by default to support gzip compressed images.

CONFIG_BZIP2

If this option is set, support for bzip2 compressed
images is included. If not, only uncompressed and gzip
compressed images are supported.

NOTE: the bzip2 algorithm requires a lot of RAM, so
the malloc area (as defined by CONFIG_SYS_MALLOC_LEN) should
be at least 4MB.

- MII/PHY support:
CONFIG_PHY_CLOCK_FREQ (ppc4xx)

The clock frequency of the MII bus

CONFIG_PHY_RESET_DELAY

Some PHY like Intel LXT971A need extra delay after
reset before any MII register access is possible.
For such PHY, set this option to the usec delay
required. (minimum 300usec for LXT971A)

CONFIG_PHY_CMD_DELAY (ppc4xx)

Some PHY like Intel LXT971A need extra delay after
command issued before MII status register can be read

Define a default value for the IP address to use for
the default Ethernet interface, in case this is not
determined through e.g. bootp.

CONFIG_SERVERIP

Defines a default value for the IP address of a TFTP
server to contact when using the "tftboot" command.
(Environment variable "serverip")

for passing to bootargs (like Linux's netconsole option)

CONFIG_GATEWAYIP

Defines a default value for the IP address of the
default router where packets to other networks are
sent to.
(Environment variable "gatewayip")

Defines a default value for the subnet mask (or
routing prefix) which is used to determine if an IP
address belongs to the local subnet or needs to be
forwarded through a router.

- BOOTP Recovery Mode:
CONFIG_BOOTP_RANDOM_DELAY

If you have many targets in a network that try to
boot using BOOTP, you may want to avoid that all
systems send out BOOTP requests at precisely the same
moment (which would happen for instance at recovery
from a power failure, when all systems will try to
boot, thus flooding the BOOTP server. Defining
CONFIG_BOOTP_RANDOM_DELAY causes a random delay to be
inserted before sending out BOOTP requests. The
following delays are inserted then:

1st BOOTP request:	delay 0 ... 1 sec
2nd BOOTP request:	delay 0 ... 2 sec
3rd BOOTP request:	delay 0 ... 4 sec
4th and following
BOOTP requests:		delay 0 ... 8 sec

CONFIG_BOOTP_ID_CACHE_SIZE

BOOTP packets are uniquely identified using a 32-bit ID. The
server will copy the ID from client requests to responses and
U-Boot will use this to determine if it is the destination of
an incoming response. Some servers will check that addresses
aren't in use before handing them out (usually using an ARP
ping) and therefore take up to a few hundred milliseconds to
respond. Network congestion may also influence the time it
takes for a response to make it back to the client. If that
time is too long, U-Boot will retransmit requests. In order
to allow earlier responses to still be accepted after these
retransmissions, U-Boot's BOOTP client keeps a small cache of
IDs. The CONFIG_BOOTP_ID_CACHE_SIZE controls the size of this
cache. The default is to keep IDs for up to four outstanding
requests. Increasing this will allow U-Boot to accept offers
from a BOOTP client in networks with unusually high latency.

You can fine tune the DHCP functionality by defining
CONFIG_BOOTP_* symbols:

CONFIG_BOOTP_NISDOMAIN
CONFIG_BOOTP_BOOTFILESIZE
CONFIG_BOOTP_SEND_HOSTNAME
CONFIG_BOOTP_NTPSERVER
CONFIG_BOOTP_TIMEOFFSET
CONFIG_BOOTP_VENDOREX
CONFIG_BOOTP_MAY_FAIL

CONFIG_BOOTP_SERVERIP - TFTP server will be the serverip
environment variable, not the BOOTP server.

after the configured retry count, the call will fail
instead of starting over.  This can be used to fail over
is not available.

CONFIG_BOOTP_SEND_HOSTNAME - Some DHCP servers are capable
to do a dynamic update of a DNS server. To do this, they
need the hostname of the DHCP requester.
If CONFIG_BOOTP_SEND_HOSTNAME is defined, the content
of the "hostname" environment variable is passed as
option 12 to the DHCP server.

CONFIG_BOOTP_DHCP_REQUEST_DELAY

A 32bit value in microseconds for a delay between
receiving a "DHCP Offer" and sending the "DHCP Request".
This fixes a problem with certain DHCP servers that don't
respond 100% of the time to a "DHCP request". E.g. On an
AT91RM9200 processor running at 180MHz, this delay needed
to be *at least* 15,000 usec before a Windows Server 2003
DHCP server would reply 100% of the time. I recommend at
least 50,000 usec to be safe. The alternative is to hope
that one of the retries will be successful but note that
the DHCP timeout and retry process takes a longer than
this delay.

Negotiate with other link-local clients on the local network
for an address that doesn't require explicit configuration.
This is especially useful if a DHCP server cannot be guaranteed
to exist in all environments that the device must operate.

- MAC address from environment variables

Fix-up device tree with MAC addresses fetched sequentially from
environment variables. This config work on assumption that
non-usable ethernet node of device-tree are either not present
or their status has been marked as "disabled".

- CDP Options:
CONFIG_CDP_DEVICE_ID

The device id used in CDP trigger frames.

CONFIG_CDP_DEVICE_ID_PREFIX

A two character string which is prefixed to the MAC address
of the device.

CONFIG_CDP_PORT_ID

A printf format string which contains the ascii name of
the port. Normally is set to "eth%d" which sets
eth0 for the first Ethernet, eth1 for the second etc.

CONFIG_CDP_CAPABILITIES

A 32bit integer which indicates the device capabilities;
0x00000010 for a normal host which does not forwards.

CONFIG_CDP_VERSION

An ascii string containing the version of the software.

CONFIG_CDP_PLATFORM

An ascii string containing the name of the platform.

CONFIG_CDP_TRIGGER

A 32bit integer sent on the trigger.

CONFIG_CDP_POWER_CONSUMPTION

A 16bit integer containing the power consumption of the
device in .1 of milliwatts.

CONFIG_CDP_APPLIANCE_VLAN_TYPE

A byte containing the id of the VLAN.

- Status LED:	CONFIG_LED_STATUS

Several configurations allow to display the current
status using a LED. For instance, the LED will blink
fast while running U-Boot code, stop blinking as
start blinking slow once the Linux kernel is running
(supported by a status LED driver in the Linux
kernel). Defining CONFIG_LED_STATUS enables this
feature in U-Boot.

CONFIG_LED_STATUS_GPIO
The status LED can be connected to a GPIO pin.
In such cases, the gpio_led driver can be used as a
status LED backend implementation. Define CONFIG_LED_STATUS_GPIO
to include the gpio_led driver in the U-Boot binary.

CONFIG_GPIO_LED_INVERTED_TABLE
Some GPIO connected LEDs may have inverted polarity in which
case the GPIO high value corresponds to LED off state and
GPIO low value corresponds to LED on state.
In such cases CONFIG_GPIO_LED_INVERTED_TABLE may be defined
with a list of GPIO LEDs that have inverted polarity.

- I2C Support:	CONFIG_SYS_I2C

This enable the NEW i2c subsystem, and will allow you to use
i2c commands at the u-boot command line (as long as you set
CONFIG_CMD_I2C in CONFIG_COMMANDS) and communicate with i2c
based realtime clock chips or other i2c devices. See
common/cmd_i2c.c for a description of the command line
interface.

ported i2c driver to the new framework:
- drivers/i2c/soft_i2c.c:
- activate first bus with CONFIG_SYS_I2C_SOFT define
CONFIG_SYS_I2C_SOFT_SPEED and CONFIG_SYS_I2C_SOFT_SLAVE
for defining speed and slave address
- activate second bus with I2C_SOFT_DECLARATIONS2 define
CONFIG_SYS_I2C_SOFT_SPEED_2 and CONFIG_SYS_I2C_SOFT_SLAVE_2
for defining speed and slave address
- activate third bus with I2C_SOFT_DECLARATIONS3 define
CONFIG_SYS_I2C_SOFT_SPEED_3 and CONFIG_SYS_I2C_SOFT_SLAVE_3
for defining speed and slave address
- activate fourth bus with I2C_SOFT_DECLARATIONS4 define
CONFIG_SYS_I2C_SOFT_SPEED_4 and CONFIG_SYS_I2C_SOFT_SLAVE_4
for defining speed and slave address

- drivers/i2c/fsl_i2c.c:
- activate i2c driver with CONFIG_SYS_I2C_FSL
define CONFIG_SYS_FSL_I2C_OFFSET for setting the register
offset CONFIG_SYS_FSL_I2C_SPEED for the i2c speed and
CONFIG_SYS_FSL_I2C_SLAVE for the slave addr of the first
bus.
- If your board supports a second fsl i2c bus, define
CONFIG_SYS_FSL_I2C2_OFFSET for the register offset
CONFIG_SYS_FSL_I2C2_SPEED for the speed and
CONFIG_SYS_FSL_I2C2_SLAVE for the slave address of the
second bus.

- drivers/i2c/tegra_i2c.c:
- activate this driver with CONFIG_SYS_I2C_TEGRA
- This driver adds 4 i2c buses with a fix speed from
100000 and the slave addr 0!

- drivers/i2c/ppc4xx_i2c.c
- activate this driver with CONFIG_SYS_I2C_PPC4XX
- CONFIG_SYS_I2C_PPC4XX_CH0 activate hardware channel 0
- CONFIG_SYS_I2C_PPC4XX_CH1 activate hardware channel 1

- drivers/i2c/i2c_mxc.c
- activate this driver with CONFIG_SYS_I2C_MXC
- enable bus 1 with CONFIG_SYS_I2C_MXC_I2C1
- enable bus 2 with CONFIG_SYS_I2C_MXC_I2C2
- enable bus 3 with CONFIG_SYS_I2C_MXC_I2C3
- enable bus 4 with CONFIG_SYS_I2C_MXC_I2C4
- define speed for bus 1 with CONFIG_SYS_MXC_I2C1_SPEED
- define slave for bus 1 with CONFIG_SYS_MXC_I2C1_SLAVE
- define speed for bus 2 with CONFIG_SYS_MXC_I2C2_SPEED
- define slave for bus 2 with CONFIG_SYS_MXC_I2C2_SLAVE
- define speed for bus 3 with CONFIG_SYS_MXC_I2C3_SPEED
- define slave for bus 3 with CONFIG_SYS_MXC_I2C3_SLAVE
- define speed for bus 4 with CONFIG_SYS_MXC_I2C4_SPEED
- define slave for bus 4 with CONFIG_SYS_MXC_I2C4_SLAVE
If those defines are not set, default value is 100000
for speed, and 0 for slave.

- drivers/i2c/rcar_i2c.c:
- activate this driver with CONFIG_SYS_I2C_RCAR
- This driver adds 4 i2c buses

- drivers/i2c/sh_i2c.c:
- activate this driver with CONFIG_SYS_I2C_SH
- This driver adds from 2 to 5 i2c buses

- CONFIG_SYS_I2C_SH_BASE0 for setting the register channel 0
- CONFIG_SYS_I2C_SH_SPEED0 for for the speed channel 0
- CONFIG_SYS_I2C_SH_BASE1 for setting the register channel 1
- CONFIG_SYS_I2C_SH_SPEED1 for for the speed channel 1
- CONFIG_SYS_I2C_SH_BASE2 for setting the register channel 2
- CONFIG_SYS_I2C_SH_SPEED2 for for the speed channel 2
- CONFIG_SYS_I2C_SH_BASE3 for setting the register channel 3
- CONFIG_SYS_I2C_SH_SPEED3 for for the speed channel 3
- CONFIG_SYS_I2C_SH_BASE4 for setting the register channel 4
- CONFIG_SYS_I2C_SH_SPEED4 for for the speed channel 4
- CONFIG_SYS_I2C_SH_NUM_CONTROLLERS for number of i2c buses

- drivers/i2c/omap24xx_i2c.c
- activate this driver with CONFIG_SYS_I2C_OMAP24XX
- CONFIG_SYS_OMAP24_I2C_SPEED speed channel 0
- CONFIG_SYS_OMAP24_I2C_SLAVE slave addr channel 0
- CONFIG_SYS_OMAP24_I2C_SPEED1 speed channel 1
- CONFIG_SYS_OMAP24_I2C_SLAVE1 slave addr channel 1
- CONFIG_SYS_OMAP24_I2C_SPEED2 speed channel 2
- CONFIG_SYS_OMAP24_I2C_SLAVE2 slave addr channel 2
- CONFIG_SYS_OMAP24_I2C_SPEED3 speed channel 3
- CONFIG_SYS_OMAP24_I2C_SLAVE3 slave addr channel 3
- CONFIG_SYS_OMAP24_I2C_SPEED4 speed channel 4
- CONFIG_SYS_OMAP24_I2C_SLAVE4 slave addr channel 4

- drivers/i2c/s3c24x0_i2c.c:
- activate this driver with CONFIG_SYS_I2C_S3C24X0
- This driver adds i2c buses (11 for Exynos5250, Exynos5420
9 i2c buses for Exynos4 and 1 for S3C24X0 SoCs from Samsung)
with a fix speed from 100000 and the slave addr 0!

- drivers/i2c/ihs_i2c.c
- activate this driver with CONFIG_SYS_I2C_IHS
- CONFIG_SYS_I2C_IHS_CH0 activate hardware channel 0
- CONFIG_SYS_I2C_IHS_SPEED_0 speed channel 0
- CONFIG_SYS_I2C_IHS_SLAVE_0 slave addr channel 0
- CONFIG_SYS_I2C_IHS_CH1 activate hardware channel 1
- CONFIG_SYS_I2C_IHS_SPEED_1 speed channel 1
- CONFIG_SYS_I2C_IHS_SLAVE_1 slave addr channel 1
- CONFIG_SYS_I2C_IHS_CH2 activate hardware channel 2
- CONFIG_SYS_I2C_IHS_SPEED_2 speed channel 2
- CONFIG_SYS_I2C_IHS_SLAVE_2 slave addr channel 2
- CONFIG_SYS_I2C_IHS_CH3 activate hardware channel 3
- CONFIG_SYS_I2C_IHS_SPEED_3 speed channel 3
- CONFIG_SYS_I2C_IHS_SLAVE_3 slave addr channel 3
- activate dual channel with CONFIG_SYS_I2C_IHS_DUAL
- CONFIG_SYS_I2C_IHS_SPEED_0_1 speed channel 0_1
- CONFIG_SYS_I2C_IHS_SLAVE_0_1 slave addr channel 0_1
- CONFIG_SYS_I2C_IHS_SPEED_1_1 speed channel 1_1
- CONFIG_SYS_I2C_IHS_SLAVE_1_1 slave addr channel 1_1
- CONFIG_SYS_I2C_IHS_SPEED_2_1 speed channel 2_1
- CONFIG_SYS_I2C_IHS_SLAVE_2_1 slave addr channel 2_1
- CONFIG_SYS_I2C_IHS_SPEED_3_1 speed channel 3_1
- CONFIG_SYS_I2C_IHS_SLAVE_3_1 slave addr channel 3_1

CONFIG_SYS_NUM_I2C_BUSES
Hold the number of i2c buses you want to use.

CONFIG_SYS_I2C_DIRECT_BUS
define this, if you don't use i2c muxes on your hardware.
if CONFIG_SYS_I2C_MAX_HOPS is not defined or == 0 you can
omit this define.

CONFIG_SYS_I2C_MAX_HOPS
define how many muxes are maximal consecutively connected
on one i2c bus. If you not use i2c muxes, omit this
define.

CONFIG_SYS_I2C_BUSES
hold a list of buses you want to use, only used if
CONFIG_SYS_I2C_DIRECT_BUS is not defined, for example
a board with CONFIG_SYS_I2C_MAX_HOPS = 1 and
CONFIG_SYS_NUM_I2C_BUSES = 9:

CONFIG_SYS_I2C_BUSES	{{0, {I2C_NULL_HOP}}, \
{0, {{I2C_MUX_PCA9547, 0x70, 1}}}, \
{0, {{I2C_MUX_PCA9547, 0x70, 2}}}, \
{0, {{I2C_MUX_PCA9547, 0x70, 3}}}, \
{0, {{I2C_MUX_PCA9547, 0x70, 4}}}, \
{0, {{I2C_MUX_PCA9547, 0x70, 5}}}, \
{1, {I2C_NULL_HOP}}, \
{1, {{I2C_MUX_PCA9544, 0x72, 1}}}, \
{1, {{I2C_MUX_PCA9544, 0x72, 2}}}, \
}

which defines
bus 0 on adapter 0 without a mux
bus 1 on adapter 0 with a PCA9547 on address 0x70 port 1
bus 2 on adapter 0 with a PCA9547 on address 0x70 port 2
bus 3 on adapter 0 with a PCA9547 on address 0x70 port 3
bus 4 on adapter 0 with a PCA9547 on address 0x70 port 4
bus 5 on adapter 0 with a PCA9547 on address 0x70 port 5
bus 6 on adapter 1 without a mux
bus 7 on adapter 1 with a PCA9544 on address 0x72 port 1
bus 8 on adapter 1 with a PCA9544 on address 0x72 port 2

If you do not have i2c muxes on your board, omit this define.

- Legacy I2C Support:
If you use the software i2c interface (CONFIG_SYS_I2C_SOFT)
then the following macros need to be defined (examples are
from include/configs/lwmon.h):

I2C_INIT

(Optional). Any commands necessary to enable the I2C
controller or configure ports.

eg: #define I2C_INIT (immr->im_cpm.cp_pbdir |=	PB_SCL)

I2C_ACTIVE

The code necessary to make the I2C data line active
(driven).  If the data line is open collector, this
define can be null.

eg: #define I2C_ACTIVE (immr->im_cpm.cp_pbdir |=  PB_SDA)

I2C_TRISTATE

The code necessary to make the I2C data line tri-stated
(inactive).  If the data line is open collector, this
define can be null.

eg: #define I2C_TRISTATE (immr->im_cpm.cp_pbdir &= ~PB_SDA)

Code that returns true if the I2C data line is high,
false if it is low.

eg: #define I2C_READ ((immr->im_cpm.cp_pbdat & PB_SDA) != 0)

I2C_SDA(bit)

If <bit> is true, sets the I2C data line high. If it
is false, it clears it (low).

eg: #define I2C_SDA(bit) \
if(bit) immr->im_cpm.cp_pbdat |=  PB_SDA; \
else	immr->im_cpm.cp_pbdat &= ~PB_SDA

I2C_SCL(bit)

If <bit> is true, sets the I2C clock line high. If it
is false, it clears it (low).

eg: #define I2C_SCL(bit) \
if(bit) immr->im_cpm.cp_pbdat |=  PB_SCL; \
else	immr->im_cpm.cp_pbdat &= ~PB_SCL

I2C_DELAY

This delay is invoked four times per clock cycle so this
controls the rate of data transfer.  The data rate thus
is 1 / (I2C_DELAY * 4). Often defined to be something
like:

#define I2C_DELAY  udelay(2)

CONFIG_SOFT_I2C_GPIO_SCL / CONFIG_SOFT_I2C_GPIO_SDA

If your arch supports the generic GPIO framework (asm/gpio.h),
then you may alternatively define the two GPIOs that are to be
used as SCL / SDA.  Any of the previous I2C_xxx macros will
have GPIO-based defaults assigned to them as appropriate.

You should define these to the GPIO value as given directly to
the generic GPIO functions.

CONFIG_SYS_I2C_INIT_BOARD

When a board is reset during an i2c bus transfer
chips might think that the current transfer is still
in progress. On some boards it is possible to access
the i2c SCLK line directly, either by using the
processor pin as a GPIO or by having a second pin
connected to the bus. If this option is defined a
custom i2c_init_board() routine in boards/xxx/board.c
is run early in the boot sequence.

CONFIG_I2C_MULTI_BUS

This option allows the use of multiple I2C buses, each of which
must have a controller.	 At any point in time, only one bus is
active.	 To switch to a different bus, use the 'i2c dev' command.
Note that bus numbering is zero-based.

CONFIG_SYS_I2C_NOPROBES

This option specifies a list of I2C devices that will be skipped
when the 'i2c probe' command is issued.	 If CONFIG_I2C_MULTI_BUS
is set, specify a list of bus-device pairs.  Otherwise, specify
a 1D array of device addresses

e.g.
#undef	CONFIG_I2C_MULTI_BUS
#define CONFIG_SYS_I2C_NOPROBES {0x50,0x68}

will skip addresses 0x50 and 0x68 on a board with one I2C bus

#define CONFIG_I2C_MULTI_BUS
#define CONFIG_SYS_I2C_NOPROBES	{{0,0x50},{0,0x68},{1,0x54}}

will skip addresses 0x50 and 0x68 on bus 0 and address 0x54 on bus 1

CONFIG_SYS_SPD_BUS_NUM

If defined, then this indicates the I2C bus number for DDR SPD.
If not defined, then U-Boot assumes that SPD is on I2C bus 0.

CONFIG_SYS_RTC_BUS_NUM

If defined, then this indicates the I2C bus number for the RTC.
If not defined, then U-Boot assumes that RTC is on I2C bus 0.

defining this will force the i2c_read() function in
the soft_i2c driver to perform an I2C repeated start
data.  If this define is omitted the default behaviour
of doing a stop-start sequence will be used.  Most I2C
devices can use either method, but some require one or
the other.

- SPI Support:	CONFIG_SPI

Enables SPI driver (so far only tested with
SPI EEPROM, also an instance works with Crystal A/D and
D/As on the SACSng board)

CONFIG_SOFT_SPI

Enables a software (bit-bang) SPI driver rather than
using hardware support. This is a general purpose
driver that only requires three general I/O port pins
(two outputs, one input) to function. If this is
defined, the board configuration must define several
SPI configuration items (port pins to use, etc). For
an example, see include/configs/sacsng.h.

CONFIG_SYS_SPI_MXC_WAIT
Timeout for waiting until spi transfer completed.
default: (CONFIG_SYS_HZ/100)     /* 10 ms */

- FPGA Support: CONFIG_FPGA

Enables FPGA subsystem.

CONFIG_FPGA_<vendor>

Enables support for specific chip vendors.
(ALTERA, XILINX)

CONFIG_FPGA_<family>

Enables support for FPGA family.
(SPARTAN2, SPARTAN3, VIRTEX2, CYCLONE2, ACEX1K, ACEX)

CONFIG_FPGA_COUNT

Specify the number of FPGA devices to support.

CONFIG_SYS_FPGA_PROG_FEEDBACK

Enable printing of hash marks during FPGA configuration.

CONFIG_SYS_FPGA_CHECK_BUSY

Enable checks on FPGA configuration interface busy
status by the configuration function. This option
will require a board or device specific function to
be written.

CONFIG_FPGA_DELAY

If defined, a function that provides delays in the FPGA
configuration driver.

CONFIG_SYS_FPGA_CHECK_CTRLC
Allow Control-C to interrupt FPGA configuration

CONFIG_SYS_FPGA_CHECK_ERROR

Check for configuration errors during FPGA bitfile
configuration if the INIT_B line goes low (which
indicated a CRC error).

CONFIG_SYS_FPGA_WAIT_INIT

Maximum time to wait for the INIT_B line to de-assert
after PROB_B has been de-asserted during a Virtex II
FPGA configuration sequence. The default time is 500
ms.

CONFIG_SYS_FPGA_WAIT_BUSY

Maximum time to wait for BUSY to de-assert during
Virtex II FPGA configuration. The default is 5 ms.

CONFIG_SYS_FPGA_WAIT_CONFIG

Time to wait after FPGA configuration. The default is
200 ms.

- Configuration Management:

CONFIG_IDENT_STRING

If defined, this string will be added to the U-Boot
version information (U_BOOT_VERSION)

- Vendor Parameter Protection:

U-Boot considers the values of the environment
variables "serial#" (Board Serial Number) and
are set once by the board vendor / manufacturer, and
protects these variables from casual modification by
the user. Once set, these variables are read-only,
and write or delete attempts are rejected. You can
change this behaviour:

If CONFIG_ENV_OVERWRITE is #defined in your config
file, the write protection for vendor parameters is
completely disabled. Anybody can change or delete
these parameters.

Alternatively, if you define _both_ an ethaddr in the
default env _and_ CONFIG_OVERWRITE_ETHADDR_ONCE, a default
Ethernet address is installed in the environment,
which can be changed exactly ONCE by the user. [The
serial# is unaffected by this, i. e. it remains

The same can be accomplished in a more flexible way
for any variable by configuring the type of access
to allow for those variables in the ".flags" variable
or define CONFIG_ENV_FLAGS_LIST_STATIC.

- Protected RAM:
CONFIG_PRAM

Define this variable to enable the reservation of
"protected RAM", i. e. RAM which is not overwritten
by U-Boot. Define CONFIG_PRAM to hold the number of
kB you want to reserve for pRAM. You can overwrite
this default value by defining an environment
variable "pram" to the number of kB you want to
reserve. Note that the board info structure will
still show the full amount of RAM. If pRAM is
reserved, a new environment variable "mem" will
automatically be defined to hold the amount of
remaining RAM in a form that can be passed as boot
argument to Linux, for instance like that:

setenv bootargs ... mem=\${mem} saveenv This way you can tell Linux not to use this memory, either, which results in a memory region that will not be affected by reboots. *WARNING* If your board configuration uses automatic detection of the RAM size, you must make sure that this memory test is non-destructive. So far, the following board configurations are known to be "pRAM-clean": IVMS8, IVML24, SPD8xx, HERMES, IP860, RPXlite, LWMON, FLAGADM - Access to physical memory region (> 4GB) Some basic support is provided for operations on memory not normally accessible to U-Boot - e.g. some architectures support access to more than 4GB of memory on 32-bit machines using physical address extension or similar. Define CONFIG_PHYSMEM to access this basic support, which currently only supports clearing the memory. - Error Recovery: CONFIG_NET_RETRY_COUNT This variable defines the number of retries for network operations like ARP, RARP, TFTP, or BOOTP before giving up the operation. If not defined, a default value of 5 is used. CONFIG_ARP_TIMEOUT Timeout waiting for an ARP reply in milliseconds. CONFIG_NFS_TIMEOUT Timeout in milliseconds used in NFS protocol. If you encounter "ERROR: Cannot umount" in nfs command, try longer timeout such as #define CONFIG_NFS_TIMEOUT 10000UL - Command Interpreter: CONFIG_SYS_PROMPT_HUSH_PS2 This defines the secondary prompt string, which is printed when the command interpreter needs more input to complete a command. Usually "> ". Note: In the current implementation, the local variables space and global environment variables space are separated. Local variables are those you define by simply typing name=value'. To access a local variable later on, you have write $name' or
${name}'; to execute the contents of a variable directly type $name' at the command prompt.

Global environment variables are those you use
setenv/printenv to work with. To run a command stored
in such a variable, you need to use the run command,
and you must not use the '' sign to access them. To store commands and special characters in a variable, please use double quotation marks surrounding the whole text of the variable, instead of the backslashes before semicolons and special symbols. - Command Line Editing and History: CONFIG_CMDLINE_PS_SUPPORT Enable support for changing the command prompt string at run-time. Only static string is supported so far. The string is obtained from environment variables PS1 and PS2. - Default Environment: CONFIG_EXTRA_ENV_SETTINGS Define this to contain any number of null terminated strings (variable = value pairs) that will be part of the default environment compiled into the boot image. For example, place something like this in your board's config file: #define CONFIG_EXTRA_ENV_SETTINGS \ "myvar1=value1\0" \ "myvar2=value2\0" Warning: This method is based on knowledge about the internal format how the environment is stored by the U-Boot code. This is NOT an official, exported interface! Although it is unlikely that this format will change soon, there is no guarantee either. You better know what you are doing here. Note: overly (ab)use of the default environment is discouraged. Make sure to check other ways to preset the environment like the "source" command or the boot command first. CONFIG_DELAY_ENVIRONMENT Normally the environment is loaded when the board is initialised so that it is available to U-Boot. This inhibits that so that the environment is not available until explicitly loaded later by U-Boot code. With CONFIG_OF_CONTROL this is instead controlled by the value of /config/load-environment. - TFTP Fixed UDP Port: CONFIG_TFTP_PORT If this is defined, the environment variable tftpsrcp is used to supply the TFTP UDP source port value. If tftpsrcp isn't defined, the normal pseudo-random port number generator is used. Also, the environment variable tftpdstp is used to supply the TFTP UDP destination port value. If tftpdstp isn't defined, the normal port 69 is used. The purpose for tftpsrcp is to allow a TFTP server to blindly start the TFTP transfer using the pre-configured target IP address and UDP port. This has the effect of "punching through" the (Windows XP) firewall, allowing the remainder of the TFTP transfer to proceed normally. A better solution is to properly configure the firewall, but sometimes that is not allowed. CONFIG_STANDALONE_LOAD_ADDR This option defines a board specific value for the address where standalone program gets loaded, thus overwriting the architecture dependent default settings. - Frame Buffer Address: CONFIG_FB_ADDR Define CONFIG_FB_ADDR if you want to use specific address for frame buffer. This is typically the case when using a graphics controller has separate video memory. U-Boot will then place the frame buffer at the given address instead of dynamically reserving it in system RAM by calling lcd_setmem(), which grabs the memory for the frame buffer depending on the configured panel size. Please see board_init_f function. - Automatic software updates via TFTP server CONFIG_UPDATE_TFTP CONFIG_UPDATE_TFTP_CNT_MAX CONFIG_UPDATE_TFTP_MSEC_MAX These options enable and control the auto-update feature; for a more detailed description refer to doc/README.update. - MTD Support (mtdparts command, UBI support) CONFIG_MTD_UBI_WL_THRESHOLD This parameter defines the maximum difference between the highest erase counter value and the lowest erase counter value of eraseblocks of UBI devices. When this threshold is exceeded, UBI starts performing wear leveling by means of moving data from eraseblock with low erase counter to eraseblocks with high erase counter. The default value should be OK for SLC NAND flashes, NOR flashes and other flashes which have eraseblock life-cycle 100000 or more. However, in case of MLC NAND flashes which typically have eraseblock life-cycle less than 10000, the threshold should be lessened (e.g., to 128 or 256, although it does not have to be power of 2). default: 4096 CONFIG_MTD_UBI_BEB_LIMIT This option specifies the maximum bad physical eraseblocks UBI expects on the MTD device (per 1024 eraseblocks). If the underlying flash does not admit of bad eraseblocks (e.g. NOR flash), this value is ignored. NAND datasheets often specify the minimum and maximum NVM (Number of Valid Blocks) for the flashes' endurance lifetime. The maximum expected bad eraseblocks per 1024 eraseblocks then can be calculated as "1024 * (1 - MinNVB / MaxNVB)", which gives 20 for most NANDs (MaxNVB is basically the total count of eraseblocks on the chip). To put it differently, if this value is 20, UBI will try to reserve about 1.9% of physical eraseblocks for bad blocks handling. And that will be 1.9% of eraseblocks on the entire NAND chip, not just the MTD partition UBI attaches. This means that if you have, say, a NAND flash chip admits maximum 40 bad eraseblocks, and it is split on two MTD partitions of the same size, UBI will reserve 40 eraseblocks when attaching a partition. default: 20 CONFIG_MTD_UBI_FASTMAP Fastmap is a mechanism which allows attaching an UBI device in nearly constant time. Instead of scanning the whole MTD device it only has to locate a checkpoint (called fastmap) on the device. The on-flash fastmap contains all information needed to attach the device. Using fastmap makes only sense on large devices where attaching by scanning takes long. UBI will not automatically install a fastmap on old images, but you can set the UBI parameter CONFIG_MTD_UBI_FASTMAP_AUTOCONVERT to 1 if you want so. Please note that fastmap-enabled images are still usable with UBI implementations without fastmap support. On typical flash devices the whole fastmap fits into one PEB. UBI will reserve PEBs to hold two fastmaps. CONFIG_MTD_UBI_FASTMAP_AUTOCONVERT Set this parameter to enable fastmap automatically on images without a fastmap. default: 0 CONFIG_MTD_UBI_FM_DEBUG Enable UBI fastmap debug default: 0 - SPL framework CONFIG_SPL Enable building of SPL globally. CONFIG_SPL_LDSCRIPT LDSCRIPT for linking the SPL binary. CONFIG_SPL_MAX_FOOTPRINT Maximum size in memory allocated to the SPL, BSS included. When defined, the linker checks that the actual memory used by SPL from _start to __bss_end does not exceed it. CONFIG_SPL_MAX_FOOTPRINT and CONFIG_SPL_BSS_MAX_SIZE must not be both defined at the same time. CONFIG_SPL_MAX_SIZE Maximum size of the SPL image (text, data, rodata, and linker lists sections), BSS excluded. When defined, the linker checks that the actual size does not exceed it. CONFIG_SPL_RELOC_TEXT_BASE Address to relocate to. If unspecified, this is equal to CONFIG_SPL_TEXT_BASE (i.e. no relocation is done). CONFIG_SPL_BSS_START_ADDR Link address for the BSS within the SPL binary. CONFIG_SPL_BSS_MAX_SIZE Maximum size in memory allocated to the SPL BSS. When defined, the linker checks that the actual memory used by SPL from __bss_start to __bss_end does not exceed it. CONFIG_SPL_MAX_FOOTPRINT and CONFIG_SPL_BSS_MAX_SIZE must not be both defined at the same time. CONFIG_SPL_STACK Adress of the start of the stack SPL will use CONFIG_SPL_PANIC_ON_RAW_IMAGE When defined, SPL will panic() if the image it has loaded does not have a signature. Defining this is useful when code which loads images in SPL cannot guarantee that absolutely all read errors will be caught. An example is the LPC32XX MLC NAND driver, which will consider that a completely unreadable NAND block is bad, and thus should be skipped silently. CONFIG_SPL_RELOC_STACK Adress of the start of the stack SPL will use after relocation. If unspecified, this is equal to CONFIG_SPL_STACK. CONFIG_SYS_SPL_MALLOC_START Starting address of the malloc pool used in SPL. When this option is set the full malloc is used in SPL and it is set up by spl_init() and before that, the simple malloc() can be used if CONFIG_SYS_MALLOC_F is defined. CONFIG_SYS_SPL_MALLOC_SIZE The size of the malloc pool used in SPL. CONFIG_SPL_OS_BOOT Enable booting directly to an OS from SPL. See also: doc/README.falcon CONFIG_SPL_DISPLAY_PRINT For ARM, enable an optional function to print more information about the running system. CONFIG_SPL_INIT_MINIMAL Arch init code should be built for a very small image CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_PARTITION Partition on the MMC to load U-Boot from when the MMC is being used in raw mode CONFIG_SYS_MMCSD_RAW_MODE_KERNEL_SECTOR Sector to load kernel uImage from when MMC is being used in raw mode (for Falcon mode) CONFIG_SYS_MMCSD_RAW_MODE_ARGS_SECTOR, CONFIG_SYS_MMCSD_RAW_MODE_ARGS_SECTORS Sector and number of sectors to load kernel argument parameters from when MMC is being used in raw mode (for falcon mode) CONFIG_SYS_MMCSD_FS_BOOT_PARTITION Partition on the MMC to load U-Boot from when the MMC is being used in fs mode CONFIG_SPL_FS_LOAD_PAYLOAD_NAME Filename to read to load U-Boot when reading from filesystem CONFIG_SPL_FS_LOAD_KERNEL_NAME Filename to read to load kernel uImage when reading from filesystem (for Falcon mode) CONFIG_SPL_FS_LOAD_ARGS_NAME Filename to read to load kernel argument parameters when reading from filesystem (for Falcon mode) CONFIG_SPL_MPC83XX_WAIT_FOR_NAND Set this for NAND SPL on PPC mpc83xx targets, so that start.S waits for the rest of the SPL to load before continuing (the hardware starts execution after just loading the first page rather than the full 4K). CONFIG_SPL_SKIP_RELOCATE Avoid SPL relocation CONFIG_SPL_NAND_BASE Include nand_base.c in the SPL. Requires CONFIG_SPL_NAND_DRIVERS. CONFIG_SPL_NAND_DRIVERS SPL uses normal NAND drivers, not minimal drivers. CONFIG_SPL_NAND_IDENT SPL uses the chip ID list to identify the NAND flash. Requires CONFIG_SPL_NAND_BASE. CONFIG_SPL_NAND_ECC Include standard software ECC in the SPL CONFIG_SPL_NAND_SIMPLE Support for NAND boot using simple NAND drivers that expose the cmd_ctrl() interface. CONFIG_SPL_UBI Support for a lightweight UBI (fastmap) scanner and loader CONFIG_SPL_NAND_RAW_ONLY Support to boot only raw u-boot.bin images. Use this only if you need to save space. CONFIG_SPL_COMMON_INIT_DDR Set for common ddr init with serial presence detect in SPL binary. CONFIG_SYS_NAND_5_ADDR_CYCLE, CONFIG_SYS_NAND_PAGE_COUNT, CONFIG_SYS_NAND_PAGE_SIZE, CONFIG_SYS_NAND_OOBSIZE, CONFIG_SYS_NAND_BLOCK_SIZE, CONFIG_SYS_NAND_BAD_BLOCK_POS, CONFIG_SYS_NAND_ECCPOS, CONFIG_SYS_NAND_ECCSIZE, CONFIG_SYS_NAND_ECCBYTES Defines the size and behavior of the NAND that SPL uses to read U-Boot CONFIG_SYS_NAND_U_BOOT_OFFS Location in NAND to read U-Boot from CONFIG_SYS_NAND_U_BOOT_DST Location in memory to load U-Boot to CONFIG_SYS_NAND_U_BOOT_SIZE Size of image to load CONFIG_SYS_NAND_U_BOOT_START Entry point in loaded image to jump to CONFIG_SYS_NAND_HW_ECC_OOBFIRST Define this if you need to first read the OOB and then the data. This is used, for example, on davinci platforms. CONFIG_SPL_RAM_DEVICE Support for running image already present in ram, in SPL binary CONFIG_SPL_PAD_TO Image offset to which the SPL should be padded before appending the SPL payload. By default, this is defined as CONFIG_SPL_MAX_SIZE, or 0 if CONFIG_SPL_MAX_SIZE is undefined. CONFIG_SPL_PAD_TO must be either 0, meaning to append the SPL payload without any padding, or >= CONFIG_SPL_MAX_SIZE. CONFIG_SPL_TARGET Final target image containing SPL and payload. Some SPLs use an arch-specific makefile fragment instead, for example if more than one image needs to be produced. CONFIG_SPL_FIT_PRINT Printing information about a FIT image adds quite a bit of code to SPL. So this is normally disabled in SPL. Use this option to re-enable it. This will affect the output of the bootm command when booting a FIT image. - TPL framework CONFIG_TPL Enable building of TPL globally. CONFIG_TPL_PAD_TO Image offset to which the TPL should be padded before appending the TPL payload. By default, this is defined as CONFIG_SPL_MAX_SIZE, or 0 if CONFIG_SPL_MAX_SIZE is undefined. CONFIG_SPL_PAD_TO must be either 0, meaning to append the SPL payload without any padding, or >= CONFIG_SPL_MAX_SIZE. - Interrupt support (PPC): There are common interrupt_init() and timer_interrupt() for all PPC archs. interrupt_init() calls interrupt_init_cpu() for CPU specific initialization. interrupt_init_cpu() should set decrementer_count to appropriate value. If CPU resets decrementer automatically after interrupt (ppc4xx) it should set decrementer_count to zero. timer_interrupt() calls timer_interrupt_cpu() for CPU specific handling. If board has watchdog / status_led / other_activity_monitor it works automatically from general timer_interrupt(). Board initialization settings: ------------------------------ During Initialization u-boot calls a number of board specific functions to allow the preparation of board specific prerequisites, e.g. pin setup before drivers are initialized. To enable these callbacks the following configuration macros have to be defined. Currently this is architecture specific, so please check arch/your_architecture/lib/board.c typically in board_init_f() and board_init_r(). - CONFIG_BOARD_EARLY_INIT_F: Call board_early_init_f() - CONFIG_BOARD_EARLY_INIT_R: Call board_early_init_r() - CONFIG_BOARD_LATE_INIT: Call board_late_init() - CONFIG_BOARD_POSTCLK_INIT: Call board_postclk_init() Configuration Settings: ----------------------- - MEM_SUPPORT_64BIT_DATA: Defined automatically if compiled as 64-bit. Optionally it can be defined to support 64-bit memory commands. - CONFIG_SYS_LONGHELP: Defined when you want long help messages included; undefine this when you're short of memory. - CONFIG_SYS_HELP_CMD_WIDTH: Defined when you want to override the default width of the commands listed in the 'help' command output. - CONFIG_SYS_PROMPT: This is what U-Boot prints on the console to prompt for user input. - CONFIG_SYS_CBSIZE: Buffer size for input from the Console - CONFIG_SYS_PBSIZE: Buffer size for Console output - CONFIG_SYS_MAXARGS: max. Number of arguments accepted for monitor commands - CONFIG_SYS_BARGSIZE: Buffer size for Boot Arguments which are passed to the application (usually a Linux kernel) when it is booted - CONFIG_SYS_BAUDRATE_TABLE: List of legal baudrate settings for this board. - CONFIG_SYS_MEMTEST_START, CONFIG_SYS_MEMTEST_END: Begin and End addresses of the area used by the simple memory test. - CONFIG_SYS_MEMTEST_SCRATCH: Scratch address used by the alternate memory test You only need to set this if address zero isn't writeable - CONFIG_SYS_MEM_RESERVE_SECURE Only implemented for ARMv8 for now. If defined, the size of CONFIG_SYS_MEM_RESERVE_SECURE memory is substracted from total RAM and won't be reported to OS. This memory can be used as secure memory. A variable gd->arch.secure_ram is used to track the location. In systems the RAM base is not zero, or RAM is divided into banks, this variable needs to be recalcuated to get the address. - CONFIG_SYS_MEM_TOP_HIDE: If CONFIG_SYS_MEM_TOP_HIDE is defined in the board config header, this specified memory area will get subtracted from the top (end) of RAM and won't get "touched" at all by U-Boot. By fixing up gd->ram_size the Linux kernel should gets passed the now "corrected" memory size and won't touch it either. This should work for arch/ppc and arch/powerpc. Only Linux board ports in arch/powerpc with bootwrapper support that recalculate the memory size from the SDRAM controller setup will have to get fixed in Linux additionally. This option can be used as a workaround for the 440EPx/GRx CHIP 11 errata where the last 256 bytes in SDRAM shouldn't be touched. WARNING: Please make sure that this value is a multiple of the Linux page size (normally 4k). If this is not the case, then the end address of the Linux memory will be located at a non page size aligned address and this could cause major problems. - CONFIG_SYS_LOADS_BAUD_CHANGE: Enable temporary baudrate change while serial download - CONFIG_SYS_SDRAM_BASE: Physical start address of SDRAM. _Must_ be 0 here. - CONFIG_SYS_FLASH_BASE: Physical start address of Flash memory. - CONFIG_SYS_MONITOR_BASE: Physical start address of boot monitor code (set by make config files to be same as the text base address (CONFIG_SYS_TEXT_BASE) used when linking) - same as CONFIG_SYS_FLASH_BASE when booting from flash. - CONFIG_SYS_MONITOR_LEN: Size of memory reserved for monitor code, used to determine _at_compile_time_ (!) if the environment is embedded within the U-Boot image, or in a separate flash sector. - CONFIG_SYS_MALLOC_LEN: Size of DRAM reserved for malloc() use. - CONFIG_SYS_MALLOC_F_LEN Size of the malloc() pool for use before relocation. If this is defined, then a very simple malloc() implementation will become available before relocation. The address is just below the global data, and the stack is moved down to make space. This feature allocates regions with increasing addresses within the region. calloc() is supported, but realloc() is not available. free() is supported but does nothing. The memory will be freed (or in fact just forgotten) when U-Boot relocates itself. - CONFIG_SYS_MALLOC_SIMPLE Provides a simple and small malloc() and calloc() for those boards which do not use the full malloc in SPL (which is enabled with CONFIG_SYS_SPL_MALLOC_START). - CONFIG_SYS_NONCACHED_MEMORY: Size of non-cached memory area. This area of memory will be typically located right below the malloc() area and mapped uncached in the MMU. This is useful for drivers that would otherwise require a lot of explicit cache maintenance. For some drivers it's also impossible to properly maintain the cache. For example if the regions that need to be flushed are not a multiple of the cache-line size, *and* padding cannot be allocated between the regions to align them (i.e. if the HW requires a contiguous array of regions, and the size of each region is not cache-aligned), then a flush of one region may result in overwriting data that hardware has written to another region in the same cache-line. This can happen for example in network drivers where descriptors for buffers are typically smaller than the CPU cache-line (e.g. 16 bytes vs. 32 or 64 bytes). Non-cached memory is only supported on 32-bit ARM at present. - CONFIG_SYS_BOOTM_LEN: Normally compressed uImages are limited to an uncompressed size of 8 MBytes. If this is not enough, you can define CONFIG_SYS_BOOTM_LEN in your board config file to adjust this setting to your needs. - CONFIG_SYS_BOOTMAPSZ: Maximum size of memory mapped by the startup code of the Linux kernel; all data that must be processed by the Linux kernel (bd_info, boot arguments, FDT blob if used) must be put below this limit, unless "bootm_low" environment variable is defined and non-zero. In such case all data for the Linux kernel must be between "bootm_low" and "bootm_low" + CONFIG_SYS_BOOTMAPSZ. The environment variable "bootm_mapsize" will override the value of CONFIG_SYS_BOOTMAPSZ. If CONFIG_SYS_BOOTMAPSZ is undefined, then the value in "bootm_size" will be used instead. - CONFIG_SYS_BOOT_RAMDISK_HIGH: Enable initrd_high functionality. If defined then the initrd_high feature is enabled and the bootm ramdisk subcommand is enabled. - CONFIG_SYS_BOOT_GET_CMDLINE: Enables allocating and saving kernel cmdline in space between "bootm_low" and "bootm_low" + BOOTMAPSZ. - CONFIG_SYS_BOOT_GET_KBD: Enables allocating and saving a kernel copy of the bd_info in space between "bootm_low" and "bootm_low" + BOOTMAPSZ. - CONFIG_SYS_MAX_FLASH_BANKS: Max number of Flash memory banks - CONFIG_SYS_MAX_FLASH_SECT: Max number of sectors on a Flash chip - CONFIG_SYS_FLASH_ERASE_TOUT: Timeout for Flash erase operations (in ms) - CONFIG_SYS_FLASH_WRITE_TOUT: Timeout for Flash write operations (in ms) - CONFIG_SYS_FLASH_LOCK_TOUT Timeout for Flash set sector lock bit operation (in ms) - CONFIG_SYS_FLASH_UNLOCK_TOUT Timeout for Flash clear lock bits operation (in ms) - CONFIG_SYS_FLASH_PROTECTION If defined, hardware flash sectors protection is used instead of U-Boot software protection. - CONFIG_SYS_DIRECT_FLASH_TFTP: Enable TFTP transfers directly to flash memory; without this option such a download has to be performed in two steps: (1) download to RAM, and (2) copy from RAM to flash. The two-step approach is usually more reliable, since you can check if the download worked before you erase the flash, but in some situations (when system RAM is too limited to allow for a temporary copy of the downloaded image) this option may be very useful. - CONFIG_SYS_FLASH_CFI: Define if the flash driver uses extra elements in the common flash structure for storing flash geometry. - CONFIG_FLASH_CFI_DRIVER This option also enables the building of the cfi_flash driver in the drivers directory - CONFIG_FLASH_CFI_MTD This option enables the building of the cfi_mtd driver in the drivers directory. The driver exports CFI flash to the MTD layer. - CONFIG_SYS_FLASH_USE_BUFFER_WRITE Use buffered writes to flash. - CONFIG_FLASH_SPANSION_S29WS_N s29ws-n MirrorBit flash has non-standard addresses for buffered write commands. - CONFIG_SYS_FLASH_QUIET_TEST If this option is defined, the common CFI flash doesn't print it's warning upon not recognized FLASH banks. This is useful, if some of the configured banks are only optionally available. - CONFIG_FLASH_SHOW_PROGRESS If defined (must be an integer), print out countdown digits and dots. Recommended value: 45 (9..1) for 80 column displays, 15 (3..1) for 40 column displays. - CONFIG_FLASH_VERIFY If defined, the content of the flash (destination) is compared against the source after the write operation. An error message will be printed when the contents are not identical. Please note that this option is useless in nearly all cases, since such flash programming errors usually are detected earlier while unprotecting/erasing/programming. Please only enable this option if you really know what you are doing. - CONFIG_SYS_RX_ETH_BUFFER: Defines the number of Ethernet receive buffers. On some Ethernet controllers it is recommended to set this value to 8 or even higher (EEPRO100 or 405 EMAC), since all buffers can be full shortly after enabling the interface on high Ethernet traffic. Defaults to 4 if not defined. - CONFIG_ENV_MAX_ENTRIES Maximum number of entries in the hash table that is used internally to store the environment settings. The default setting is supposed to be generous and should work in most cases. This setting can be used to tune behaviour; see lib/hashtable.c for details. - CONFIG_ENV_FLAGS_LIST_DEFAULT - CONFIG_ENV_FLAGS_LIST_STATIC Enable validation of the values given to environment variables when calling env set. Variables can be restricted to only decimal, hexadecimal, or boolean. If CONFIG_CMD_NET is also defined, the variables can also be restricted to IP address or MAC address. The format of the list is: type_attribute = [s|d|x|b|i|m] access_attribute = [a|r|o|c] attributes = type_attribute[access_attribute] entry = variable_name[:attributes] list = entry[,list] The type attributes are: s - String (default) d - Decimal x - Hexadecimal b - Boolean ([1yYtT|0nNfF]) i - IP address m - MAC address The access attributes are: a - Any (default) r - Read-only o - Write-once c - Change-default - CONFIG_ENV_FLAGS_LIST_DEFAULT Define this to a list (string) to define the ".flags" environment variable in the default or embedded environment. - CONFIG_ENV_FLAGS_LIST_STATIC Define this to a list (string) to define validation that should be done if an entry is not found in the ".flags" environment variable. To override a setting in the static list, simply add an entry for the same variable name to the ".flags" variable. If CONFIG_REGEX is defined, the variable_name above is evaluated as a regular expression. This allows multiple variables to define the same flags without explicitly listing them for each variable. - CONFIG_ENV_ACCESS_IGNORE_FORCE If defined, don't allow the -f switch to env set override variable access flags. The following definitions that deal with the placement and management of environment data (variable area); in general, we support the following configurations: - CONFIG_BUILD_ENVCRC: Builds up envcrc with the target environment so that external utils may easily extract it and embed it in final U-Boot images. BE CAREFUL! The first access to the environment happens quite early in U-Boot initialization (when we try to get the setting of for the console baudrate). You *MUST* have mapped your NVRAM area then, or U-Boot will hang. Please note that even with NVRAM we still use a copy of the environment in RAM: we could work on NVRAM directly, but we want to keep settings there always unmodified except somebody uses "saveenv" to save the current settings. BE CAREFUL! For some special cases, the local device can not use "saveenv" command. For example, the local device will get the environment stored in a remote NOR flash by SRIO or PCIE link, but it can not erase, write this NOR flash by SRIO or PCIE interface. - CONFIG_NAND_ENV_DST Defines address in RAM to which the nand_spl code should copy the environment. If redundant environment is used, it will be copied to CONFIG_NAND_ENV_DST + CONFIG_ENV_SIZE. Please note that the environment is read-only until the monitor has been relocated to RAM and a RAM copy of the environment has been created; also, when using EEPROM you will have to use env_get_f() until then to read environment variables. The environment is protected by a CRC32 checksum. Before the monitor is relocated into RAM, as a result of a bad CRC you will be working with the compiled-in default environment - *silently*!!! [This is necessary, because the first environment variable we need is the "baudrate" setting for the console - if we have a bad CRC, we don't have any device yet where we could complain.] Note: once the monitor has been relocated, then it will complain if the default environment is used; a new CRC is computed as soon as you use the "saveenv" command to store a valid environment. - CONFIG_SYS_FAULT_ECHO_LINK_DOWN: Echo the inverted Ethernet link state to the fault LED. Note: If this option is active, then CONFIG_SYS_FAULT_MII_ADDR also needs to be defined. - CONFIG_SYS_FAULT_MII_ADDR: MII address of the PHY to check for the Ethernet link state. - CONFIG_NS16550_MIN_FUNCTIONS: Define this if you desire to only have use of the NS16550_init and NS16550_putc functions for the serial driver located at drivers/serial/ns16550.c. This option is useful for saving space for already greatly restricted images, including but not limited to NAND_SPL configurations. - CONFIG_DISPLAY_BOARDINFO Display information about the board that U-Boot is running on when U-Boot starts up. The board function checkboard() is called to do this. - CONFIG_DISPLAY_BOARDINFO_LATE Similar to the previous option, but display this information later, once stdio is running and output goes to the LCD, if present. - CONFIG_BOARD_SIZE_LIMIT: Maximum size of the U-Boot image. When defined, the build system checks that the actual size does not exceed it. Low Level (hardware related) configuration options: --------------------------------------------------- - CONFIG_SYS_CACHELINE_SIZE: Cache Line Size of the CPU. - CONFIG_SYS_CCSRBAR_DEFAULT: Default (power-on reset) physical address of CCSR on Freescale PowerPC SOCs. - CONFIG_SYS_CCSRBAR: Virtual address of CCSR. On a 32-bit build, this is typically the same value as CONFIG_SYS_CCSRBAR_DEFAULT. - CONFIG_SYS_CCSRBAR_PHYS: Physical address of CCSR. CCSR can be relocated to a new physical address, if desired. In this case, this macro should be set to that address. Otherwise, it should be set to the same value as CONFIG_SYS_CCSRBAR_DEFAULT. For example, CCSR is typically relocated on 36-bit builds. It is recommended that this macro be defined via the _HIGH and _LOW macros: #define CONFIG_SYS_CCSRBAR_PHYS ((CONFIG_SYS_CCSRBAR_PHYS_HIGH * 1ull) << 32 | CONFIG_SYS_CCSRBAR_PHYS_LOW) - CONFIG_SYS_CCSRBAR_PHYS_HIGH: Bits 33-36 of CONFIG_SYS_CCSRBAR_PHYS. This value is typically either 0 (32-bit build) or 0xF (36-bit build). This macro is used in assembly code, so it must not contain typecasts or integer size suffixes (e.g. "ULL"). - CONFIG_SYS_CCSRBAR_PHYS_LOW: Lower 32-bits of CONFIG_SYS_CCSRBAR_PHYS. This macro is used in assembly code, so it must not contain typecasts or integer size suffixes (e.g. "ULL"). - CONFIG_SYS_CCSR_DO_NOT_RELOCATE: If this macro is defined, then CONFIG_SYS_CCSRBAR_PHYS will be forced to a value that ensures that CCSR is not relocated. - CONFIG_IDE_AHB: Most IDE controllers were designed to be connected with PCI interface. Only few of them were designed for AHB interface. When software is doing ATA command and data transfer to IDE devices through IDE-AHB controller, some additional registers accessing to these kind of IDE-AHB controller is required. - CONFIG_SYS_IMMR: Physical address of the Internal Memory. DO NOT CHANGE unless you know exactly what you're doing! (11-4) [MPC8xx systems only] - CONFIG_SYS_INIT_RAM_ADDR: Start address of memory area that can be used for initial data and stack; please note that this must be writable memory that is working WITHOUT special initialization, i. e. you CANNOT use normal RAM which will become available only after programming the memory controller and running certain initialization sequences. U-Boot uses the following memory types: - MPC8xx: IMMR (internal memory of the CPU) - CONFIG_SYS_GBL_DATA_OFFSET: Offset of the initial data structure in the memory area defined by CONFIG_SYS_INIT_RAM_ADDR. Usually CONFIG_SYS_GBL_DATA_OFFSET is chosen such that the initial data is located at the end of the available space (sometimes written as (CONFIG_SYS_INIT_RAM_SIZE - GENERATED_GBL_DATA_SIZE), and the initial stack is just below that area (growing from (CONFIG_SYS_INIT_RAM_ADDR + CONFIG_SYS_GBL_DATA_OFFSET) downward. Note: On the MPC824X (or other systems that use the data cache for initial memory) the address chosen for CONFIG_SYS_INIT_RAM_ADDR is basically arbitrary - it must point to an otherwise UNUSED address space between the top of RAM and the start of the PCI space. - CONFIG_SYS_SCCR: System Clock and reset Control Register (15-27) - CONFIG_SYS_OR_TIMING_SDRAM: SDRAM timing - CONFIG_SYS_MAMR_PTA: periodic timer for refresh - FLASH_BASE0_PRELIM, FLASH_BASE1_PRELIM, CONFIG_SYS_REMAP_OR_AM, CONFIG_SYS_PRELIM_OR_AM, CONFIG_SYS_OR_TIMING_FLASH, CONFIG_SYS_OR0_REMAP, CONFIG_SYS_OR0_PRELIM, CONFIG_SYS_BR0_PRELIM, CONFIG_SYS_OR1_REMAP, CONFIG_SYS_OR1_PRELIM, CONFIG_SYS_BR1_PRELIM: Memory Controller Definitions: BR0/1 and OR0/1 (FLASH) - SDRAM_BASE2_PRELIM, SDRAM_BASE3_PRELIM, SDRAM_MAX_SIZE, CONFIG_SYS_OR_TIMING_SDRAM, CONFIG_SYS_OR2_PRELIM, CONFIG_SYS_BR2_PRELIM, CONFIG_SYS_OR3_PRELIM, CONFIG_SYS_BR3_PRELIM: Memory Controller Definitions: BR2/3 and OR2/3 (SDRAM) - CONFIG_PCI_ENUM_ONLY Only scan through and get the devices on the buses. Don't do any setup work, presumably because someone or something has already done it, and we don't need to do it a second time. Useful for platforms that are pre-booted by coreboot or similar. - CONFIG_PCI_INDIRECT_BRIDGE: Enable support for indirect PCI bridges. - CONFIG_SYS_SRIO: Chip has SRIO or not - CONFIG_SRIO1: Board has SRIO 1 port available - CONFIG_SRIO2: Board has SRIO 2 port available - CONFIG_SRIO_PCIE_BOOT_MASTER Board can support master function for Boot from SRIO and PCIE - CONFIG_SYS_SRIOn_MEM_VIRT: Virtual Address of SRIO port 'n' memory region - CONFIG_SYS_SRIOn_MEM_PHYxS: Physical Address of SRIO port 'n' memory region - CONFIG_SYS_SRIOn_MEM_SIZE: Size of SRIO port 'n' memory region - CONFIG_SYS_NAND_BUSWIDTH_16BIT Defined to tell the NAND controller that the NAND chip is using a 16 bit bus. Not all NAND drivers use this symbol. Example of drivers that use it: - drivers/mtd/nand/raw/ndfc.c - drivers/mtd/nand/raw/mxc_nand.c - CONFIG_SYS_NDFC_EBC0_CFG Sets the EBC0_CFG register for the NDFC. If not defined a default value will be used. - CONFIG_SPD_EEPROM Get DDR timing information from an I2C EEPROM. Common with pluggable memory modules such as SODIMMs SPD_EEPROM_ADDRESS I2C address of the SPD EEPROM - CONFIG_SYS_SPD_BUS_NUM If SPD EEPROM is on an I2C bus other than the first one, specify here. Note that the value must resolve to something your driver can deal with. - CONFIG_SYS_DDR_RAW_TIMING Get DDR timing information from other than SPD. Common with soldered DDR chips onboard without SPD. DDR raw timing parameters are extracted from datasheet and hard-coded into header files or board specific files. - CONFIG_FSL_DDR_INTERACTIVE Enable interactive DDR debugging. See doc/README.fsl-ddr. - CONFIG_FSL_DDR_SYNC_REFRESH Enable sync of refresh for multiple controllers. - CONFIG_FSL_DDR_BIST Enable built-in memory test for Freescale DDR controllers. - CONFIG_SYS_83XX_DDR_USES_CS0 Only for 83xx systems. If specified, then DDR should be configured using CS0 and CS1 instead of CS2 and CS3. - CONFIG_RMII Enable RMII mode for all FECs. Note that this is a global option, we can't have one FEC in standard MII mode and another in RMII mode. - CONFIG_CRC32_VERIFY Add a verify option to the crc32 command. The syntax is: => crc32 -v <address> <count> <crc32> Where address/count indicate a memory area and crc32 is the correct crc32 which the area should have. - CONFIG_LOOPW Add the "loopw" memory command. This only takes effect if the memory commands are activated globally (CONFIG_CMD_MEMORY). - CONFIG_CMD_MX_CYCLIC Add the "mdc" and "mwc" memory commands. These are cyclic "md/mw" commands. Examples: => mdc.b 10 4 500 This command will print 4 bytes (10,11,12,13) each 500 ms. => mwc.l 100 12345678 10 This command will write 12345678 to address 100 all 10 ms. This only takes effect if the memory commands are activated globally (CONFIG_CMD_MEMORY). - CONFIG_SKIP_LOWLEVEL_INIT [ARM, NDS32, MIPS, RISC-V only] If this variable is defined, then certain low level initializations (like setting up the memory controller) are omitted and/or U-Boot does not relocate itself into RAM. Normally this variable MUST NOT be defined. The only exception is when U-Boot is loaded (to RAM) by some other boot loader or by a debugger which performs these initializations itself. - CONFIG_SKIP_LOWLEVEL_INIT_ONLY [ARM926EJ-S only] This allows just the call to lowlevel_init() to be skipped. The normal CP15 init (such as enabling the instruction cache) is still performed. - CONFIG_SPL_BUILD Set when the currently-running compilation is for an artifact that will end up in the SPL (as opposed to the TPL or U-Boot proper). Code that needs stage-specific behavior should check this. - CONFIG_TPL_BUILD Set when the currently-running compilation is for an artifact that will end up in the TPL (as opposed to the SPL or U-Boot proper). Code that needs stage-specific behavior should check this. - CONFIG_SYS_MPC85XX_NO_RESETVEC Only for 85xx systems. If this variable is specified, the section .resetvec is not kept and the section .bootpg is placed in the previous 4k of the .text section. - CONFIG_ARCH_MAP_SYSMEM Generally U-Boot (and in particular the md command) uses effective address. It is therefore not necessary to regard U-Boot address as virtual addresses that need to be translated to physical addresses. However, sandbox requires this, since it maintains its own little RAM buffer which contains all addressable memory. This option causes some memory accesses to be mapped through map_sysmem() / unmap_sysmem(). - CONFIG_X86_RESET_VECTOR If defined, the x86 reset vector code is included. This is not needed when U-Boot is running from Coreboot. - CONFIG_SYS_NAND_NO_SUBPAGE_WRITE Option to disable subpage write in NAND driver driver that uses this: drivers/mtd/nand/raw/davinci_nand.c Freescale QE/FMAN Firmware Support: ----------------------------------- The Freescale QUICCEngine (QE) and Frame Manager (FMAN) both support the loading of "firmware", which is encoded in the QE firmware binary format. This firmware often needs to be loaded during U-Boot booting, so macros are used to identify the storage device (NOR flash, SPI, etc) and the address within that device. - CONFIG_SYS_FMAN_FW_ADDR The address in the storage device where the FMAN microcode is located. The meaning of this address depends on which CONFIG_SYS_QE_FMAN_FW_IN_xxx macro is also specified. - CONFIG_SYS_QE_FW_ADDR The address in the storage device where the QE microcode is located. The meaning of this address depends on which CONFIG_SYS_QE_FMAN_FW_IN_xxx macro is also specified. - CONFIG_SYS_QE_FMAN_FW_LENGTH The maximum possible size of the firmware. The firmware binary format has a field that specifies the actual size of the firmware, but it might not be possible to read any part of the firmware unless some local storage is allocated to hold the entire firmware first. - CONFIG_SYS_QE_FMAN_FW_IN_NOR Specifies that QE/FMAN firmware is located in NOR flash, mapped as normal addressable memory via the LBC. CONFIG_SYS_FMAN_FW_ADDR is the virtual address in NOR flash. - CONFIG_SYS_QE_FMAN_FW_IN_NAND Specifies that QE/FMAN firmware is located in NAND flash. CONFIG_SYS_FMAN_FW_ADDR is the offset within NAND flash. - CONFIG_SYS_QE_FMAN_FW_IN_MMC Specifies that QE/FMAN firmware is located on the primary SD/MMC device. CONFIG_SYS_FMAN_FW_ADDR is the byte offset on that device. - CONFIG_SYS_QE_FMAN_FW_IN_REMOTE Specifies that QE/FMAN firmware is located in the remote (master) memory space. CONFIG_SYS_FMAN_FW_ADDR is a virtual address which can be mapped from slave TLB->slave LAW->slave SRIO or PCIE outbound window->master inbound window->master LAW->the ucode address in master's memory space. Freescale Layerscape Management Complex Firmware Support: --------------------------------------------------------- The Freescale Layerscape Management Complex (MC) supports the loading of "firmware". This firmware often needs to be loaded during U-Boot booting, so macros are used to identify the storage device (NOR flash, SPI, etc) and the address within that device. - CONFIG_FSL_MC_ENET Enable the MC driver for Layerscape SoCs. Freescale Layerscape Debug Server Support: ------------------------------------------- The Freescale Layerscape Debug Server Support supports the loading of "Debug Server firmware" and triggering SP boot-rom. This firmware often needs to be loaded during U-Boot booting. - CONFIG_SYS_MC_RSV_MEM_ALIGN Define alignment of reserved memory MC requires Reproducible builds ------------------- In order to achieve reproducible builds, timestamps used in the U-Boot build process have to be set to a fixed value. This is done using the SOURCE_DATE_EPOCH environment variable. SOURCE_DATE_EPOCH is to be set on the build host's shell, not as a configuration option for U-Boot or an environment variable in U-Boot. SOURCE_DATE_EPOCH should be set to a number of seconds since the epoch, in UTC. Building the Software: ====================== Building U-Boot has been tested in several native build environments and in many different cross environments. Of course we cannot support all possibly existing versions of cross development tools in all (potentially obsolete) versions. In case of tool chain problems we recommend to use the ELDK (see http://www.denx.de/wiki/DULG/ELDK) which is extensively used to build and test U-Boot. If you are not using a native environment, it is assumed that you have GNU cross compiling tools available in your path. In this case, you must set the environment variable CROSS_COMPILE in your shell. Note that no changes to the Makefile or any other source files are necessary. For example using the ELDK on a 4xx CPU, please enter: CROSS_COMPILE=ppc_4xx-
$export CROSS_COMPILE U-Boot is intended to be simple to build. After installing the sources you must configure U-Boot for one specific board type. This is done by typing: make NAME_defconfig where "NAME_defconfig" is the name of one of the existing configu- rations; see configs/*_defconfig for supported names. Note: for some boards special configuration names may exist; check if additional information is available from the board vendor; for instance, the TQM823L systems are available without (standard) or with LCD support. You can select such additional "features" when choosing the configuration, i. e. make TQM823L_defconfig - will configure for a plain TQM823L, i. e. no LCD support make TQM823L_LCD_defconfig - will configure for a TQM823L with U-Boot console on LCD etc. Finally, type "make all", and you should get some working U-Boot images ready for download to / installation on your system: - "u-boot.bin" is a raw binary image - "u-boot" is an image in ELF binary format - "u-boot.srec" is in Motorola S-Record format By default the build is performed locally and the objects are saved in the source directory. One of the two methods can be used to change this behavior and build U-Boot to some external directory: 1. Add O= to the make command line invocations: make O=/tmp/build distclean make O=/tmp/build NAME_defconfig make O=/tmp/build all 2. Set environment variable KBUILD_OUTPUT to point to the desired location: export KBUILD_OUTPUT=/tmp/build make distclean make NAME_defconfig make all Note that the command line "O=" setting overrides the KBUILD_OUTPUT environment variable. User specific CPPFLAGS, AFLAGS and CFLAGS can be passed to the compiler by setting the according environment variables KCPPFLAGS, KAFLAGS and KCFLAGS. For example to treat all compiler warnings as errors: make KCFLAGS=-Werror Please be aware that the Makefiles assume you are using GNU make, so for instance on NetBSD you might need to use "gmake" instead of native "make". If the system board that you have is not listed, then you will need to port U-Boot to your hardware platform. To do this, follow these steps: 1. Create a new directory to hold your board specific code. Add any files you need. In your board directory, you will need at least the "Makefile" and a "<board>.c". 2. Create a new configuration file "include/configs/<board>.h" for your board. 3. If you're porting U-Boot to a new CPU, then also create a new directory to hold your CPU specific code. Add any files you need. 4. Run "make <board>_defconfig" with your new name. 5. Type "make", and you should get a working "u-boot.srec" file to be installed on your target system. 6. Debug and solve any problems that might arise. [Of course, this last step is much harder than it sounds.] Testing of U-Boot Modifications, Ports to New Hardware, etc.: ============================================================== If you have modified U-Boot sources (for instance added a new board or support for new devices, a new CPU, etc.) you are expected to provide feedback to the other developers. The feedback normally takes the form of a "patch", i.e. a context diff against a certain (latest official or latest in the git repository) version of U-Boot sources. But before you submit such a patch, please verify that your modifi- cation did not break existing code. At least make sure that *ALL* of the supported boards compile WITHOUT ANY compiler warnings. To do so, just run the buildman script (tools/buildman/buildman), which will configure and build U-Boot for ALL supported system. Be warned, this will take a while. Please see the buildman README, or run 'buildman -H' for documentation. See also "U-Boot Porting Guide" below. Monitor Commands - Overview: ============================ go - start application at address 'addr' run - run commands in an environment variable bootm - boot application image from memory bootp - boot image via network using BootP/TFTP protocol bootz - boot zImage from memory tftpboot- boot image via network using TFTP protocol and env variables "ipaddr" and "serverip" (and eventually "gatewayip") tftpput - upload a file via network using TFTP protocol rarpboot- boot image via network using RARP/TFTP protocol diskboot- boot from IDE devicebootd - boot default, i.e., run 'bootcmd' loads - load S-Record file over serial line loadb - load binary file over serial line (kermit mode) md - memory display mm - memory modify (auto-incrementing) nm - memory modify (constant address) mw - memory write (fill) cp - memory copy cmp - memory compare crc32 - checksum calculation i2c - I2C sub-system sspi - SPI utility commands base - print or set address offset printenv- print environment variables setenv - set environment variables saveenv - save environment variables to persistent storage protect - enable or disable FLASH write protection erase - erase FLASH memory flinfo - print FLASH memory information nand - NAND memory operations (see doc/README.nand) bdinfo - print Board Info structure iminfo - print header information for application image coninfo - print console devices and informations ide - IDE sub-system loop - infinite loop on address range loopw - infinite write loop on address range mtest - simple RAM test icache - enable or disable instruction cache dcache - enable or disable data cache reset - Perform RESET of the CPU echo - echo args to console version - print monitor version help - print online help ? - alias for 'help' Monitor Commands - Detailed Description: ======================================== TODO. For now: just type "help <command>". Environment Variables: ====================== U-Boot supports user configuration using Environment Variables which can be made persistent by saving to Flash memory. Environment Variables are set using "setenv", printed using "printenv", and saved to Flash using "saveenv". Using "setenv" without a value can be used to delete a variable from the environment. As long as you don't save the environment you are working with an in-memory copy. In case the Flash area containing the environment is erased by accident, a default environment is provided. Some configuration options can be set using Environment Variables. List of environment variables (most likely not complete): baudrate - see CONFIG_BAUDRATE bootdelay - see CONFIG_BOOTDELAY bootcmd - see CONFIG_BOOTCOMMAND bootargs - Boot arguments when booting an RTOS image bootfile - Name of the image to load with TFTP bootm_low - Memory range available for image processing in the bootm command can be restricted. This variable is given as a hexadecimal number and defines lowest address allowed for use by the bootm command. See also "bootm_size" environment variable. Address defined by "bootm_low" is also the base of the initial memory mapping for the Linux kernel -- see the description of CONFIG_SYS_BOOTMAPSZ and bootm_mapsize. bootm_mapsize - Size of the initial memory mapping for the Linux kernel. This variable is given as a hexadecimal number and it defines the size of the memory region starting at base address bootm_low that is accessible by the Linux kernel during early boot. If unset, CONFIG_SYS_BOOTMAPSZ is used as the default value if it is defined, and bootm_size is used otherwise. bootm_size - Memory range available for image processing in the bootm command can be restricted. This variable is given as a hexadecimal number and defines the size of the region allowed for use by the bootm command. See also "bootm_low" environment variable. bootstopkeysha256, bootdelaykey, bootstopkey - See README.autoboot updatefile - Location of the software update file on a TFTP server, used by the automatic software update feature. Please refer to documentation in doc/README.update for more details. autoload - if set to "no" (any string beginning with 'n'), "bootp" will just load perform a lookup of the configuration from the BOOTP server, but not try to load any image using TFTP autostart - if set to "yes", an image loaded using the "bootp", "rarpboot", "tftpboot" or "diskboot" commands will be automatically started (by internally calling "bootm") If set to "no", a standalone image passed to the "bootm" command will be copied to the load address (and eventually uncompressed), but NOT be started. This can be used to load and uncompress arbitrary data. fdt_high - if set this restricts the maximum address that the flattened device tree will be copied into upon boot. For example, if you have a system with 1 GB memory at physical address 0x10000000, while Linux kernel only recognizes the first 704 MB as low memory, you may need to set fdt_high as 0x3C000000 to have the device tree blob be copied to the maximum address of the 704 MB low memory, so that Linux kernel can access it during the boot procedure. If this is set to the special value 0xFFFFFFFF then the fdt will not be copied at all on boot. For this to work it must reside in writable memory, have sufficient padding on the end of it for u-boot to add the information it needs into it, and the memory must be accessible by the kernel. fdtcontroladdr- if set this is the address of the control flattened device tree used by U-Boot when CONFIG_OF_CONTROL is defined. i2cfast - (PPC405GP|PPC405EP only) if set to 'y' configures Linux I2C driver for fast mode (400kHZ). This environment variable is used in initialization code. So, for changes to be effective it must be saved and board must be reset. initrd_high - restrict positioning of initrd images: If this variable is not set, initrd images will be copied to the highest possible address in RAM; this is usually what you want since it allows for maximum initrd size. If for some reason you want to make sure that the initrd image is loaded below the CONFIG_SYS_BOOTMAPSZ limit, you can set this environment variable to a value of "no" or "off" or "0". Alternatively, you can set it to a maximum upper address to use (U-Boot will still check that it does not overwrite the U-Boot stack and data). For instance, when you have a system with 16 MB RAM, and want to reserve 4 MB from use by Linux, you can do this by adding "mem=12M" to the value of the "bootargs" variable. However, now you must make sure that the initrd image is placed in the first 12 MB as well - this can be done with setenv initrd_high 00c00000 If you set initrd_high to 0xFFFFFFFF, this is an indication to U-Boot that all addresses are legal for the Linux kernel, including addresses in flash memory. In this case U-Boot will NOT COPY the ramdisk at all. This may be useful to reduce the boot time on your system, but requires that this feature is supported by your Linux kernel. ipaddr - IP address; needed for tftpboot command loadaddr - Default load address for commands like "bootp", "rarpboot", "tftpboot", "loadb" or "diskboot" loads_echo - see CONFIG_LOADS_ECHO serverip - TFTP server IP address; needed for tftpboot command bootretry - see CONFIG_BOOT_RETRY_TIME bootdelaykey - see CONFIG_AUTOBOOT_DELAY_STR bootstopkey - see CONFIG_AUTOBOOT_STOP_STR ethprime - controls which interface is used first. ethact - controls which interface is currently active. For example you can do the following => setenv ethact FEC => ping 192.168.0.1 # traffic sent on FEC => setenv ethact SCC => ping 10.0.0.1 # traffic sent on SCC ethrotate - When set to "no" U-Boot does not go through all available network interfaces. It just stays at the currently selected interface. netretry - When set to "no" each network operation will either succeed or fail without retrying. When set to "once" the network operation will fail when all the available network interfaces are tried once without success. Useful on scripts which control the retry operation themselves. npe_ucode - set load address for the NPE microcode silent_linux - If set then Linux will be told to boot silently, by changing the console to be empty. If "yes" it will be made silent. If "no" it will not be made silent. If unset, then it will be made silent if the U-Boot console is silent. tftpsrcp - If this is set, the value is used for TFTP's UDP source port. tftpdstp - If this is set, the value is used for TFTP's UDP destination port instead of the Well Know Port 69. tftpblocksize - Block size to use for TFTP transfers; if not set, we use the TFTP server's default block size tftptimeout - Retransmission timeout for TFTP packets (in milli- seconds, minimum value is 1000 = 1 second). Defines when a packet is considered to be lost so it has to be retransmitted. The default is 5000 = 5 seconds. Lowering this value may make downloads succeed faster in networks with high packet loss rates or with unreliable TFTP servers. tftptimeoutcountmax - maximum count of TFTP timeouts (no unit, minimum value = 0). Defines how many timeouts can happen during a single file transfer before that transfer is aborted. The default is 10, and 0 means 'no timeouts allowed'. Increasing this value may help downloads succeed with high packet loss rates, or with unreliable TFTP servers or client hardware. vlan - When set to a value < 4095 the traffic over Ethernet is encapsulated/received over 802.1q VLAN tagged frames. bootpretryperiod - Period during which BOOTP/DHCP sends retries. Unsigned value, in milliseconds. If not set, the period will be either the default (28000), or a value based on CONFIG_NET_RETRY_COUNT, if defined. This value has precedence over the valu based on CONFIG_NET_RETRY_COUNT. The following image location variables contain the location of images used in booting. The "Image" column gives the role of the image and is not an environment variable name. The other columns are environment variable names. "File Name" gives the name of the file on a TFTP server, "RAM Address" gives the location in RAM the image will be loaded to, and "Flash Location" gives the image's address in NOR flash or offset in NAND flash. *Note* - these variables don't have to be defined for all boards, some boards currently use other variables for these purposes, and some boards use these variables for other purposes. Image File Name RAM Address Flash Location ----- --------- ----------- -------------- u-boot u-boot u-boot_addr_r u-boot_addr Linux kernel bootfile kernel_addr_r kernel_addr device tree blob fdtfile fdt_addr_r fdt_addr ramdisk ramdiskfile ramdisk_addr_r ramdisk_addr The following environment variables may be used and automatically updated by the network boot commands ("bootp" and "rarpboot"), depending the information provided by your boot server: bootfile - see above dnsip - IP address of your Domain Name Server dnsip2 - IP address of your secondary Domain Name Server gatewayip - IP address of the Gateway (Router) to use hostname - Target hostname ipaddr - see above netmask - Subnet Mask rootpath - Pathname of the root filesystem on the NFS server serverip - see above There are two special Environment Variables: serial# - contains hardware identification information such as type string and/or serial number ethaddr - Ethernet address These variables can be set only once (usually during manufacturing of the board). U-Boot refuses to delete or overwrite these variables once they have been set once. Further special Environment Variables: ver - Contains the U-Boot version string as printed with the "version" command. This variable is readonly (see CONFIG_VERSION_VARIABLE). Please note that changes to some configuration parameters may take only effect after the next boot (yes, that's just like Windoze :-). Callback functions for environment variables: --------------------------------------------- For some environment variables, the behavior of u-boot needs to change when their values are changed. This functionality allows functions to be associated with arbitrary variables. On creation, overwrite, or deletion, the callback will provide the opportunity for some side effect to happen or for the change to be rejected. The callbacks are named and associated with a function using the U_BOOT_ENV_CALLBACK macro in your board or driver code. These callbacks are associated with variables in one of two ways. The static list can be added to by defining CONFIG_ENV_CALLBACK_LIST_STATIC in the board configuration to a string that defines a list of associations. The list must be in the following format: entry = variable_name[:callback_name] list = entry[,list] If the callback name is not specified, then the callback is deleted. Spaces are also allowed anywhere in the list. Callbacks can also be associated by defining the ".callbacks" variable with the same list format above. Any association in ".callbacks" will override any association in the static list. You can define CONFIG_ENV_CALLBACK_LIST_DEFAULT to a list (string) to define the ".callbacks" environment variable in the default or embedded environment. If CONFIG_REGEX is defined, the variable_name above is evaluated as a regular expression. This allows multiple variables to be connected to the same callback without explicitly listing them all out. The signature of the callback functions is: int callback(const char *name, const char *value, enum env_op op, int flags) * name - changed environment variable * value - new value of the environment variable * op - operation (create, overwrite, or delete) * flags - attributes of the environment variable change, see flags H_* in include/search.h The return value is 0 if the variable change is accepted and 1 otherwise. Command Line Parsing: ===================== There are two different command line parsers available with U-Boot: the old "simple" one, and the much more powerful "hush" shell: Old, simple command line parser: -------------------------------- - supports environment variables (through setenv / saveenv commands) - several commands on one line, separated by ';' - variable substitution using "...${name} ..." syntax
- special characters ('$', ';') can be escaped by prefixing with '\', for example: setenv bootcmd bootm \${address}
- You can also escape text by enclosing in single apostrophes, for example:
setenv addip 'setenv bootargs $bootargs ip=$ipaddr:$serverip:$gatewayip:$netmask:$hostname::off'

Hush shell:
-----------

- similar to Bourne shell, with control structures like
if...then...else...fi, for...do...done; while...do...done,
until...do...done, ...
- supports environment ("global") variables (through setenv / saveenv
commands) and local shell variables (through standard shell syntax
"name=value"); only environment variables can be used with "run"
command

General rules:
--------------

(1) If a command line (or an environment variable executed by a "run"
command) contains several commands separated by semicolon, and
one of these commands fails, then the remaining commands will be
executed anyway.

(2) If you execute several variables with one call to run (i. e.
calling run with a list of variables as arguments), any failing
command will cause "run" to terminate, i. e. the remaining
variables are not executed.

Note for Redundant Ethernet Interfaces:
=======================================

Some boards come with redundant Ethernet interfaces; U-Boot supports
such configurations and is capable of automatic selection of a
"working" interface when needed. MAC assignment works as follows:

Network interfaces are numbered eth0, eth1, eth2, ... Corresponding

If the network interface stores some valid MAC address (for instance
in SROM), this is used as default address if there is NO correspon-
ding setting in the environment; if the corresponding environment
variable is set, this overrides the settings in the card; that means:

o If the SROM has a valid MAC address, and there is no address in the
environment, the SROM's address is used.

o If there is no valid address in the SROM, and a definition in the
environment exists, then the value from the environment variable is
used.

o If both the SROM and the environment contain a MAC address, and

o If both the SROM and the environment contain a MAC address, and the
addresses differ, the value from the environment is used and a
warning is printed.

o If neither SROM nor the environment contain a MAC address, an error
is raised. If CONFIG_NET_RANDOM_ETHADDR is defined, then in this case
a random, locally-assigned MAC is used.

will be programmed into hardware as part of the initialization process.	 This
may be skipped by setting the appropriate 'ethmacskip' environment variable.
The naming convention is as follows:
"ethmacskip" (=>eth0), "eth1macskip" (=>eth1) etc.

Image Formats:
==============

U-Boot is capable of booting (and performing other auxiliary operations on)
images in two formats:

New uImage format (FIT)
-----------------------

Flexible and powerful format based on Flattened Image Tree -- FIT (similar
to Flattened Device Tree). It allows the use of images with multiple
components (several kernels, ramdisks, etc.), with contents protected by
SHA1, MD5 or CRC32. More details are found in the doc/uImage.FIT directory.

Old uImage format
-----------------

Old image format is based on binary files which can be basically anything,
preceded by a special header; see the definitions in include/image.h for
details; basically, the header defines the following image properties:

* Target Operating System (Provisions for OpenBSD, NetBSD, FreeBSD,
4.4BSD, Linux, SVR4, Esix, Solaris, Irix, SCO, Dell, NCR, VxWorks,
LynxOS, pSOS, QNX, RTEMS, INTEGRITY;
Currently supported: Linux, NetBSD, VxWorks, QNX, RTEMS, LynxOS,
INTEGRITY).
* Target CPU Architecture (Provisions for Alpha, ARM, Intel x86,
IA64, MIPS, NDS32, Nios II, PowerPC, IBM S390, SuperH, Sparc, Sparc 64 Bit;
Currently supported: ARM, Intel x86, MIPS, NDS32, Nios II, PowerPC).
* Compression Type (uncompressed, gzip, bzip2)
* Entry Point
* Image Name
* Image Timestamp

The header is marked by a special Magic Number, and both the header
and the data portions of the image are secured against corruption by
CRC32 checksums.

Linux Support:
==============

Although U-Boot should support any OS or standalone application
easily, the main focus has always been on Linux during the design of
U-Boot.

U-Boot includes many features that so far have been part of some
special "boot loader" code within the Linux kernel. Also, any
"initrd" images to be used are no longer part of one big Linux image;
instead, kernel and "initrd" are separate images. This implementation
serves several purposes:

- the same features can be used for other OS or standalone
applications (for instance: using compressed images to reduce the
Flash memory footprint)

- it becomes much easier to port new Linux kernel versions because
lots of low-level, hardware dependent stuff are done by U-Boot

- the same Linux kernel image can now be used with different "initrd"
images; of course this also means that different kernel images can
be run with the same "initrd". This makes testing easier (you don't
have to build a new "zImage.initrd" Linux image when you just
software is easier now.

Linux HOWTO:
============

Porting Linux to U-Boot based systems:
---------------------------------------

U-Boot cannot save you from doing all the necessary modifications to
configure the Linux device drivers for use with your target hardware
(no, we don't intend to provide a full virtual machine interface to
Linux :-).

But now you can ignore ALL boot loader code (in arch/powerpc/mbxboot).

include/asm-ppc/tqm8xx.h) includes the same definition of the Board
Information structure as we define in include/asm-<arch>/u-boot.h,
and make sure that your definition of IMAP_ADDR uses the same value
as your U-Boot configuration in CONFIG_SYS_IMMR.

Note that U-Boot now has a driver model, a unified model for drivers.
If you are adding a new driver, plumb it into driver model. If there
is no uclass available, you are encouraged to create one. See
doc/driver-model.

Configuring the Linux kernel:
-----------------------------

No specific requirements for U-Boot. Make sure you have some root
device (initial ramdisk, NFS) for your target system.

Building a Linux Image:
-----------------------

With U-Boot, "normal" build targets like "zImage" or "bzImage" are
not used. If you use recent kernel source, a new build target
"uImage" will exist which automatically builds an image usable by
U-Boot. Most older kernels also have support for a "pImage" target,
which was introduced for our predecessor project PPCBoot and uses a
100% compatible format.

Example:

make TQM850L_defconfig
make oldconfig
make dep
make uImage

The "uImage" build target uses a special tool (in 'tools/mkimage') to
encapsulate a compressed Linux kernel image with header	 information,
CRC32 checksum etc. for use with U-Boot. This is what we are doing:

* build a standard "vmlinux" kernel image (in ELF binary format):

* convert the kernel into a raw binary image:

${CROSS_COMPILE}-objcopy -O binary \ -R .note -R .comment \ -S vmlinux linux.bin * compress the binary image: gzip -9 linux.bin * package compressed binary image for U-Boot: mkimage -A ppc -O linux -T kernel -C gzip \ -a 0 -e 0 -n "Linux Kernel Image" \ -d linux.bin.gz uImage The "mkimage" tool can also be used to create ramdisk images for use with U-Boot, either separated from the Linux kernel image, or combined into one file. "mkimage" encapsulates the images with a 64 byte header containing information about target architecture, operating system, image type, compression method, entry points, time stamp, CRC32 checksums, etc. "mkimage" can be called in two ways: to verify existing images and print the header information, or to build new images. In the first form (with "-l" option) mkimage lists the information contained in the header of an existing U-Boot image; this includes checksum verification: tools/mkimage -l image -l ==> list image header information The second form (with "-d" option) is used to build a U-Boot image from a "data file" which is used as image payload: tools/mkimage -A arch -O os -T type -C comp -a addr -e ep \ -n name -d data_file image -A ==> set architecture to 'arch' -O ==> set operating system to 'os' -T ==> set image type to 'type' -C ==> set compression type 'comp' -a ==> set load address to 'addr' (hex) -e ==> set entry point to 'ep' (hex) -n ==> set image name to 'name' -d ==> use image data from 'datafile' Right now, all Linux kernels for PowerPC systems use the same load address (0x00000000), but the entry point address depends on the kernel version: - 2.2.x kernels have the entry point at 0x0000000C, - 2.3.x and later kernels have the entry point at 0x00000000. So a typical call to build a U-Boot image would read: -> tools/mkimage -n '2.4.4 kernel for TQM850L' \ > -A ppc -O linux -T kernel -C gzip -a 0 -e 0 \ > -d /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux.gz \ > examples/uImage.TQM850L Image Name: 2.4.4 kernel for TQM850L Created: Wed Jul 19 02:34:59 2000 Image Type: PowerPC Linux Kernel Image (gzip compressed) Data Size: 335725 Bytes = 327.86 kB = 0.32 MB Load Address: 0x00000000 Entry Point: 0x00000000 To verify the contents of the image (or check for corruption): -> tools/mkimage -l examples/uImage.TQM850L Image Name: 2.4.4 kernel for TQM850L Created: Wed Jul 19 02:34:59 2000 Image Type: PowerPC Linux Kernel Image (gzip compressed) Data Size: 335725 Bytes = 327.86 kB = 0.32 MB Load Address: 0x00000000 Entry Point: 0x00000000 NOTE: for embedded systems where boot time is critical you can trade speed for memory and install an UNCOMPRESSED image instead: this needs more space in Flash, but boots much faster since it does not need to be uncompressed: -> gunzip /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux.gz -> tools/mkimage -n '2.4.4 kernel for TQM850L' \ > -A ppc -O linux -T kernel -C none -a 0 -e 0 \ > -d /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux \ > examples/uImage.TQM850L-uncompressed Image Name: 2.4.4 kernel for TQM850L Created: Wed Jul 19 02:34:59 2000 Image Type: PowerPC Linux Kernel Image (uncompressed) Data Size: 792160 Bytes = 773.59 kB = 0.76 MB Load Address: 0x00000000 Entry Point: 0x00000000 Similar you can build U-Boot images from a 'ramdisk.image.gz' file when your kernel is intended to use an initial ramdisk: -> tools/mkimage -n 'Simple Ramdisk Image' \ > -A ppc -O linux -T ramdisk -C gzip \ > -d /LinuxPPC/images/SIMPLE-ramdisk.image.gz examples/simple-initrd Image Name: Simple Ramdisk Image Created: Wed Jan 12 14:01:50 2000 Image Type: PowerPC Linux RAMDisk Image (gzip compressed) Data Size: 566530 Bytes = 553.25 kB = 0.54 MB Load Address: 0x00000000 Entry Point: 0x00000000 The "dumpimage" is a tool to disassemble images built by mkimage. Its "-i" option performs the converse operation of the mkimage's second form (the "-d" option). Given an image built by mkimage, the dumpimage extracts a "data file" from the image: tools/dumpimage -i image -T type -p position data_file -i ==> extract from the 'image' a specific 'data_file' -T ==> set image type to 'type' -p ==> 'position' (starting at 0) of the 'data_file' inside the 'image' Installing a Linux Image: ------------------------- To downloading a U-Boot image over the serial (console) interface, you must convert the image to S-Record format: objcopy -I binary -O srec examples/image examples/image.srec The 'objcopy' does not understand the information in the U-Boot image header, so the resulting S-Record file will be relative to address 0x00000000. To load it to a given address, you need to specify the target address as 'offset' parameter with the 'loads' command. Example: install the image to address 0x40100000 (which on the TQM8xxL is in the first Flash bank): => erase 40100000 401FFFFF .......... done Erased 8 sectors => loads 40100000 ## Ready for S-Record download ... ~>examples/image.srec 1 2 3 4 5 6 7 8 9 10 11 12 13 ... ... 15989 15990 15991 15992 [file transfer complete] [connected] ## Start Addr = 0x00000000 You can check the success of the download using the 'iminfo' command; this includes a checksum verification so you can be sure no data corruption happened: => imi 40100000 ## Checking Image at 40100000 ... Image Name: 2.2.13 for initrd on TQM850L Image Type: PowerPC Linux Kernel Image (gzip compressed) Data Size: 335725 Bytes = 327 kB = 0 MB Load Address: 00000000 Entry Point: 0000000c Verifying Checksum ... OK Boot Linux: ----------- The "bootm" command is used to boot an application that is stored in memory (RAM or Flash). In case of a Linux kernel image, the contents of the "bootargs" environment variable is passed to the kernel as parameters. You can check and modify this variable using the "printenv" and "setenv" commands: => printenv bootargs bootargs=root=/dev/ram => setenv bootargs root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2 => printenv bootargs bootargs=root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2 => bootm 40020000 ## Booting Linux kernel at 40020000 ... Image Name: 2.2.13 for NFS on TQM850L Image Type: PowerPC Linux Kernel Image (gzip compressed) Data Size: 381681 Bytes = 372 kB = 0 MB Load Address: 00000000 Entry Point: 0000000c Verifying Checksum ... OK Uncompressing Kernel Image ... OK Linux version 2.2.13 (wd@denx.local.net) (gcc version 2.95.2 19991024 (release)) #1 Wed Jul 19 02:35:17 MEST 2000 Boot arguments: root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2 time_init: decrementer frequency = 187500000/60 Calibrating delay loop... 49.77 BogoMIPS Memory: 15208k available (700k kernel code, 444k data, 32k init) [c0000000,c1000000] ... If you want to boot a Linux kernel with initial RAM disk, you pass the memory addresses of both the kernel and the initrd image (PPBCOOT format!) to the "bootm" command: => imi 40100000 40200000 ## Checking Image at 40100000 ... Image Name: 2.2.13 for initrd on TQM850L Image Type: PowerPC Linux Kernel Image (gzip compressed) Data Size: 335725 Bytes = 327 kB = 0 MB Load Address: 00000000 Entry Point: 0000000c Verifying Checksum ... OK ## Checking Image at 40200000 ... Image Name: Simple Ramdisk Image Image Type: PowerPC Linux RAMDisk Image (gzip compressed) Data Size: 566530 Bytes = 553 kB = 0 MB Load Address: 00000000 Entry Point: 00000000 Verifying Checksum ... OK => bootm 40100000 40200000 ## Booting Linux kernel at 40100000 ... Image Name: 2.2.13 for initrd on TQM850L Image Type: PowerPC Linux Kernel Image (gzip compressed) Data Size: 335725 Bytes = 327 kB = 0 MB Load Address: 00000000 Entry Point: 0000000c Verifying Checksum ... OK Uncompressing Kernel Image ... OK ## Loading RAMDisk Image at 40200000 ... Image Name: Simple Ramdisk Image Image Type: PowerPC Linux RAMDisk Image (gzip compressed) Data Size: 566530 Bytes = 553 kB = 0 MB Load Address: 00000000 Entry Point: 00000000 Verifying Checksum ... OK Loading Ramdisk ... OK Linux version 2.2.13 (wd@denx.local.net) (gcc version 2.95.2 19991024 (release)) #1 Wed Jul 19 02:32:08 MEST 2000 Boot arguments: root=/dev/ram time_init: decrementer frequency = 187500000/60 Calibrating delay loop... 49.77 BogoMIPS ... RAMDISK: Compressed image found at block 0 VFS: Mounted root (ext2 filesystem). bash# Boot Linux and pass a flat device tree: ----------- First, U-Boot must be compiled with the appropriate defines. See the section titled "Linux Kernel Interface" above for a more in depth explanation. The following is an example of how to start a kernel and pass an updated flat device tree: => print oftaddr oftaddr=0x300000 => print oft oft=oftrees/mpc8540ads.dtb => tftp$oftaddr $oft Speed: 1000, full duplex Using TSEC0 device TFTP from server 192.168.1.1; our IP address is 192.168.1.101 Filename 'oftrees/mpc8540ads.dtb'. Load address: 0x300000 Loading: # done Bytes transferred = 4106 (100a hex) => tftp$loadaddr $bootfile Speed: 1000, full duplex Using TSEC0 device TFTP from server 192.168.1.1; our IP address is 192.168.1.2 Filename 'uImage'. Load address: 0x200000 Loading:############ done Bytes transferred = 1029407 (fb51f hex) => print loadaddr loadaddr=200000 => print oftaddr oftaddr=0x300000 => bootm$loadaddr - oftaddr ## Booting image at 00200000 ... Image Name: Linux-2.6.17-dirty Image Type: PowerPC Linux Kernel Image (gzip compressed) Data Size: 1029343 Bytes = 1005.2 kB Load Address: 00000000 Entry Point: 00000000 Verifying Checksum ... OK Uncompressing Kernel Image ... OK Booting using flat device tree at 0x300000 Using MPC85xx ADS machine description Memory CAM mapping: CAM0=256Mb, CAM1=256Mb, CAM2=0Mb residual: 0Mb [snip] More About U-Boot Image Types: ------------------------------ U-Boot supports the following image types: "Standalone Programs" are directly runnable in the environment provided by U-Boot; it is expected that (if they behave well) you can continue to work in U-Boot after return from the Standalone Program. "OS Kernel Images" are usually images of some Embedded OS which will take over control completely. Usually these programs will install their own set of exception handlers, device drivers, set up the MMU, etc. - this means, that you cannot expect to re-enter U-Boot except by resetting the CPU. "RAMDisk Images" are more or less just data blocks, and their parameters (address, size) are passed to an OS kernel that is being started. "Multi-File Images" contain several images, typically an OS (Linux) kernel image and one or more data images like RAMDisks. This construct is useful for instance when you want to boot over the network using BOOTP etc., where the boot server provides just a single image file, but you want to get for instance an OS kernel and a RAMDisk image. "Multi-File Images" start with a list of image sizes, each image size (in bytes) specified by an "uint32_t" in network byte order. This list is terminated by an "(uint32_t)0". Immediately after the terminating 0 follow the images, one by one, all aligned on "uint32_t" boundaries (size rounded up to a multiple of 4 bytes). "Firmware Images" are binary images containing firmware (like U-Boot or FPGA images) which usually will be programmed to flash memory. "Script files" are command sequences that will be executed by U-Boot's command interpreter; this feature is especially useful when you configure U-Boot to use a real shell (hush) as command interpreter. Booting the Linux zImage: ------------------------- On some platforms, it's possible to boot Linux zImage. This is done using the "bootz" command. The syntax of "bootz" command is the same as the syntax of "bootm" command. Note, defining the CONFIG_SUPPORT_RAW_INITRD allows user to supply kernel with raw initrd images. The syntax is slightly different, the address of the initrd must be augmented by it's size, in the following format: "<initrd addres>:<initrd size>". Standalone HOWTO: ================= One of the features of U-Boot is that you can dynamically load and run "standalone" applications, which can use some resources of U-Boot like console I/O functions or interrupt services. Two simple examples are included with the sources: "Hello World" Demo: ------------------- 'examples/hello_world.c' contains a small "Hello World" Demo application; it is automatically compiled when you build U-Boot. It's configured to run at address 0x00040004, so you can play with it like that: => loads ## Ready for S-Record download ... ~>examples/hello_world.srec 1 2 3 4 5 6 7 8 9 10 11 ... [file transfer complete] [connected] ## Start Addr = 0x00040004 => go 40004 Hello World! This is a test. ## Starting application at 0x00040004 ... Hello World argc = 7 argv[0] = "40004" argv[1] = "Hello" argv[2] = "World!" argv[3] = "This" argv[4] = "is" argv[5] = "a" argv[6] = "test." argv[7] = "<NULL>" Hit any key to exit ... ## Application terminated, rc = 0x0 Another example, which demonstrates how to register a CPM interrupt handler with the U-Boot code, can be found in 'examples/timer.c'. Here, a CPM timer is set up to generate an interrupt every second. The interrupt service routine is trivial, just printing a '.' character, but this is just a demo program. The application can be controlled by the following keys: ? - print current values og the CPM Timer registers b - enable interrupts and start timer e - stop timer and disable interrupts q - quit application => loads ## Ready for S-Record download ... ~>examples/timer.srec 1 2 3 4 5 6 7 8 9 10 11 ... [file transfer complete] [connected] ## Start Addr = 0x00040004 => go 40004 ## Starting application at 0x00040004 ... TIMERS=0xfff00980 Using timer 1 tgcr @ 0xfff00980, tmr @ 0xfff00990, trr @ 0xfff00994, tcr @ 0xfff00998, tcn @ 0xfff0099c, ter @ 0xfff009b0 Hit 'b': [q, b, e, ?] Set interval 1000000 us Enabling timer Hit '?': [q, b, e, ?] ........ tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0xef6, ter=0x0 Hit '?': [q, b, e, ?] . tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x2ad4, ter=0x0 Hit '?': [q, b, e, ?] . tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x1efc, ter=0x0 Hit '?': [q, b, e, ?] . tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x169d, ter=0x0 Hit 'e': [q, b, e, ?] ...Stopping timer Hit 'q': [q, b, e, ?] ## Application terminated, rc = 0x0 Minicom warning: ================ Over time, many people have reported problems when trying to use the "minicom" terminal emulation program for serial download. I (wd) consider minicom to be broken, and recommend not to use it. Under Unix, I recommend to use C-Kermit for general purpose use (and especially for kermit binary protocol download ("loadb" command), and use "cu" for S-Record download ("loads" command). See http://www.denx.de/wiki/view/DULG/SystemSetup#Section_4.3. for help with kermit. Nevertheless, if you absolutely want to use it try adding this configuration to your "File transfer protocols" section: Name Program Name U/D FullScr IO-Red. Multi X kermit /usr/bin/kermit -i -l %l -s Y U Y N N Y kermit /usr/bin/kermit -i -l %l -r N D Y N N NetBSD Notes: ============= Starting at version 0.9.2, U-Boot supports NetBSD both as host (build U-Boot) and target system (boots NetBSD/mpc8xx). Building requires a cross environment; it is known to work on NetBSD/i386 with the cross-powerpc-netbsd-1.3 package (you will also need gmake since the Makefiles are not compatible with BSD make). Note that the cross-powerpc package does not install include files; attempting to build U-Boot will fail because <machine/ansi.h> is missing. This file has to be installed and patched manually: # cd /usr/pkg/cross/powerpc-netbsd/include # mkdir powerpc # ln -s powerpc machine # cp /usr/src/sys/arch/powerpc/include/ansi.h powerpc/ansi.h #{EDIT} powerpc/ansi.h	## must remove __va_list, _BSD_VA_LIST

Native builds *don't* work due to incompatibilities between native
and U-Boot include files.

Booting assumes that (the first part of) the image booted is a
proper. Loader sources will eventually appear in the NetBSD source
tree (probably in sys/arc/mpc8xx/stand/u-boot_stage2/); in the
meantime, see ftp://ftp.denx.de/pub/u-boot/ppcboot_stage2.tar.gz

Implementation Internals:
=========================

The following is not intended to be a complete description of every
implementation detail. However, it should help to understand the
inner workings of U-Boot and make it easier to port it to custom
hardware.

Initial Stack, Global Data:
---------------------------

The implementation of U-Boot is complicated by the fact that U-Boot
system RAM (because the memory controller is not initialized yet).
This means that we don't have writable Data or BSS segments, and BSS
is not initialized as zero. To be able to get a C environment working
at all, we have to allocate at least a minimal stack. Implementation
options for this are defined and restricted by the CPU used: Some CPU
models provide on-chip memory (like the IMMR area on MPC8xx and
MPC826x processors), on others (parts of) the data cache can be
locked as (mis-) used as memory, etc.

Chris Hallinan posted a good summary of these issues to the
U-Boot mailing list:

Subject: RE: [U-Boot-Users] RE: More On Memory Bank x (nothingness)?
From: "Chris Hallinan" <clh@net1plus.com>
Date: Mon, 10 Feb 2003 16:43:46 -0500 (22:43 MET)
...

Correct me if I'm wrong, folks, but the way I understand it
is this: Using DCACHE as initial RAM for Stack, etc, does not
require any physical RAM backing up the cache. The cleverness
is that the cache is being used as a temporary supply of
necessary storage before the SDRAM controller is setup. It's
beyond the scope of this list to explain the details, but you
can see how this works by studying the cache architecture and
operation in the architecture and processor-specific manuals.

OCM is On Chip Memory, which I believe the 405GP has 4K. It
is another option for the system designer to use as an
initial stack/RAM area prior to SDRAM being available. Either
option should work for you. Using CS 4 should be fine if your
board designers haven't used it for something that would
cause you grief during the initial boot! It is frequently not
used.

CONFIG_SYS_INIT_RAM_ADDR should be somewhere that won't interfere
with your processor/board/system design. The default value
you will find in any recent u-boot distribution in
walnut.h should work for you. I'd set it to a value larger
than your SDRAM module. If you have a 64MB SDRAM module, set
it above 400_0000. Just make sure your board has no resources
that are supposed to respond to that address! That code in
start.S has been around a while and should work as is when
you get the config right.

-Chris Hallinan
DS4.COM, Inc.

It is essential to remember this, since it has some impact on the C
code for the initialization procedures:

* Initialized global data (data segment) is read-only. Do not attempt
to write it.

* Do not use any uninitialized global data (or implicitly initialized
as zero data - BSS segment) at all - this is undefined, initiali-
zation is performed later (when relocating to RAM).

* Stack space is very limited. Avoid big data buffers or things like
that.

Having only the stack as writable memory limits means we cannot use
normal global data to share information between the code. But it
turned out that the implementation of U-Boot can be greatly
simplified by making a global data structure (gd_t) available to all
functions. We could pass a pointer to this data as argument to _all_
functions, but this would bloat the code. Instead we use a feature of
the GCC compiler (Global Register Variables) to share the data: we
place a pointer (gd) to the global data into a register which we
reserve for this purpose.

When choosing a register for such a purpose we are restricted by the
relevant  (E)ABI  specifications for the current architecture, and by
GCC's implementation.

For PowerPC, the following registers have specific use:
R1:	stack pointer
R2:	reserved for system use
R3-R4:	parameter passing and return values
R5-R10: parameter passing
R13:	small data area pointer
R30:	GOT pointer
R31:	frame pointer

(U-Boot also uses R12 as internal GOT pointer. r12
is a volatile register so r12 needs to be reset when
going back and forth between asm and C)

==> U-Boot will use R2 to hold a pointer to the global data

Note: on PPC, we could use a static initializer (since the
address of the global data structure is known at compile time),
but it turned out that reserving a register results in somewhat
smaller code - although the code savings are not that big (on
average for all boards 752 bytes for the whole U-Boot image,
624 text + 127 data).

On ARM, the following registers are used:

R0:	function argument word/integer result
R1-R3:	function argument word
R9:	platform specific
R10:	stack limit (used only if stack checking is enabled)
R11:	argument (frame) pointer
R12:	temporary workspace
R13:	stack pointer
R15:	program counter

==> U-Boot will use R9 to hold a pointer to the global data

Note: on ARM, only R_ARM_RELATIVE relocations are supported.

On Nios II, the ABI is documented here:
http://www.altera.com/literature/hb/nios2/n2cpu_nii51016.pdf

==> U-Boot will use gp to hold a pointer to the global data

Note: on Nios II, we give "-G0" option to gcc and don't use gp
to access small data sections, so gp is free.

On NDS32, the following registers are used:

R0-R1:	argument/return
R2-R5:	argument
R15:	temporary register for assembler
R16:	trampoline register
R28:	frame pointer (FP)
R29:	global pointer (GP)
R31:	stack pointer (SP)
PC:	program counter (PC)

==> U-Boot will use R10 to hold a pointer to the global data

NOTE: DECLARE_GLOBAL_DATA_PTR must be used with file-global scope,
or current versions of GCC may "optimize" the code too much.

On RISC-V, the following registers are used:

x0: hard-wired zero (zero)
x2:	stack pointer (sp)
x3:	global pointer (gp)
x8:	frame pointer (fp)
x10-x11:	arguments/return values (a0-1)
x12-x17:	arguments (a2-7)
x28-31:	 temporaries (t3-6)
pc:	program counter (pc)

==> U-Boot will use gp to hold a pointer to the global data

Memory Management:
------------------

U-Boot runs in system state and uses physical addresses, i.e. the
MMU is not used either for address mapping nor for memory protection.

The available memory is mapped to fixed addresses using the memory
controller. In this process, a contiguous block is formed for each
memory type (Flash, SDRAM, SRAM), even when it consists of several
physical memory banks.

U-Boot is installed in the first 128 kB of the first Flash bank (on
TQM8xxL modules this is the range 0x40000000 ... 0x4001FFFF). After
booting and sizing and initializing DRAM, the code relocates itself
to the upper end of DRAM. Immediately below the U-Boot code some
memory is reserved for use by malloc() [see CONFIG_SYS_MALLOC_LEN
configuration setting]. Below that, a structure with global Board
Info data is placed, followed by the stack (growing downward).

Additionally, some exception handler code is copied to the low 8 kB
of DRAM (0x00000000 ... 0x00001FFF).

So a typical memory configuration with 16 MB of DRAM could look like
this:

0x0000 0000	Exception Vector code
:
0x0000 1FFF
0x0000 2000	Free for Application Use
:
:

:
:
0x00FB FF20	Monitor Stack (Growing downward)
0x00FB FFAC	Board Info Data and permanent copy of global data
0x00FC 0000	Malloc Arena
:
0x00FD FFFF
0x00FE 0000	RAM Copy of Monitor Code
...		eventually: LCD or video framebuffer
...		eventually: pRAM (Protected RAM - unchanged by reset)
0x00FF FFFF	[End of RAM]

System Initialization:
----------------------

In the reset configuration, U-Boot starts at the reset entry point
(on most PowerPC systems at address 0x00000100). Because of the reset
configuration for CS0# this is a mirror of the on board Flash memory.
To be able to re-map memory U-Boot then jumps to its link address.
To be able to implement the initialization code in C, a (small!)
initial stack is set up in the internal Dual Ported RAM (in case CPUs
which provide such a feature like), or in a locked part of the data
cache. After that, U-Boot initializes the CPU core, the caches and
the SIU.

Next, all (potentially) available memory banks are mapped using a
preliminary mapping. For example, we put them on 512 MB boundaries
(multiples of 0x20000000: SDRAM on 0x00000000 and 0x20000000, Flash
on 0x40000000 and 0x60000000, SRAM on 0x80000000). Then UPM A is
programmed for SDRAM access. Using the temporary configuration, a
simple memory test is run that determines the size of the SDRAM
banks.

When there is more than one SDRAM bank, and the banks are of
different size, the largest is mapped first. For equal size, the first
bank (CS2#) is mapped first. The first mapping is always for address
0x00000000, with any additional banks following immediately to create
contiguous memory starting from 0.

Then, the monitor installs itself at the upper end of the SDRAM area
and allocates memory for use by malloc() and for the global Board
Info data; also, the exception vector code is copied to the low RAM
pages, and the final stack is set up.

Only after this relocation will you have a "normal" C environment;
until that you are restricted in several ways, mostly because you are
running from ROM, and because the code will have to be relocated to a

U-Boot Porting Guide:
----------------------

[Based on messages by Jerry Van Baren in the U-Boot-Users mailing
list, October 2002]

int main(int argc, char *argv[])
{
sighandler_t no_more_time;

signal(SIGALRM, no_more_time);
alarm(PROJECT_DEADLINE - toSec (3 * WEEK));

if (available_money > available_manpower) {
Pay consultant to port U-Boot;
return 0;
}

Subscribe to u-boot mailing list;

if (clueless)
email("Hi, I am new to U-Boot, how do I get started?");

while (learning) {
/* find . -name "*.[chS]" | xargs grep -i <keyword> */
}

if (available_money > toLocalCurrency (\$2500))
else
Add a lot of aggravation and time;

if (a similar board exists) {	/* hopefully... */
cp -a board/<similar> board/<myboard>
cp include/configs/<similar>.h include/configs/<myboard>.h
} else {
Create your own board support subdirectory;
Create your own board include/configs/<myboard>.h file;
}
Edit new board/<myboard> files
Edit new include/configs/<myboard>.h

while (!accepted) {
while (!running) {
do {
} until (compiles);
Debug;
if (clueless)
email("Hi, I am having problems...");
}
Send patch file to the U-Boot email list;
if (reasonable critiques)
Incorporate improvements from email list code review;
else
Defend code as written;
}

return 0;
}

void no_more_time (int sig)
{
hire_a_guru();
}

Coding Standards:
-----------------

All contributions to U-Boot should conform to the Linux kernel
coding style; see the kernel coding style guide at
https://www.kernel.org/doc/html/latest/process/coding-style.html, and the
script "scripts/Lindent" in your Linux kernel source directory.

Source files originating from a different project (for example the
MTD subsystem) are generally exempt from these guidelines and are not
reformatted to ease subsequent migration to newer versions of those
sources.

Please note that U-Boot is implemented in C (and to some small parts in
Assembler); no C++ is used, so please do not use C++ style comments (//)

Please also stick to the following formatting rules:
- remove any trailing white space
- use TAB characters for indentation and vertical alignment, not spaces
- make sure NOT to use DOS '\r\n' line feeds
- do not add more than 2 consecutive empty lines to source files
- do not add trailing empty lines to source files

Submissions which do not conform to the standards may be returned
with a request to reformat the changes.

Submitting Patches:
-------------------

Since the number of patches for U-Boot is growing, we need to
establish some rules. Submissions which do not conform to these rules
may be rejected, even when they contain important and valuable stuff.

Patches shall be sent to the u-boot mailing list <u-boot@lists.denx.de>;
see https://lists.denx.de/listinfo/u-boot

When you send a patch, please include the following information with
it:

* For bug fixes: a description of the bug and how your patch fixes
this bug. Please try to include a way of demonstrating that the
patch actually fixes something.

* For new features: a description of the feature and your
implementation.

* For major contributions, add a MAINTAINERS file with your
information and associated file and directory references.

* When you add support for a new board, don't forget to add a
maintainer e-mail address to the boards.cfg file, too.

document these in the README file.

* The patch itself. If you are using git (which is *strongly*
recommended) you can easily generate the patch using the
"git format-patch". If you then use "git send-email" to send it to
the U-Boot mailing list, you will avoid most of the common problems
with some other mail clients.

If you cannot use git, use "diff -purN OLD NEW". If your version of
diff does not support these options, then get the latest version of
GNU diff.

The current directory when running this command shall be the parent
directory of the U-Boot source tree (i. e. please make sure that
your patch includes sufficient directory information for the
affected files).

We prefer patches as plain text. MIME attachments are discouraged,
and compressed attachments must not be used.

* If one logical set of modifications affects or creates several
files, all these changes shall be submitted in a SINGLE patch file.

* Changesets that contain different, unrelated modifications shall be
submitted as SEPARATE patches, one patch per changeset.

Notes:

* Before sending the patch, run the buildman script on your patched
source tree and make sure that no errors or warnings are reported
for any of the boards.

* Keep your modifications to the necessary minimum: A patch
containing several unrelated changes or arbitrary reformats will be
returned with a request to re-formatting / split it.

* If you modify existing code, make sure that your new code does not
add to the memory footprint of the code ;-) Small is beautiful!
When adding new features, these should compile conditionally only
(using #ifdef), and the resulting code with the new feature
disabled must not need more memory than the old code without your
modification.

* Remember that there is a size limit of 100 kB per message on the
u-boot mailing list. Bigger patches will be moderated. If they are
reasonable and not too big, they will be acknowledged. But patches
bigger than the size limit should be avoided.

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