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ATMEL公司的AT91RM9200芯片在嵌入式系统中应用非常多

- 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.

- Console UART Number:
		CONFIG_UART1_CONSOLE

		IBM PPC4xx only.
		If defined internal UART1 (and not UART0) is used
		as default U-Boot console.

- 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_FAT	  FAT partition 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_MMC	  MMC memory mapped support
		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_DS1338	- use Maxim, Inc. DS1338 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_E1000
		Support for Intel 8254x gigabit chips.

		CONFIG_EEPRO100
		Support for Intel 82557/82559/82559ER chips.
		Optional CONFIG_EEPRO100_SROM_WRITE enables eeprom
		write routine for first time initialisation.

		CONFIG_TULIP
		Support for Digital 2114x chips.
		Optional CONFIG_TULIP_SELECT_MEDIA for board specific
		modem chip initialisation (KS8761/QS6611).

		CONFIG_NATSEMI
		Support for National dp83815 chips.

		CONFIG_NS8382X
		Support for National dp8382[01] gigabit chips.

- NETWORK Support (other):

		CONFIG_DRIVER_LAN91C96
		Support for SMSC's LAN91C96 chips.

			CONFIG_LAN91C96_BASE
			Define this to hold the physical address
			of the LAN91C96's I/O space

			CONFIG_LAN91C96_USE_32_BIT
			Define this to enable 32 bit addressing

- 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).

- MMC Support:
  		The MMC controller on the Intel PXA is supported. To
		enable this define CONFIG_MMC. The MMC can be 
		accessed from the boot prompt by mapping the device 
		to physical memory similar to flash. Command line is
		enabled with CFG_CMD_MMC. The MMC driver also works with
		the FAT fs. This is enabled with CFG_CMD_FAT. 

- 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;)