command_syntax_extensions.txt

uboot详细解读可用启动引导LINUX2.6内核

Command syntax extensions for the new uImage format
===================================================

Author: Bartlomiej Sieka <[e-mail]>

With the introduction of the new uImage format, bootm command (and other
commands as well) have to understand new syntax of the arguments. This is
necessary in order to specify objects contained in the new uImage, on which
bootm has to operate. This note attempts to first summarize bootm usage
scenarios, and then introduces new argument syntax.


bootm usage scenarios
---------------------

Below is a summary of bootm usage scenarios, focused on booting a PowerPC
Linux kernel. The purpose of the following list is to document a complete list
of supported bootm usages.

Note: U-Boot supports two methods of booting a PowerPC Linux kernel: old way,
i.e., without passing the Flattened Device Tree (FDT), and new way, where the
kernel is passed a pointer to the FDT. The boot method is indicated for each
scenario.


1.  bootm		boot image at the current address, equivalent to 2,3,8

Old uImage:
2.  bootm <addr1>		    /* single image at <addr1> */
3.  bootm <addr1>		    /* multi-image at <addr1>  */
4.  bootm <addr1> -		    /* multi-image at <addr1>  */
5.  bootm <addr1> <addr2>	    /* single image at <addr1> */
6.  bootm <addr1> <addr2> <addr3>   /* single image at <addr1> */
7.  bootm <addr1> -	  <addr3>   /* single image at <addr1> */

New uImage:
8.  bootm <addr1>
9.  bootm [<addr1>]:<subimg1>
10. bootm [<addr1>]#<conf>
11. bootm [<addr1>]:<subimg1> [<addr2>]:<subimg2>
12. bootm [<addr1>]:<subimg1> [<addr2>]:<subimg2> [<addr3>]:<subimg3>
13. bootm [<addr1>]:<subimg1> [<addr2>]:<subimg2> <addr3>
14. bootm [<addr1>]:<subimg1> -			  [<addr3>]:<subimg3>
15. bootm [<addr1>]:<subimg1> -			  <addr3>


Ad. 1. This is equivalent to cases 2,3,8, depending on the type of image at
the current image address.
- boot method: see cases 2,3,8

Ad. 2. Boot kernel image located at <addr1>.
- boot method: non-FDT

Ad. 3. First and second components of the image at <addr1> are assumed to be a
kernel and a ramdisk, respectively. The kernel is booted with initrd loaded
with the ramdisk from the image.
- boot method: depends on the number of components at <addr1>, and on whether
  U-Boot is compiled with OF support:

		    |	       2 components |	       3 components |
		    |	   (kernel, initrd) | (kernel, initrd, fdt) |
---------------------------------------------------------------------
#ifdef CONFIG_OF_*  |		    non-FDT |			FDT |
#ifndef CONFIG_OF_* |		    non-FDT |		    non-FDT |

Ad. 4. Similar to case 3, but the kernel is booted without initrd.  Second
component of the multi-image is irrelevant (it can be a dummy, 1-byte file).
- boot method: see case 3

Ad. 5. Boot kernel image located at <addr1> with initrd loaded with ramdisk
from the image at <addr2>.
- boot method: non-FDT

Ad. 6. <addr1> is the address of a kernel image, <addr2> is the address of a
ramdisk image, and <addr3> is the address of a FDT binary blob.  Kernel is
booted with initrd loaded with ramdisk from the image at <addr2>.
- boot method: FDT

Ad. 7. <addr1> is the address of a kernel image and <addr3> is the address of
a FDT binary blob. Kernel is booted without initrd.
- boot method: FDT

Ad. 8. Image at <addr1> is assumed to contain a default configuration, which
is booted.
- boot method: FDT or non-FDT, depending on whether the default configuration
  defines FDT

Ad. 9. Similar to case 2: boot kernel stored in <subimg1> from the image at
address <addr1>.
- boot method: non-FDT

Ad. 10. Boot configuration <conf> from the image at <addr1>.
- boot method: FDT or non-FDT, depending on whether the configuration given
  defines FDT

Ad. 11. Equivalent to case 5: boot kernel stored in <subimg1> from the image
at <addr1> with initrd loaded with ramdisk <subimg2> from the image at
<addr2>.
- boot method: non-FDT

Ad. 12. Equivalent to case 6: boot kernel stored in <subimg1> from the image
at <addr1> with initrd loaded with ramdisk <subimg2> from the image at
<addr2>, and pass FDT blob <subimg3> from the image at <addr3>.
- boot method: FDT

Ad. 13. Similar to case 12, the difference being that <addr3> is the address
of FDT binary blob that is to be passed to the kernel.
- boot method: FDT

Ad. 14. Equivalent to case 7: boot kernel stored in <subimg1> from the image
at <addr1>, without initrd, and pass FDT blob <subimg3> from the image at
<addr3>.
- boot method: FDT

Ad. 15. Similar to case 14, the difference being that <addr3> is the address
of the FDT binary blob that is to be passed to the kernel.
- boot method: FDT


New uImage argument syntax
--------------------------

New uImage support introduces two new forms for bootm arguments, with the
following syntax:

- new uImage sub-image specification
<addr>:<sub-image unit_name>

- new uImage configuration specification
<addr>#<configuration unit_name>


Examples:

- boot kernel "kernel@1" stored in a new uImage located at 200000:
bootm 200000:kernel@1

- boot configuration "cfg@1" from a new uImage located at 200000:
bootm 200000#cfg@1

- boot "kernel@1" from a new uImage at 200000 with initrd "ramdisk@2" found in
  some other new uImage stored at address 800000:
bootm 200000:kernel@1 800000:ramdisk@2

- boot "kernel@2" from a new uImage at 200000, with initrd "ramdisk@1" and FDT
  "fdt@1", both stored in some other new uImage located at 800000:
bootm 200000:kernel@1 800000:ramdisk@1 800000:fdt@1

- boot kernel "kernel@2" with initrd "ramdisk@2", both stored in a new uImage
  at address 200000, with a raw FDT blob stored at address 600000:
bootm 200000:kernel@2 200000:ramdisk@2 600000

- boot kernel "kernel@2" from new uImage at 200000 with FDT "fdt@1" from the
  same new uImage:
bootm 200000:kernel@2 - 200000:fdt@1


Note on current image address
-----------------------------

When bootm is called without arguments, the image at current image address is
booted. The current image address is the address set most recently by a load
command, etc, and is by default equal to CFG_LOAD_ADDR. For example, consider
the following commands:

tftp 200000 /tftpboot/kernel
bootm
Last command is equivalent to:
bootm 200000

In case of the new uImage argument syntax, the address portion of any argument
can be omitted. If <addr3> is omitted, then it is assumed that image at
<addr2> should be used. Similarly, when <addr2> is omitted, is is assumed that
image at <addr1> should be used. If <addr1> is omitted, it is assumed that the
current image address is to be used. For example, consider the following
commands:

tftp 200000 /tftpboot/uImage
bootm :kernel@1
Last command is equivalent to:
bootm 200000:kernel@1

tftp 200000 /tftpboot/uImage
bootm 400000:kernel@1 :ramdisk@1
Last command is equivalent to:
bootm 400000:kernel@1 400000:ramdisk@1

tftp 200000 /tftpboot/uImage
bootm :kernel@1 400000:ramdisk@1 :fdt@1
Last command is equivalent to:
bootm 200000:kernel@1 400000:ramdisk@1 400000:fdt@1