[coreboot] C720 swapparoo
jlewis at johnlewis.ie
Wed Jan 29 22:49:18 CET 2014
On 29/01/14 20:54, Duncan Laurie wrote:
> - The SPI flash descriptor, which lives at the bottom 4K of the SPI
> chip in the SI_DESC region of the flashmap. It is readable from the
> host but not writable.
> - The Management Engine binary, which lives at the bottom 2MB (-4K for
> the descriptor) of the SPI chip in the SI_ME region of the flashmap.
> It is neither readable or writable from the host.
Okay, I have the descriptor and ME binaries already (I guess it doesn't
matter too much about the ME anyway, since it being missing wouldn't
prevent boot, just cause half-hourly power-off).
> For the basic coreboot+payload (BOOT_STUB region in flashmap) the
> binaries are all in CBFS and can be read out with the usual 'cbfstool
> bios.bin extract -n NAME -f NAME'
> - The mainboard-specific DIMM SPDs, stored as "spd.bin" (also checked
> in to the mainboard directory in coreboot)
> - The reference code binary, which is stored as "mrc.bin"
> - The Video BIOS, which is stored as "pci8086,0406.rom"
> - The microcode, which is stored as "cpu_microcode_blob.bin" (with
> recent changes this may be handled differently upstream now)
This is where we reach the crux of the matter - In the stock/shellball
firmware, extracting BOOT_STUB doesn't yield a file which cbfstool in
upstream coreboot or CrOS coreboot can decipher. Looking at the file in
hexedit it appears to be almost identical to a CBFS that is recognised,
but that's it. I have managed to extract the SVGA binary from the CBFS
in the RW_LEGACY slot, and I've made an educated guess as to where the
system-agent begins and ends in the unrecognised CBFS (section beginning
"LARCHIVE mrc.bin" or similar with the binary itself following,
surrounded by FF's) copying and pasting it to a file. I would like to
know if I am correct in my assumptions about extracting that file
manually and what size it should be, in bytes?
Further more, trying to use upstream coreboot to compile with that 2 MB
management engine yields:
Created CBFS image (capacity = 8386544 bytes)
E: Not enough space for content.
E: Could not add [c720-me.bin, 2093056 bytes (2044 KB)@0x7a0000]; too big?
E: Failed to add 'c720-me.bin' into ROM image.
I have tried 2, 4, 6, and 8 MB CBFS in coreboot menuconfig. Not sure why
building for Peppy tries to put the ME in CBFS when other builds don't.
Building using CrOS coreboot works, but I am loath to recommend someone
foolhardy with a C720 try it, unless I know there is a reasonable chance
the binaries are okay/correct.
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