| Author: | Lord Crass (guest: search) |
|---|---|---|
| Date: | Thu, May 12th, 2011 @ 21:00 ( . ) |
The protection doesn't seem that odd. The drive code is simple: It uses the job queue to load $28/$0e (track 40, sector 14) into the $400 buffer of the drive. The C64 then reads that buffer to $5200, checks that the byte at $527B is an $83. If it is, then it jumps to the "code" that was loaded at $5200, otherwise it resets the machine. The problem is that when told to load 40/14, it seems to read in 40/04 instead and returns a disk error 27 (checksum error in header block), so you get garbage in the $400 buffer. Unless I'm missing something odd about this track, I believe it's a bad dump. It could be that most of the sector headers are bad and in a non-standard order and due to some track sync, it has to land on the correct one (it looks like there's only one sector on this whole track that has any data). I'll look a bit more later. After the last sector, there's a whole bunch of bad GCR, so this might be throwing off the 1541-II drives. |
5/13/2011 @ 20:32--Lord Crass 6/23/2011 @ 18:10------hyper active --- 0 Users Online --- 0 Recent Unique Posters |