README

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

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 and CREDITS files to find out
who contributed the specific port. The boards.cfg file lists board
maintainers.

Note: There is no CHANGELOG file in the actual U-Boot source tree;
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
  * PCMCIA / CompactFlash / 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 candiate 1 for September 2010 release


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

/arch			Architecture specific files
  /arc			Files generic to ARC architecture
    /cpu		CPU specific files
      /arc700		Files specific to ARC 700 CPUs
    /lib		Architecture specific library files
  /arm			Files generic to ARM architecture
    /cpu		CPU specific files
      /arm720t		Files specific to ARM 720 CPUs
      /arm920t		Files specific to ARM 920 CPUs
	/at91		Files specific to Atmel AT91RM9200 CPU
	/imx		Files specific to Freescale MC9328 i.MX CPUs
	/s3c24x0	Files specific to Samsung S3C24X0 CPUs
      /arm926ejs	Files specific to ARM 926 CPUs
      /arm1136		Files specific to ARM 1136 CPUs
      /pxa		Files specific to Intel XScale PXA CPUs
      /sa1100		Files specific to Intel StrongARM SA1100 CPUs
    /lib		Architecture specific library files
  /avr32		Files generic to AVR32 architecture
    /cpu		CPU specific files
    /lib		Architecture specific library files
  /blackfin		Files generic to Analog Devices Blackfin architecture
    /cpu		CPU specific files
    /lib		Architecture specific library files
  /m68k			Files generic to m68k architecture
    /cpu		CPU specific files
      /mcf52x2		Files specific to Freescale ColdFire MCF52x2 CPUs
      /mcf5227x		Files specific to Freescale ColdFire MCF5227x CPUs
      /mcf532x		Files specific to Freescale ColdFire MCF5329 CPUs
      /mcf5445x		Files specific to Freescale ColdFire MCF5445x CPUs
      /mcf547x_8x	Files specific to Freescale ColdFire MCF547x_8x CPUs
    /lib		Architecture specific library files
  /microblaze		Files generic to microblaze architecture
    /cpu		CPU specific files
    /lib		Architecture specific library files
  /mips			Files generic to MIPS architecture
    /cpu		CPU specific files
      /mips32		Files specific to MIPS32 CPUs
      /mips64		Files specific to MIPS64 CPUs
    /lib		Architecture specific library files
  /nds32		Files generic to NDS32 architecture
    /cpu		CPU specific files
      /n1213		Files specific to Andes Technology N1213 CPUs
    /lib		Architecture specific library files
  /nios2		Files generic to Altera NIOS2 architecture
    /cpu		CPU specific files
    /lib		Architecture specific library files
  /openrisc		Files generic to OpenRISC architecture
    /cpu		CPU specific files
    /lib		Architecture specific library files
  /powerpc		Files generic to PowerPC architecture
    /cpu		CPU specific files
      /74xx_7xx		Files specific to Freescale MPC74xx and 7xx CPUs
      /mpc5xx		Files specific to Freescale MPC5xx CPUs
      /mpc5xxx		Files specific to Freescale MPC5xxx CPUs
      /mpc8xx		Files specific to Freescale MPC8xx CPUs
      /mpc824x		Files specific to Freescale MPC824x CPUs
      /mpc8260		Files specific to Freescale MPC8260 CPUs
      /mpc85xx		Files specific to Freescale MPC85xx CPUs
      /ppc4xx		Files specific to AMCC PowerPC 4xx CPUs
    /lib		Architecture specific library files
  /sh			Files generic to SH architecture
    /cpu		CPU specific files
      /sh2		Files specific to sh2 CPUs
      /sh3		Files specific to sh3 CPUs
      /sh4		Files specific to sh4 CPUs
    /lib		Architecture specific library files
  /sparc		Files generic to SPARC architecture
    /cpu		CPU specific files
      /leon2		Files specific to Gaisler LEON2 SPARC CPU
      /leon3		Files specific to Gaisler LEON3 SPARC CPU
    /lib		Architecture specific library files
  /x86			Files generic to x86 architecture
    /cpu		CPU specific files
    /lib		Architecture specific library files
/api			Machine/arch independent API for external apps
/board			Board dependent files
/common			Misc architecture independent functions
/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			Files generic to all architectures
  /libfdt		Library files to support flattened device trees
  /lzma			Library files to support LZMA decompression
  /lzo			Library files to support LZO decompression
/net			Networking code
/post			Power On Self Test
/spl			Secondary Program Loader framework
/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_".

Later we will add a configuration tool - probably similar to or even
identical to what's used for the Linux kernel. Right now, we have to
do the configuration by hand, which means creating some symbolic
links and editing some configuration files. We use the TQM8xxL boards
as an example here.


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

For the Cogent platform, you need to specify the CPU type as well;
e.g. "make cogent_mpc8xx_defconfig". And also configure the cogent
directory according to the instructions in cogent/README.


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 board/sandbox/README.sandbox for more details.


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.


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.

- CPU Daughterboard Type: (if CONFIG_ATSTK1000 is defined)
		Define exactly one, e.g. CONFIG_ATSTK1002

- CPU Module Type: (if CONFIG_COGENT is defined)
		Define exactly one of
		CONFIG_CMA286_60_OLD
--- FIXME --- not tested yet:
		CONFIG_CMA286_60, CONFIG_CMA286_21, CONFIG_CMA286_60P,
		CONFIG_CMA287_23, CONFIG_CMA287_50

- Motherboard Type: (if CONFIG_COGENT is defined)
		Define exactly one of
		CONFIG_CMA101, CONFIG_CMA102

- Motherboard I/O Modules: (if CONFIG_COGENT is defined)
		Define one or more of
		CONFIG_CMA302

- Motherboard Options: (if CONFIG_CMA101 or CONFIG_CMA102 are defined)
		Define one or more of
		CONFIG_LCD_HEARTBEAT	- update a character position on
					  the LCD display every second with
					  a "rotator" |\-/|\-/

- Marvell Family Member
		CONFIG_SYS_MVFS		- define it if you want to enable
					  multiple fs option at one time
					  for marvell soc family

- MPC824X Family Member (if CONFIG_MPC824X is defined)
		Define exactly one of
		CONFIG_MPC8240, CONFIG_MPC8245

- 8xx CPU Options: (if using an MPC8xx CPU)
		CONFIG_8xx_GCLK_FREQ	- deprecated: CPU clock if
					  get_gclk_freq() cannot work
					  e.g. if there is no 32KHz
					  reference PIT/RTC clock
		CONFIG_8xx_OSCLK	- PLL input clock (either EXTCLK
					  or XTAL/EXTAL)

- 859/866/885 CPU options: (if using a MPC859 or MPC866 or MPC885 CPU):
		CONFIG_SYS_8xx_CPUCLK_MIN
		CONFIG_SYS_8xx_CPUCLK_MAX
		CONFIG_8xx_CPUCLK_DEFAULT
			See doc/README.MPC866

		CONFIG_SYS_MEASURE_CPUCLK

		Define this to measure the actual CPU clock instead
		of relying on the correctness of the configured
		values. Mostly useful for board bringup to make sure
		the PLL is locked at the intended frequency. Note
		that this requires a (stable) reference clock (32 kHz
		RTC clock or CONFIG_SYS_8XX_XIN)

		CONFIG_SYS_DELAYED_ICACHE

		Define this option if you want to enable the
		ICache only when Code runs from RAM.

- 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_PPC_E500_DEBUG_TLB

		Enables a temporary TLB entry to be used during boot to work
		around limitations in e500v1 and e500v2 external debugger
		support. This reduces the portions of the boot code where
		breakpoints and single stepping do not work.  The value of this
		symbol should be set to the TLB1 entry to be used for this
		purpose.

		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
		requred during NOR boot.

		CONFIG_A008044_WORKAROUND
		Enables a workaround for T1040/T1042 erratum A008044. It is only
		requred 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
		Inidcates 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_GENERIC_GLOBAL_DATA
		Defines global data is initialized in generic board board_init_f().
		If this macro is defined, global data is created and cleared in
		generic board board_init_f(). Without this macro, architecture/board
		should initialize global data before calling board_init_f().

		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 eanbeld 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_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_SPL_FSL_PBL
		It adds a target to create boot binary having SPL binary in PBI format
		concatenated with u-boot binary.

		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_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

- Intel Monahans options:
		CONFIG_SYS_MONAHANS_RUN_MODE_OSC_RATIO

		Defines the Monahans run mode to oscillator
		ratio. Valid values are 8, 16, 24, 31. The core
		frequency is this value multiplied by 13 MHz.

		CONFIG_SYS_MONAHANS_TURBO_RUN_MODE_RATIO

		Defines the Monahans turbo mode to oscillator
		ratio. Valid values are 1 (default if undefined) and
		2. The core frequency as calculated above is multiplied
		by this value.

- 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_SYS_MIPS_CACHE_MODE

		Cache operation mode for the MIPS CPU.
		See also arch/mips/include/asm/mipsregs.h.
		Possible values are:
			CONF_CM_CACHABLE_NO_WA
			CONF_CM_CACHABLE_WA
			CONF_CM_UNCACHED
			CONF_CM_CACHABLE_NONCOHERENT
			CONF_CM_CACHABLE_CE
			CONF_CM_CACHABLE_COW
			CONF_CM_CACHABLE_CUW
			CONF_CM_CACHABLE_ACCELERATED

		CONFIG_SYS_XWAY_EBU_BOOTCFG

		Special option for Lantiq XWAY SoCs for booting from NOR flash.
		See also arch/mips/cpu/mips32/start.S.

		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.

		CONFIG_SYS_THUMB_BUILD

		Use this flag to build U-Boot using the Thumb instruction
		set for ARM architectures. Thumb instruction set provides
		better code density. For ARM architectures that support
		Thumb2 this flag will result in Thumb2 code generated by
		GCC.

		CONFIG_ARM_ERRATA_716044
		CONFIG_ARM_ERRATA_742230
		CONFIG_ARM_ERRATA_743622
		CONFIG_ARM_ERRATA_751472
		CONFIG_ARM_ERRATA_794072
		CONFIG_ARM_ERRATA_761320

		If set, the workarounds for these ARM errata are applied early
		during U-Boot startup. Note that these options force the
		workarounds to be applied; no CPU-type/version detection
		exists, unlike the similar options in the Linux kernel. Do not
		set these options unless they apply!

- Driver Model
		Driver model is a new framework for devices in U-Boot
		introduced in early 2014. U-Boot is being progressively
		moved over to this. It offers a consistent device structure,
		supports grouping devices into classes and has built-in
		handling of platform data and device tree.

		To enable transition to driver model in a relatively
		painful fashion, each subsystem can be independently
		switched between the legacy/ad-hoc approach and the new
		driver model using the options below. Also, many uclass
		interfaces include compatibility features which may be
		removed once the conversion of that subsystem is complete.
		As a result, the API provided by the subsystem may in fact
		not change with driver model.

		See doc/driver-model/README.txt for more information.

		CONFIG_DM

		Enable driver model. This brings in the core support,
		including scanning of platform data on start-up. If
		CONFIG_OF_CONTROL is enabled, the device tree will be
		scanned also when available.

		CONFIG_CMD_DM

		Enable driver model test commands. These allow you to print
		out the driver model tree and the uclasses.

		CONFIG_DM_DEMO

		Enable some demo devices and the 'demo' command. These are
		really only useful for playing around while trying to
		understand driver model in sandbox.

		CONFIG_SPL_DM

		Enable driver model in SPL. You will need to provide a
		suitable malloc() implementation. If you are not using the
		full malloc() enabled by CONFIG_SYS_SPL_MALLOC_START,
		consider using CONFIG_SYS_MALLOC_SIMPLE. In that case you
		must provide CONFIG_SYS_MALLOC_F_LEN to set the size.
		In most cases driver model will only allocate a few uclasses
		and devices in SPL, so 1KB should be enable. See
		CONFIG_SYS_MALLOC_F_LEN for more details on how to enable
		it.

		CONFIG_DM_SERIAL

		Enable driver model for serial. This replaces
		drivers/serial/serial.c with the serial uclass, which
		implements serial_putc() etc. The uclass interface is
		defined in include/serial.h.

		CONFIG_DM_GPIO

		Enable driver model for GPIO access. The standard GPIO
		interface (gpio_get_value(), etc.) is then implemented by
		the GPIO uclass. Drivers provide methods to query the
		particular GPIOs that they provide. The uclass interface
		is defined in include/asm-generic/gpio.h.

		CONFIG_DM_SPI

		Enable driver model for SPI. The SPI slave interface
		(spi_setup_slave(), spi_xfer(), etc.) is then implemented by
		the SPI uclass. Drivers provide methods to access the SPI
		buses that they control. The uclass interface is defined in
		include/spi.h. The existing spi_slave structure is attached
		as 'parent data' to every slave on each bus. Slaves
		typically use driver-private data instead of extending the
		spi_slave structure.

		CONFIG_DM_SPI_FLASH

		Enable driver model for SPI flash. This SPI flash interface
		(spi_flash_probe(), spi_flash_write(), etc.) is then
		implemented by the SPI flash uclass. There is one standard
		SPI flash driver which knows how to probe most chips
		supported by U-Boot. The uclass interface is defined in
		include/spi_flash.h, but is currently fully compatible
		with the old interface to avoid confusion and duplication
		during the transition parent. SPI and SPI flash must be
		enabled together (it is not possible to use driver model
		for one and not the other).

		CONFIG_DM_CROS_EC

		Enable driver model for the Chrome OS EC interface. This
		allows the cros_ec SPI driver to operate with CONFIG_DM_SPI
		but otherwise makes few changes. Since cros_ec also supports
		I2C and LPC (which don't support driver model yet), a full
		conversion is not yet possible.


		** Code size options: The following options are enabled by
		default except in SPL. Enable them explicitly to get these
		features in SPL.

		CONFIG_DM_WARN

		Enable the dm_warn() function. This can use up quite a bit
		of space for its strings.

		CONFIG_DM_STDIO

		Enable registering a serial device with the stdio library.

		CONFIG_DM_DEVICE_REMOVE

		Enable removing of devices.


- 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_CPU - The proper name of the cpus node (only required for
			MPC512X and MPC5xxx based boards).
		OF_SOC - The proper name of the soc node (only required for
			MPC512X and MPC5xxx based boards).
		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_BOOT_CPU

		This define fills in the correct boot CPU in the boot
		param header, the default value is zero if undefined.

		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: bootfile, ipaddr, serverip, hostname.
		It loads the vxWorks image pointed bootfile.

		CONFIG_SYS_VXWORKS_BOOT_DEVICE - The vxworks device name
		CONFIG_SYS_VXWORKS_MAC_PTR - Ethernet 6 byte MA -address
		CONFIG_SYS_VXWORKS_SERVERNAME - Name of the server
		CONFIG_SYS_VXWORKS_BOOT_ADDR - Address of boot parameters

		CONFIG_SYS_VXWORKS_ADD_PARAMS

		Add it at the end of the bootline. E.g "u=username pw=secret"

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

- Cache Configuration:
		CONFIG_SYS_ICACHE_OFF - Do not enable instruction cache in U-Boot
		CONFIG_SYS_DCACHE_OFF - Do not enable data cache in U-Boot
		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_PL011_SERIAL_RLCR

		Some vendor versions of PL011 serial ports (e.g. ST-Ericsson U8500)
		have separate receive and transmit line control registers.  Set
		this variable to initialize the extra register.

		CONFIG_PL011_SERIAL_FLUSH_ON_INIT

		On some platforms (e.g. U8500) U-Boot is loaded by a second stage
		boot loader that has already initialized the UART.  Define this
		variable to flush the UART at init time.

		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 Interface:
		Depending on board, define exactly one serial port
		(like CONFIG_8xx_CONS_SMC1, CONFIG_8xx_CONS_SMC2,
		CONFIG_8xx_CONS_SCC1, ...), or switch off the serial
		console by defining CONFIG_8xx_CONS_NONE

		Note: if CONFIG_8xx_CONS_NONE is defined, the serial
		port routines must be defined elsewhere
		(i.e. serial_init(), serial_getc(), ...)

		CONFIG_CFB_CONSOLE
		Enables console device for a color framebuffer. Needs following
		defines (cf. smiLynxEM, i8042)
			VIDEO_FB_LITTLE_ENDIAN	graphic memory organisation
						(default big endian)
			VIDEO_HW_RECTFILL	graphic chip supports
						rectangle fill
						(cf. smiLynxEM)
			VIDEO_HW_BITBLT		graphic chip supports
						bit-blit (cf. smiLynxEM)
			VIDEO_VISIBLE_COLS	visible pixel columns
						(cols=pitch)
			VIDEO_VISIBLE_ROWS	visible pixel rows
			VIDEO_PIXEL_SIZE	bytes per pixel
			VIDEO_DATA_FORMAT	graphic data format
						(0-5, cf. cfb_console.c)
			VIDEO_FB_ADRS		framebuffer address
			VIDEO_KBD_INIT_FCT	keyboard int fct
						(i.e. i8042_kbd_init())
			VIDEO_TSTC_FCT		test char fct
						(i.e. i8042_tstc)
			VIDEO_GETC_FCT		get char fct
						(i.e. i8042_getc)
			CONFIG_CONSOLE_CURSOR	cursor drawing on/off
						(requires blink timer
						cf. i8042.c)
			CONFIG_SYS_CONSOLE_BLINK_COUNT blink interval (cf. i8042.c)
			CONFIG_CONSOLE_TIME	display time/date info in
						upper right corner
						(requires CONFIG_CMD_DATE)
			CONFIG_VIDEO_LOGO	display Linux logo in
						upper left corner
			CONFIG_VIDEO_BMP_LOGO	use bmp_logo.h instead of
						linux_logo.h for logo.
						Requires CONFIG_VIDEO_LOGO
			CONFIG_CONSOLE_EXTRA_INFO
						additional board info beside
						the logo

		When CONFIG_CFB_CONSOLE_ANSI is defined, console will support
		a limited number of ANSI escape sequences (cursor control,
		erase functions and limited graphics rendition control).

		When CONFIG_CFB_CONSOLE is defined, video console is
		default i/o. Serial console can be forced with
		environment 'console=serial'.

		When CONFIG_SILENT_CONSOLE is defined, all console
		messages (by U-Boot and Linux!) can be silenced with
		the "silent" environment variable. See
		doc/README.silent for more information.

		CONFIG_SYS_CONSOLE_BG_COL: define the backgroundcolor, default
			is 0x00.
		CONFIG_SYS_CONSOLE_FG_COL: define the foregroundcolor, default
			is 0xa0.

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

- Console Rx buffer length
		With CONFIG_SYS_SMC_RXBUFLEN it is possible to define
		the maximum receive buffer length for the SMC.
		This option is actual only for 82xx and 8xx possible.
		If using CONFIG_SYS_SMC_RXBUFLEN also CONFIG_SYS_MAXIDLE
		must be defined, to setup the maximum idle timeout for
		the SMC.

- Pre-Console Buffer:
		Prior to the console being initialised (i.e. serial UART
		initialised etc) all console output is silently discarded.
		Defining CONFIG_PRE_CONSOLE_BUFFER will cause U-Boot to
		buffer any console messages prior to the console being
		initialised to a buffer of size CONFIG_PRE_CON_BUF_SZ
		bytes located at CONFIG_PRE_CON_BUF_ADDR. The buffer is
		a circular buffer, so if more than CONFIG_PRE_CON_BUF_SZ
		bytes are output before the console is initialised, the
		earlier bytes are discarded.

		'Sane' compilers will generate smaller code if
		CONFIG_PRE_CON_BUF_SZ is a power of 2

- Safe printf() functions
		Define CONFIG_SYS_VSNPRINTF to compile in safe versions of
		the printf() functions. These are defined in
		include/vsprintf.h and include snprintf(), vsnprintf() and
		so on. Code size increase is approximately 300-500 bytes.
		If this option is not given then these functions will
		silently discard their buffer size argument - this means
		you are not getting any overflow checking in this case.

- Boot Delay:	CONFIG_BOOTDELAY - in seconds
		Delay before automatically booting the default image;
		set to -1 to disable autoboot.
		set to -2 to autoboot with no delay and not check for abort
		(even when CONFIG_ZERO_BOOTDELAY_CHECK is defined).

		See doc/README.autoboot for these options that
		work with CONFIG_BOOTDELAY. None are required.
		CONFIG_BOOT_RETRY_TIME
		CONFIG_BOOT_RETRY_MIN
		CONFIG_AUTOBOOT_KEYED
		CONFIG_AUTOBOOT_PROMPT
		CONFIG_AUTOBOOT_DELAY_STR
		CONFIG_AUTOBOOT_STOP_STR
		CONFIG_AUTOBOOT_DELAY_STR2
		CONFIG_AUTOBOOT_STOP_STR2
		CONFIG_ZERO_BOOTDELAY_CHECK
		CONFIG_RESET_TO_RETRY

- 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_BOOTARGS
		This can be used to pass arguments to the bootm
		command. The value of CONFIG_BOOTARGS goes into the
		environment value "bootargs".

		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.

- Bootcount:
		CONFIG_BOOTCOUNT_LIMIT
		Implements a mechanism for detecting a repeating reboot
		cycle, see:
		http://www.denx.de/wiki/view/DULG/UBootBootCountLimit

		CONFIG_BOOTCOUNT_ENV
		If no softreset save registers are found on the hardware
		"bootcount" is stored in the environment. To prevent a
		saveenv on all reboots, the environment variable
		"upgrade_available" is used. If "upgrade_available" is
		0, "bootcount" is always 0, if "upgrade_available" is
		1 "bootcount" is incremented in the environment.
		So the Userspace Applikation must set the "upgrade_available"
		and "bootcount" variable to 0, if a boot was successfully.

- Pre-Boot Commands:
		CONFIG_PREBOOT

		When this option is #defined, the existence of the
		environment variable "preboot" will be checked
		immediately before starting the CONFIG_BOOTDELAY
		countdown and/or running the auto-boot command resp.
		entering interactive mode.

		This feature is especially useful when "preboot" is
		automatically generated or modified. For an example
		see the LWMON board specific code: here "preboot" is
		modified when the user holds down a certain
		combination of keys on the (special) keyboard when
		booting the systems

- 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.

- Monitor Functions:
		Monitor commands can be included or excluded
		from the build by using the #include files
		<config_cmd_all.h> and #undef'ing unwanted
		commands, or using <config_cmd_default.h>
		and augmenting with additional #define's
		for wanted commands.

		The default command configuration includes all commands
		except those marked below with a "*".

		CONFIG_CMD_AES		  AES 128 CBC encrypt/decrypt
		CONFIG_CMD_ASKENV	* ask for env variable
		CONFIG_CMD_BDI		  bdinfo
		CONFIG_CMD_BEDBUG	* Include BedBug Debugger
		CONFIG_CMD_BMP		* BMP support
		CONFIG_CMD_BSP		* Board specific commands
		CONFIG_CMD_BOOTD	  bootd
		CONFIG_CMD_BOOTI	* ARM64 Linux kernel Image support
		CONFIG_CMD_CACHE	* icache, dcache
		CONFIG_CMD_CLK   	* clock command support
		CONFIG_CMD_CONSOLE	  coninfo
		CONFIG_CMD_CRC32	* crc32
		CONFIG_CMD_DATE		* support for RTC, date/time...
		CONFIG_CMD_DHCP		* DHCP support
		CONFIG_CMD_DIAG		* Diagnostics
		CONFIG_CMD_DS4510	* ds4510 I2C gpio commands
		CONFIG_CMD_DS4510_INFO	* ds4510 I2C info command
		CONFIG_CMD_DS4510_MEM	* ds4510 I2C eeprom/sram commansd
		CONFIG_CMD_DS4510_RST	* ds4510 I2C rst command
		CONFIG_CMD_DTT		* Digital Therm and Thermostat
		CONFIG_CMD_ECHO		  echo arguments
		CONFIG_CMD_EDITENV	  edit env variable
		CONFIG_CMD_EEPROM	* EEPROM read/write support
		CONFIG_CMD_ELF		* bootelf, bootvx
		CONFIG_CMD_ENV_CALLBACK	* display details about env callbacks
		CONFIG_CMD_ENV_FLAGS	* display details about env flags
		CONFIG_CMD_ENV_EXISTS	* check existence of env variable
		CONFIG_CMD_EXPORTENV	* export the environment
		CONFIG_CMD_EXT2		* ext2 command support
		CONFIG_CMD_EXT4		* ext4 command support
		CONFIG_CMD_FS_GENERIC	* filesystem commands (e.g. load, ls)
					  that work for multiple fs types
		CONFIG_CMD_FS_UUID	* Look up a filesystem UUID
		CONFIG_CMD_SAVEENV	  saveenv
		CONFIG_CMD_FDC		* Floppy Disk Support
		CONFIG_CMD_FAT		* FAT command support
		CONFIG_CMD_FLASH	  flinfo, erase, protect
		CONFIG_CMD_FPGA		  FPGA device initialization support
		CONFIG_CMD_FUSE		* Device fuse support
		CONFIG_CMD_GETTIME	* Get time since boot
		CONFIG_CMD_GO		* the 'go' command (exec code)
		CONFIG_CMD_GREPENV	* search environment
		CONFIG_CMD_HASH		* calculate hash / digest
		CONFIG_CMD_HWFLOW	* RTS/CTS hw flow control
		CONFIG_CMD_I2C		* I2C serial bus support
		CONFIG_CMD_IDE		* IDE harddisk support
		CONFIG_CMD_IMI		  iminfo
		CONFIG_CMD_IMLS		  List all images found in NOR flash
		CONFIG_CMD_IMLS_NAND	* List all images found in NAND flash
		CONFIG_CMD_IMMAP	* IMMR dump support
		CONFIG_CMD_IOTRACE	* I/O tracing for debugging
		CONFIG_CMD_IMPORTENV	* import an environment
		CONFIG_CMD_INI		* import data from an ini file into the env
		CONFIG_CMD_IRQ		* irqinfo
		CONFIG_CMD_ITEST	  Integer/string test of 2 values
		CONFIG_CMD_JFFS2	* JFFS2 Support
		CONFIG_CMD_KGDB		* kgdb
		CONFIG_CMD_LDRINFO	* ldrinfo (display Blackfin loader)
		CONFIG_CMD_LINK_LOCAL	* link-local IP address auto-configuration
					  (169.254.*.*)
		CONFIG_CMD_LOADB	  loadb
		CONFIG_CMD_LOADS	  loads
		CONFIG_CMD_MD5SUM	* print md5 message digest
					  (requires CONFIG_CMD_MEMORY and CONFIG_MD5)
		CONFIG_CMD_MEMINFO	* Display detailed memory information
		CONFIG_CMD_MEMORY	  md, mm, nm, mw, cp, cmp, crc, base,
					  loop, loopw
		CONFIG_CMD_MEMTEST	* mtest
		CONFIG_CMD_MISC		  Misc functions like sleep etc
		CONFIG_CMD_MMC		* MMC memory mapped support
		CONFIG_CMD_MII		* MII utility commands
		CONFIG_CMD_MTDPARTS	* MTD partition support
		CONFIG_CMD_NAND		* NAND support
		CONFIG_CMD_NET		  bootp, tftpboot, rarpboot
		CONFIG_CMD_NFS		  NFS support
		CONFIG_CMD_PCA953X	* PCA953x I2C gpio commands
		CONFIG_CMD_PCA953X_INFO * PCA953x I2C gpio info command
		CONFIG_CMD_PCI		* pciinfo
		CONFIG_CMD_PCMCIA		* PCMCIA support
		CONFIG_CMD_PING		* send ICMP ECHO_REQUEST to network
					  host
		CONFIG_CMD_PORTIO	* Port I/O
		CONFIG_CMD_READ		* Read raw data from partition
		CONFIG_CMD_REGINFO	* Register dump
		CONFIG_CMD_RUN		  run command in env variable
		CONFIG_CMD_SANDBOX	* sb command to access sandbox features
		CONFIG_CMD_SAVES	* save S record dump
		CONFIG_CMD_SCSI		* SCSI Support
		CONFIG_CMD_SDRAM	* print SDRAM configuration information
					  (requires CONFIG_CMD_I2C)
		CONFIG_CMD_SETGETDCR	  Support for DCR Register access
					  (4xx only)
		CONFIG_CMD_SF		* Read/write/erase SPI NOR flash
		CONFIG_CMD_SHA1SUM	* print sha1 memory digest
					  (requires CONFIG_CMD_MEMORY)
		CONFIG_CMD_SOFTSWITCH	* Soft switch setting command for BF60x
		CONFIG_CMD_SOURCE	  "source" command Support
		CONFIG_CMD_SPI		* SPI serial bus support
		CONFIG_CMD_TFTPSRV	* TFTP transfer in server mode
		CONFIG_CMD_TFTPPUT	* TFTP put command (upload)
		CONFIG_CMD_TIME		* run command and report execution time (ARM specific)
		CONFIG_CMD_TIMER	* access to the system tick timer
		CONFIG_CMD_USB		* USB support
		CONFIG_CMD_CDP		* Cisco Discover Protocol support
		CONFIG_CMD_MFSL		* Microblaze FSL support
		CONFIG_CMD_XIMG		  Load part of Multi Image
		CONFIG_CMD_UUID		* Generate random UUID or GUID string

		EXAMPLE: If you want all functions except of network
		support you can write:

		#include "config_cmd_all.h"
		#undef CONFIG_CMD_NET

	Other Commands:
		fdt (flattened device tree) command: CONFIG_OF_LIBFDT

	Note:	Don't enable the "icache" and "dcache" commands
		(configuration option CONFIG_CMD_CACHE) unless you know
		what you (and your U-Boot users) are doing. Data
		cache cannot be enabled on systems like the 8xx or
		8260 (where accesses to the IMMR region must be
		uncached), and it cannot be disabled on all other
		systems where we (mis-) use the data cache to hold an
		initial stack and some data.


		XXX - this list needs to get updated!

- 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 two 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->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.

- 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 and 8260
		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.

- U-Boot Version:
		CONFIG_VERSION_VARIABLE
		If this variable is defined, an environment variable
		named "ver" is created by U-Boot showing the U-Boot
		version as printed by the "version" command.
		Any change to this variable will be reverted at the
		next reset.

- 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_MPC8xx	- use internal RTC of MPC8xx
		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_SYS_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_DOS_PARTITION   MS Dos partition table, traditional on the
				       Intel architecture, USB sticks, etc.
		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_MTD_PARTITIONS  Memory Technology Device partition table.

		If IDE or SCSI support is enabled (CONFIG_CMD_IDE or
		CONFIG_CMD_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:
		At the moment only there is only support for the
		SYM53C8XX SCSI controller; define
		CONFIG_SCSI_SYM53C8XX to enable it.

		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.
		CONFIG_SYS_SCSI_SYM53C8XX_CCF to fix clock timing (80Mhz)

		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_CMD_E1000
		Management command for E1000 devices.  When used on devices
		with SPI support you can reprogram the EEPROM from U-Boot.

		CONFIG_E1000_FALLBACK_MAC
		default MAC for empty EEPROM after production.

		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_BASE
			Define this to hold the physical address
			of the LAN91C96's I/O space

			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_DRIVER_TI_EMAC
		Support for davinci emac

			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_SMC911X
		Support for SMSC's LAN911x and LAN921x chips

			CONFIG_SMC911X_BASE
			Define this to hold the physical address
			of the device (I/O space)

			CONFIG_SMC911X_32_BIT
			Define this if data bus is 32 bits

			CONFIG_SMC911X_16_BIT
			Define this if data bus is 16 bits. If your processor
			automatically converts one 32 bit word to two 16 bit
			words you may also try CONFIG_SMC911X_32_BIT.

		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.

- PWM Support:
		CONFIG_PWM_IMX
		Support for PWM modul on the imx6.

- TPM Support:
		CONFIG_TPM
		Support TPM devices.