On Thu, Sep 16, 2010 at 5:06 PM, Wolfgang Denk wd@denx.de wrote:
Dear Alessandro Rubini,
I agree that it would be nice to have U-Boot completely position- independent and completelky restartable, but this would be a new feature, which newer existed before.
x86 has a nice feature whereby I can build two images that differ only by TEXT_BASE. I can build using TEXT_BASE somewhere in low memory, tftp the image and the 'go' directly to the base address of the image
e.g.
tftp 6000000 u-boot.bin go 6000000
This works because the x86 reset vector is at top of memory (0xfffffff0), not bottom (0x00000000) so the very first bytes of u-boot.bin are not the reset vector, but rather where the reset vector jumps to after performing some very low-level hardware init
Both images, as a very first step, relocate to the highest available memory location and adjust all the relocation offsets in the image and jump into the relocated image.
As long as I do not mess with the low-level init code, I can be confident that an image that 'boots' using the 'go' command will boot from Flash
No, it is not a 'fully relocatable' image, but it is so close as to not make any real difference to me.
Regards,
Graeme