uboot-linux.txt

9200的开发资料：包括uboot

	Linux Support:
	==============

	Although U-Boot should support any OS or standalone application
	easily, the main focus has always been on Linux during the design of
	U-Boot.

	U-Boot includes many features that so far have been part of some
	special "boot loader" code within the Linux kernel. Also, any
	"initrd" images to be used are no longer part of one big Linux image;
	instead, kernel and "initrd" are separate images. This implementation
	serves several purposes:

	- the same features can be used for other OS or standalone
	  applications (for instance: using compressed images to reduce the
	  Flash memory footprint)

	- it becomes much easier to port new Linux kernel versions because
	  lots of low-level, hardware dependent stuff are done by U-Boot

	- the same Linux kernel image can now be used with different "initrd"
	  images; of course this also means that different kernel images can
	  be run with the same "initrd". This makes testing easier (you don't
	  have to build a new "zImage.initrd" Linux image when you just
	  change a file in your "initrd"). Also, a field-upgrade of the
	  software is easier now.


	Linux HOWTO:
	============

	Porting Linux to U-Boot based systems:
	---------------------------------------

	U-Boot cannot save you from doing all the necessary modifications to
	configure the Linux device drivers for use with your target hardware
	(no, we don't intend to provide a full virtual machine interface to
	Linux :-).

	But now you can ignore ALL boot loader code (in arch/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 ([e-mail]) (gcc version 2.95.2 19991024 (release)) #1 Wed Jul 19 02:35:17 MEST 2000
		Boot arguments: root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
		time_init: decrementer frequency = 187500000/60
		Calibrating delay loop... 49.77 BogoMIPS
		Memory: 15208k available (700k kernel code, 444k data, 32k init) [c0000000,c1000000]
		...

	If you want to boot a Linux kernel with initial ram disk, you pass
	the memory addresses of both the kernel and the initrd image (PPBCOOT
	format!) to the "bootm" command:

		=> imi 40100000 40200000

		## Checking Image at 40100000 ...
		   Image Name:	 2.2.13 for initrd on TQM850L
		   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
		   Data Size:	 335725 Bytes = 327 kB = 0 MB
		   Load Address: 00000000
		   Entry Point:	 0000000c
		   Verifying Checksum ... OK

		## Checking Image at 40200000 ...
		   Image Name:	 Simple Ramdisk Image
		   Image Type:	 PowerPC Linux RAMDisk Image (gzip compressed)
		   Data Size:	 566530 Bytes = 553 kB = 0 MB
		   Load Address: 00000000
		   Entry Point:	 00000000
		   Verifying Checksum ... OK

		=> bootm 40100000 40200000
		## Booting Linux kernel at 40100000 ...
		   Image Name:	 2.2.13 for initrd on TQM850L
		   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
		   Data Size:	 335725 Bytes = 327 kB = 0 MB
		   Load Address: 00000000
		   Entry Point:	 0000000c
		   Verifying Checksum ... OK
		   Uncompressing Kernel Image ... OK
		## Loading RAMDisk Image at 40200000 ...
		   Image Name:	 Simple Ramdisk Image
		   Image Type:	 PowerPC Linux RAMDisk Image (gzip compressed)
		   Data Size:	 566530 Bytes = 553 kB = 0 MB
		   Load Address: 00000000
		   Entry Point:	 00000000
		   Verifying Checksum ... OK
		   Loading Ramdisk ... OK
		Linux version 2.2.13 ([e-mail]) (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#