On Nov 5, 2008, at 2:31 AM, Finn Thain wrote:
On Tue, 4 Nov 2008, Joshua Juran wrote:
On Nov 4, 2008, at 12:06 PM, Brad Boyer wrote:
On Tue, Nov 04, 2008 at 07:34:41PM +0100, Riccardo wrote:
Hopefully there's a logical way to detect this upgrade, but it
would be
interesting to know if the update changes the gestalt ID.
You would detect an upgraded ROM by reading the ROM, I imagine.
Good point. But I think we'd need the ROM base to be supplied by
Penguin?
Or even just the ROM checksum.
It's probably a good idea for the kernel to know the address and size
of the ROM, and given those (or just the former) it can determine the
checksum. Penguin can get these from low memory and Gestalt()
respectively. EMILE can too iff they're set up in ROM -- I don't know.
By the way, does anyone know how to calculate a ROM checksum, or
will I
have to reverse-engineer CopyROM or somesuch?
I assumed that CopyROM etc did not validate anything, they just
reported
the checksum contained in the ROM (first 4 bytes).
Oh. Red herring, then. So for our purposes it's just a magic
number, and the "checksum" algorithm would be:
inline unsigned long checksum( const void* rom, unsigned long size )
{
return *(const unsigned long*) rom;
}
:-)
The code must be part
of the POST though, since a bad rom checksum is a sad mac error. So
you
could reverse engineer that. But IIRC there is a card ROM checksum
algorithm given in Designing Card and Drivers for the Mac II and
Mac SE.
It's probably the same algorithm. I don't have access to my copy at
the
moment.
Might be interesting, but not necessary -- if we really wanted to
verify the ROM was intact we could use any checksum algorithm we
wished, with a table mapping one to the other.
But one of these days I should spend some quality time disassembling
ROM anyway.
Josh
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