Hi Rick et al.,
as I mentioned before U-Boot is running on our AT91RM9200 based board. I went down the path ATMEL was suggesting. They use this memory map on their eval board AT91RM9200DK:
24k Boot Image 32KB free 8KB Environment 64KB gzipped U-Boot image
The "Boot image" is a small (11k) piece of code which initialises clocks, flash, SDRAM and serial port. Then it decompresses the "gzipped U-Boot image" into SDRAM and jumps to it. The reason for that seems to be:
We chose, to put a compressed boot due to memory mapping constraints. We need to keep a sector for environment variables the 8Kbyte-size sector is enough.
They probably overlooked that you could embedded the environment into U-Boot. By using a correct u-boot.lds linker file one can reserve an 8Kbyte-size sector in the middle of U-Boot. So instead one could use this memory map:
56KB U-Boot 8KB Environment 64KB U-Boot
using the same 128KB of flash.
Since the CPU was setup by the bootloader there's no init and relocation code for the AT91RM9200 in U-Boot (yet).
So I spend a day, "wrote" some init and relocation code and now U-Boot is starting directly from flash and relocates itself to RAM. No Preboot needed. Nor gzipped image of U-Boot.
I would like to change the official U-Boot code for the AT91RM9200 and AT91RM9200DK so that it can be used without the need of another bootloader. This way it would be a lot easier for people to port U-Boot to their hardware.
What do you think? Anyone interessted?
I'd love to hear suggestion, where to put specific parts of the init code. Other ARM cpus use a board specific memsetup.S file. For an AT91RM9200 we have to setup more than just the SDRAM. Should we put all the init code into cpu/at91rm9200/{start.S} and use CONFIG_ and CFG_? Or should every AT91 based board copy the same code again and again into thier own subdirectory?
Looking forward to your ideas!
Thanks. And sorry for the long mail!