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Diffstat (limited to 'README.fmap')
| -rw-r--r-- | README.fmap | 40 |
1 files changed, 40 insertions, 0 deletions
diff --git a/README.fmap b/README.fmap new file mode 100644 index 0000000000..416d27fe50 --- /dev/null +++ b/README.fmap @@ -0,0 +1,40 @@ +In the most general case, the flash layout looks something like this: + + +---------------------+ + | Reserved for EC use | + +---------------------+ + + +---------------------+ + | Vblock B | + +---------------------+ + | RW firmware B | + +---------------------+ + + +---------------------+ + | Vblock A | + +---------------------+ + | RW firmware A | + +---------------------+ + + +---------------------+ + | FMAP | + +---------------------+ + | Public root key | + +---------------------+ + | Read-only firmware | + +---------------------+ + + +BIOS firmware (and kernel) put the vblock info at the start of each image +where it's easy to find. The Blizzard EC expects the firmware vector table +to come first, so we have to put the vblock at the end. This means we have +to know where to look for it, but that's built into the FMAP and the RO +firmware anyway, so that's not an issue. + +The RO firmware doesn't need a vblock of course, but it does need some +reserved space for vboot-related things. + +Using SHA256/RSA4096, the vblock is 2468 bytes (0x9a4), while the public +root key is 1064 bytes (0x428) and the current FMAP is 644 bytes (0x284). If +we reserve 4K at the top of each FW image, that should give us plenty of +room for vboot-related stuff. |