While U-Boot can boot a variety of file types (ldr files, elf files, binary files) and it includes support for its own special format - the U-Boot image format (or uImage).
The format stores information about the operating system type, the load address, the entry point, basic integrity verification (via CRC), compression types, and free description text. Some common bootable U-Boot images you will encounter are files typically named uImage or vmImage.
These images are operated on in directly addressable memory regions. So you can boot directly out of external memory or flash hooked up to the asynchronous memory banks. If the image is stored elsewhere (say serial or NAND flash), you'll have to boot indirectly.
For information on loading a bootable image into the board, please consult the loading files via TFTP or the loading files via the serial port documents. For information on writing an image into storage, please consult the appropriate page (see the U-Boot index).
iminfo command just displays information about the image stored at the specified memory address and verifies the checksum.
bfin> iminfo 0x1000000 ## Checking Image at 01000000 ... Image Name: Linux-22.214.171.124-ADI-2008R2-pre-sv Created: 2008-03-31 20:07:15 UTC Image Type: Blackfin Linux Kernel Image (gzip compressed) Data Size: 5142286 Bytes = 4.9 MB Load Address: 00001000 Entry Point: 00244000 Verifying Checksum ... OK
If you wish to actually boot an image, you give the
bootm command the address in memory where the image is stored.
bfin> bootm 0x1000000 ## Booting image at 01000000 ... Image Name: Linux-126.96.36.199-ADI-2008R2-pre-sv Created: 2008-03-31 20:07:15 UTC Image Type: Blackfin Linux Kernel Image (gzip compressed) Data Size: 5142286 Bytes = 4.9 MB Load Address: 00001000 Entry Point: 00244000 Verifying Checksum ... OK Uncompressing Kernel Image ... OK Starting Kernel at = 244000 Linux version 188.8.131.52-ADI-2008R2-pre-svn4516 (vapier@G5) (gcc version 4.1.2 (ADI svn)) #89 Mon Mar 31 16:07:02 EDT 2008
This does the following things:
Normally you do not need to create a boot image yourself as the uClinux-dist and Linux kernel will generate appropriate images for you. But in case you need to, the command to use is called
mkimage. You can either find this with the toolchain (just add the corresponding
bfin-… prefix), or you can find it in the U-Boot source directory in the tools folder.
The help for the
Usage: mkimage -l image -l ==> list image header information mkimage [-x] -A arch -O os -T type -C comp -a addr -e ep -n name -d data_file[: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' -x ==> set XIP (execute in place)
For example, if we want to create an image with a gzipped compressed kernel in it, we would just do:
$ gzip -9 vmlinux $ mkimage \ -A blackfin -O linux -T kernel \ -C gzip \ -n 'My Linux Image' \ -a 0x1000 -e 0x1000 \ -d vmlinux.gz vmImageHere we create an image for the Blackfin Linux kernel that will load and boot at 0x1000. You'll obviously need to change these values for your own needs.