How to run from flash with U-Boot.

Keywords: U-Boot, embedded

1. Ask U-Boot: "what do you support to boot?"

Normally, U-Boot use special image for kernel/ramfs packing. But we need to know which compression support U-Boot that fleshed to our target board.

First way: use mkimage utility (/usr/ports/devel/u-boot) and make test images for all supported by mkimage compression types.

mkimage -A ${TARGET} -O linux -T kernel \
            -C ${COMPRESSION_TYPE} \
            -a ${RAM_START_ADDRESS} \
            -e ${RAM_START_ADDRESS} \
            -n 'FreeBSD Kernel Image' \
            -d SOME_SMALL_FILE_NAME \

Then for each file, do transfer to board and run from image with `bootm' command. And check what U-Boot answer you, if answer like "Unimplemented compression type ?", then you know :).

Second way: From running Linux or U-Boot get first 64k block from kernel partition in flash.

Break your mkimage utility: avoid exit when we do "show info" (key -i) CRC failed. And check compression type of 64k file we get from device.

Or just delete U-Boot image header from file

dd if=64k.file of=just_kern bs=64 skip=1

and check with file(1) utility

2. Create image 2.1. More canonical way, we have mkimage, gzip or bz2 and compiled kernel, maybe kernel.bin also.

gzip --best --force vmlinux.bin

for ELF kernel:

mkimage -A mips -O linux -T kernel \
            -C gzip \
            -a ${LOAD_ADDRESS} \
            -e ${START_ADDRESS} \
            -n 'FreeBSD Kernel Image' \
            -d kernel \

LOAD_ADDRESS - in most cases this is RAM base address

for kernel.bin:


Don't forget to check/change KERNLOADADDR of kernel config file. KERNLOADADDR must be equal to START_ADDRESS.

2.2. Longest way, but have smallest footprint, used only if U-Boot support LZMA.

Problem 1: Current version of mkimage from ports, don't support LZMA. So we need new:

Problem 2: Devices I know support only old LZMA. I use LZMA 4.17.

Then mkimage, like in 2.2., but -C lzma.

3. Now we have kernel U-Boot image, so transfer it to device and try with `bootm' command.

4. If all fine, write image to flash kernel partition.

AleksandrRybalko/Run from flash with U-Boot (last edited 2011-04-12T09:24:02+0000 by AleksandrRybalko)