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U-boot源码 ARM7启动代码

		This will allow you to use i2c commands at the u-boot
		command line (as long as you set CONFIG_CMD_I2C in
		CONFIG_COMMANDS) and communicate with i2c based realtime
		clock chips. See common/cmd_i2c.c for a description of the
		command line interface.

		CONFIG_I2C_CMD_TREE is a recommended option that places
		all I2C commands under a single 'i2c' root command.  The
		older 'imm', 'imd', 'iprobe' etc. commands are considered
		deprecated and may disappear in the future.

		CONFIG_HARD_I2C selects a hardware I2C controller.

		CONFIG_SOFT_I2C configures u-boot to use a software (aka
		bit-banging) driver instead of CPM or similar hardware
		support for I2C.

		There are several other quantities that must also be
		defined when you define CONFIG_HARD_I2C or CONFIG_SOFT_I2C.

		In both cases you will need to define CFG_I2C_SPEED
		to be the frequency (in Hz) at which you wish your i2c bus
		to run and CFG_I2C_SLAVE to be the address of this node (ie
		the cpu's i2c node address).

		Now, the u-boot i2c code for the mpc8xx (cpu/mpc8xx/i2c.c)
		sets the cpu up as a master node and so its address should
		therefore be cleared to 0 (See, eg, MPC823e User's Manual
		p.16-473). So, set CFG_I2C_SLAVE to 0.

		That's all that's required for CONFIG_HARD_I2C.

		If you use the software i2c interface (CONFIG_SOFT_I2C)
		then the following macros need to be defined (examples are
		from include/configs/lwmon.h):

		I2C_INIT

		(Optional). Any commands necessary to enable the I2C
		controller or configure ports.

		eg: #define I2C_INIT (immr->im_cpm.cp_pbdir |=	PB_SCL)

		I2C_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.

		eg: #define I2C_ACTIVE (immr->im_cpm.cp_pbdir |=  PB_SDA)

		I2C_TRISTATE

		The code necessary to make the I2C data line tri-stated
		(inactive).  If the data line is open collector, this
		define can be null.

		eg: #define I2C_TRISTATE (immr->im_cpm.cp_pbdir &= ~PB_SDA)

		I2C_READ

		Code that returns TRUE if the I2C data line is high,
		FALSE if it is low.

		eg: #define I2C_READ ((immr->im_cpm.cp_pbdat & PB_SDA) != 0)

		I2C_SDA(bit)

		If <bit> is TRUE, sets the I2C data line high. If it
		is FALSE, it clears it (low).

		eg: #define I2C_SDA(bit) \
			if(bit) immr->im_cpm.cp_pbdat |=  PB_SDA; \
			else	immr->im_cpm.cp_pbdat &= ~PB_SDA

		I2C_SCL(bit)

		If <bit> is TRUE, sets the I2C clock line high. If it
		is FALSE, it clears it (low).

		eg: #define I2C_SCL(bit) \
			if(bit) immr->im_cpm.cp_pbdat |=  PB_SCL; \
			else	immr->im_cpm.cp_pbdat &= ~PB_SCL

		I2C_DELAY

		This delay is invoked four times per clock cycle so this
		controls the rate of data transfer.  The data rate thus
		is 1 / (I2C_DELAY * 4). Often defined to be something
		like:

		#define I2C_DELAY  udelay(2)

		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.

		CONFIG_I2CFAST (PPC405GP|PPC405EP only)

		This option enables configuration of bi_iic_fast[] flags
		in u-boot bd_info structure based on u-boot environment
		variable "i2cfast". (see also i2cfast)

		CONFIG_I2C_MULTI_BUS

		This option allows the use of multiple I2C buses, each of which
		must have a controller.  At any point in time, only one bus is
		active.  To switch to a different bus, use the 'i2c dev' command.
		Note that bus numbering is zero-based.

		CFG_I2C_NOPROBES

		This option specifies a list of I2C devices that will be skipped
		when the 'i2c probe' command is issued (or 'iprobe' using the legacy
		command).  If CONFIG_I2C_MULTI_BUS is set, specify a list of bus-device
		pairs.  Otherwise, specify a 1D array of device addresses

		e.g.
			#undef	CONFIG_I2C_MULTI_BUS
			#define CFG_I2C_NOPROBES	{0x50,0x68}

		will skip addresses 0x50 and 0x68 on a board with one I2C bus

			#define	CONFIG_I2C_MULTI_BUS
			#define CFG_I2C_MULTI_NOPROBES	{{0,0x50},{0,0x68},{1,0x54}}

		will skip addresses 0x50 and 0x68 on bus 0 and address 0x54 on bus 1

		CFG_SPD_BUS_NUM

		If defined, then this indicates the I2C bus number for DDR SPD.
		If not defined, then U-Boot assumes that SPD is on I2C bus 0.

		CFG_RTC_BUS_NUM

		If defined, then this indicates the I2C bus number for the RTC.
		If not defined, then U-Boot assumes that RTC is on I2C bus 0.

		CFG_DTT_BUS_NUM

		If defined, then this indicates the I2C bus number for the DTT.
		If not defined, then U-Boot assumes that DTT is on I2C bus 0.

		CONFIG_FSL_I2C

		Define this option if you want to use Freescale's I2C driver in
		drivers/fsl_i2c.c.


- 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.

- Configuration Management:
		CONFIG_IDENT_STRING

		If defined, this string will be added to the U-Boot
		version information (U_BOOT_VERSION)

- Vendor Parameter Protection:

		U-Boot considers the values of the environment
		variables "serial#" (Board Serial Number) and
		"ethaddr" (Ethernet Address) to be parameters that
		are set once by the board vendor / manufacturer, and
		protects these variables from casual modification by
		the user. Once set, these variables are read-only,
		and write or delete attempts are rejected. You can
		change this 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:
		CONFIG_AUTO_COMPLETE

		Enable auto completion of commands using TAB.

		Note that this feature has NOT been implemented yet
		for the "hush" shell.


		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 `name=value'. To access a local
		variable later on, you have write `$name' or
		`${name}'; to execute the contents of a variable
		directly type `$name' at the command prompt.

		Global environment variables are those you use
		setenv/printenv to work with. To run a command stored
		in such a variable, you need to use the run command,
		and you must not use the '$' sign to access them.

		To store commands and special characters in a
		variable, please use double quotation marks
		surrounding the whole text of the variable, instead
		of the backslashes before semicolons and special
		symbols.

- Commandline Editing and History:
		CONFIG_CMDLINE_EDITING

		Enable editiong and History functions for interactive
		commandline input operations

- Default Environment:
		CONFIG_EXTRA_ENV_SETTINGS

		Define this to contain any number of null terminated
		strings (variable = value pairs) that will be part of
		the default environment compiled into the boot image.

		For example, place something like this in your
		board's config file:

		#define CONFIG_EXTRA_ENV_SETTINGS \
			"myvar1=value1\0" \
			"myvar2=value2\0"

		Warning: This method is based on knowledge about the
		internal format how the environment is stored by the
		U-Boot code. This is NOT an official, exported
		interface! Although it is unlikely that this format
		will change soon, there is no guarantee either.
		You better know what you are doing here.

		Note: overly (ab)use of the default environment is
		discouraged. Make sure to check other ways to preset
		the environment like the autoscript function or the
		boot command first.

- DataFlash Support:
		CONFIG_HAS_DATAFLASH