# 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 http://lists.denx.de/pipermail/u-boot and
  http://dir.gmane.org/gmane.comp.boot-loaders.u-boot

  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
  
  The "snapshot" links on this page allow you to download tarballs of

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

  available for FTP download from the ftp://ftp.denx.de/pub/u-boot/
  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
    * S-Record download
    * 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.)
  /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/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
  		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_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
  		 * Adds the "fdt" command

  		 * 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
  		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 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

  		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 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.

  - 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_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
  			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.

  - 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

  		specified in "splashimage" is loaded instead. The
  		console is redirected to the "nulldev", too. This
  		allows for a "silent" boot where a splash screen is
  		loaded very quickly after power-on.

  		CONFIG_SPLASHIMAGE_GUARD
  
  		If this option is set, then U-Boot will prevent the environment
  		variable "splashimage" from being set to a problematic address

  		(see doc/README.displaying-bmps).

  		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

  - 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_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.

  		CONFIG_BOOTP_MAY_FAIL - If the DHCP server is not found
  		after the configured retry count, the call will fail
  		instead of starting over.  This can be used to fail over
  		to Link-local IP address configuration if the DHCP server
  		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.

   - Link-local IP address negotiation:
  		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.
  
  		See doc/README.link-local for more information.

   - MAC address from environment variables
  
  		FDT_SEQ_MACADDR_FROM_ENV
  
  		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
  		soon as a reply to a BOOTP request was received, and
  		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.

  		Additional options:

  		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
  
  		  - CONFIG_SYS_RCAR_I2C0_BASE for setting the register channel 0
  		  - CONFIG_SYS_RCAR_I2C0_SPEED for for the speed channel 0
  		  - CONFIG_SYS_RCAR_I2C1_BASE for setting the register channel 1
  		  - CONFIG_SYS_RCAR_I2C1_SPEED for for the speed channel 1
  		  - CONFIG_SYS_RCAR_I2C2_BASE for setting the register channel 2
  		  - CONFIG_SYS_RCAR_I2C2_SPEED for for the speed channel 2
  		  - CONFIG_SYS_RCAR_I2C3_BASE for setting the register channel 3
  		  - CONFIG_SYS_RCAR_I2C3_SPEED for for the speed channel 3
  		  - CONFIF_SYS_RCAR_I2C_NUM_CONTROLLERS for number of 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

  		additional defines:
  
  		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)

  		I2C_READ

  		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.

  		CONFIG_SOFT_I2C_READ_REPEATED_START
  
  		defining this will force the i2c_read() function in
  		the soft_i2c driver to perform an I2C repeated start
  		between writing the address pointer and reading the
  		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
  		loading. For example, abort during Virtex II
  		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

  		"ethaddr" (Ethernet Address) to be parameters that

  		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
  		read-only.]

  		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.