README
    # SPDX-License-Identifier: GPL-2.0+
    #
    # (C) Copyright 2000 - 2013
    # Wolfgang Denk, DENX Software Engineering, wd@denx.de.
    
    Summary:
    ========
    
    This directory contains the source code for U-Boot, a boot loader for
    Embedded boards based on PowerPC, ARM, MIPS and several other
    processors, which can be installed in a boot ROM and used to
    initialize and test the hardware or to download and run application
    code.
    
    The development of U-Boot is closely related to Linux: some parts of
    the source code originate in the Linux source tree, we have some
    header files in common, and special provision has been made to
    support booting of Linux images.
    
    Some attention has been paid to make this software easily
    configurable and extendable. For instance, all monitor commands are
    implemented with the same call interface, so that it's very easy to
    add new commands. Also, instead of permanently adding rarely used
    code (for instance hardware test utilities) to the monitor, you can
    load and run it dynamically.
    
    
    Status:
    =======
    
    In general, all boards for which a configuration option exists in the
    Makefile have been tested to some extent and can be considered
    "working". In fact, many of them are used in production systems.
    
    In case of problems see the CHANGELOG file to find out who contributed
    the specific port. In addition, there are various MAINTAINERS files
    scattered throughout the U-Boot source identifying the people or
    companies responsible for various boards and subsystems.
    
    Note: As of August, 2010, there is no longer a CHANGELOG file in the
    actual U-Boot source tree; however, it can be created dynamically
    from the Git log using:
    
    	make CHANGELOG
    
    
    Where to get help:
    ==================
    
    In case you have questions about, problems with or contributions for
    U-Boot, you should send a message to the U-Boot mailing list at
    <u-boot@lists.denx.de>. There is also an archive of previous traffic
    on the mailing list - please search the archive before asking FAQ's.
    Please see https://lists.denx.de/pipermail/u-boot and
    https://marc.info/?l=u-boot
    
    Where to get source code:
    =========================
    
    The U-Boot source code is maintained in the Git repository at
    https://source.denx.de/u-boot/u-boot.git ; you can browse it online at
    https://source.denx.de/u-boot/u-boot
    
    The "Tags" links on this page allow you to download tarballs of
    any version you might be interested in. Official releases are also
    available from the DENX file server through HTTPS or FTP.
    https://ftp.denx.de/pub/u-boot/
    ftp://ftp.denx.de/pub/u-boot/
    
    
    Where we come from:
    ===================
    
    - start from 8xxrom sources
    - create PPCBoot project (https://sourceforge.net/projects/ppcboot)
    - clean up code
    - make it easier to add custom boards
    - make it possible to add other [PowerPC] CPUs
    - extend functions, especially:
      * Provide extended interface to Linux boot loader
      * S-Record download
      * network boot
      * ATA disk / SCSI ... boot
    - create ARMBoot project (https://sourceforge.net/projects/armboot)
    - add other CPU families (starting with ARM)
    - create U-Boot project (https://sourceforge.net/projects/u-boot)
    - current project page: see https://www.denx.de/wiki/U-Boot
    
    
    Names and Spelling:
    ===================
    
    The "official" name of this project is "Das U-Boot". The spelling
    "U-Boot" shall be used in all written text (documentation, comments
    in source files etc.). Example:
    
    	This is the README file for the U-Boot project.
    
    File names etc. shall be based on the string "u-boot". Examples:
    
    	include/asm-ppc/u-boot.h
    
    	#include <asm/u-boot.h>
    
    Variable names, preprocessor constants etc. shall be either based on
    the string "u_boot" or on "U_BOOT". Example:
    
    	U_BOOT_VERSION		u_boot_logo
    	IH_OS_U_BOOT		u_boot_hush_start
    
    
    Versioning:
    ===========
    
    Starting with the release in October 2008, the names of the releases
    were changed from numerical release numbers without deeper meaning
    into a time stamp based numbering. Regular releases are identified by
    names consisting of the calendar year and month of the release date.
    Additional fields (if present) indicate release candidates or bug fix
    releases in "stable" maintenance trees.
    
    Examples:
    	U-Boot v2009.11	    - Release November 2009
    	U-Boot v2009.11.1   - Release 1 in version November 2009 stable tree
    	U-Boot v2010.09-rc1 - Release candidate 1 for September 2010 release
    
    
    Directory Hierarchy:
    ====================
    
    /arch			Architecture-specific files
      /arc			Files generic to ARC architecture
      /arm			Files generic to ARM architecture
      /m68k			Files generic to m68k architecture
      /microblaze		Files generic to microblaze architecture
      /mips			Files generic to MIPS architecture
      /nios2		Files generic to Altera NIOS2 architecture
      /powerpc		Files generic to PowerPC architecture
      /riscv		Files generic to RISC-V architecture
      /sandbox		Files generic to HW-independent "sandbox"
      /sh			Files generic to SH architecture
      /x86			Files generic to x86 architecture
      /xtensa		Files generic to Xtensa architecture
    /api			Machine/arch-independent API for external apps
    /board			Board-dependent files
    /boot			Support for images and booting
    /cmd			U-Boot commands functions
    /common			Misc architecture-independent functions
    /configs		Board default configuration files
    /disk			Code for disk drive partition handling
    /doc			Documentation (a mix of ReST and READMEs)
    /drivers		Device drivers
    /dts			Makefile for building internal U-Boot fdt.
    /env			Environment support
    /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 and sign FIT images, etc.
    
    Software Configuration:
    =======================
    
    Configuration is usually done using C preprocessor defines; the
    rationale behind that is to avoid dead code whenever possible.
    
    There are two classes of configuration variables:
    
    * Configuration _OPTIONS_:
      These are selectable by the user and have names beginning with
      "CONFIG_".
    
    * Configuration _SETTINGS_:
      These depend on the hardware etc. and should not be meddled with if
      you don't know what you're doing; they have names beginning with
      "CONFIG_SYS_".
    
    Previously, all configuration was done by hand, which involved creating
    symbolic links and editing configuration files manually. More recently,
    U-Boot has added the Kbuild infrastructure used by the Linux kernel,
    allowing you to use the "make menuconfig" command to configure your
    build.
    
    
    Selection of Processor Architecture and Board Type:
    ---------------------------------------------------
    
    For all supported boards there are ready-to-use default
    configurations available; just type "make <board_name>_defconfig".
    
    Example: For a TQM823L module type:
    
    	cd u-boot
    	make TQM823L_defconfig
    
    Note: If you're looking for the default configuration file for a board
    you're sure used to be there but is now missing, check the file
    doc/README.scrapyard for a list of no longer supported boards.
    
    Sandbox Environment:
    --------------------
    
    U-Boot can be built natively to run on a Linux host using the 'sandbox'
    board. This allows feature development which is not board- or architecture-
    specific to be undertaken on a native platform. The sandbox is also used to
    run some of U-Boot's tests.
    
    See doc/arch/sandbox.rst for more details.
    
    
    Board Initialisation Flow:
    --------------------------
    
    This is the intended start-up flow for boards. This should apply for both
    SPL and U-Boot proper (i.e. they both follow the same rules).
    
    Note: "SPL" stands for "Secondary Program Loader," which is explained in
    more detail later in this file.
    
    At present, SPL mostly uses a separate code path, but the function names
    and roles of each function are the same. Some boards or architectures
    may not conform to this.  At least most ARM boards which use
    CONFIG_SPL_FRAMEWORK conform to this.
    
    Execution typically starts with an architecture-specific (and possibly
    CPU-specific) start.S file, such as:
    
    	- arch/arm/cpu/armv7/start.S
    	- arch/powerpc/cpu/mpc83xx/start.S
    	- arch/mips/cpu/start.S
    
    and so on. From there, three functions are called; the purpose and
    limitations of each of these functions are described below.
    
    lowlevel_init():
    	- purpose: essential init to permit execution to reach board_init_f()
    	- no global_data or BSS
    	- there is no stack (ARMv7 may have one but it will soon be removed)
    	- must not set up SDRAM or use console
    	- must only do the bare minimum to allow execution to continue to
    		board_init_f()
    	- this is almost never needed
    	- return normally from this function
    
    board_init_f():
    	- purpose: set up the machine ready for running board_init_r():
    		i.e. SDRAM and serial UART
    	- global_data is available
    	- stack is in SRAM
    	- BSS is not available, so you cannot use global/static variables,
    		only stack variables and global_data
    
    	Non-SPL-specific notes:
    	- dram_init() is called to set up DRAM. If already done in SPL this
    		can do nothing
    
    	SPL-specific notes:
    	- you can override the entire board_init_f() function with your own
    		version as needed.
    	- preloader_console_init() can be called here in extremis
    	- should set up SDRAM, and anything needed to make the UART work
    	- there is no need to clear BSS, it will be done by crt0.S
    	- for specific scenarios on certain architectures an early BSS *can*
    	  be made available (via CONFIG_SPL_EARLY_BSS by moving the clearing
    	  of BSS prior to entering board_init_f()) but doing so is discouraged.
    	  Instead it is strongly recommended to architect any code changes
    	  or additions such to not depend on the availability of BSS during
    	  board_init_f() as indicated in other sections of this README to
    	  maintain compatibility and consistency across the entire code base.
    	- must return normally from this function (don't call board_init_r()
    		directly)
    
    Here the BSS is cleared. For SPL, if CONFIG_SPL_STACK_R is defined, then at
    this point the stack and global_data are relocated to below
    CONFIG_SPL_STACK_R_ADDR. For non-SPL, U-Boot is relocated to run at the top of
    memory.
    
    board_init_r():
    	- purpose: main execution, common code
    	- global_data is available
    	- SDRAM is available
    	- BSS is available, all static/global variables can be used
    	- execution eventually continues to main_loop()
    
    	Non-SPL-specific notes:
    	- U-Boot is relocated to the top of memory and is now running from
    		there.
    
    	SPL-specific notes:
    	- stack is optionally in SDRAM, if CONFIG_SPL_STACK_R is defined and
    		CONFIG_SPL_STACK_R_ADDR points into SDRAM
    	- preloader_console_init() can be called here - typically this is
    		done by selecting CONFIG_SPL_BOARD_INIT and then supplying a
    		spl_board_init() function containing this call
    	- loads U-Boot or (in falcon mode) Linux
    
    
    Configuration Options:
    ----------------------
    
    Configuration depends on the combination of board and CPU type; all
    such information is kept in a configuration file
    "include/configs/<board_name>.h".
    
    Example: For a TQM823L module, all configuration settings are in
    "include/configs/TQM823L.h".
    
    
    Many of the options are named exactly as the corresponding Linux
    kernel configuration options. The intention is to make it easier to
    build a config tool - later.
    
    - ARM Platform Bus Type(CCI):
    		CoreLink Cache Coherent Interconnect (CCI) is ARM BUS which
    		provides full cache coherency between two clusters of multi-core
    		CPUs and I/O coherency for devices and I/O masters
    
    		CONFIG_SYS_FSL_HAS_CCI400
    
    		Defined For SoC that has cache coherent interconnect
    		CCN-400
    
    		CONFIG_SYS_FSL_HAS_CCN504
    
    		Defined for SoC that has cache coherent interconnect CCN-504
    
    The following options need to be configured:
    
    - CPU Type:	Define exactly one, e.g. CONFIG_MPC85XX.
    
    - Board Type:	Define exactly one, e.g. CONFIG_MPC8540ADS.
    
    - 85xx CPU Options:
    		CONFIG_SYS_PPC64
    
    		Specifies that the core is a 64-bit PowerPC implementation (implements
    		the "64" category of the Power ISA). This is necessary for ePAPR
    		compliance, among other possible reasons.
    
    		CONFIG_SYS_FSL_TBCLK_DIV
    
    		Defines the core time base clock divider ratio compared to the
    		system clock.  On most PQ3 devices this is 8, on newer QorIQ
    		devices it can be 16 or 32.  The ratio varies from SoC to Soc.
    
    		CONFIG_SYS_FSL_PCIE_COMPAT
    
    		Defines the string to utilize when trying to match PCIe device
    		tree nodes for the given platform.
    
    		CONFIG_SYS_FSL_ERRATUM_A004510
    
    		Enables a workaround for erratum A004510.  If set,
    		then CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV and
    		CONFIG_SYS_FSL_CORENET_SNOOPVEC_COREONLY must be set.
    
    		CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV
    		CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV2 (optional)
    
    		Defines one or two SoC revisions (low 8 bits of SVR)
    		for which the A004510 workaround should be applied.
    
    		The rest of SVR is either not relevant to the decision
    		of whether the erratum is present (e.g. p2040 versus
    		p2041) or is implied by the build target, which controls
    		whether CONFIG_SYS_FSL_ERRATUM_A004510 is set.
    
    		See Freescale App Note 4493 for more information about
    		this erratum.
    
    		CONFIG_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.
    
    - 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 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_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_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
    
    - MIPS CPU options:
    		CONFIG_SYS_INIT_SP_OFFSET
    
    		Offset relative to CONFIG_SYS_SDRAM_BASE for initial stack
    		pointer. This is needed for the temporary stack before
    		relocation.
    
    		CONFIG_XWAY_SWAP_BYTES
    
    		Enable compilation of tools/xway-swap-bytes needed for Lantiq
    		XWAY SoCs for booting from NOR flash. The U-Boot image needs to
    		be swapped if a flash programmer is used.
    
    - ARM options:
    		CONFIG_SYS_EXCEPTION_VECTORS_HIGH
    
    		Select high exception vectors of the ARM core, e.g., do not
    		clear the V bit of the c1 register of CP15.
    
    		COUNTER_FREQUENCY
    		Generic timer clock source frequency.
    
    		COUNTER_FREQUENCY_REAL
    		Generic timer clock source frequency if the real clock is
    		different from COUNTER_FREQUENCY, and can only be determined
    		at run time.
    
    - Tegra SoC options:
    		CONFIG_TEGRA_SUPPORT_NON_SECURE
    
    		Support executing U-Boot in non-secure (NS) mode. Certain
    		impossible actions will be skipped if the CPU is in NS mode,
    		such as ARM architectural timer initialization.
    
    - Linux Kernel Interface:
    		CONFIG_MEMSIZE_IN_BYTES		[relevant for MIPS only]
    
    		When transferring memsize parameter to Linux, some versions
    		expect it to be in bytes, others in MB.
    		Define CONFIG_MEMSIZE_IN_BYTES to make it in bytes.
    
    		CONFIG_OF_LIBFDT
    
    		New kernel versions are expecting firmware settings to be
    		passed using flattened device trees (based on open firmware
    		concepts).
    
    		CONFIG_OF_LIBFDT
    		 * New libfdt-based support
    		 * Adds the "fdt" command
    		 * The bootm command automatically updates the fdt
    
    		OF_TBCLK - The timebase frequency.
    
    		boards with QUICC Engines require OF_QE to set UCC MAC
    		addresses
    
    		CONFIG_OF_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.
    
    - vxWorks boot parameters:
    
    		bootvx constructs a valid bootline using the following
    		environments variables: bootdev, bootfile, ipaddr, netmask,
    		serverip, gatewayip, hostname, othbootargs.
    		It loads the vxWorks image pointed bootfile.
    
    		Note: If a "bootargs" environment is defined, it will override
    		the defaults discussed just above.
    
    - Cache Configuration 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_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
    
    - 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.
    
    - 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".
    
    - Watchdog:
    		CONFIG_SYS_WATCHDOG_FREQ
    		Some platforms automatically call WATCHDOG_RESET()
    		from the timer interrupt handler every
    		CONFIG_SYS_WATCHDOG_FREQ interrupts. If not set by the
    		board configuration file, a default of CONFIG_SYS_HZ/2
    		(i.e. 500) is used. Setting CONFIG_SYS_WATCHDOG_FREQ
    		to 0 disables calling WATCHDOG_RESET() from the timer
    		interrupt.
    
    - 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.
    
    - 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.
    
    - NETWORK Support (PCI):
    		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_NATSEMI
    		Support for National dp83815 chips.
    
    		CONFIG_NS8382X
    		Support for National dp8382[01] gigabit chips.
    
    - NETWORK Support (other):
    		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.
    
    		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_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.
    
    - 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_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.
    
    - MII/PHY support:
    		CONFIG_PHY_CLOCK_FREQ (ppc4xx)
    
    		The clock frequency of the MII bus
    
    		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")
    
    - 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:
    
     - 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_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_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.
    
    - 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
    
    - Error Recovery:
    	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.
    
    - 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.
    
    		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_MAX_FOOTPRINT
    		Maximum size in memory allocated to the SPL, BSS included.
    		When defined, the linker checks that the actual memory
    		used by SPL from _start to __bss_end does not exceed it.
    		CONFIG_SPL_MAX_FOOTPRINT and CONFIG_SPL_BSS_MAX_SIZE
    		must not be both defined at the same time.
    
    		CONFIG_SPL_MAX_SIZE
    		Maximum size of the SPL image (text, data, rodata, and
    		linker lists sections), BSS excluded.
    		When defined, the linker checks that the actual size does
    		not exceed it.
    
    		CONFIG_SPL_RELOC_TEXT_BASE
    		Address to relocate to.  If unspecified, this is equal to
    		CONFIG_SPL_TEXT_BASE (i.e. no relocation is done).
    
    		CONFIG_SPL_BSS_START_ADDR
    		Link address for the BSS within the SPL binary.
    
    		CONFIG_SPL_BSS_MAX_SIZE
    		Maximum size in memory allocated to the SPL BSS.
    		When defined, the linker checks that the actual memory used
    		by SPL from __bss_start to __bss_end does not exceed it.
    		CONFIG_SPL_MAX_FOOTPRINT and CONFIG_SPL_BSS_MAX_SIZE
    		must not be both defined at the same time.
    
    		CONFIG_SPL_STACK
    		Adress of the start of the stack SPL will use
    
    		CONFIG_SPL_PANIC_ON_RAW_IMAGE
    		When defined, SPL will panic() if the image it has
    		loaded does not have a signature.
    		Defining this is useful when code which loads images
    		in SPL cannot guarantee that absolutely all read errors
    		will be caught.
    		An example is the LPC32XX MLC NAND driver, which will
    		consider that a completely unreadable NAND block is bad,
    		and thus should be skipped silently.
    
    		CONFIG_SPL_RELOC_STACK
    		Adress of the start of the stack SPL will use after
    		relocation.  If unspecified, this is equal to
    		CONFIG_SPL_STACK.
    
    		CONFIG_SYS_SPL_MALLOC_START
    		Starting address of the malloc pool used in SPL.
    		When this option is set the full malloc is used in SPL and
    		it is set up by spl_init() and before that, the simple malloc()
    		can be used if CONFIG_SYS_MALLOC_F is defined.
    
    		CONFIG_SYS_SPL_MALLOC_SIZE
    		The size of the malloc pool used in SPL.
    
    		CONFIG_SPL_DISPLAY_PRINT
    		For ARM, enable an optional function to print more information
    		about the running system.
    
    		CONFIG_SPL_INIT_MINIMAL
    		Arch init code should be built for a very small image
    
    		CONFIG_SYS_MMCSD_RAW_MODE_ARGS_SECTOR,
    		CONFIG_SYS_MMCSD_RAW_MODE_ARGS_SECTORS
    		Sector and number of sectors to load kernel argument
    		parameters from when MMC is being used in raw mode
    		(for falcon mode)
    
    		CONFIG_SPL_FS_LOAD_PAYLOAD_NAME
    		Filename to read to load U-Boot when reading from filesystem
    
    		CONFIG_SPL_FS_LOAD_KERNEL_NAME
    		Filename to read to load kernel uImage when reading
    		from filesystem (for Falcon mode)
    
    		CONFIG_SPL_FS_LOAD_ARGS_NAME
    		Filename to read to load kernel argument parameters
    		when reading from filesystem (for Falcon mode)
    
    		CONFIG_SPL_MPC83XX_WAIT_FOR_NAND
    		Set this for NAND SPL on PPC mpc83xx targets, so that
    		start.S waits for the rest of the SPL to load before
    		continuing (the hardware starts execution after just
    		loading the first page rather than the full 4K).
    
    		CONFIG_SPL_SKIP_RELOCATE
    		Avoid SPL relocation
    
    		CONFIG_SPL_UBI
    		Support for a lightweight UBI (fastmap) scanner and
    		loader
    
    		CONFIG_SPL_NAND_RAW_ONLY
    		Support to boot only raw u-boot.bin images. Use this only
    		if you need to save space.
    
    		CONFIG_SPL_COMMON_INIT_DDR
    		Set for common ddr init with serial presence detect in
    		SPL binary.
    
    		CONFIG_SYS_NAND_5_ADDR_CYCLE, CONFIG_SYS_NAND_PAGE_COUNT,
    		CONFIG_SYS_NAND_PAGE_SIZE, CONFIG_SYS_NAND_OOBSIZE,
    		CONFIG_SYS_NAND_BLOCK_SIZE, CONFIG_SYS_NAND_BAD_BLOCK_POS,
    		CONFIG_SYS_NAND_ECCPOS, CONFIG_SYS_NAND_ECCSIZE,
    		CONFIG_SYS_NAND_ECCBYTES
    		Defines the size and behavior of the NAND that SPL uses
    		to read U-Boot
    
    		CONFIG_SYS_NAND_U_BOOT_DST
    		Location in memory to load U-Boot to
    
    		CONFIG_SYS_NAND_U_BOOT_SIZE
    		Size of image to load
    
    		CONFIG_SYS_NAND_U_BOOT_START
    		Entry point in loaded image to jump to
    
    		CONFIG_SYS_NAND_HW_ECC_OOBFIRST
    		Define this if you need to first read the OOB and then the
    		data. This is used, for example, on davinci platforms.
    
    		CONFIG_SPL_RAM_DEVICE
    		Support for running image already present in ram, in SPL binary
    
    		CONFIG_SPL_PAD_TO
    		Image offset to which the SPL should be padded before appending
    		the SPL payload. By default, this is defined as
    		CONFIG_SPL_MAX_SIZE, or 0 if CONFIG_SPL_MAX_SIZE is undefined.
    		CONFIG_SPL_PAD_TO must be either 0, meaning to append the SPL
    		payload without any padding, or >= CONFIG_SPL_MAX_SIZE.
    
    		CONFIG_SPL_TARGET
    		Final target image containing SPL and payload.  Some SPLs
    		use an arch-specific makefile fragment instead, for
    		example if more than one image needs to be produced.
    
    		CONFIG_SPL_FIT_PRINT
    		Printing information about a FIT image adds quite a bit of
    		code to SPL. So this is normally disabled in SPL. Use this
    		option to re-enable it. This will affect the output of the
    		bootm command when booting a FIT image.
    
    - TPL framework
    		CONFIG_TPL
    		Enable building of TPL globally.
    
    		CONFIG_TPL_PAD_TO
    		Image offset to which the TPL should be padded before appending
    		the TPL payload. By default, this is defined as
    		CONFIG_SPL_MAX_SIZE, or 0 if CONFIG_SPL_MAX_SIZE is undefined.
    		CONFIG_SPL_PAD_TO must be either 0, meaning to append the SPL
    		payload without any padding, or >= CONFIG_SPL_MAX_SIZE.
    
    - Interrupt support (PPC):
    
    		There are common interrupt_init() and timer_interrupt()
    		for all PPC archs. interrupt_init() calls interrupt_init_cpu()
    		for CPU specific initialization. interrupt_init_cpu()
    		should set decrementer_count to appropriate value. If
    		CPU resets decrementer automatically after interrupt
    		(ppc4xx) it should set decrementer_count to zero.
    		timer_interrupt() calls timer_interrupt_cpu() for CPU
    		specific handling. If board has watchdog / status_led
    		/ other_activity_monitor it works automatically from
    		general timer_interrupt().
    
    
    Board initialization settings:
    ------------------------------
    
    During Initialization u-boot calls a number of board specific functions
    to allow the preparation of board specific prerequisites, e.g. pin setup
    before drivers are initialized. To enable these callbacks the
    following configuration macros have to be defined. Currently this is
    architecture specific, so please check arch/your_architecture/lib/board.c
    typically in board_init_f() and board_init_r().
    
    - CONFIG_BOARD_EARLY_INIT_F: Call board_early_init_f()
    - CONFIG_BOARD_EARLY_INIT_R: Call board_early_init_r()
    - CONFIG_BOARD_LATE_INIT: Call board_late_init()
    
    Configuration Settings:
    -----------------------
    
    - MEM_SUPPORT_64BIT_DATA: Defined automatically if compiled as 64-bit.
    		Optionally it can be defined to support 64-bit memory commands.
    
    - CONFIG_SYS_LONGHELP: Defined when you want long help messages included;
    		undefine this when you're short of memory.
    
    - CONFIG_SYS_HELP_CMD_WIDTH: Defined when you want to override the default
    		width of the commands listed in the 'help' command output.
    
    - CONFIG_SYS_PROMPT:	This is what U-Boot prints on the console to
    		prompt for user input.
    
    - CONFIG_SYS_CBSIZE:	Buffer size for input from the Console
    
    - CONFIG_SYS_PBSIZE:	Buffer size for Console output
    
    - CONFIG_SYS_MAXARGS:	max. Number of arguments accepted for monitor commands
    
    - CONFIG_SYS_BARGSIZE: Buffer size for Boot Arguments which are passed to
    		the application (usually a Linux kernel) when it is
    		booted
    
    - CONFIG_SYS_BAUDRATE_TABLE:
    		List of legal baudrate settings for this board.
    
    - CONFIG_SYS_MEM_RESERVE_SECURE
    		Only implemented for ARMv8 for now.
    		If defined, the size of CONFIG_SYS_MEM_RESERVE_SECURE memory
    		is substracted from total RAM and won't be reported to OS.
    		This memory can be used as secure memory. A variable
    		gd->arch.secure_ram is used to track the location. In systems
    		the RAM base is not zero, or RAM is divided into banks,
    		this variable needs to be recalcuated to get the address.
    
    - CONFIG_SYS_LOADS_BAUD_CHANGE:
    		Enable temporary baudrate change while serial download
    
    - CONFIG_SYS_SDRAM_BASE:
    		Physical start address of SDRAM. _Must_ be 0 here.
    
    - CONFIG_SYS_FLASH_BASE:
    		Physical start address of Flash memory.
    
    - CONFIG_SYS_MONITOR_LEN:
    		Size of memory reserved for monitor code, used to
    		determine _at_compile_time_ (!) if the environment is
    		embedded within the U-Boot image, or in a separate
    		flash sector.
    
    - CONFIG_SYS_MALLOC_LEN:
    		Size of DRAM reserved for malloc() use.
    
    - CONFIG_SYS_MALLOC_F_LEN
    		Size of the malloc() pool for use before relocation. If
    		this is defined, then a very simple malloc() implementation
    		will become available before relocation. The address is just
    		below the global data, and the stack is moved down to make
    		space.
    
    		This feature allocates regions with increasing addresses
    		within the region. calloc() is supported, but realloc()
    		is not available. free() is supported but does nothing.
    		The memory will be freed (or in fact just forgotten) when
    		U-Boot relocates itself.
    
    - CONFIG_SYS_MALLOC_SIMPLE
    		Provides a simple and small malloc() and calloc() for those
    		boards which do not use the full malloc in SPL (which is
    		enabled with CONFIG_SYS_SPL_MALLOC_START).
    
    - CONFIG_SYS_NONCACHED_MEMORY:
    		Size of non-cached memory area. This area of memory will be
    		typically located right below the malloc() area and mapped
    		uncached in the MMU. This is useful for drivers that would
    		otherwise require a lot of explicit cache maintenance. For
    		some drivers it's also impossible to properly maintain the
    		cache. For example if the regions that need to be flushed
    		are not a multiple of the cache-line size, *and* padding
    		cannot be allocated between the regions to align them (i.e.
    		if the HW requires a contiguous array of regions, and the
    		size of each region is not cache-aligned), then a flush of
    		one region may result in overwriting data that hardware has
    		written to another region in the same cache-line. This can
    		happen for example in network drivers where descriptors for
    		buffers are typically smaller than the CPU cache-line (e.g.
    		16 bytes vs. 32 or 64 bytes).
    
    		Non-cached memory is only supported on 32-bit ARM at present.
    
    - CONFIG_SYS_BOOTM_LEN:
    		Normally compressed uImages are limited to an
    		uncompressed size of 8 MBytes. If this is not enough,
    		you can define CONFIG_SYS_BOOTM_LEN in your board config file
    		to adjust this setting to your needs.
    
    - CONFIG_SYS_BOOTMAPSZ:
    		Maximum size of memory mapped by the startup code of
    		the Linux kernel; all data that must be processed by
    		the Linux kernel (bd_info, boot arguments, FDT blob if
    		used) must be put below this limit, unless "bootm_low"
    		environment variable is defined and non-zero. In such case
    		all data for the Linux kernel must be between "bootm_low"
    		and "bootm_low" + CONFIG_SYS_BOOTMAPSZ.	 The environment
    		variable "bootm_mapsize" will override the value of
    		CONFIG_SYS_BOOTMAPSZ.  If CONFIG_SYS_BOOTMAPSZ is undefined,
    		then the value in "bootm_size" will be used instead.
    
    - CONFIG_SYS_BOOT_RAMDISK_HIGH:
    		Enable initrd_high functionality.  If defined then the
    		initrd_high feature is enabled and the bootm ramdisk subcommand
    		is enabled.
    
    - CONFIG_SYS_BOOT_GET_CMDLINE:
    		Enables allocating and saving kernel cmdline in space between
    		"bootm_low" and "bootm_low" + BOOTMAPSZ.
    
    - CONFIG_SYS_BOOT_GET_KBD:
    		Enables allocating and saving a kernel copy of the bd_info in
    		space between "bootm_low" and "bootm_low" + BOOTMAPSZ.
    
    - CONFIG_SYS_MAX_FLASH_SECT:
    		Max number of sectors on a Flash chip
    
    - CONFIG_SYS_FLASH_ERASE_TOUT:
    		Timeout for Flash erase operations (in ms)
    
    - CONFIG_SYS_FLASH_WRITE_TOUT:
    		Timeout for Flash write operations (in ms)
    
    - CONFIG_SYS_FLASH_LOCK_TOUT
    		Timeout for Flash set sector lock bit operation (in ms)
    
    - CONFIG_SYS_FLASH_UNLOCK_TOUT
    		Timeout for Flash clear lock bits operation (in ms)
    
    - CONFIG_SYS_FLASH_PROTECTION
    		If defined, hardware flash sectors protection is used
    		instead of U-Boot software protection.
    
    - CONFIG_SYS_DIRECT_FLASH_TFTP:
    
    		Enable TFTP transfers directly to flash memory;
    		without this option such a download has to be
    		performed in two steps: (1) download to RAM, and (2)
    		copy from RAM to flash.
    
    		The two-step approach is usually more reliable, since
    		you can check if the download worked before you erase
    		the flash, but in some situations (when system RAM is
    		too limited to allow for a temporary copy of the
    		downloaded image) this option may be very useful.
    
    - CONFIG_SYS_FLASH_CFI:
    		Define if the flash driver uses extra elements in the
    		common flash structure for storing flash geometry.
    
    - CONFIG_FLASH_CFI_DRIVER
    		This option also enables the building of the cfi_flash driver
    		in the drivers directory
    
    - CONFIG_FLASH_CFI_MTD
    		This option enables the building of the cfi_mtd driver
    		in the drivers directory. The driver exports CFI flash
    		to the MTD layer.
    
    - CONFIG_SYS_FLASH_USE_BUFFER_WRITE
    		Use buffered writes to flash.
    
    - CONFIG_FLASH_SPANSION_S29WS_N
    		s29ws-n MirrorBit flash has non-standard addresses for buffered
    		write commands.
    
    - CONFIG_SYS_FLASH_QUIET_TEST
    		If this option is defined, the common CFI flash doesn't
    		print it's warning upon not recognized FLASH banks. This
    		is useful, if some of the configured banks are only
    		optionally available.
    
    - CONFIG_FLASH_SHOW_PROGRESS
    		If defined (must be an integer), print out countdown
    		digits and dots.  Recommended value: 45 (9..1) for 80
    		column displays, 15 (3..1) for 40 column displays.
    
    - CONFIG_FLASH_VERIFY
    		If defined, the content of the flash (destination) is compared
    		against the source after the write operation. An error message
    		will be printed when the contents are not identical.
    		Please note that this option is useless in nearly all cases,
    		since such flash programming errors usually are detected earlier
    		while unprotecting/erasing/programming. Please only enable
    		this option if you really know what you are doing.
    
    - CONFIG_ENV_MAX_ENTRIES
    
    	Maximum number of entries in the hash table that is used
    	internally to store the environment settings. The default
    	setting is supposed to be generous and should work in most
    	cases. This setting can be used to tune behaviour; see
    	lib/hashtable.c for details.
    
    - CONFIG_ENV_FLAGS_LIST_DEFAULT
    - CONFIG_ENV_FLAGS_LIST_STATIC
    	Enable validation of the values given to environment variables when
    	calling env set.  Variables can be restricted to only decimal,
    	hexadecimal, or boolean.  If CONFIG_CMD_NET is also defined,
    	the variables can also be restricted to IP address or MAC address.
    
    	The format of the list is:
    		type_attribute = [s|d|x|b|i|m]
    		access_attribute = [a|r|o|c]
    		attributes = type_attribute[access_attribute]
    		entry = variable_name[:attributes]
    		list = entry[,list]
    
    	The type attributes are:
    		s - String (default)
    		d - Decimal
    		x - Hexadecimal
    		b - Boolean ([1yYtT|0nNfF])
    		i - IP address
    		m - MAC address
    
    	The access attributes are:
    		a - Any (default)
    		r - Read-only
    		o - Write-once
    		c - Change-default
    
    	- CONFIG_ENV_FLAGS_LIST_DEFAULT
    		Define this to a list (string) to define the ".flags"
    		environment variable in the default or embedded environment.
    
    	- CONFIG_ENV_FLAGS_LIST_STATIC
    		Define this to a list (string) to define validation that
    		should be done if an entry is not found in the ".flags"
    		environment variable.  To override a setting in the static
    		list, simply add an entry for the same variable name to the
    		".flags" variable.
    
    	If CONFIG_REGEX is defined, the variable_name above is evaluated as a
    	regular expression. This allows multiple variables to define the same
    	flags without explicitly listing them for each variable.
    
    The following definitions that deal with the placement and management
    of environment data (variable area); in general, we support the
    following configurations:
    
    - CONFIG_BUILD_ENVCRC:
    
    	Builds up envcrc with the target environment so that external utils
    	may easily extract it and embed it in final U-Boot images.
    
    BE CAREFUL! The first access to the environment happens quite early
    in U-Boot initialization (when we try to get the setting of for the
    console baudrate). You *MUST* have mapped your NVRAM area then, or
    U-Boot will hang.
    
    Please note that even with NVRAM we still use a copy of the
    environment in RAM: we could work on NVRAM directly, but we want to
    keep settings there always unmodified except somebody uses "saveenv"
    to save the current settings.
    
    BE CAREFUL! For some special cases, the local device can not use
    "saveenv" command. For example, the local device will get the
    environment stored in a remote NOR flash by SRIO or PCIE link,
    but it can not erase, write this NOR flash by SRIO or PCIE interface.
    
    - CONFIG_NAND_ENV_DST
    
    	Defines address in RAM to which the nand_spl code should copy the
    	environment. If redundant environment is used, it will be copied to
    	CONFIG_NAND_ENV_DST + CONFIG_ENV_SIZE.
    
    Please note that the environment is read-only until the monitor
    has been relocated to RAM and a RAM copy of the environment has been
    created; also, when using EEPROM you will have to use env_get_f()
    until then to read environment variables.
    
    The environment is protected by a CRC32 checksum. Before the monitor
    is relocated into RAM, as a result of a bad CRC you will be working
    with the compiled-in default environment - *silently*!!! [This is
    necessary, because the first environment variable we need is the
    "baudrate" setting for the console - if we have a bad CRC, we don't
    have any device yet where we could complain.]
    
    Note: once the monitor has been relocated, then it will complain if
    the default environment is used; a new CRC is computed as soon as you
    use the "saveenv" command to store a valid environment.
    
    - CONFIG_SYS_FAULT_MII_ADDR:
    		MII address of the PHY to check for the Ethernet link state.
    
    - CONFIG_NS16550_MIN_FUNCTIONS:
    		Define this if you desire to only have use of the NS16550_init
    		and NS16550_putc functions for the serial driver located at
    		drivers/serial/ns16550.c.  This option is useful for saving
    		space for already greatly restricted images, including but not
    		limited to NAND_SPL configurations.
    
    - CONFIG_DISPLAY_BOARDINFO
    		Display information about the board that U-Boot is running on
    		when U-Boot starts up. The board function checkboard() is called
    		to do this.
    
    - CONFIG_DISPLAY_BOARDINFO_LATE
    		Similar to the previous option, but display this information
    		later, once stdio is running and output goes to the LCD, if
    		present.
    
    Low Level (hardware related) configuration options:
    ---------------------------------------------------
    
    - CONFIG_SYS_CACHELINE_SIZE:
    		Cache Line Size of the CPU.
    
    - CONFIG_SYS_CCSRBAR_DEFAULT:
    		Default (power-on reset) physical address of CCSR on Freescale
    		PowerPC SOCs.
    
    - CONFIG_SYS_CCSRBAR:
    		Virtual address of CCSR.  On a 32-bit build, this is typically
    		the same value as CONFIG_SYS_CCSRBAR_DEFAULT.
    
    - CONFIG_SYS_CCSRBAR_PHYS:
    		Physical address of CCSR.  CCSR can be relocated to a new
    		physical address, if desired.  In this case, this macro should
    		be set to that address.	 Otherwise, it should be set to the
    		same value as CONFIG_SYS_CCSRBAR_DEFAULT.  For example, CCSR
    		is typically relocated on 36-bit builds.  It is recommended
    		that this macro be defined via the _HIGH and _LOW macros:
    
    		#define CONFIG_SYS_CCSRBAR_PHYS ((CONFIG_SYS_CCSRBAR_PHYS_HIGH
    			* 1ull) << 32 | CONFIG_SYS_CCSRBAR_PHYS_LOW)
    
    - CONFIG_SYS_CCSRBAR_PHYS_HIGH:
    		Bits 33-36 of CONFIG_SYS_CCSRBAR_PHYS.	This value is typically
    		either 0 (32-bit build) or 0xF (36-bit build).	This macro is
    		used in assembly code, so it must not contain typecasts or
    		integer size suffixes (e.g. "ULL").
    
    - CONFIG_SYS_CCSRBAR_PHYS_LOW:
    		Lower 32-bits of CONFIG_SYS_CCSRBAR_PHYS.  This macro is
    		used in assembly code, so it must not contain typecasts or
    		integer size suffixes (e.g. "ULL").
    
    - CONFIG_SYS_CCSR_DO_NOT_RELOCATE:
    		If this macro is defined, then CONFIG_SYS_CCSRBAR_PHYS will be
    		forced to a value that ensures that CCSR is not relocated.
    
    - CONFIG_SYS_IMMR:	Physical address of the Internal Memory.
    		DO NOT CHANGE unless you know exactly what you're
    		doing! (11-4) [MPC8xx systems only]
    
    - CONFIG_SYS_INIT_RAM_ADDR:
    
    		Start address of memory area that can be used for
    		initial data and stack; please note that this must be
    		writable memory that is working WITHOUT special
    		initialization, i. e. you CANNOT use normal RAM which
    		will become available only after programming the
    		memory controller and running certain initialization
    		sequences.
    
    		U-Boot uses the following memory types:
    		- MPC8xx: IMMR (internal memory of the CPU)
    
    - CONFIG_SYS_GBL_DATA_OFFSET:
    
    		Offset of the initial data structure in the memory
    		area defined by CONFIG_SYS_INIT_RAM_ADDR. Usually
    		CONFIG_SYS_GBL_DATA_OFFSET is chosen such that the initial
    		data is located at the end of the available space
    		(sometimes written as (CONFIG_SYS_INIT_RAM_SIZE -
    		GENERATED_GBL_DATA_SIZE), and the initial stack is just
    		below that area (growing from (CONFIG_SYS_INIT_RAM_ADDR +
    		CONFIG_SYS_GBL_DATA_OFFSET) downward.
    
    	Note:
    		On the MPC824X (or other systems that use the data
    		cache for initial memory) the address chosen for
    		CONFIG_SYS_INIT_RAM_ADDR is basically arbitrary - it must
    		point to an otherwise UNUSED address space between
    		the top of RAM and the start of the PCI space.
    
    - CONFIG_SYS_SCCR:	System Clock and reset Control Register (15-27)
    
    - CONFIG_SYS_OR_TIMING_SDRAM:
    		SDRAM timing
    
    - CONFIG_SYS_MAMR_PTA:
    		periodic timer for refresh
    
    - CONFIG_SYS_SRIO:
    		Chip has SRIO or not
    
    - CONFIG_SRIO1:
    		Board has SRIO 1 port available
    
    - CONFIG_SRIO2:
    		Board has SRIO 2 port available
    
    - CONFIG_SRIO_PCIE_BOOT_MASTER
    		Board can support master function for Boot from SRIO and PCIE
    
    - CONFIG_SYS_SRIOn_MEM_VIRT:
    		Virtual Address of SRIO port 'n' memory region
    
    - CONFIG_SYS_SRIOn_MEM_PHYxS:
    		Physical Address of SRIO port 'n' memory region
    
    - CONFIG_SYS_SRIOn_MEM_SIZE:
    		Size of SRIO port 'n' memory region
    
    - CONFIG_SYS_NAND_BUSWIDTH_16BIT
    		Defined to tell the NAND controller that the NAND chip is using
    		a 16 bit bus.
    		Not all NAND drivers use this symbol.
    		Example of drivers that use it:
    		- drivers/mtd/nand/raw/ndfc.c
    		- drivers/mtd/nand/raw/mxc_nand.c
    
    - CONFIG_SYS_NDFC_EBC0_CFG
    		Sets the EBC0_CFG register for the NDFC. If not defined
    		a default value will be used.
    
    - CONFIG_SPD_EEPROM
    		Get DDR timing information from an I2C EEPROM. Common
    		with pluggable memory modules such as SODIMMs
    
      SPD_EEPROM_ADDRESS
    		I2C address of the SPD EEPROM
    
    - CONFIG_SYS_SPD_BUS_NUM
    		If SPD EEPROM is on an I2C bus other than the first
    		one, specify here. Note that the value must resolve
    		to something your driver can deal with.
    
    - CONFIG_SYS_DDR_RAW_TIMING
    		Get DDR timing information from other than SPD. Common with
    		soldered DDR chips onboard without SPD. DDR raw timing
    		parameters are extracted from datasheet and hard-coded into
    		header files or board specific files.
    
    - CONFIG_FSL_DDR_INTERACTIVE
    		Enable interactive DDR debugging. See doc/README.fsl-ddr.
    
    - CONFIG_FSL_DDR_SYNC_REFRESH
    		Enable sync of refresh for multiple controllers.
    
    - CONFIG_FSL_DDR_BIST
    		Enable built-in memory test for Freescale DDR controllers.
    
    - CONFIG_SYS_83XX_DDR_USES_CS0
    		Only for 83xx systems. If specified, then DDR should
    		be configured using CS0 and CS1 instead of CS2 and CS3.
    
    - CONFIG_RMII
    		Enable RMII mode for all FECs.
    		Note that this is a global option, we can't
    		have one FEC in standard MII mode and another in RMII mode.
    
    - CONFIG_CRC32_VERIFY
    		Add a verify option to the crc32 command.
    		The syntax is:
    
    		=> crc32 -v <address> <count> <crc32>
    
    		Where address/count indicate a memory area
    		and crc32 is the correct crc32 which the
    		area should have.
    
    - CONFIG_LOOPW
    		Add the "loopw" memory command. This only takes effect if
    		the memory commands are activated globally (CONFIG_CMD_MEMORY).
    
    - CONFIG_CMD_MX_CYCLIC
    		Add the "mdc" and "mwc" memory commands. These are cyclic
    		"md/mw" commands.
    		Examples:
    
    		=> mdc.b 10 4 500
    		This command will print 4 bytes (10,11,12,13) each 500 ms.
    
    		=> mwc.l 100 12345678 10
    		This command will write 12345678 to address 100 all 10 ms.
    
    		This only takes effect if the memory commands are activated
    		globally (CONFIG_CMD_MEMORY).
    
    - CONFIG_SPL_BUILD
    		Set when the currently-running compilation is for an artifact
    		that will end up in the SPL (as opposed to the TPL or U-Boot
    		proper). Code that needs stage-specific behavior should check
    		this.
    
    - CONFIG_TPL_BUILD
    		Set when the currently-running compilation is for an artifact
    		that will end up in the TPL (as opposed to the SPL or U-Boot
    		proper). Code that needs stage-specific behavior should check
    		this.
    
    - CONFIG_SYS_MPC85XX_NO_RESETVEC
    		Only for 85xx systems. If this variable is specified, the section
    		.resetvec is not kept and the section .bootpg is placed in the
    		previous 4k of the .text section.
    
    - CONFIG_ARCH_MAP_SYSMEM
    		Generally U-Boot (and in particular the md command) uses
    		effective address. It is therefore not necessary to regard
    		U-Boot address as virtual addresses that need to be translated
    		to physical addresses. However, sandbox requires this, since
    		it maintains its own little RAM buffer which contains all
    		addressable memory. This option causes some memory accesses
    		to be mapped through map_sysmem() / unmap_sysmem().
    
    - CONFIG_X86_RESET_VECTOR
    		If defined, the x86 reset vector code is included. This is not
    		needed when U-Boot is running from Coreboot.
    
    - CONFIG_SYS_NAND_NO_SUBPAGE_WRITE
    		Option to disable subpage write in NAND driver
    		driver that uses this:
    		drivers/mtd/nand/raw/davinci_nand.c
    
    Freescale QE/FMAN Firmware Support:
    -----------------------------------
    
    The Freescale QUICCEngine (QE) and Frame Manager (FMAN) both support the
    loading of "firmware", which is encoded in the QE firmware binary format.
    This firmware often needs to be loaded during U-Boot booting, so macros
    are used to identify the storage device (NOR flash, SPI, etc) and the address
    within that device.
    
    - CONFIG_SYS_FMAN_FW_ADDR
    	The address in the storage device where the FMAN microcode is located.  The
    	meaning of this address depends on which CONFIG_SYS_QE_FMAN_FW_IN_xxx macro
    	is also specified.
    
    - CONFIG_SYS_QE_FW_ADDR
    	The address in the storage device where the QE microcode is located.  The
    	meaning of this address depends on which CONFIG_SYS_QE_FMAN_FW_IN_xxx macro
    	is also specified.
    
    - CONFIG_SYS_QE_FMAN_FW_LENGTH
    	The maximum possible size of the firmware.  The firmware binary format
    	has a field that specifies the actual size of the firmware, but it
    	might not be possible to read any part of the firmware unless some
    	local storage is allocated to hold the entire firmware first.
    
    - CONFIG_SYS_QE_FMAN_FW_IN_NOR
    	Specifies that QE/FMAN firmware is located in NOR flash, mapped as
    	normal addressable memory via the LBC.  CONFIG_SYS_FMAN_FW_ADDR is the
    	virtual address in NOR flash.
    
    - CONFIG_SYS_QE_FMAN_FW_IN_NAND
    	Specifies that QE/FMAN firmware is located in NAND flash.
    	CONFIG_SYS_FMAN_FW_ADDR is the offset within NAND flash.
    
    - CONFIG_SYS_QE_FMAN_FW_IN_MMC
    	Specifies that QE/FMAN firmware is located on the primary SD/MMC
    	device.  CONFIG_SYS_FMAN_FW_ADDR is the byte offset on that device.
    
    - CONFIG_SYS_QE_FMAN_FW_IN_REMOTE
    	Specifies that QE/FMAN firmware is located in the remote (master)
    	memory space.	CONFIG_SYS_FMAN_FW_ADDR is a virtual address which
    	can be mapped from slave TLB->slave LAW->slave SRIO or PCIE outbound
    	window->master inbound window->master LAW->the ucode address in
    	master's memory space.
    
    Freescale Layerscape Management Complex Firmware Support:
    ---------------------------------------------------------
    The Freescale Layerscape Management Complex (MC) supports the loading of
    "firmware".
    This firmware often needs to be loaded during U-Boot booting, so macros
    are used to identify the storage device (NOR flash, SPI, etc) and the address
    within that device.
    
    - CONFIG_FSL_MC_ENET
    	Enable the MC driver for Layerscape SoCs.
    
    Freescale Layerscape Debug Server Support:
    -------------------------------------------
    The Freescale Layerscape Debug Server Support supports the loading of
    "Debug Server firmware" and triggering SP boot-rom.
    This firmware often needs to be loaded during U-Boot booting.
    
    - CONFIG_SYS_MC_RSV_MEM_ALIGN
    	Define alignment of reserved memory MC requires
    
    Reproducible builds
    -------------------
    
    In order to achieve reproducible builds, timestamps used in the U-Boot build
    process have to be set to a fixed value.
    
    This is done using the SOURCE_DATE_EPOCH environment variable.
    SOURCE_DATE_EPOCH is to be set on the build host's shell, not as a configuration
    option for U-Boot or an environment variable in U-Boot.
    
    SOURCE_DATE_EPOCH should be set to a number of seconds since the epoch, in UTC.
    
    Building the Software:
    ======================
    
    Building U-Boot has been tested in several native build environments
    and in many different cross environments. Of course we cannot support
    all possibly existing versions of cross development tools in all
    (potentially obsolete) versions. In case of tool chain problems we
    recommend to use the ELDK (see https://www.denx.de/wiki/DULG/ELDK)
    which is extensively used to build and test U-Boot.
    
    If you are not using a native environment, it is assumed that you
    have GNU cross compiling tools available in your path. In this case,
    you must set the environment variable CROSS_COMPILE in your shell.
    Note that no changes to the Makefile or any other source files are
    necessary. For example using the ELDK on a 4xx CPU, please enter:
    
    	$ CROSS_COMPILE=ppc_4xx-
    	$ export CROSS_COMPILE
    
    U-Boot is intended to be simple to build. After installing the
    sources you must configure U-Boot for one specific board type. This
    is done by typing:
    
    	make NAME_defconfig
    
    where "NAME_defconfig" is the name of one of the existing configu-
    rations; see configs/*_defconfig for supported names.
    
    Note: for some boards special configuration names may exist; check if
          additional information is available from the board vendor; for
          instance, the TQM823L systems are available without (standard)
          or with LCD support. You can select such additional "features"
          when choosing the configuration, i. e.
    
          make TQM823L_defconfig
    	- will configure for a plain TQM823L, i. e. no LCD support
    
          make TQM823L_LCD_defconfig
    	- will configure for a TQM823L with U-Boot console on LCD
    
          etc.
    
    
    Finally, type "make all", and you should get some working U-Boot
    images ready for download to / installation on your system:
    
    - "u-boot.bin" is a raw binary image
    - "u-boot" is an image in ELF binary format
    - "u-boot.srec" is in Motorola S-Record format
    
    By default the build is performed locally and the objects are saved
    in the source directory. One of the two methods can be used to change
    this behavior and build U-Boot to some external directory:
    
    1. Add O= to the make command line invocations:
    
    	make O=/tmp/build distclean
    	make O=/tmp/build NAME_defconfig
    	make O=/tmp/build all
    
    2. Set environment variable KBUILD_OUTPUT to point to the desired location:
    
    	export KBUILD_OUTPUT=/tmp/build
    	make distclean
    	make NAME_defconfig
    	make all
    
    Note that the command line "O=" setting overrides the KBUILD_OUTPUT environment
    variable.
    
    User specific CPPFLAGS, AFLAGS and CFLAGS can be passed to the compiler by
    setting the according environment variables KCPPFLAGS, KAFLAGS and KCFLAGS.
    For example to treat all compiler warnings as errors:
    
    	make KCFLAGS=-Werror
    
    Please be aware that the Makefiles assume you are using GNU make, so
    for instance on NetBSD you might need to use "gmake" instead of
    native "make".
    
    
    If the system board that you have is not listed, then you will need
    to port U-Boot to your hardware platform. To do this, follow these
    steps:
    
    1.  Create a new directory to hold your board specific code. Add any
        files you need. In your board directory, you will need at least
        the "Makefile" and a "<board>.c".
    2.  Create a new configuration file "include/configs/<board>.h" for
        your board.
    3.  If you're porting U-Boot to a new CPU, then also create a new
        directory to hold your CPU specific code. Add any files you need.
    4.  Run "make <board>_defconfig" with your new name.
    5.  Type "make", and you should get a working "u-boot.srec" file
        to be installed on your target system.
    6.  Debug and solve any problems that might arise.
        [Of course, this last step is much harder than it sounds.]
    
    
    Testing of U-Boot Modifications, Ports to New Hardware, etc.:
    ==============================================================
    
    If you have modified U-Boot sources (for instance added a new board
    or support for new devices, a new CPU, etc.) you are expected to
    provide feedback to the other developers. The feedback normally takes
    the form of a "patch", i.e. a context diff against a certain (latest
    official or latest in the git repository) version of U-Boot sources.
    
    But before you submit such a patch, please verify that your modifi-
    cation did not break existing code. At least make sure that *ALL* of
    the supported boards compile WITHOUT ANY compiler warnings. To do so,
    just run the buildman script (tools/buildman/buildman), which will
    configure and build U-Boot for ALL supported system. Be warned, this
    will take a while. Please see the buildman README, or run 'buildman -H'
    for documentation.
    
    
    See also "U-Boot Porting Guide" below.
    
    
    Monitor Commands - Overview:
    ============================
    
    go	- start application at address 'addr'
    run	- run commands in an environment variable
    bootm	- boot application image from memory
    bootp	- boot image via network using BootP/TFTP protocol
    bootz   - boot zImage from memory
    tftpboot- boot image via network using TFTP protocol
    	       and env variables "ipaddr" and "serverip"
    	       (and eventually "gatewayip")
    tftpput - upload a file via network using TFTP protocol
    rarpboot- boot image via network using RARP/TFTP protocol
    diskboot- boot from IDE devicebootd   - boot default, i.e., run 'bootcmd'
    loads	- load S-Record file over serial line
    loadb	- load binary file over serial line (kermit mode)
    md	- memory display
    mm	- memory modify (auto-incrementing)
    nm	- memory modify (constant address)
    mw	- memory write (fill)
    ms	- memory search
    cp	- memory copy
    cmp	- memory compare
    crc32	- checksum calculation
    i2c	- I2C sub-system
    sspi	- SPI utility commands
    base	- print or set address offset
    printenv- print environment variables
    pwm	- control pwm channels
    setenv	- set environment variables
    saveenv - save environment variables to persistent storage
    protect - enable or disable FLASH write protection
    erase	- erase FLASH memory
    flinfo	- print FLASH memory information
    nand	- NAND memory operations (see doc/README.nand)
    bdinfo	- print Board Info structure
    iminfo	- print header information for application image
    coninfo - print console devices and informations
    ide	- IDE sub-system
    loop	- infinite loop on address range
    loopw	- infinite write loop on address range
    mtest	- simple RAM test
    icache	- enable or disable instruction cache
    dcache	- enable or disable data cache
    reset	- Perform RESET of the CPU
    echo	- echo args to console
    version - print monitor version
    help	- print online help
    ?	- alias for 'help'
    
    
    Monitor Commands - Detailed Description:
    ========================================
    
    TODO.
    
    For now: just type "help <command>".
    
    
    Note for Redundant Ethernet Interfaces:
    =======================================
    
    Some boards come with redundant Ethernet interfaces; U-Boot supports
    such configurations and is capable of automatic selection of a
    "working" interface when needed. MAC assignment works as follows:
    
    Network interfaces are numbered eth0, eth1, eth2, ... Corresponding
    MAC addresses can be stored in the environment as "ethaddr" (=>eth0),
    "eth1addr" (=>eth1), "eth2addr", ...
    
    If the network interface stores some valid MAC address (for instance
    in SROM), this is used as default address if there is NO correspon-
    ding setting in the environment; if the corresponding environment
    variable is set, this overrides the settings in the card; that means:
    
    o If the SROM has a valid MAC address, and there is no address in the
      environment, the SROM's address is used.
    
    o If there is no valid address in the SROM, and a definition in the
      environment exists, then the value from the environment variable is
      used.
    
    o If both the SROM and the environment contain a MAC address, and
      both addresses are the same, this MAC address is used.
    
    o If both the SROM and the environment contain a MAC address, and the
      addresses differ, the value from the environment is used and a
      warning is printed.
    
    o If neither SROM nor the environment contain a MAC address, an error
      is raised. If CONFIG_NET_RANDOM_ETHADDR is defined, then in this case
      a random, locally-assigned MAC is used.
    
    If Ethernet drivers implement the 'write_hwaddr' function, valid MAC addresses
    will be programmed into hardware as part of the initialization process.	 This
    may be skipped by setting the appropriate 'ethmacskip' environment variable.
    The naming convention is as follows:
    "ethmacskip" (=>eth0), "eth1macskip" (=>eth1) etc.
    
    Image Formats:
    ==============
    
    U-Boot is capable of booting (and performing other auxiliary operations on)
    images in two formats:
    
    New uImage format (FIT)
    -----------------------
    
    Flexible and powerful format based on Flattened Image Tree -- FIT (similar
    to Flattened Device Tree). It allows the use of images with multiple
    components (several kernels, ramdisks, etc.), with contents protected by
    SHA1, MD5 or CRC32. More details are found in the doc/uImage.FIT directory.
    
    
    Old uImage format
    -----------------
    
    Old image format is based on binary files which can be basically anything,
    preceded by a special header; see the definitions in include/image.h for
    details; basically, the header defines the following image properties:
    
    * Target Operating System (Provisions for OpenBSD, NetBSD, FreeBSD,
      4.4BSD, Linux, SVR4, Esix, Solaris, Irix, SCO, Dell, NCR, VxWorks,
      LynxOS, pSOS, QNX, RTEMS, INTEGRITY;
      Currently supported: Linux, NetBSD, VxWorks, QNX, RTEMS, INTEGRITY).
    * Target CPU Architecture (Provisions for Alpha, ARM, Intel x86,
      IA64, MIPS, Nios II, PowerPC, IBM S390, SuperH, Sparc, Sparc 64 Bit;
      Currently supported: ARM, Intel x86, MIPS, Nios II, PowerPC).
    * Compression Type (uncompressed, gzip, bzip2)
    * Load Address
    * Entry Point
    * Image Name
    * Image Timestamp
    
    The header is marked by a special Magic Number, and both the header
    and the data portions of the image are secured against corruption by
    CRC32 checksums.
    
    
    Linux Support:
    ==============
    
    Although U-Boot should support any OS or standalone application
    easily, the main focus has always been on Linux during the design of
    U-Boot.
    
    U-Boot includes many features that so far have been part of some
    special "boot loader" code within the Linux kernel. Also, any
    "initrd" images to be used are no longer part of one big Linux image;
    instead, kernel and "initrd" are separate images. This implementation
    serves several purposes:
    
    - the same features can be used for other OS or standalone
      applications (for instance: using compressed images to reduce the
      Flash memory footprint)
    
    - it becomes much easier to port new Linux kernel versions because
      lots of low-level, hardware dependent stuff are done by U-Boot
    
    - the same Linux kernel image can now be used with different "initrd"
      images; of course this also means that different kernel images can
      be run with the same "initrd". This makes testing easier (you don't
      have to build a new "zImage.initrd" Linux image when you just
      change a file in your "initrd"). Also, a field-upgrade of the
      software is easier now.
    
    
    Linux HOWTO:
    ============
    
    Porting Linux to U-Boot based systems:
    ---------------------------------------
    
    U-Boot cannot save you from doing all the necessary modifications to
    configure the Linux device drivers for use with your target hardware
    (no, we don't intend to provide a full virtual machine interface to
    Linux :-).
    
    But now you can ignore ALL boot loader code (in arch/powerpc/mbxboot).
    
    Just make sure your machine specific header file (for instance
    include/asm-ppc/tqm8xx.h) includes the same definition of the Board
    Information structure as we define in include/asm-<arch>/u-boot.h,
    and make sure that your definition of IMAP_ADDR uses the same value
    as your U-Boot configuration in CONFIG_SYS_IMMR.
    
    Note that U-Boot now has a driver model, a unified model for drivers.
    If you are adding a new driver, plumb it into driver model. If there
    is no uclass available, you are encouraged to create one. See
    doc/driver-model.
    
    
    Configuring the Linux kernel:
    -----------------------------
    
    No specific requirements for U-Boot. Make sure you have some root
    device (initial ramdisk, NFS) for your target system.
    
    
    Building a Linux Image:
    -----------------------
    
    With U-Boot, "normal" build targets like "zImage" or "bzImage" are
    not used. If you use recent kernel source, a new build target
    "uImage" will exist which automatically builds an image usable by
    U-Boot. Most older kernels also have support for a "pImage" target,
    which was introduced for our predecessor project PPCBoot and uses a
    100% compatible format.
    
    Example:
    
    	make TQM850L_defconfig
    	make oldconfig
    	make dep
    	make uImage
    
    The "uImage" build target uses a special tool (in 'tools/mkimage') to
    encapsulate a compressed Linux kernel image with header	 information,
    CRC32 checksum etc. for use with U-Boot. This is what we are doing:
    
    * build a standard "vmlinux" kernel image (in ELF binary format):
    
    * convert the kernel into a raw binary image:
    
    	${CROSS_COMPILE}-objcopy -O binary \
    				 -R .note -R .comment \
    				 -S vmlinux linux.bin
    
    * compress the binary image:
    
    	gzip -9 linux.bin
    
    * package compressed binary image for U-Boot:
    
    	mkimage -A ppc -O linux -T kernel -C gzip \
    		-a 0 -e 0 -n "Linux Kernel Image" \
    		-d linux.bin.gz uImage
    
    
    The "mkimage" tool can also be used to create ramdisk images for use
    with U-Boot, either separated from the Linux kernel image, or
    combined into one file. "mkimage" encapsulates the images with a 64
    byte header containing information about target architecture,
    operating system, image type, compression method, entry points, time
    stamp, CRC32 checksums, etc.
    
    "mkimage" can be called in two ways: to verify existing images and
    print the header information, or to build new images.
    
    In the first form (with "-l" option) mkimage lists the information
    contained in the header of an existing U-Boot image; this includes
    checksum verification:
    
    	tools/mkimage -l image
    	  -l ==> list image header information
    
    The second form (with "-d" option) is used to build a U-Boot image
    from a "data file" which is used as image payload:
    
    	tools/mkimage -A arch -O os -T type -C comp -a addr -e ep \
    		      -n name -d data_file image
    	  -A ==> set architecture to 'arch'
    	  -O ==> set operating system to 'os'
    	  -T ==> set image type to 'type'
    	  -C ==> set compression type 'comp'
    	  -a ==> set load address to 'addr' (hex)
    	  -e ==> set entry point to 'ep' (hex)
    	  -n ==> set image name to 'name'
    	  -d ==> use image data from 'datafile'
    
    Right now, all Linux kernels for PowerPC systems use the same load
    address (0x00000000), but the entry point address depends on the
    kernel version:
    
    - 2.2.x kernels have the entry point at 0x0000000C,
    - 2.3.x and later kernels have the entry point at 0x00000000.
    
    So a typical call to build a U-Boot image would read:
    
    	-> tools/mkimage -n '2.4.4 kernel for TQM850L' \
    	> -A ppc -O linux -T kernel -C gzip -a 0 -e 0 \
    	> -d /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux.gz \
    	> examples/uImage.TQM850L
    	Image Name:   2.4.4 kernel for TQM850L
    	Created:      Wed Jul 19 02:34:59 2000
    	Image Type:   PowerPC Linux Kernel Image (gzip compressed)
    	Data Size:    335725 Bytes = 327.86 kB = 0.32 MB
    	Load Address: 0x00000000
    	Entry Point:  0x00000000
    
    To verify the contents of the image (or check for corruption):
    
    	-> tools/mkimage -l examples/uImage.TQM850L
    	Image Name:   2.4.4 kernel for TQM850L
    	Created:      Wed Jul 19 02:34:59 2000
    	Image Type:   PowerPC Linux Kernel Image (gzip compressed)
    	Data Size:    335725 Bytes = 327.86 kB = 0.32 MB
    	Load Address: 0x00000000
    	Entry Point:  0x00000000
    
    NOTE: for embedded systems where boot time is critical you can trade
    speed for memory and install an UNCOMPRESSED image instead: this
    needs more space in Flash, but boots much faster since it does not
    need to be uncompressed:
    
    	-> gunzip /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux.gz
    	-> tools/mkimage -n '2.4.4 kernel for TQM850L' \
    	> -A ppc -O linux -T kernel -C none -a 0 -e 0 \
    	> -d /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux \
    	> examples/uImage.TQM850L-uncompressed
    	Image Name:   2.4.4 kernel for TQM850L
    	Created:      Wed Jul 19 02:34:59 2000
    	Image Type:   PowerPC Linux Kernel Image (uncompressed)
    	Data Size:    792160 Bytes = 773.59 kB = 0.76 MB
    	Load Address: 0x00000000
    	Entry Point:  0x00000000
    
    
    Similar you can build U-Boot images from a 'ramdisk.image.gz' file
    when your kernel is intended to use an initial ramdisk:
    
    	-> tools/mkimage -n 'Simple Ramdisk Image' \
    	> -A ppc -O linux -T ramdisk -C gzip \
    	> -d /LinuxPPC/images/SIMPLE-ramdisk.image.gz examples/simple-initrd
    	Image Name:   Simple Ramdisk Image
    	Created:      Wed Jan 12 14:01:50 2000
    	Image Type:   PowerPC Linux RAMDisk Image (gzip compressed)
    	Data Size:    566530 Bytes = 553.25 kB = 0.54 MB
    	Load Address: 0x00000000
    	Entry Point:  0x00000000
    
    The "dumpimage" tool can be used to disassemble or list the contents of images
    built by mkimage. See dumpimage's help output (-h) for details.
    
    Installing a Linux Image:
    -------------------------
    
    To downloading a U-Boot image over the serial (console) interface,
    you must convert the image to S-Record format:
    
    	objcopy -I binary -O srec examples/image examples/image.srec
    
    The 'objcopy' does not understand the information in the U-Boot
    image header, so the resulting S-Record file will be relative to
    address 0x00000000. To load it to a given address, you need to
    specify the target address as 'offset' parameter with the 'loads'
    command.
    
    Example: install the image to address 0x40100000 (which on the
    TQM8xxL is in the first Flash bank):
    
    	=> erase 40100000 401FFFFF
    
    	.......... done
    	Erased 8 sectors
    
    	=> loads 40100000
    	## Ready for S-Record download ...
    	~>examples/image.srec
    	1 2 3 4 5 6 7 8 9 10 11 12 13 ...
    	...
    	15989 15990 15991 15992
    	[file transfer complete]
    	[connected]
    	## Start Addr = 0x00000000
    
    
    You can check the success of the download using the 'iminfo' command;
    this includes a checksum verification so you can be sure no data
    corruption happened:
    
    	=> imi 40100000
    
    	## Checking Image at 40100000 ...
    	   Image Name:	 2.2.13 for initrd on TQM850L
    	   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
    	   Data Size:	 335725 Bytes = 327 kB = 0 MB
    	   Load Address: 00000000
    	   Entry Point:	 0000000c
    	   Verifying Checksum ... OK
    
    
    Boot Linux:
    -----------
    
    The "bootm" command is used to boot an application that is stored in
    memory (RAM or Flash). In case of a Linux kernel image, the contents
    of the "bootargs" environment variable is passed to the kernel as
    parameters. You can check and modify this variable using the
    "printenv" and "setenv" commands:
    
    
    	=> printenv bootargs
    	bootargs=root=/dev/ram
    
    	=> setenv bootargs root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
    
    	=> printenv bootargs
    	bootargs=root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
    
    	=> bootm 40020000
    	## Booting Linux kernel at 40020000 ...
    	   Image Name:	 2.2.13 for NFS on TQM850L
    	   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
    	   Data Size:	 381681 Bytes = 372 kB = 0 MB
    	   Load Address: 00000000
    	   Entry Point:	 0000000c
    	   Verifying Checksum ... OK
    	   Uncompressing Kernel Image ... OK
    	Linux version 2.2.13 (wd@denx.local.net) (gcc version 2.95.2 19991024 (release)) #1 Wed Jul 19 02:35:17 MEST 2000
    	Boot arguments: root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
    	time_init: decrementer frequency = 187500000/60
    	Calibrating delay loop... 49.77 BogoMIPS
    	Memory: 15208k available (700k kernel code, 444k data, 32k init) [c0000000,c1000000]
    	...
    
    If you want to boot a Linux kernel with initial RAM disk, you pass
    the memory addresses of both the kernel and the initrd image (PPBCOOT
    format!) to the "bootm" command:
    
    	=> imi 40100000 40200000
    
    	## Checking Image at 40100000 ...
    	   Image Name:	 2.2.13 for initrd on TQM850L
    	   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
    	   Data Size:	 335725 Bytes = 327 kB = 0 MB
    	   Load Address: 00000000
    	   Entry Point:	 0000000c
    	   Verifying Checksum ... OK
    
    	## Checking Image at 40200000 ...
    	   Image Name:	 Simple Ramdisk Image
    	   Image Type:	 PowerPC Linux RAMDisk Image (gzip compressed)
    	   Data Size:	 566530 Bytes = 553 kB = 0 MB
    	   Load Address: 00000000
    	   Entry Point:	 00000000
    	   Verifying Checksum ... OK
    
    	=> bootm 40100000 40200000
    	## Booting Linux kernel at 40100000 ...
    	   Image Name:	 2.2.13 for initrd on TQM850L
    	   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
    	   Data Size:	 335725 Bytes = 327 kB = 0 MB
    	   Load Address: 00000000
    	   Entry Point:	 0000000c
    	   Verifying Checksum ... OK
    	   Uncompressing Kernel Image ... OK
    	## Loading RAMDisk Image at 40200000 ...
    	   Image Name:	 Simple Ramdisk Image
    	   Image Type:	 PowerPC Linux RAMDisk Image (gzip compressed)
    	   Data Size:	 566530 Bytes = 553 kB = 0 MB
    	   Load Address: 00000000
    	   Entry Point:	 00000000
    	   Verifying Checksum ... OK
    	   Loading Ramdisk ... OK
    	Linux version 2.2.13 (wd@denx.local.net) (gcc version 2.95.2 19991024 (release)) #1 Wed Jul 19 02:32:08 MEST 2000
    	Boot arguments: root=/dev/ram
    	time_init: decrementer frequency = 187500000/60
    	Calibrating delay loop... 49.77 BogoMIPS
    	...
    	RAMDISK: Compressed image found at block 0
    	VFS: Mounted root (ext2 filesystem).
    
    	bash#
    
    Boot Linux and pass a flat device tree:
    -----------
    
    First, U-Boot must be compiled with the appropriate defines. See the section
    titled "Linux Kernel Interface" above for a more in depth explanation. The
    following is an example of how to start a kernel and pass an updated
    flat device tree:
    
    => print oftaddr
    oftaddr=0x300000
    => print oft
    oft=oftrees/mpc8540ads.dtb
    => tftp $oftaddr $oft
    Speed: 1000, full duplex
    Using TSEC0 device
    TFTP from server 192.168.1.1; our IP address is 192.168.1.101
    Filename 'oftrees/mpc8540ads.dtb'.
    Load address: 0x300000
    Loading: #
    done
    Bytes transferred = 4106 (100a hex)
    => tftp $loadaddr $bootfile
    Speed: 1000, full duplex
    Using TSEC0 device
    TFTP from server 192.168.1.1; our IP address is 192.168.1.2
    Filename 'uImage'.
    Load address: 0x200000
    Loading:############
    done
    Bytes transferred = 1029407 (fb51f hex)
    => print loadaddr
    loadaddr=200000
    => print oftaddr
    oftaddr=0x300000
    => bootm $loadaddr - $oftaddr
    ## Booting image at 00200000 ...
       Image Name:	 Linux-2.6.17-dirty
       Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
       Data Size:	 1029343 Bytes = 1005.2 kB
       Load Address: 00000000
       Entry Point:	 00000000
       Verifying Checksum ... OK
       Uncompressing Kernel Image ... OK
    Booting using flat device tree at 0x300000
    Using MPC85xx ADS machine description
    Memory CAM mapping: CAM0=256Mb, CAM1=256Mb, CAM2=0Mb residual: 0Mb
    [snip]
    
    
    More About U-Boot Image Types:
    ------------------------------
    
    U-Boot supports the following image types:
    
       "Standalone Programs" are directly runnable in the environment
    	provided by U-Boot; it is expected that (if they behave
    	well) you can continue to work in U-Boot after return from
    	the Standalone Program.
       "OS Kernel Images" are usually images of some Embedded OS which
    	will take over control completely. Usually these programs
    	will install their own set of exception handlers, device
    	drivers, set up the MMU, etc. - this means, that you cannot
    	expect to re-enter U-Boot except by resetting the CPU.
       "RAMDisk Images" are more or less just data blocks, and their
    	parameters (address, size) are passed to an OS kernel that is
    	being started.
       "Multi-File Images" contain several images, typically an OS
    	(Linux) kernel image and one or more data images like
    	RAMDisks. This construct is useful for instance when you want
    	to boot over the network using BOOTP etc., where the boot
    	server provides just a single image file, but you want to get
    	for instance an OS kernel and a RAMDisk image.
    
    	"Multi-File Images" start with a list of image sizes, each
    	image size (in bytes) specified by an "uint32_t" in network
    	byte order. This list is terminated by an "(uint32_t)0".
    	Immediately after the terminating 0 follow the images, one by
    	one, all aligned on "uint32_t" boundaries (size rounded up to
    	a multiple of 4 bytes).
    
       "Firmware Images" are binary images containing firmware (like
    	U-Boot or FPGA images) which usually will be programmed to
    	flash memory.
    
       "Script files" are command sequences that will be executed by
    	U-Boot's command interpreter; this feature is especially
    	useful when you configure U-Boot to use a real shell (hush)
    	as command interpreter.
    
    Booting the Linux zImage:
    -------------------------
    
    On some platforms, it's possible to boot Linux zImage. This is done
    using the "bootz" command. The syntax of "bootz" command is the same
    as the syntax of "bootm" command.
    
    Note, defining the CONFIG_SUPPORT_RAW_INITRD allows user to supply
    kernel with raw initrd images. The syntax is slightly different, the
    address of the initrd must be augmented by it's size, in the following
    format: "<initrd addres>:<initrd size>".
    
    
    Standalone HOWTO:
    =================
    
    One of the features of U-Boot is that you can dynamically load and
    run "standalone" applications, which can use some resources of
    U-Boot like console I/O functions or interrupt services.
    
    Two simple examples are included with the sources:
    
    "Hello World" Demo:
    -------------------
    
    'examples/hello_world.c' contains a small "Hello World" Demo
    application; it is automatically compiled when you build U-Boot.
    It's configured to run at address 0x00040004, so you can play with it
    like that:
    
    	=> loads
    	## Ready for S-Record download ...
    	~>examples/hello_world.srec
    	1 2 3 4 5 6 7 8 9 10 11 ...
    	[file transfer complete]
    	[connected]
    	## Start Addr = 0x00040004
    
    	=> go 40004 Hello World! This is a test.
    	## Starting application at 0x00040004 ...
    	Hello World
    	argc = 7
    	argv[0] = "40004"
    	argv[1] = "Hello"
    	argv[2] = "World!"
    	argv[3] = "This"
    	argv[4] = "is"
    	argv[5] = "a"
    	argv[6] = "test."
    	argv[7] = "<NULL>"
    	Hit any key to exit ...
    
    	## Application terminated, rc = 0x0
    
    Another example, which demonstrates how to register a CPM interrupt
    handler with the U-Boot code, can be found in 'examples/timer.c'.
    Here, a CPM timer is set up to generate an interrupt every second.
    The interrupt service routine is trivial, just printing a '.'
    character, but this is just a demo program. The application can be
    controlled by the following keys:
    
    	? - print current values og the CPM Timer registers
    	b - enable interrupts and start timer
    	e - stop timer and disable interrupts
    	q - quit application
    
    	=> loads
    	## Ready for S-Record download ...
    	~>examples/timer.srec
    	1 2 3 4 5 6 7 8 9 10 11 ...
    	[file transfer complete]
    	[connected]
    	## Start Addr = 0x00040004
    
    	=> go 40004
    	## Starting application at 0x00040004 ...
    	TIMERS=0xfff00980
    	Using timer 1
    	  tgcr @ 0xfff00980, tmr @ 0xfff00990, trr @ 0xfff00994, tcr @ 0xfff00998, tcn @ 0xfff0099c, ter @ 0xfff009b0
    
    Hit 'b':
    	[q, b, e, ?] Set interval 1000000 us
    	Enabling timer
    Hit '?':
    	[q, b, e, ?] ........
    	tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0xef6, ter=0x0
    Hit '?':
    	[q, b, e, ?] .
    	tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x2ad4, ter=0x0
    Hit '?':
    	[q, b, e, ?] .
    	tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x1efc, ter=0x0
    Hit '?':
    	[q, b, e, ?] .
    	tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x169d, ter=0x0
    Hit 'e':
    	[q, b, e, ?] ...Stopping timer
    Hit 'q':
    	[q, b, e, ?] ## Application terminated, rc = 0x0
    
    
    Minicom warning:
    ================
    
    Over time, many people have reported problems when trying to use the
    "minicom" terminal emulation program for serial download. I (wd)
    consider minicom to be broken, and recommend not to use it. Under
    Unix, I recommend to use C-Kermit for general purpose use (and
    especially for kermit binary protocol download ("loadb" command), and
    use "cu" for S-Record download ("loads" command).  See
    https://www.denx.de/wiki/view/DULG/SystemSetup#Section_4.3.
    for help with kermit.
    
    
    Nevertheless, if you absolutely want to use it try adding this
    configuration to your "File transfer protocols" section:
    
    	   Name	   Program			Name U/D FullScr IO-Red. Multi
    	X  kermit  /usr/bin/kermit -i -l %l -s	 Y    U	   Y	   N	  N
    	Y  kermit  /usr/bin/kermit -i -l %l -r	 N    D	   Y	   N	  N
    
    
    NetBSD Notes:
    =============
    
    Starting at version 0.9.2, U-Boot supports NetBSD both as host
    (build U-Boot) and target system (boots NetBSD/mpc8xx).
    
    Building requires a cross environment; it is known to work on
    NetBSD/i386 with the cross-powerpc-netbsd-1.3 package (you will also
    need gmake since the Makefiles are not compatible with BSD make).
    Note that the cross-powerpc package does not install include files;
    attempting to build U-Boot will fail because <machine/ansi.h> is
    missing.  This file has to be installed and patched manually:
    
    	# cd /usr/pkg/cross/powerpc-netbsd/include
    	# mkdir powerpc
    	# ln -s powerpc machine
    	# cp /usr/src/sys/arch/powerpc/include/ansi.h powerpc/ansi.h
    	# ${EDIT} powerpc/ansi.h	## must remove __va_list, _BSD_VA_LIST
    
    Native builds *don't* work due to incompatibilities between native
    and U-Boot include files.
    
    Booting assumes that (the first part of) the image booted is a
    stage-2 loader which in turn loads and then invokes the kernel
    proper. Loader sources will eventually appear in the NetBSD source
    tree (probably in sys/arc/mpc8xx/stand/u-boot_stage2/); in the
    meantime, see ftp://ftp.denx.de/pub/u-boot/ppcboot_stage2.tar.gz
    
    
    Implementation Internals:
    =========================
    
    The following is not intended to be a complete description of every
    implementation detail. However, it should help to understand the
    inner workings of U-Boot and make it easier to port it to custom
    hardware.
    
    
    Initial Stack, Global Data:
    ---------------------------
    
    The implementation of U-Boot is complicated by the fact that U-Boot
    starts running out of ROM (flash memory), usually without access to
    system RAM (because the memory controller is not initialized yet).
    This means that we don't have writable Data or BSS segments, and BSS
    is not initialized as zero. To be able to get a C environment working
    at all, we have to allocate at least a minimal stack. Implementation
    options for this are defined and restricted by the CPU used: Some CPU
    models provide on-chip memory (like the IMMR area on MPC8xx and
    MPC826x processors), on others (parts of) the data cache can be
    locked as (mis-) used as memory, etc.
    
    	Chris Hallinan posted a good summary of these issues to the
    	U-Boot mailing list:
    
    	Subject: RE: [U-Boot-Users] RE: More On Memory Bank x (nothingness)?
    	From: "Chris Hallinan" <clh@net1plus.com>
    	Date: Mon, 10 Feb 2003 16:43:46 -0500 (22:43 MET)
    	...
    
    	Correct me if I'm wrong, folks, but the way I understand it
    	is this: Using DCACHE as initial RAM for Stack, etc, does not
    	require any physical RAM backing up the cache. The cleverness
    	is that the cache is being used as a temporary supply of
    	necessary storage before the SDRAM controller is setup. It's
    	beyond the scope of this list to explain the details, but you
    	can see how this works by studying the cache architecture and
    	operation in the architecture and processor-specific manuals.
    
    	OCM is On Chip Memory, which I believe the 405GP has 4K. It
    	is another option for the system designer to use as an
    	initial stack/RAM area prior to SDRAM being available. Either
    	option should work for you. Using CS 4 should be fine if your
    	board designers haven't used it for something that would
    	cause you grief during the initial boot! It is frequently not
    	used.
    
    	CONFIG_SYS_INIT_RAM_ADDR should be somewhere that won't interfere
    	with your processor/board/system design. The default value
    	you will find in any recent u-boot distribution in
    	walnut.h should work for you. I'd set it to a value larger
    	than your SDRAM module. If you have a 64MB SDRAM module, set
    	it above 400_0000. Just make sure your board has no resources
    	that are supposed to respond to that address! That code in
    	start.S has been around a while and should work as is when
    	you get the config right.
    
    	-Chris Hallinan
    	DS4.COM, Inc.
    
    It is essential to remember this, since it has some impact on the C
    code for the initialization procedures:
    
    * Initialized global data (data segment) is read-only. Do not attempt
      to write it.
    
    * Do not use any uninitialized global data (or implicitly initialized
      as zero data - BSS segment) at all - this is undefined, initiali-
      zation is performed later (when relocating to RAM).
    
    * Stack space is very limited. Avoid big data buffers or things like
      that.
    
    Having only the stack as writable memory limits means we cannot use
    normal global data to share information between the code. But it
    turned out that the implementation of U-Boot can be greatly
    simplified by making a global data structure (gd_t) available to all
    functions. We could pass a pointer to this data as argument to _all_
    functions, but this would bloat the code. Instead we use a feature of
    the GCC compiler (Global Register Variables) to share the data: we
    place a pointer (gd) to the global data into a register which we
    reserve for this purpose.
    
    When choosing a register for such a purpose we are restricted by the
    relevant  (E)ABI  specifications for the current architecture, and by
    GCC's implementation.
    
    For PowerPC, the following registers have specific use:
    	R1:	stack pointer
    	R2:	reserved for system use
    	R3-R4:	parameter passing and return values
    	R5-R10: parameter passing
    	R13:	small data area pointer
    	R30:	GOT pointer
    	R31:	frame pointer
    
    	(U-Boot also uses R12 as internal GOT pointer. r12
    	is a volatile register so r12 needs to be reset when
    	going back and forth between asm and C)
    
        ==> U-Boot will use R2 to hold a pointer to the global data
    
        Note: on PPC, we could use a static initializer (since the
        address of the global data structure is known at compile time),
        but it turned out that reserving a register results in somewhat
        smaller code - although the code savings are not that big (on
        average for all boards 752 bytes for the whole U-Boot image,
        624 text + 127 data).
    
    On ARM, the following registers are used:
    
    	R0:	function argument word/integer result
    	R1-R3:	function argument word
    	R9:	platform specific
    	R10:	stack limit (used only if stack checking is enabled)
    	R11:	argument (frame) pointer
    	R12:	temporary workspace
    	R13:	stack pointer
    	R14:	link register
    	R15:	program counter
    
        ==> U-Boot will use R9 to hold a pointer to the global data
    
        Note: on ARM, only R_ARM_RELATIVE relocations are supported.
    
    On Nios II, the ABI is documented here:
    	https://www.altera.com/literature/hb/nios2/n2cpu_nii51016.pdf
    
        ==> U-Boot will use gp to hold a pointer to the global data
    
        Note: on Nios II, we give "-G0" option to gcc and don't use gp
        to access small data sections, so gp is free.
    
    On RISC-V, the following registers are used:
    
    	x0: hard-wired zero (zero)
    	x1: return address (ra)
    	x2:	stack pointer (sp)
    	x3:	global pointer (gp)
    	x4:	thread pointer (tp)
    	x5:	link register (t0)
    	x8:	frame pointer (fp)
    	x10-x11:	arguments/return values (a0-1)
    	x12-x17:	arguments (a2-7)
    	x28-31:	 temporaries (t3-6)
    	pc:	program counter (pc)
    
        ==> U-Boot will use gp to hold a pointer to the global data
    
    Memory Management:
    ------------------
    
    U-Boot runs in system state and uses physical addresses, i.e. the
    MMU is not used either for address mapping nor for memory protection.
    
    The available memory is mapped to fixed addresses using the memory
    controller. In this process, a contiguous block is formed for each
    memory type (Flash, SDRAM, SRAM), even when it consists of several
    physical memory banks.
    
    U-Boot is installed in the first 128 kB of the first Flash bank (on
    TQM8xxL modules this is the range 0x40000000 ... 0x4001FFFF). After
    booting and sizing and initializing DRAM, the code relocates itself
    to the upper end of DRAM. Immediately below the U-Boot code some
    memory is reserved for use by malloc() [see CONFIG_SYS_MALLOC_LEN
    configuration setting]. Below that, a structure with global Board
    Info data is placed, followed by the stack (growing downward).
    
    Additionally, some exception handler code is copied to the low 8 kB
    of DRAM (0x00000000 ... 0x00001FFF).
    
    So a typical memory configuration with 16 MB of DRAM could look like
    this:
    
    	0x0000 0000	Exception Vector code
    	      :
    	0x0000 1FFF
    	0x0000 2000	Free for Application Use
    	      :
    	      :
    
    	      :
    	      :
    	0x00FB FF20	Monitor Stack (Growing downward)
    	0x00FB FFAC	Board Info Data and permanent copy of global data
    	0x00FC 0000	Malloc Arena
    	      :
    	0x00FD FFFF
    	0x00FE 0000	RAM Copy of Monitor Code
    	...		eventually: LCD or video framebuffer
    	...		eventually: pRAM (Protected RAM - unchanged by reset)
    	0x00FF FFFF	[End of RAM]
    
    
    System Initialization:
    ----------------------
    
    In the reset configuration, U-Boot starts at the reset entry point
    (on most PowerPC systems at address 0x00000100). Because of the reset
    configuration for CS0# this is a mirror of the on board Flash memory.
    To be able to re-map memory U-Boot then jumps to its link address.
    To be able to implement the initialization code in C, a (small!)
    initial stack is set up in the internal Dual Ported RAM (in case CPUs
    which provide such a feature like), or in a locked part of the data
    cache. After that, U-Boot initializes the CPU core, the caches and
    the SIU.
    
    Next, all (potentially) available memory banks are mapped using a
    preliminary mapping. For example, we put them on 512 MB boundaries
    (multiples of 0x20000000: SDRAM on 0x00000000 and 0x20000000, Flash
    on 0x40000000 and 0x60000000, SRAM on 0x80000000). Then UPM A is
    programmed for SDRAM access. Using the temporary configuration, a
    simple memory test is run that determines the size of the SDRAM
    banks.
    
    When there is more than one SDRAM bank, and the banks are of
    different size, the largest is mapped first. For equal size, the first
    bank (CS2#) is mapped first. The first mapping is always for address
    0x00000000, with any additional banks following immediately to create
    contiguous memory starting from 0.
    
    Then, the monitor installs itself at the upper end of the SDRAM area
    and allocates memory for use by malloc() and for the global Board
    Info data; also, the exception vector code is copied to the low RAM
    pages, and the final stack is set up.
    
    Only after this relocation will you have a "normal" C environment;
    until that you are restricted in several ways, mostly because you are
    running from ROM, and because the code will have to be relocated to a
    new address in RAM.
    
    
    U-Boot Porting Guide:
    ----------------------
    
    [Based on messages by Jerry Van Baren in the U-Boot-Users mailing
    list, October 2002]
    
    
    int main(int argc, char *argv[])
    {
    	sighandler_t no_more_time;
    
    	signal(SIGALRM, no_more_time);
    	alarm(PROJECT_DEADLINE - toSec (3 * WEEK));
    
    	if (available_money > available_manpower) {
    		Pay consultant to port U-Boot;
    		return 0;
    	}
    
    	Download latest U-Boot source;
    
    	Subscribe to u-boot mailing list;
    
    	if (clueless)
    		email("Hi, I am new to U-Boot, how do I get started?");
    
    	while (learning) {
    		Read the README file in the top level directory;
    		Read https://www.denx.de/wiki/bin/view/DULG/Manual;
    		Read applicable doc/README.*;
    		Read the source, Luke;
    		/* find . -name "*.[chS]" | xargs grep -i <keyword> */
    	}
    
    	if (available_money > toLocalCurrency ($2500))
    		Buy a BDI3000;
    	else
    		Add a lot of aggravation and time;
    
    	if (a similar board exists) {	/* hopefully... */
    		cp -a board/<similar> board/<myboard>
    		cp include/configs/<similar>.h include/configs/<myboard>.h
    	} else {
    		Create your own board support subdirectory;
    		Create your own board include/configs/<myboard>.h file;
    	}
    	Edit new board/<myboard> files
    	Edit new include/configs/<myboard>.h
    
    	while (!accepted) {
    		while (!running) {
    			do {
    				Add / modify source code;
    			} until (compiles);
    			Debug;
    			if (clueless)
    				email("Hi, I am having problems...");
    		}
    		Send patch file to the U-Boot email list;
    		if (reasonable critiques)
    			Incorporate improvements from email list code review;
    		else
    			Defend code as written;
    	}
    
    	return 0;
    }
    
    void no_more_time (int sig)
    {
          hire_a_guru();
    }
    
    
    Coding Standards:
    -----------------
    
    All contributions to U-Boot should conform to the Linux kernel
    coding style; see the kernel coding style guide at
    https://www.kernel.org/doc/html/latest/process/coding-style.html, and the
    script "scripts/Lindent" in your Linux kernel source directory.
    
    Source files originating from a different project (for example the
    MTD subsystem) are generally exempt from these guidelines and are not
    reformatted to ease subsequent migration to newer versions of those
    sources.
    
    Please note that U-Boot is implemented in C (and to some small parts in
    Assembler); no C++ is used, so please do not use C++ style comments (//)
    in your code.
    
    Please also stick to the following formatting rules:
    - remove any trailing white space
    - use TAB characters for indentation and vertical alignment, not spaces
    - make sure NOT to use DOS '\r\n' line feeds
    - do not add more than 2 consecutive empty lines to source files
    - do not add trailing empty lines to source files
    
    Submissions which do not conform to the standards may be returned
    with a request to reformat the changes.
    
    
    Submitting Patches:
    -------------------
    
    Since the number of patches for U-Boot is growing, we need to
    establish some rules. Submissions which do not conform to these rules
    may be rejected, even when they contain important and valuable stuff.
    
    Please see https://www.denx.de/wiki/U-Boot/Patches for details.
    
    Patches shall be sent to the u-boot mailing list <u-boot@lists.denx.de>;
    see https://lists.denx.de/listinfo/u-boot
    
    When you send a patch, please include the following information with
    it:
    
    * For bug fixes: a description of the bug and how your patch fixes
      this bug. Please try to include a way of demonstrating that the
      patch actually fixes something.
    
    * For new features: a description of the feature and your
      implementation.
    
    * For major contributions, add a MAINTAINERS file with your
      information and associated file and directory references.
    
    * When you add support for a new board, don't forget to add a
      maintainer e-mail address to the boards.cfg file, too.
    
    * If your patch adds new configuration options, don't forget to
      document these in the README file.
    
    * The patch itself. If you are using git (which is *strongly*
      recommended) you can easily generate the patch using the
      "git format-patch". If you then use "git send-email" to send it to
      the U-Boot mailing list, you will avoid most of the common problems
      with some other mail clients.
    
      If you cannot use git, use "diff -purN OLD NEW". If your version of
      diff does not support these options, then get the latest version of
      GNU diff.
    
      The current directory when running this command shall be the parent
      directory of the U-Boot source tree (i. e. please make sure that
      your patch includes sufficient directory information for the
      affected files).
    
      We prefer patches as plain text. MIME attachments are discouraged,
      and compressed attachments must not be used.
    
    * If one logical set of modifications affects or creates several
      files, all these changes shall be submitted in a SINGLE patch file.
    
    * Changesets that contain different, unrelated modifications shall be
      submitted as SEPARATE patches, one patch per changeset.
    
    
    Notes:
    
    * Before sending the patch, run the buildman script on your patched
      source tree and make sure that no errors or warnings are reported
      for any of the boards.
    
    * Keep your modifications to the necessary minimum: A patch
      containing several unrelated changes or arbitrary reformats will be
      returned with a request to re-formatting / split it.
    
    * If you modify existing code, make sure that your new code does not
      add to the memory footprint of the code ;-) Small is beautiful!
      When adding new features, these should compile conditionally only
      (using #ifdef), and the resulting code with the new feature
      disabled must not need more memory than the old code without your
      modification.
    
    * Remember that there is a size limit of 100 kB per message on the
      u-boot mailing list. Bigger patches will be moderated. If they are
      reasonable and not too big, they will be acknowledged. But patches
      bigger than the size limit should be avoided.
    

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