Hello:
Another newbie question, I'm afraid ...
What I am trying to do is run another copy of U-Boot from SRAM, i.e. treating U-Boot #2 as a standalone application to be loaded by U-Boot #1. This way I don't have to overwrite the boot code stored in the flash.
Now, U-Boot is power-on-reset code as well as C code, and the CPU has already *been* initialized, so not all of the code needs to be re-run. I am wondering what is the most straightforward way to modify the early code for running from SRAM.
The board I'm using (PPChameleonEVB) has 1 MB SRAM at 0xff800000. I've modified the .lds file and the flash base in include/configs so that "flash" is now taken to be the SRAM. (I know this is quick and dirty, not elegant. Also I know that the PPChameleonEVB has a jumper which swaps CS0# [flash] and CS1# [SRAM], but I don't have a BDI so I'm not able to load the SRAM.) Then I make an image file with mkimage file, address 0xff800000 and entry point 0xff800100, TFTP it to the board and execute it. I obtain:
[board.c, 767] Calling env_relocate ... env_relocate[203] offset = 0x2700000 env_relocate[221] malloced ENV at 01f7f908 U-Boot relocated to 01fc0000 [board.c, 907] Calling interrupt_init ... Bus Fault @ 0x01fc2f84, fixup 0x00000000 Machine check in kernel mode. Caused by (from msr): regs 01f7f618 Machine check signal - probably due to mm ft with mmu off NIP: 01FC2F84 XER: 00000000 LR: 01FC219C REGS: 01f7f618 TRAP: 0200 DAR: 7C6B1B78 MSR: 00001000 EE: 0 PR: 0 FP: 0 ME: 1 IR/DR: 00
GPR00: 00028000 01F7F708 01AB0000 01F7F718 0000000A 00000000 00000000 0A972F76 GPR08: 01FCA404 0A7C5AC5 00000004 00000001 00000000 00000080 01FE5300 02700000 GPR16: 00000000 00000000 00000000 00000001 00001000 01F7F708 00000000 01FC219C GPR24: 01FC2F84 01FC0000 01F7F88C 01F7F8FA 01FEA68C 01F7F860 01FE5384 00000006 Call backtrace: machine check
which is a machine check in PITException. I can and will debug this further, but I wonder if some things are already known. Namely:
* What I'm doing is re-running all the init code. This is overkill, since the CPU has already been initialized, but it is easiest to code, since I just need to modify the .lds et al.
* The other extreme would be to re-run none of the init code (except installing handlers, etc.), which I don't mind doing except that it sounds like a several-day project.
* Is there a happy medium?
* There is a __DEBUG_START_FROM_SRAM__ macro which I see in the code, but it doesn't appear to be used very many places.
* I think someone else out there must have tried something similar before ... however, if there's something in the U-Boot manual on this topic, I've missed it.
Thanks for any and all info, and for your patience. :)