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    #
    # (C) Copyright 2000 - 2002
    # Wolfgang Denk, DENX Software Engineering, wd@denx.de.
    #
    # See file CREDITS for list of people who contributed to this
    # project.
    #
    # This program is free software; you can redistribute it and/or
    # modify it under the terms of the GNU General Public License as
    # published by the Free Software Foundation; either version 2 of
    # the License, or (at your option) any later version.
    #
    # This program is distributed in the hope that it will be useful,
    # but WITHOUT ANY WARRANTY; without even the implied warranty of
    # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	See the
    # GNU General Public License for more details.
    #
    # You should have received a copy of the GNU General Public License
    # along with this program; if not, write to the Free Software
    # Foundation, Inc., 59 Temple Place, Suite 330, Boston,
    # MA 02111-1307 USA
    #
    
    Summary:
    ========
    
    This directory contains the source code for U-Boot, a boot loader for
    Embedded boards based on PowerPC and ARM processors, which can be
    installed in a boot ROM and used to initialize and test the hardware
    or to download and run application code.
    
    The development of U-Boot is closely related to Linux: some parts of
    the source code originate in the Linux source tree, we have some
    header files in common, and special provision has been made to
    support booting of Linux images.
    
    Some attention has been paid to make this software easily
    configurable and extendable. For instance, all monitor commands are
    implemented with the same call interface, so that it's very easy to
    add new commands. Also, instead of permanently adding rarely used
    code (for instance hardware test utilities) to the monitor, you can
    load and run it dynamically.
    
    
    Status:
    =======
    
    In general, all boards for which a configuration option exists in the
    Makefile have been tested to some extent and can be considered
    "working". In fact, many of them are used in production systems.
    
    In case of problems see the CHANGELOG and CREDITS files to find out
    who contributed the specific port.
    
    
    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-users@lists.sourceforge.net>. There is also an archive of
    previous traffic on the mailing list - please search the archive
    before asking FAQ's. Please see
    http://lists.sourceforge.net/lists/listinfo/u-boot-users/
    
    
    Where we come from:
    ===================
    
    - start from 8xxrom sources
    - create PPCBoot project (http://sourceforge.net/projects/ppcboot)
    - clean up code
    - make it easier to add custom boards
    - make it possible to add other [PowerPC] CPUs
    - extend functions, especially:
      * Provide extended interface to Linux boot loader
      * S-Record download
      * network boot
      * PCMCIA / CompactFLash / ATA disk / SCSI ... boot
    - create ARMBoot project (http://sourceforge.net/projects/armboot)
    - add other CPU families (starting with ARM)
    - create U-Boot project (http://sourceforge.net/projects/u-boot)
    
    
    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:
    ===========
    
    U-Boot uses a 3 level version number containing a version, a
    sub-version, and a patchlevel: "U-Boot-2.34.5" means version "2",
    sub-version "34", and patchlevel "4".
    
    The patchlevel is used to indicate certain stages of development
    between released versions, i. e. officially released versions of
    U-Boot will always have a patchlevel of "0".
    
    
    Directory Hierarchy:
    ====================
    
    - board		Board dependend files
    - common	Misc architecture independend functions
    - cpu		CPU specific files
    - disk		Code for disk drive partition handling
    - doc		Documentation (don't expect too much)
    - drivers	Common used device drivers
    - dtt		Digital Thermometer and Thermostat drivers
    - examples	Example code for standalone applications, etc.
    - include	Header Files
    - disk		Harddisk interface code
    - net		Networking code
    - ppc		Files generic to PowerPC architecture
    - post		Power On Self Test
    - post/arch		Symlink to architecture specific Power On Self Test
    - post/arch-ppc		PowerPC architecture specific Power On Self Test
    - post/cpu/mpc8260	MPC8260 CPU specific Power On Self Test
    - post/cpu/mpc8xx	MPC8xx CPU specific Power On Self Test
    - rtc		Real Time Clock drivers
    - tools		Tools to build S-Record or U-Boot images, etc.
    
    - cpu/74xx_7xx	Files specific to Motorola MPC74xx and 7xx CPUs
    - cpu/mpc5xx	Files specific to Motorola MPC5xx  CPUs
    - cpu/mpc8xx	Files specific to Motorola MPC8xx  CPUs
    - cpu/mpc824x	Files specific to Motorola MPC824x CPUs
    - cpu/mpc8260	Files specific to Motorola MPC8260 CPU
    - cpu/ppc4xx	Files specific to IBM	   4xx	   CPUs
    
    - board/LEOX/   Files specific to boards manufactured by The LEOX team
    - board/LEOX/elpt860	Files specific to ELPT860 boards
    - board/RPXClassic
    		Files specific to RPXClassic boards
    - board/RPXlite	Files specific to RPXlite    boards
    - board/c2mon	Files specific to c2mon	     boards
    - board/cmi	Files specific to cmi        boards
    - board/cogent	Files specific to Cogent     boards
    		(need further configuration)
    		Files specific to CPCIISER4  boards
    - board/cpu86	Files specific to CPU86      boards
    - board/cray/	Files specific to boards manufactured by Cray
    - board/cray/L1		Files specific to L1         boards
    - board/cu824	Files specific to CU824	     boards
    - board/ebony   Files specific to IBM Ebony board
    - board/eric	Files specific to ERIC	     boards
    - board/esd/	Files specific to boards manufactured by ESD
    - board/esd/adciop	Files specific to ADCIOP     boards
    - board/esd/ar405	Files specific to AR405	     boards
    - board/esd/canbt	Files specific to CANBT	     boards
    - board/esd/cpci405	Files specific to CPCI405    boards
    - board/esd/cpciiser4	Files specific to CPCIISER4  boards
    - board/esd/common	Common files for ESD boards
    - board/esd/dasa_sim	Files specific to DASA_SIM   boards
    - board/esd/du405	Files specific to DU405      boards
    - board/esd/ocrtc	Files specific to OCRTC      boards
    - board/esd/pci405	Files specific to PCI405     boards
    - board/esteem192e
    		Files specific to ESTEEM192E boards
    - board/etx094	Files specific to ETX_094    boards
    - board/evb64260
    		Files specific to EVB64260   boards
    - board/fads	Files specific to FADS	     boards
    - board/flagadm Files specific to FLAGADM    boards
    - board/gen860t Files specific to GEN860T    boards
    - board/genietv Files specific to GENIETV    boards
    - board/gth	Files specific to GTH	     boards
    - board/hermes	Files specific to HERMES     boards
    - board/hymod	Files specific to HYMOD	     boards
    - board/icu862	Files specific to ICU862     boards
    - board/ip860	Files specific to IP860	     boards
    - board/iphase4539
    		Files specific to Interphase4539 boards
    - board/ivm	Files specific to IVMS8/IVML24 boards
    - board/lantec	Files specific to LANTEC     boards
    - board/lwmon	Files specific to LWMON	     boards
    - board/mbx8xx	Files specific to MBX	     boards
    - board/mpc8260ads
    		Files specific to MMPC8260ADS boards
    - board/mpl/	Files specific to boards manufactured by MPL
    - board/mpl/common	Common files for MPL boards
    - board/mpl/pip405	Files specific to PIP405     boards
    - board/mpl/mip405	Files specific to MIP405     boards
    - board/musenki	Files specific to MUSEKNI    boards
    - board/mvs1	Files specific to MVS1       boards
    - board/nx823   Files specific to NX823      boards
    - board/oxc	Files specific to OXC        boards
    - board/pcippc2	Files specific to PCIPPC2/PCIPPC6 boards
    - board/pm826	Files specific to PM826      boards
    - board/ppmc8260
    		Files specific to PPMC8260   boards
    - board/rpxsuper
    		Files specific to RPXsuper   boards
    - board/rsdproto
    		Files specific to RSDproto   boards
    - board/sandpoint
    		Files specific to Sandpoint  boards
    - board/sbc8260	Files specific to SBC8260    boards
    - board/sacsng	Files specific to SACSng     boards
    - board/siemens Files specific to boards manufactured by Siemens AG
    - board/siemens/CCM	Files specific to CCM	     boards
    - board/siemens/IAD210	Files specific to IAD210     boards
    - board/siemens/SCM	Files specific to SCM        boards
    - board/siemens/pcu_e	Files specific to PCU_E	     boards
    - board/sixnet	Files specific to SIXNET     boards
    - board/spd8xx	Files specific to SPD8xxTS   boards
    - board/tqm8260 Files specific to TQM8260    boards
    - board/tqm8xx	Files specific to TQM8xxL    boards
    - board/w7o	Files specific to W7O        boards
    - board/walnut405
    		Files specific to Walnut405  boards
    - board/westel/	Files specific to boards manufactured by Westel Wireless
    - board/westel/amx860	Files specific to AMX860     boards
    - board/utx8245	Files specific to UTX8245   boards
    
    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
      "CFG_".
    
    Later we will add a configuration tool - probably similar to or even
    identical to what's used for the Linux kernel. Right now, we have to
    do the configuration by hand, which means creating some symbolic
    links and editing some configuration files. We use the TQM8xxL boards
    as an example here.
    
    
    Selection of Processor Architecture and Board Type:
    ---------------------------------------------------
    
    For all supported boards there are ready-to-use default
    configurations available; just type "make <board_name>_config".
    
    Example: For a TQM823L module type:
    
    	cd u-boot
    	make TQM823L_config
    
    For the Cogent platform, you need to specify the cpu type as well;
    e.g. "make cogent_mpc8xx_config". And also configure the cogent
    directory according to the instructions in cogent/README.
    
    
    Configuration Options:
    ----------------------
    
    Configuration depends on the combination of board and CPU type; all
    such information is kept in a configuration file
    "include/configs/<board_name>.h".
    
    Example: For a TQM823L module, all configuration settings are in
    "include/configs/TQM823L.h".
    
    
    Many of the options are named exactly as the corresponding Linux
    kernel configuration options. The intention is to make it easier to
    build a config tool - later.
    
    
    The following options need to be configured:
    
    - CPU Type:	Define exactly one of
    
    		PowerPC based CPUs:
    		-------------------
    		CONFIG_MPC823,	CONFIG_MPC850,	CONFIG_MPC855,	CONFIG_MPC860
    	or	CONFIG_MPC5xx
    	or	CONFIG_MPC824X, CONFIG_MPC8260
    	or	CONFIG_IOP480
    	or	CONFIG_405GP
    	or	CONFIG_440
    	or	CONFIG_MPC74xx
    
    		ARM based CPUs:
    		---------------
    		CONFIG_SA1110
    		CONFIG_ARM7
    		CONFIG_PXA250
    
    
    - Board Type:	Define exactly one of
    
    		PowerPC based boards:
    		---------------------
    
    		CONFIG_ADCIOP,     CONFIG_ICU862      CONFIG_RPXsuper,
    		CONFIG_ADS860,     CONFIG_IP860,      CONFIG_SM850,
    		CONFIG_AMX860,     CONFIG_IPHASE4539, CONFIG_SPD823TS,
    		CONFIG_AR405,      CONFIG_IVML24,     CONFIG_SXNI855T,
    		CONFIG_BAB7xx,     CONFIG_IVML24_128, CONFIG_Sandpoint8240,
    		CONFIG_CANBT,      CONFIG_IVML24_256, CONFIG_Sandpoint8245,
    		CONFIG_CCM,        CONFIG_IVMS8,      CONFIG_TQM823L,
    		CONFIG_CPCI405,    CONFIG_IVMS8_128,  CONFIG_TQM850L,
    		CONFIG_CPCI4052,   CONFIG_IVMS8_256,  CONFIG_TQM855L,
    		CONFIG_CPCIISER4,  CONFIG_LANTEC,     CONFIG_TQM860L,
    		CONFIG_CPU86,      CONFIG_MBX,        CONFIG_TQM8260,
    		CONFIG_CRAYL1,     CONFIG_MBX860T,    CONFIG_TTTech,
    		CONFIG_CU824,      CONFIG_MHPC,       CONFIG_UTX8245,
    		CONFIG_DASA_SIM,   CONFIG_MIP405,     CONFIG_W7OLMC,
    		CONFIG_DU405,      CONFIG_MOUSSE,     CONFIG_W7OLMG,
    		CONFIG_ELPPC,      CONFIG_MPC8260ADS, CONFIG_WALNUT405,
    		CONFIG_ERIC,       CONFIG_MUSENKI,    CONFIG_ZUMA,
    		CONFIG_ESTEEM192E, CONFIG_MVS1,       CONFIG_c2mon,
    		CONFIG_ETX094,     CONFIG_NX823,      CONFIG_cogent_mpc8260,
    		CONFIG_EVB64260,   CONFIG_OCRTC,      CONFIG_cogent_mpc8xx,
    		CONFIG_FADS823,    CONFIG_ORSG,       CONFIG_ep8260,
    		CONFIG_FADS850SAR, CONFIG_OXC,        CONFIG_gw8260,
    		CONFIG_FADS860T,   CONFIG_PCI405,     CONFIG_hermes,
    		CONFIG_FLAGADM,    CONFIG_PCIPPC2,    CONFIG_hymod,
    		CONFIG_FPS850L,    CONFIG_PCIPPC6,    CONFIG_lwmon,
    		CONFIG_GEN860T,    CONFIG_PIP405,     CONFIG_pcu_e,
    		CONFIG_GENIETV,    CONFIG_PM826,      CONFIG_ppmc8260,
    		CONFIG_GTH,        CONFIG_RPXClassic, CONFIG_rsdproto,
    		CONFIG_IAD210,     CONFIG_RPXlite,    CONFIG_sbc8260,
    		CONFIG_EBONY,      CONFIG_sacsng,     CONFIG_FPS860L,
    		CONFIG_V37,        CONFIG_ELPT860,    CONFIG_CMI
    
    		ARM based boards:
    		-----------------
    
    		CONFIG_HHP_CRADLE,  CONFIG_DNP1110,    CONFIG_EP7312,
    		CONFIG_IMPA7,       CONFIG_LART,       CONFIG_LUBBOCK,
    		CONFIG_SHANNON,     CONFIG_SMDK2400,   CONFIG_SMDK2410,
    		CONFIG_TRAB
    
    
    - CPU Module Type: (if CONFIG_COGENT is defined)
    		Define exactly one of
    		CONFIG_CMA286_60_OLD
    --- FIXME --- not tested yet:
    		CONFIG_CMA286_60, CONFIG_CMA286_21, CONFIG_CMA286_60P,
    		CONFIG_CMA287_23, CONFIG_CMA287_50
    
    - Motherboard Type: (if CONFIG_COGENT is defined)
    		Define exactly one of
    		CONFIG_CMA101, CONFIG_CMA102
    
    - Motherboard I/O Modules: (if CONFIG_COGENT is defined)
    		Define one or more of
    		CONFIG_CMA302
    
    - Motherboard Options: (if CONFIG_CMA101 or CONFIG_CMA102 are defined)
    		Define one or more of
    		CONFIG_LCD_HEARTBEAT	- update a character position on
    					  the lcd display every second with
    					  a "rotator" |\-/|\-/
    
    - MPC824X Family Member (if CONFIG_MPC824X is defined)
    	Define exactly one of
    	CONFIG_MPC8240, CONFIG_MPC8245
    
    - 8xx CPU Options: (if using an 8xx cpu)
    		Define one or more of
    		CONFIG_8xx_GCLK_FREQ	- if get_gclk_freq() can not work e.g.
    					  no 32KHz reference PIT/RTC clock
    
    - Clock Interface:
    		CONFIG_CLOCKS_IN_MHZ
    
    		U-Boot stores all clock information in Hz
    		internally. For binary compatibility with older Linux
    		kernels (which expect the clocks passed in the
    		bd_info data to be in MHz) the environment variable
    		"clocks_in_mhz" can be defined so that U-Boot
    		converts clock data to MHZ before passing it to the
    		Linux kernel.
    
    		When CONFIG_CLOCKS_IN_MHZ is defined, a definition of
    		"clocks_in_mhz=1" is  automatically  included  in  the
    		default environment.
    
    - Console Interface:
    		Depending on board, define exactly one serial port
    		(like CONFIG_8xx_CONS_SMC1, CONFIG_8xx_CONS_SMC2,
    		CONFIG_8xx_CONS_SCC1, ...), or switch off the serial
    		console by defining CONFIG_8xx_CONS_NONE
    
    		Note: if CONFIG_8xx_CONS_NONE is defined, the serial
    		port routines must be defined elsewhere
    		(i.e. serial_init(), serial_getc(), ...)
    
    		CONFIG_CFB_CONSOLE
    		Enables console device for a color framebuffer. Needs following
    		defines (cf. smiLynxEM, i8042, board/eltec/bab7xx)
    			VIDEO_FB_LITTLE_ENDIAN	graphic memory organisation
    						(default big endian)
    			VIDEO_HW_RECTFILL	graphic chip supports
    						rectangle fill
    						(cf. smiLynxEM)
    			VIDEO_HW_BITBLT		graphic chip supports
    						bit-blit (cf. smiLynxEM)
    			VIDEO_VISIBLE_COLS	visible pixel columns
    						(cols=pitch)
    			VIDEO_VISIBLE_ROWS      visible pixel rows
    			VIDEO_PIXEL_SIZE        bytes per pixel
    			VIDEO_DATA_FORMAT	graphic data format
    						(0-5, cf. cfb_console.c)
    			VIDEO_FB_ADRS           framebuffer address
    			VIDEO_KBD_INIT_FCT	keyboard int fct
    						(i.e. i8042_kbd_init())
    			VIDEO_TSTC_FCT		test char fct
    						(i.e. i8042_tstc)
    			VIDEO_GETC_FCT		get char fct
    						(i.e. i8042_getc)
    			CONFIG_CONSOLE_CURSOR	cursor drawing on/off
    						(requires blink timer
    						cf. i8042.c)
    			CFG_CONSOLE_BLINK_COUNT blink interval (cf. i8042.c)
    			CONFIG_CONSOLE_TIME	display time/date info in
    						upper right corner
    						(requires CFG_CMD_DATE)
    			CONFIG_VIDEO_LOGO	display Linux logo in
    						upper left corner
    			CONFIG_VIDEO_BMP_LOGO	use bmp_logo.h instead of
    						linux_logo.h for logo.
    						Requires CONFIG_VIDEO_LOGO
    			CONFIG_CONSOLE_EXTRA_INFO
    						addional board info beside
    						the logo
    
    		When CONFIG_CFB_CONSOLE is defined, video console is
    		default i/o. Serial console can be forced with
    		environment 'console=serial'.
    
    - Console Baudrate:
    		CONFIG_BAUDRATE - in bps
    		Select one of the baudrates listed in
    		CFG_BAUDRATE_TABLE, see below.
    
    - Interrupt driven serial port input:
    		CONFIG_SERIAL_SOFTWARE_FIFO
    
    		PPC405GP only.
    		Use an interrupt handler for receiving data on the
    		serial port. It also enables using hardware handshake
    		(RTS/CTS) and UART's built-in FIFO. Set the number of
    		bytes the interrupt driven input buffer should have.
    
    		Set to 0 to disable this feature (this is the default).
    		This will also disable hardware handshake.
    
    - Boot Delay:	CONFIG_BOOTDELAY - in seconds
    		Delay before automatically booting the default image;
    		set to -1 to disable autoboot.
    
    		See doc/README.autoboot for these options that
    		work with CONFIG_BOOTDELAY. None are required.
    		CONFIG_BOOT_RETRY_TIME
    		CONFIG_BOOT_RETRY_MIN
    		CONFIG_AUTOBOOT_KEYED
    		CONFIG_AUTOBOOT_PROMPT
    		CONFIG_AUTOBOOT_DELAY_STR
    		CONFIG_AUTOBOOT_STOP_STR
    		CONFIG_AUTOBOOT_DELAY_STR2
    		CONFIG_AUTOBOOT_STOP_STR2
    		CONFIG_ZERO_BOOTDELAY_CHECK
    		CONFIG_RESET_TO_RETRY
    
    - Autoboot Command:
    		CONFIG_BOOTCOMMAND
    		Only needed when CONFIG_BOOTDELAY is enabled;
    		define a command string that is automatically executed
    		when no character is read on the console interface
    		within "Boot Delay" after reset.
    
    		CONFIG_BOOTARGS
    		This can be used to pass arguments to the bootm
    		command. The value of CONFIG_BOOTARGS goes into the
    		environment value "bootargs".
    
    		CONFIG_RAMBOOT and CONFIG_NFSBOOT
    		The value of these goes into the environment as
    		"ramboot" and "nfsboot" respectively, and can be used
    		as a convenience, when switching between booting from
    		ram and nfs.
    
    - Pre-Boot Commands:
    		CONFIG_PREBOOT
    
    		When this option is #defined, the existence of the
    		environment variable "preboot" will be checked
    		immediately before starting the CONFIG_BOOTDELAY
    		countdown and/or running the auto-boot command resp.
    		entering interactive mode.
    
    		This feature is especially useful when "preboot" is
    		automatically generated or modified. For an example
    		see the LWMON board specific code: here "preboot" is
    		modified when the user holds down a certain
    		combination of keys on the (special) keyboard when
    		booting the systems
    
    - Serial Download Echo Mode:
    		CONFIG_LOADS_ECHO
    		If defined to 1, all characters received during a
    		serial download (using the "loads" command) are
    		echoed back. This might be needed by some terminal
    		emulations (like "cu"), but may as well just take
    		time on others. This setting #define's the initial
    		value of the "loads_echo" environment variable.
    
    - Kgdb Serial Baudrate: (if CFG_CMD_KGDB is defined)
    		CONFIG_KGDB_BAUDRATE
    		Select one of the baudrates listed in
    		CFG_BAUDRATE_TABLE, see below.
    
    - Monitor Functions:
    		CONFIG_COMMANDS
    		Most monitor functions can be selected (or
    		de-selected) by adjusting the definition of
    		CONFIG_COMMANDS; to select individual functions,
    		#define CONFIG_COMMANDS by "OR"ing any of the
    		following values:
    
    		#define enables commands:
    		-------------------------
    		CFG_CMD_ASKENV	* ask for env variable
    		CFG_CMD_BDI	  bdinfo
    		CFG_CMD_BEDBUG	  Include BedBug Debugger
    		CFG_CMD_BOOTD	  bootd
    		CFG_CMD_CACHE	  icache, dcache
    		CFG_CMD_CONSOLE	  coninfo
    		CFG_CMD_DATE	* support for RTC, date/time...
    		CFG_CMD_DHCP	  DHCP support
    		CFG_CMD_ECHO	* echo arguments
    		CFG_CMD_EEPROM	* EEPROM read/write support
    		CFG_CMD_ELF	  bootelf, bootvx
    		CFG_CMD_ENV	  saveenv
    		CFG_CMD_FDC	* Floppy Disk Support
    		CFG_CMD_FDOS	* Dos diskette Support
    		CFG_CMD_FLASH	  flinfo, erase, protect
    		CFG_CMD_FPGA	  FPGA device initialization support
    		CFG_CMD_I2C	* I2C serial bus support
    		CFG_CMD_IDE	* IDE harddisk support
    		CFG_CMD_IMI	  iminfo
    		CFG_CMD_IMMAP	* IMMR dump support
    		CFG_CMD_IRQ	* irqinfo
    		CFG_CMD_KGDB	* kgdb
    		CFG_CMD_LOADB	  loadb
    		CFG_CMD_LOADS	  loads
    		CFG_CMD_MEMORY	  md, mm, nm, mw, cp, cmp, crc, base,
    				  loop, mtest
    		CFG_CMD_MII	  MII utility commands
    		CFG_CMD_NET	  bootp, tftpboot, rarpboot
    		CFG_CMD_PCI	* pciinfo
    		CFG_CMD_PCMCIA	* PCMCIA support
    		CFG_CMD_REGINFO * Register dump
    		CFG_CMD_RUN	  run command in env variable
    		CFG_CMD_SCSI	* SCSI Support
    		CFG_CMD_SETGETDCR Support for DCR Register access (4xx only)
    		CFG_CMD_SPI	* SPI serial bus support
    		CFG_CMD_USB	* USB support
    		CFG_CMD_BSP	* Board SPecific functions
    		-----------------------------------------------
    		CFG_CMD_ALL	all
    
    		CFG_CMD_DFL	Default configuration; at the moment
    				this is includes all commands, except
    				the ones marked with "*" in the list
    				above.
    
    		If you don't define CONFIG_COMMANDS it defaults to
    		CFG_CMD_DFL in include/cmd_confdefs.h. A board can
    		override the default settings in the respective
    		include file.
    
    		EXAMPLE: If you want all functions except of network
    		support you can write:
    
    		#define CONFIG_COMMANDS (CFG_CMD_ALL & ~CFG_CMD_NET)
    
    
    	Note:	Don't enable the "icache" and "dcache" commands
    		(configuration option CFG_CMD_CACHE) unless you know
    		what you (and your U-Boot users) are doing. Data
    		cache cannot be enabled on systems like the 8xx or
    		8260 (where accesses to the IMMR region must be
    		uncached), and it cannot be disabled on all other
    		systems where we (mis-) use the data cache to hold an
    		initial stack and some data.
    
    
    		XXX - this list needs to get updated!
    
    - Watchdog:
    		CONFIG_WATCHDOG
    		If this variable is defined, it enables watchdog
    		support. There must support in the platform specific
    		code for a watchdog. For the 8xx and 8260 CPUs, the
    		SIU Watchdog feature is enabled in the SYPCR
    		register.
    
    - U-Boot Version:
    		CONFIG_VERSION_VARIABLE
    		If this variable is defined, an environment variable
    		named "ver" is created by U-Boot showing the U-Boot
    		version as printed by the "version" command.
    		This variable is readonly.
    
    - Real-Time Clock:
    
    		When CFG_CMD_DATE is selected, the type of the RTC
    		has to be selected, too. Define exactly one of the
    		following options:
    
    		CONFIG_RTC_MPC8xx	- use internal RTC of MPC8xx
    		CONFIG_RTC_PCF8563	- use Philips PCF8563 RTC
    		CONFIG_RTC_MC146818	- use MC146818 RTC
    		CONFIG_RTC_DS1307	- use Maxim, Inc. DS1307 RTC
    		CONFIG_RTC_DS1337	- use Maxim, Inc. DS1337 RTC
    		CONFIG_RTC_DS164x	- use Dallas DS164x RTC
    
    - 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 CFG_CMD_DATE .
    
    - Partition Support:
    		CONFIG_MAC_PARTITION and/or CONFIG_DOS_PARTITION
    		and/or CONFIG_ISO_PARTITION
    
    		If IDE or SCSI support	is  enabled  (CFG_CMD_IDE  or
    		CFG_CMD_SCSI) you must configure support for at least
    		one partition type as well.
    
    - IDE Reset method:
    		CONFIG_IDE_RESET_ROUTINE
    
    		Set this to define that instead of a reset Pin, the
    		routine ide_set_reset(int idereset) will be used.
    
    - ATAPI Support:
    		CONFIG_ATAPI
    
    		Set this to enable ATAPI support.
    
    - SCSI Support:
    		At the moment only there is only support for the
    		SYM53C8XX SCSI controller; define
    		CONFIG_SCSI_SYM53C8XX to enable it.
    
    		CFG_SCSI_MAX_LUN [8], CFG_SCSI_MAX_SCSI_ID [7] and
    		CFG_SCSI_MAX_DEVICE [CFG_SCSI_MAX_SCSI_ID *
    		CFG_SCSI_MAX_LUN] can be adjusted to define the
    		maximum numbers of LUNs, SCSI ID's and target
    		devices.
    		CFG_SCSI_SYM53C8XX_CCF to fix clock timing (80Mhz)
    
    - NETWORK Support (PCI):
    		CONFIG_EEPRO100
    		Support for Intel 82557/82559/82559ER chips.
    		Optional CONFIG_EEPRO100_SROM_WRITE enables eeprom
    		write routine for first time initialisation.
    
    		CONFIG_TULIP
    		Support for Digital 2114x chips.
    		Optional CONFIG_TULIP_SELECT_MEDIA for board specific
    		modem chip initialisation (KS8761/QS6611).
    
    		CONFIG_NATSEMI
    		Support for National dp83815 chips.
    
    		CONFIG_NS8382X
    		Support for National dp8382[01] gigabit chips.
    
    - 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
    		end define CONFIG_USB_STORAGE to enable the USB
    		storage devices.
    		Note:
    		Supported are USB Keyboards and USB Floppy drives
    		(TEAC FD-05PUB).
    
    - Keyboard Support:
    		CONFIG_ISA_KEYBOARD
    
    		Define this to enable standard (PC-Style) keyboard
    		support
    
    		CONFIG_I8042_KBD
    		Standard PC keyboard driver with US (is default) and
    		GERMAN key layout (switch via environment 'keymap=de') support.
    		Export function i8042_kbd_init, i8042_tstc and i8042_getc
    		for cfb_console. Supports cursor blinking.
    
    - Video support:
    		CONFIG_VIDEO
    
    		Define this to enable video support (for output to
    		video).
    
    		CONFIG_VIDEO_CT69000
    
    		Enable Chips & Technologies 69000 Video chip
    
    		CONFIG_VIDEO_SMI_LYNXEM
    		Enable Silicon Motion SMI 712/710/810 Video chip
    		Videomode are selected via environment 'videomode' with
    		standard LiLo mode numbers.
    		Following modes are supported  (* is default):
    
    			    800x600  1024x768  1280x1024
    	      256  (8bit)     303*      305       307
    	    65536 (16bit)     314       317       31a
    	16,7 Mill (24bit)     315       318       31b
    		(i.e. setenv videomode 317; saveenv; reset;)
    
    		CONFIG_VIDEO_SED13806
    		Enable Epson SED13806 driver. This driver supports 8bpp
    		and 16bpp modes defined by CONFIG_VIDEO_SED13806_8BPP
    		or CONFIG_VIDEO_SED13806_16BPP
    
    
    - 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_NL6648AC33:
    
    			NEC NL6648AC33-18. Active, color, single scan.
    
    		CONFIG_NEC_NL6648BC20
    
    			NEC NL6648BC20-08. 6.5", 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.
    
    		Normally display is black on white background; define
    		CFG_WHITE_ON_BLACK to get it inverted.
    
    - Spash Screen Support: CONFIG_SPLASH_SCREEN
    
                    If this option is set, the environment is checked for
                    a variable "splashimage". If found, the usual display
                    of logo, copyright and system information on the LCD
                    is supressed and the BMP image at the address
                    specified in "splashimage" is loaded instead. The
                    console is redirected to the "nulldev", too. This
                    allows for a "silent" boot where a splash screen is
                    loaded very quickly after power-on.
    
    
    - Ethernet address:
    		CONFIG_ETHADDR
    		CONFIG_ETH2ADDR
    		CONFIG_ETH3ADDR
    
    		Define a default value for ethernet address to use
    		for the respective ethernet interface, in case this
    		is not determined automatically.
    
    - 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.
    
    - Server IP address:
    		CONFIG_SERVERIP
    
    		Defines a default value for theIP address of a TFTP
    		server to contact when using the "tftboot" command.
    
    - 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 insterted 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
    
    - Status LED:	CONFIG_STATUS_LED
    
    		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_STATUS_LED enables this
    		feature in U-Boot.
    
    - CAN Support:	CONFIG_CAN_DRIVER
    
    		Defining CONFIG_CAN_DRIVER enables CAN driver support
    		on those systems that support this (optional)
    		feature, like the TQM8xxL modules.
    
    - I2C Support:	CONFIG_HARD_I2C | CONFIG_SOFT_I2C
    
    		Enables I2C serial bus commands.  If this is selected,
    		either CONFIG_HARD_I2C or CONFIG_SOFT_I2C must be defined
    		to include the appropriate I2C driver.
    
    		See also: common/cmd_i2c.c for a description of the
    		command line interface.
    
    
    		CONFIG_HARD_I2C
    
    		Selects the CPM hardware driver for I2C.
    
    		CONFIG_SOFT_I2C
    
    		Use software (aka bit-banging) driver instead of CPM
    		or similar hardware support for I2C.  This is configured
    		via the following defines.
    
    		I2C_INIT
    
    		(Optional). Any commands necessary to enable I2C
    		controller or configure ports.
    
    		I2C_PORT
    
    		(Only for MPC8260 CPU). The I/O port to use (the code
    		assumes both bits are on the same port). Valid values
    		are 0..3 for ports A..D.
    
    		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.
    
    		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.
    
    		I2C_READ
    
    		Code that returns TRUE if the I2C data line is high,
    		FALSE if it is low.
    
    		I2C_SDA(bit)
    
    		If <bit> is TRUE, sets the I2C data line high. If it
    		is FALSE, it clears it (low).
    
    		I2C_SCL(bit)
    
    		If <bit> is TRUE, sets the I2C clock line high. If it
    		is FALSE, it clears it (low).
    
    		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).
    
    		CFG_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.
    
    - 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_SPI_X
    
    		Enables extended (16-bit) SPI EEPROM addressing.
    		(symmetrical to CONFIG_I2C_X)
    
    		CONFIG_SOFT_SPI
    
    		Enables a software (bit-bang) SPI driver rather than
    		using hardware support. This is a general purpose
    		driver that only requires three general I/O port pins
    		(two outputs, one input) to function. If this is
    		defined, the board configuration must define several
    		SPI configuration items (port pins to use, etc). For
    		an example, see include/configs/sacsng.h.
    
    - FPGA Support: CONFIG_FPGA_COUNT
    
    		Specify the number of FPGA devices to support.
    
    		CONFIG_FPGA
    
    		Used to specify the types of FPGA devices. For
    		example,
     		#define CONFIG_FPGA  CFG_XILINX_VIRTEX2
    
     		CFG_FPGA_PROG_FEEDBACK
    
    		Enable printing of hash marks during FPGA
    		configuration.
    
    		CFG_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.
    
    		CFG_FPGA_CHECK_CTRLC
    
    		Allow Control-C to interrupt FPGA configuration
    
    		CFG_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).
    
    		CFG_FPGA_WAIT_INIT
    
    		Maximum time to wait for the INIT_B line to deassert
    		after PROB_B has been deasserted during a Virtex II
    		FPGA configuration sequence. The default time is 500 mS.
    
    		CFG_FPGA_WAIT_BUSY
    
    		Maximum time to wait for BUSY to deassert during
    		Virtex II FPGA configuration. The default is 5 mS.
    
    		CFG_FPGA_WAIT_CONFIG
    
    		Time to wait after FPGA configuration. The default is
    		200 mS.
    
    - FPGA Support:	CONFIG_FPGA_COUNT
    
     		Specify the number of FPGA devices to support.
    
     		CONFIG_FPGA
    
     		Used to specify the types of FPGA devices.  For example,
     		#define CONFIG_FPGA  CFG_XILINX_VIRTEX2
    
     		CFG_FPGA_PROG_FEEDBACK
    
     		Enable printing of hash marks during FPGA configuration.
    
    		CFG_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.
    
    		CFG_FPGA_CHECK_CTRLC
    		Allow Control-C to interrupt FPGA configuration
    
    		CFG_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).
    
    		CFG_FPGA_WAIT_INIT
    
    		Maximum time to wait for the INIT_B line to deassert
    		after PROB_B has been deasserted during a Virtex II
    		FPGA configuration sequence. The default time is 500
    		mS.
    
    		CFG_FPGA_WAIT_BUSY
    
    		Maximum time to wait for BUSY to deassert during
    		Virtex II FPGA configuration. The default is 5 mS.
    
    		CFG_FPGA_WAIT_CONFIG
    
    		Time to wait after FPGA configuration. The default is
    		200 mS.
    
    - Configuration Management:
    		CONFIG_IDENT_STRING
    
    		If defined, this string will be added to the U-Boot
    		version information (U_BOOT_VERSION)
    
    - Vendor Parameter Protection:
    
    		U-Boot considers the values of the environment
    		variables "serial#" (Board Serial Number) and
    		"ethaddr" (Ethernet Address) to bb 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 behviour:
    
    		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_ CONFIG_ETHADDR
    		_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.]
    
    - 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":
    
    			ETX094, IVMS8, IVML24, SPD8xx, TQM8xxL,
    			HERMES, IP860, RPXlite, LWMON, LANTEC,
    			PCU_E, FLAGADM, TQM8260
    
    - Error Recovery:
    		CONFIG_PANIC_HANG
    
    		Define this variable to stop the system in case of a
    		fatal error, so that you have to reset it manually.
    		This is probably NOT a good idea for an embedded
    		system where you want to system to reboot
    		automatically as fast as possible, but it may be
    		useful during development since you can try to debug
    		the conditions that lead to the situation.
    
    		CONFIG_NET_RETRY_COUNT
    
    		This variable defines the number of retries for
    		network operations like ARP, RARP, TFTP, or BOOTP
    		before giving up the operation. If not defined, a
    		default value of 5 is used.
    
    - Command Interpreter:
    		CFG_HUSH_PARSER
    
    		Define this variable to enable the "hush" shell (from
    		Busybox) as command line interpreter, thus enabling
    		powerful command line syntax like
    		if...then...else...fi conditionals or `&&' and '||'
    		constructs ("shell scripts").
    
    		If undefined, you get the old, much simpler behaviour
    		with a somewhat smaller memory footprint.
    
    
    		CFG_PROMPT_HUSH_PS2
    
    		This defines the secondary prompt string, which is
    		printed when the command interpreter needs more input
    		to complete a command. Usually "> ".
    
    	Note:
    
    		In the current implementation, the local variables
    		space and global environment variables space are
    		separated. Local variables are those you define by
    		simply typing like `name=value'. To access a local
    		variable later on, you have write `$name' or
    		`${name}'; variable directly by typing say `$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 enviroment 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, but 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 autoscript function or the
    		boot command first.
    
    - Show boot progress
    		CONFIG_SHOW_BOOT_PROGRESS
    
    		Defining this option allows to add some board-
    		specific code (calling a user-provided function
    		"show_boot_progress(int)") that enables you to show
    		the system's boot progress on some display (for
    		example, some LED's) on your board. At the moment,
    		the following checkpoints are implemented:
    
      Arg	Where			When
        1	common/cmd_bootm.c	before attempting to boot an image
       -1	common/cmd_bootm.c	Image header has bad     magic number
        2	common/cmd_bootm.c	Image header has correct magic number
       -2	common/cmd_bootm.c	Image header has bad     checksum
        3	common/cmd_bootm.c	Image header has correct checksum
       -3	common/cmd_bootm.c	Image data   has bad     checksum
        4	common/cmd_bootm.c	Image data   has correct checksum
       -4	common/cmd_bootm.c	Image is for unsupported architecture
        5	common/cmd_bootm.c	Architecture check OK
       -5	common/cmd_bootm.c	Wrong Image Type (not kernel, multi, standalone)
        6	common/cmd_bootm.c	Image Type check OK
       -6	common/cmd_bootm.c	gunzip uncompression error
       -7	common/cmd_bootm.c	Unimplemented compression type
        7	common/cmd_bootm.c	Uncompression OK
       -8	common/cmd_bootm.c	Wrong Image Type (not kernel, multi, standalone)
        8	common/cmd_bootm.c	Image Type check OK
       -9	common/cmd_bootm.c	Unsupported OS (not Linux, BSD, VxWorks, QNX)
        9	common/cmd_bootm.c	Start initial ramdisk verification
      -10	common/cmd_bootm.c	Ramdisk header has bad     magic number
      -11	common/cmd_bootm.c	Ramdisk header has bad     checksum
       10	common/cmd_bootm.c	Ramdisk header is OK
      -12	common/cmd_bootm.c	Ramdisk data   has bad     checksum
       11	common/cmd_bootm.c	Ramdisk data   has correct checksum
       12	common/cmd_bootm.c	Ramdisk verification complete, start loading
      -13	common/cmd_bootm.c	Wrong Image Type (not PPC Linux Ramdisk)
       13	common/cmd_bootm.c	Start multifile image verification
       14	common/cmd_bootm.c	No initial ramdisk, no multifile, continue.
       15	common/cmd_bootm.c	All preparation done, transferring control to OS
    
       -1	common/cmd_doc.c	Bad usage of "doc" command
       -1	common/cmd_doc.c	No boot device
       -1	common/cmd_doc.c	Unknown Chip ID on boot device
       -1	common/cmd_doc.c	Read Error on boot device
       -1	common/cmd_doc.c	Image header has bad magic number
    
       -1	common/cmd_ide.c	Bad usage of "ide" command
       -1	common/cmd_ide.c	No boot device
       -1	common/cmd_ide.c	Unknown boot device
       -1	common/cmd_ide.c	Unknown partition table
       -1	common/cmd_ide.c	Invalid partition type
       -1	common/cmd_ide.c	Read Error on boot device
       -1	common/cmd_ide.c	Image header has bad magic number
    
       -1	common/cmd_nvedit.c	Environment not changable, but has bad CRC
    
    
    Modem Support:
    --------------
    
    [so far only for SMDK2400 and TRAB boards]
    
    - Modem support endable:
    		CONFIG_MODEM_SUPPORT
    
    - RTS/CTS Flow control enable:
    		CONFIG_HWFLOW
    
    - Modem debug support:
    		CONFIG_MODEM_SUPPORT_DEBUG
    
    		Enables debugging stuff (char screen[1024], dbg())
    		for modem support. Useful only with BDI2000.
    
    - General:
    
    		In the target system modem support is enabled when a
    		specific key (key combination) is pressed during
    		power-on. Otherwise U-Boot will boot normally
    		(autoboot). The key_pressed() fuction is called from
    		board_init(). Currently key_pressed() is a dummy
    		function, returning 1 and thus enabling modem
    		initialization.
    
    		If there are no modem init strings in the
    		environment, U-Boot proceed to autoboot; the
    		previous output (banner, info printfs) will be
    		supressed, though.
    
    		See also: doc/README.Modem
    
    
    
    
    Configuration Settings:
    -----------------------
    
    - CFG_LONGHELP: Defined when you want long help messages included;
    		undefine this when you're short of memory.
    
    - CFG_PROMPT:	This is what U-Boot prints on the console to
    		prompt for user input.
    
    - CFG_CBSIZE:	Buffer size for input from the Console
    
    - CFG_PBSIZE:	Buffer size for Console output
    
    - CFG_MAXARGS:	max. Number of arguments accepted for monitor commands
    
    - CFG_BARGSIZE: Buffer size for Boot Arguments which are passed to
    		the application (usually a Linux kernel) when it is
    		booted
    
    - CFG_BAUDRATE_TABLE:
    		List of legal baudrate settings for this board.
    
    - CFG_CONSOLE_INFO_QUIET
     		Suppress display of console information at boot.
    
    - CFG_CONSOLE_IS_IN_ENV
     		If the board specific function
     			extern int overwrite_console (void);
     		returns 1, the stdin, stderr and stdout are switched to the
    		serial port, else the settings in the environment are used.
    
    - CFG_CONSOLE_OVERWRITE_ROUTINE
     		Enable the call to overwrite_console().
    
    - CFG_CONSOLE_ENV_OVERWRITE
    		Enable overwrite of previous console environment settings.
    
    - CFG_MEMTEST_START, CFG_MEMTEST_END:
    		Begin and End addresses of the area used by the
    		simple memory test.
    
    - CFG_ALT_MEMTEST:
     		Enable an alternate, more extensive memory test.
    
    - CFG_TFTP_LOADADDR:
    		Default load address for network file downloads
    
    - CFG_LOADS_BAUD_CHANGE:
    		Enable temporary baudrate change while serial download
    
    - CFG_SDRAM_BASE:
    		Physical start address of SDRAM. _Must_ be 0 here.
    
    - CFG_MBIO_BASE:
    		Physical start address of Motherboard I/O (if using a
    		Cogent motherboard)
    
    - CFG_FLASH_BASE:
    		Physical start address of Flash memory.
    
    - CFG_MONITOR_BASE:
    		Physical start address of boot monitor code (set by
    		make config files to be same as the text base address
    		(TEXT_BASE) used when linking) - same as
    		CFG_FLASH_BASE when booting from flash.
    
    - CFG_MONITOR_LEN:
    		Size of memory reserved for monitor code
    
    - CFG_MALLOC_LEN:
    		Size of DRAM reserved for malloc() use.
    
    - CFG_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, eventually
    		initrd image) must be put below this limit.
    
    - CFG_MAX_FLASH_BANKS:
    		Max number of Flash memory banks
    
    - CFG_MAX_FLASH_SECT:
    		Max number of sectors on a Flash chip
    
    - CFG_FLASH_ERASE_TOUT:
    		Timeout for Flash erase operations (in ms)
    
    - CFG_FLASH_WRITE_TOUT:
    		Timeout for Flash write operations (in ms)
    
    - CFG_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 sytem RAM is
    		too limited to allow for a tempory copy of the
    		downloaded image) this option may be very useful.
    
    - CFG_FLASH_CFI:
    		Define if the flash driver uses extra elements in the
    		common flash structure for storing flash geometry
    
    The following definitions that deal with the placement and management
    of environment data (variable area); in general, we support the
    following configurations:
    
    - CFG_ENV_IS_IN_FLASH:
    
    	Define this if the environment is in flash memory.
    
    	a) The environment occupies one whole flash sector, which is
    	   "embedded" in the text segment with the U-Boot code. This
    	   happens usually with "bottom boot sector" or "top boot
    	   sector" type flash chips, which have several smaller
    	   sectors at the start or the end. For instance, such a
    	   layout can have sector sizes of 8, 2x4, 16, Nx32 kB. In
    	   such a case you would place the environment in one of the
    	   4 kB sectors - with U-Boot code before and after it. With
    	   "top boot sector" type flash chips, you would put the
    	   environment in one of the last sectors, leaving a gap
    	   between U-Boot and the environment.
    
    	- CFG_ENV_OFFSET:
    
    	   Offset of environment data (variable area) to the
    	   beginning of flash memory; for instance, with bottom boot
    	   type flash chips the second sector can be used: the offset
    	   for this sector is given here.
    
    	   CFG_ENV_OFFSET is used relative to CFG_FLASH_BASE.
    
    	- CFG_ENV_ADDR:
    
    	   This is just another way to specify the start address of
    	   the flash sector containing the environment (instead of
    	   CFG_ENV_OFFSET).
    
    	- CFG_ENV_SECT_SIZE:
    
    	   Size of the sector containing the environment.
    
    
    	b) Sometimes flash chips have few, equal sized, BIG sectors.
    	   In such a case you don't want to spend a whole sector for
    	   the environment.
    
    	- CFG_ENV_SIZE:
    
    	   If you use this in combination with CFG_ENV_IS_IN_FLASH
    	   and CFG_ENV_SECT_SIZE, you can specify to use only a part
    	   of this flash sector for the environment. This saves
    	   memory for the RAM copy of the environment.
    
    	   It may also save flash memory if you decide to use this
    	   when your environment is "embedded" within U-Boot code,
    	   since then the remainder of the flash sector could be used
    	   for U-Boot code. It should be pointed out that this is
    	   STRONGLY DISCOURAGED from a robustness point of view:
    	   updating the environment in flash makes it always
    	   necessary to erase the WHOLE sector. If something goes
    	   wrong before the contents has been restored from a copy in
    	   RAM, your target system will be dead.
    
    	- CFG_ENV_ADDR_REDUND
    	  CFG_ENV_SIZE_REDUND
    
    	   These settings describe a second storage area used to hold
    	   a redundand copy of the environment data, so that there is
    	   a valid backup copy in case there is a power failure during
    	   a "saveenv" operation.
    
    BE CAREFUL! Any changes to the flash layout, and some changes to the
    source code will make it necessary to adapt <board>/u-boot.lds*
    accordingly!
    
    
    - CFG_ENV_IS_IN_NVRAM:
    
    	Define this if you have some non-volatile memory device
    	(NVRAM, battery buffered SRAM) which you want to use for the
    	environment.
    
    	- CFG_ENV_ADDR:
    	- CFG_ENV_SIZE:
    
    	  These two #defines are used to determin the memory area you
    	  want to use for environment. It is assumed that this memory
    	  can just be read and written to, without any special
    	  provision.
    
    BE CAREFUL! The first access to the environment happens quite early
    in U-Boot initalization (when we try to get the setting of for the
    console baudrate). You *MUST* have mappend 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.
    
    
    - CFG_ENV_IS_IN_EEPROM:
    
    	Use this if you have an EEPROM or similar serial access
    	device and a driver for it.
    
    	- CFG_ENV_OFFSET:
    	- CFG_ENV_SIZE:
    
    	  These two #defines specify the offset and size of the
    	  environment area within the total memory of your EEPROM.
    
    	- CFG_I2C_EEPROM_ADDR:
    	  If defined, specified the chip address of the EEPROM device.
    	  The default address is zero.
    
    	- CFG_EEPROM_PAGE_WRITE_BITS:
    	  If defined, the number of bits used to address bytes in a
    	  single page in the EEPROM device.  A 64 byte page, for example
    	  would require six bits.
    
    	- CFG_EEPROM_PAGE_WRITE_DELAY_MS:
    	  If defined, the number of milliseconds to delay between
    	  page writes.  The default is zero milliseconds.
    
    	- CFG_I2C_EEPROM_ADDR_LEN:
    	  The length in bytes of the EEPROM memory array address.  Note
    	  that this is NOT the chip address length!
    
    	- CFG_EEPROM_SIZE:
    	  The size in bytes of the EEPROM device.
    
    
    - CFG_SPI_INIT_OFFSET
    
    	Defines offset to the initial SPI buffer area in DPRAM. The
    	area is used at an early stage (ROM part) if the environment
    	is configured to reside in the SPI EEPROM: We need a 520 byte
    	scratch DPRAM area. It is used between the two initialization
    	calls (spi_init_f() and spi_init_r()). A value of 0xB00 seems
    	to be a good choice since it makes it far enough from the
    	start of the data area as well as from the stack pointer.
    
    Please note that the environment is read-only as long as 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 getenv_r()
    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.
    
    
    Low Level (hardware related) configuration options:
    ---------------------------------------------------
    
    - CFG_CACHELINE_SIZE:
    		Cache Line Size of the CPU.
    
    - CFG_DEFAULT_IMMR:
    		Default address of the IMMR after system reset.
    		Needed on some 8260 systems (MPC8260ADS and RPXsuper)
    		to be able to adjust the position of the IMMR
    		register after a reset.
    
    - Floppy Disk Support:
    		CFG_FDC_DRIVE_NUMBER
    
    		the default drive number (default value 0)
    
    		CFG_ISA_IO_STRIDE
    
    		defines the spacing between fdc chipset registers
    		(default value 1)
    
    		CFG_ISA_IO_OFFSET
    
    		defines the offset of register from address. It
    		depends on which part of the data bus is connected to
    		the fdc chipset. (default value 0)
    
    		If CFG_ISA_IO_STRIDE CFG_ISA_IO_OFFSET and
    		CFG_FDC_DRIVE_NUMBER are undefined, they take their
    		default value.
    
    		if CFG_FDC_HW_INIT is defined, then the function
    		fdc_hw_init() is called at the beginning of the FDC
    		setup. fdc_hw_init() must be provided by the board
    		source code. It is used to make hardware dependant
    		initializations.
    
    - CFG_IMMR:	Physical address of the Internal Memory Mapped
    		Register; DO NOT CHANGE! (11-4)
    		[MPC8xx systems only]
    
    - CFG_INIT_RAM_ADDR:
    
    		Start address of memory area tha 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 and MPC8260: IMMR (internal memory of the CPU)
    		- MPC824X: data cache
    		- PPC4xx:  data cache
    
    - CFG_GBL_DATA_OFFSET:
    
    		Offset of the initial data structure in the memory
    		area defined by CFG_INIT_RAM_ADDR. Usually
    		CFG_GBL_DATA_OFFSET is chosen such that the initial
    		data is located at the end of the available space
    		(sometimes written as (CFG_INIT_RAM_END -
    		CFG_INIT_DATA_SIZE), and the initial stack is just
    		below that area (growing from (CFG_INIT_RAM_ADDR +
    		CFG_GBL_DATA_OFFSET) downward.
    
    	Note:
    		On the MPC824X (or other systems that use the data
    		cache for initial memory) the address chosen for
    		CFG_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.
    
    - CFG_SIUMCR:	SIU Module Configuration (11-6)
    
    - CFG_SYPCR:	System Protection Control (11-9)
    
    - CFG_TBSCR:	Time Base Status and Control (11-26)
    
    - CFG_PISCR:	Periodic Interrupt Status and Control (11-31)
    
    - CFG_PLPRCR:	PLL, Low-Power, and Reset Control Register (15-30)
    
    - CFG_SCCR:	System Clock and reset Control Register (15-27)
    
    - CFG_OR_TIMING_SDRAM:
    		SDRAM timing
    
    - CFG_MAMR_PTA:
    		periodic timer for refresh
    
    - CFG_DER:	Debug Event Register (37-47)
    
    - FLASH_BASE0_PRELIM, FLASH_BASE1_PRELIM, CFG_REMAP_OR_AM,
      CFG_PRELIM_OR_AM, CFG_OR_TIMING_FLASH, CFG_OR0_REMAP,
      CFG_OR0_PRELIM, CFG_BR0_PRELIM, CFG_OR1_REMAP, CFG_OR1_PRELIM,
      CFG_BR1_PRELIM:
    		Memory Controller Definitions: BR0/1 and OR0/1 (FLASH)
    
    - SDRAM_BASE2_PRELIM, SDRAM_BASE3_PRELIM, SDRAM_MAX_SIZE,
      CFG_OR_TIMING_SDRAM, CFG_OR2_PRELIM, CFG_BR2_PRELIM,
      CFG_OR3_PRELIM, CFG_BR3_PRELIM:
    		Memory Controller Definitions: BR2/3 and OR2/3 (SDRAM)
    
    - CFG_MAMR_PTA, CFG_MPTPR_2BK_4K, CFG_MPTPR_1BK_4K, CFG_MPTPR_2BK_8K,
      CFG_MPTPR_1BK_8K, CFG_MAMR_8COL, CFG_MAMR_9COL:
    		Machine Mode Register and Memory Periodic Timer
    		Prescaler definitions (SDRAM timing)
    
    - CFG_I2C_UCODE_PATCH, CFG_I2C_DPMEM_OFFSET [0x1FC0]:
    		enable I2C microcode relocation patch (MPC8xx);
    		define relocation offset in DPRAM [DSP2]
    
    - CFG_SPI_UCODE_PATCH, CFG_SPI_DPMEM_OFFSET [0x1FC0]:
    		enable SPI microcode relocation patch (MPC8xx);
    		define relocation offset in DPRAM [SCC4]
    
    - CFG_USE_OSCCLK:
    		Use OSCM clock mode on MBX8xx board. Be careful,
    		wrong setting might damage your board. Read
    		doc/README.MBX before setting this variable!
    
    - CFG_CPM_POST_WORD_ADDR: (MPC8xx, MPC8260 only)
    		Offset of the bootmode word in DPRAM used by post
    		(Power On Self Tests). This definition overrides
    		#define'd default value in commproc.h resp.
    		cpm_8260.h.
    
    Building the Software:
    ======================
    
    Building U-Boot has been tested in native PPC environments (on a
    PowerBook G3 running LinuxPPC 2000) and in cross environments
    (running RedHat 6.x and 7.x Linux on x86, Solaris 2.6 on a SPARC, and
    NetBSD 1.5 on x86).
    
    If you are not using a native PPC environment, it is assumed that you
    have the GNU cross compiling tools available in your path and named
    with a prefix of "powerpc-linux-". If this is not the case, (e.g. if
    you are using Monta Vista's Hard Hat Linux CDK 1.2) you must change
    the definition of CROSS_COMPILE in Makefile. For HHL on a 4xx CPU,
    change it to:
    
    	CROSS_COMPILE = ppc_4xx-
    
    
    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_config
    
    where "NAME_config" is the name of one of the existing
    configurations; the following names are supported:
    
        ADCIOP_config	  GTH_config		TQM850L_config
        ADS860_config	  IP860_config		TQM855L_config
        AR405_config	  IVML24_config		TQM860L_config
        CANBT_config	  IVMS8_config		WALNUT405_config
        CPCI405_config	  LANTEC_config		cogent_common_config
        CPCIISER4_config	  MBX_config		cogent_mpc8260_config
        CU824_config	  MBX860T_config	cogent_mpc8xx_config
        ESTEEM192E_config	  RPXlite_config	hermes_config
        ETX094_config	  RPXsuper_config	hymod_config
        FADS823_config	  SM850_config		lwmon_config
        FADS850SAR_config	  SPD823TS_config	pcu_e_config
        FADS860T_config	  SXNI855T_config	rsdproto_config
        FPS850L_config	  Sandpoint8240_config	sbc8260_config
        GENIETV_config	  TQM823L_config	PIP405_config
        GEN860T_config	  EBONY_config		FPS860L_config
        ELPT860_config	  cmi_mpc5xx_config
    
    Note: for some board special configuration names may exist; check  if
          additional  information is available from the board vendor; for
          instance, the TQM8xxL systems run normally at 50 MHz and use  a
          SCC  for	10baseT	 ethernet; there are also systems with 80 MHz
          CPU clock, and an optional Fast Ethernet	module	is  available
          for  CPU's  with FEC. You can select such additional "features"
          when chosing the configuration, i. e.
    
          make TQM860L_config
    	- will configure for a plain TQM860L, i. e. 50MHz, no FEC
    
          make TQM860L_FEC_config
    	- will configure for a TQM860L at 50MHz with FEC for ethernet
    
          make TQM860L_80MHz_config
    	- will configure for a TQM860L at 80 MHz, with normal 10baseT
    	  interface
    
          make TQM860L_FEC_80MHz_config
    	- will configure for a TQM860L at 80 MHz with FEC for ethernet
    
          make TQM823L_LCD_config
    	- will configure for a TQM823L with U-Boot console on LCD
    
          make TQM823L_LCD_80MHz_config
    	- will configure for a TQM823L at 80 MHz with U-Boot console on LCD
    
          etc.
    
    
    
    Finally, type "make all", and you should get some working U-Boot
    images ready for downlod 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
    
    
    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.  Add a new configuration option for your board to the toplevel
        "Makefile" and to the "MAKEALL" script, using the existing
        entries as examples. Note that here and at many other places
        boards and other names are listed alphabetically sorted. Please
        keep this order.
    2.  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", a "<board>.c", "flash.c" and "u-boot.lds".
    3.  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>_config" 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 CVS) 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 "MAKEALL" script, which will configure and build U-Boot
    for ALL supported system. Be warned, this will take a while. You  can
    select	which  (cross)	compiler  to use py passing a `CROSS_COMPILE'
    environment variable to the script, i. e. to use the cross tools from
    MontaVista's Hard Hat Linux you can type
    
    	CROSS_COMPILE=ppc_8xx- MAKEALL
    
    or to build on a native PowerPC system you can type
    
    	CROSS_COMPILE=' ' MAKEALL
    
    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
    tftpboot- boot image via network using TFTP protocol
    	       and env variables "ipaddr" and "serverip"
    	       (and eventually "gatewayip")
    rarpboot- boot image via network using RARP/TFTP protocol
    diskboot- boot from IDE devicebootd   - boot default, i.e., run 'bootcmd'
    loads	- load S-Record file over serial line
    loadb	- load binary file over serial line (kermit mode)
    md	- memory display
    mm	- memory modify (auto-incrementing)
    nm	- memory modify (constant address)
    mw	- memory write (fill)
    cp	- memory copy
    cmp	- memory compare
    crc32	- checksum calculation
    imd     - i2c memory display
    imm     - i2c memory modify (auto-incrementing)
    inm     - i2c memory modify (constant address)
    imw     - i2c memory write (fill)
    icrc32  - i2c checksum calculation
    iprobe  - probe to discover valid I2C chip addresses
    iloop   - infinite loop on address range
    isdram  - print SDRAM configuration information
    sspi    - SPI utility commands
    base	- print or set address offset
    printenv- print environment variables
    setenv	- set environment variables
    saveenv - save environment variables to persistent storage
    protect - enable or disable FLASH write protection
    erase	- erase FLASH memory
    flinfo	- print FLASH memory information
    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
    mtest	- simple RAM test
    icache	- enable or disable instruction cache
    dcache	- enable or disable data cache
    reset	- Perform RESET of the CPU
    echo	- echo args to console
    version - print monitor version
    help	- print online help
    ?	- alias for 'help'
    
    
    Monitor Commands - Detailed Description:
    ========================================
    
    TODO.
    
    For now: just type "help <command>".
    
    
    Environment Variables:
    ======================
    
    U-Boot supports user configuration using Environment Variables which
    can be made persistent by saving to Flash memory.
    
    Environment Variables are set using "setenv", printed using
    "printenv", and saved to Flash using "saveenv". Using "setenv"
    without a value can be used to delete a variable from the
    environment. As long as you don't save the environment you are
    working with an in-memory copy. In case the Flash area containing the
    environment is erased by accident, a default environment is provided.
    
    Some configuration options can be set using Environment Variables:
    
      baudrate	- see CONFIG_BAUDRATE
    
      bootdelay	- see CONFIG_BOOTDELAY
    
      bootcmd	- see CONFIG_BOOTCOMMAND
    
      bootargs	- Boot arguments when booting an RTOS image
    
      bootfile	- Name of the image to load with TFTP
    
      autoload	- if set to "no" (any string beginning with 'n'),
    		  "bootp" will just load perform a lookup of the
    		  configuration from the BOOTP server, but not try to
    		  load any image using TFTP
    
      autostart	- if set to "yes", an image loaded using the "bootp",
    		  "rarpboot", "tftpboot" or "diskboot" commands will
    		  be automatically started (by internally calling
    		  "bootm")
    
    		  If set to "no", a standalone image passed to the
    		  "bootm" command will be copied to the load address
    		  (and eventually uncompressed), but NOT be started.
    		  This can be used to load and uncompress arbitrary
    		  data.
    
      initrd_high	- restrict positioning of initrd images:
    		  If this variable is not set, initrd images will be
    		  copied to the highest possible address in RAM; this
    		  is usually what you want since it allows for
    		  maximum initrd size. If for some reason you want to
    		  make sure that the initrd image is loaded below the
    		  CFG_BOOTMAPSZ limit, you can set this environment
    		  variable to a value of "no" or "off" or "0".
    		  Alternatively, you can set it to a maximum upper
    		  address to use (U-Boot will still check that it
    		  does not overwrite the U-Boot stack and data).
    
    		  For instance, when you have a system with 16 MB
    		  RAM, and want to reseve 4 MB from use by Linux,
    		  you can do this by adding "mem=12M" to the value of
    		  the "bootargs" variable. However, now you must make
    		  sure, that the initrd image is placed in the first
    		  12 MB as well - this can be done with
    
    		  setenv initrd_high 00c00000
    
      ipaddr	- IP address; needed for tftpboot command
    
      loadaddr	- Default load address for commands like "bootp",
    		  "rarpboot", "tftpboot", "loadb" or "diskboot"
    
      loads_echo	- see CONFIG_LOADS_ECHO
    
      serverip	- TFTP server IP address; needed for tftpboot command
    
      bootretry	- see CONFIG_BOOT_RETRY_TIME
    
      bootdelaykey	- see CONFIG_AUTOBOOT_DELAY_STR
    
      bootstopkey	- see CONFIG_AUTOBOOT_STOP_STR
    
    
    The following environment variables may be used and automatically
    updated by the network boot commands ("bootp" and "rarpboot"),
    depending the information provided by your boot server:
    
      bootfile	- see above
      dnsip		- IP address of your Domain Name Server
      gatewayip	- IP address of the Gateway (Router) to use
      hostname	- Target hostname
      ipaddr	- see above
      netmask	- Subnet Mask
      rootpath	- Pathname of the root filesystem on the NFS server
      serverip	- see above
    
    
    There are two special Environment Variables:
    
      serial#	- contains hardware identification information such
    		  as type string and/or serial number
      ethaddr	- Ethernet address
    
    These variables can be set only once (usually during manufacturing of
    the board). U-Boot refuses to delete or overwrite these variables
    once they have been set once.
    
    
    Further special Environment Variables:
    
      ver		- Contains the U-Boot version string as printed
    		  with the "version" command. This variable is
    		  readonly (see CONFIG_VERSION_VARIABLE).
    
    
    Please note that changes to some configuration parameters may take
    only effect after the next boot (yes, that's just like Windoze :-).
    
    
    Note for Redundant Ethernet Interfaces:
    =======================================
    
    Some boards come with redundand ethernet interfaces; U-Boot supports
    such configurations and is capable of automatic selection of a
    "working" interface when needed. MAC assignemnt 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.
    
    
    
    Image Formats:
    ==============
    
    The "boot" commands of this monitor operate on "image" files which
    can be basicly anything, preceeded by a special header; see the
    definitions in include/image.h for details; basicly, 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;
      Currently supported: Linux, NetBSD, VxWorks, QNX).
    * Target CPU Architecture (Provisions for Alpha, ARM, Intel x86,
      IA64, MIPS, MIPS, PowerPC, IBM S390, SuperH, Sparc, Sparc 64 Bit;
      Currently supported: PowerPC).
    * Compression Type (Provisions for uncompressed, gzip, bzip2;
      Currently supported: uncompressed, gzip).
    * 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, Linux has always been in the focus 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 serveral 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 dependend 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/ppc/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/u-boot.h, and make
    sure that your definition of IMAP_ADDR uses the same value as your
    U-Boot configuration in CFG_IMMR.
    
    
    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_config
    	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 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/ppc/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/ppc/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/ppc/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
    
    
    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 addreses 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#
    
    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.
    
    
    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 used 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  CKermit  for  general  purpose  use  (and
    especially for kermit binary protocol download ("loadb" command), and
    use "cu" for S-Record download ("loads" command).
    
    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, send mail to bruno@exet-ag.de and/or wd@denx.de for
    details.
    
    
    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 summy of  these  issues  to  the
    	u-boot-users 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 expain 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.
    
    	CFG_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
    	Walnut405.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 unitialized global data (or implicitely initialized
      as zero data - BSS segment) at all - this is undefined, initiali-
      zation is performed later (when relocationg 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 beween 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 chosing 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:	TOC pointer
    	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 R14 as internal GOT pointer.)
    
        ==> U-Boot will use R29 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:	GOT pointer
    	R10:	stack limit (used only if stack checking if enabled)
    	R11:	argument (frame) pointer
    	R12:	temporary workspace
    	R13:	stack pointer
    	R14:	link register
    	R15:	program counter
    
        ==> U-Boot will use R8 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 CFG_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 systens at address 0x00000100). Because of the reset
    configuration for CS0# this is a mirror of the onboard Flash memory.
    To be able to re-map memory U-Boot then jumps to it's 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 MPC8xx or MPC8260), 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 larger 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-users 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 http://www.denx.de/re/DPLG.html
    		Read the source, Luke;
    	}
    
    	if (available_money > toLocalCurrency ($2500)) {
    		Buy a BDI2000;
    	} else {
    		Add a lot of aggravation and time;
    	}
    
    	Create your own board support subdirectory;
    
    	Create your own board config file;
    
    	while (!running) {
    		do {
    			Add / modify source code;
    		} until (compiles);
    		Debug;
    		if (clueless)
    			email ("Hi, I am having problems...");
    	}
    	Send patch file to Wolfgang;
    
    	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 file "Documentation/CodingStyle" in your Linux
    kernel source directory.
    
    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.
    
    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.
    
    
    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.
    
    * A CHANGELOG entry as plaintext (separate from the patch)
    
    * For major contributions, your entry to the CREDITS file
    
    * When you add support for a new board, don't forget to add this
      board to the MAKEALL script, too.
    
    * If your patch adds new configuration options, don't forget to
      document these in the README file.
    
    * The patch itself. If you are accessing the CVS repository use "cvs
      update; cvs diff -puRN"; else, use "diff -purN OLD NEW". If your
      version of diff does not support these options, then get the latest
      version of GNU diff.
    
      We accept patches as plain text, MIME attachments or as uuencoded
      gzipped text.
    
    Notes:
    
    * Before sending the patch, run the MAKEALL 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.