To do what though?
This has some pin analysis:
There's a Tivo GPL release on tivo.com for it, but is long out of date.
It appears to use Roamio (intel) byte ordering. But it has a different bootloader and kernel (compiler?). Most likely they're using the code base from the Zenverge reference platform for the lower levels.
The Roamio Pro/+ would be interesting to look at, cause if it only has one Flash chip, how are two processors booting from it.