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Old 06 July 2012, 04:04   #2
Leffmann
 
Join Date: Jul 2008
Location: Sweden
Posts: 2,017
Just like in Amiga bootblocks there's no actual checksum stored, it's inferred, and the 32-bit word you're looking at is just used to correct the checksum.

At -20 bytes from the end of a Kickstart ROM there's a 32-bit word that holds the size of the ROM in bytes. I don't know if software cares about it, but maybe this is how the hardware can map ROMs so they always end at $100 0000 regardless of size.

Also, the Amiga 1000 only has a small boot ROM which loads the Kickstart from disk and verifies the checksum, so at least in this case the checksum must be correct. The checksum is the sum of all 32-bit words and the carry digits, and must be equal to -1.
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