README

# 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
initialize and test the hardware or to download and run application
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
header files in common, and special provision has been made to
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
add new commands. Also, instead of permanently adding rarely used
code (for instance hardware test utilities) to the monitor, you can
load and run it dynamically.


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.
Please see https://lists.denx.de/pipermail/u-boot and
https://marc.info/?l=u-boot

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

The U-Boot source code is maintained in the Git repository at
https://source.denx.de/u-boot/u-boot.git ; you can browse it online at
https://source.denx.de/u-boot/u-boot

The "Tags" links on this page allow you to download tarballs of
any version you might be interested in. Official releases are also
available from the DENX file server through HTTPS or FTP.
https://ftp.denx.de/pub/u-boot/
ftp://ftp.denx.de/pub/u-boot/


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

- start from 8xxrom sources
- create PPCBoot project (https://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
  * S-Record download
  * network boot
  * ATA disk / SCSI ... boot
- create ARMBoot project (https://sourceforge.net/projects/armboot)
- add other CPU families (starting with ARM)
- create U-Boot project (https://sourceforge.net/projects/u-boot)
- current project page: see https://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
  /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
  /xtensa		Files generic to Xtensa 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.
/env			Environment files
/examples		Example code for standalone applications, etc.
/fs			Filesystem code (cramfs, ext2, jffs2, etc.)
/include		Header Files
/lib			Library routines generic to all architectures
/Licenses		Various license files
/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/sandbox.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
	- there 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
		CONFIG_SPL_STACK_R_ADDR points into SDRAM
	- 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.

		See Freescale App Note 4493 for more information about
		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.

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

		CONFIG_SYS_FSL_DSP_M2_RAM_ADDR
		This value denotes start offset of M2 memory
		which is directly connected to the DSP core.

		CONFIG_SYS_FSL_DSP_M3_RAM_ADDR
		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.

		CONFIG_SYS_FSL_DDR_ADDR
		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.
		Please refer doc/README.pblimage for more details

		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.
		Please refer doc/README.pblimage for more details

		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
		interleaving mode, handled by Dickens for Freescale layerscape
		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_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
		 * Adds the "fdt" command
		 * The bootm command automatically updates the fdt

		OF_TBCLK - The timebase frequency.

		boards with QUICC Engines require OF_QE to set UCC MAC
		addresses

		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 https://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
		environments variables: bootdev, bootfile, ipaddr, netmask,
		serverip, gatewayip, hostname, othbootargs.
		It loads the vxWorks image pointed bootfile.

		Note: If a "bootargs" environment is defined, it will override
		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

- 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.

- Serial Download Echo Mode:
		CONFIG_LOADS_ECHO
		If defined to 1, all characters received during a
		serial download (using the "loads" command) are
		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
		add support for your architecture, add '#include <iotrace.h>'
		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
			Start:  10000000	(buffer start address)
			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_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
			correctnessof 10/100 link speed update.

		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_PHY_ADDR
			Define the ETH PHY's address

			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.

			CONFIG_TPM_TIS_BASE_ADDRESS
			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.

		CONFIG_USB_DWC2_REG_ADDR the physical CPU address of the DWC2
		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
			for your device
			- 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

			CONFIG_SH_MMCIF_ADDR
			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
		instead.

- 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_SYS_DIU_ADDR
			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.

- 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

- IP address:
		CONFIG_IPADDR

		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.
		(Environment variable "ipaddr")

- Server IP address:
		CONFIG_SERVERIP

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

		CONFIG_KEEP_SERVERADDR

		Keeps the server's MAC address, in the env 'serveraddr'
		for passing to bootargs (like Linux's netconsole option)

- Gateway IP address:
		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")

- Subnet mask:
		CONFIG_NETMASK

		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.
		(Environment variable "netmask")

- 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.

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

		CONFIG_BOOTP_NISDOMAIN
		CONFIG_BOOTP_BOOTFILESIZE
		CONFIG_BOOTP_NTPSERVER
		CONFIG_BOOTP_TIMEOFFSET
		CONFIG_BOOTP_VENDOREX