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Self-sync bytes should be written after a sector header

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Not after the data field marker, where the controller/RWTS don't expect
to find them.
This commit is contained in:
Peter Evans 2018-02-18 23:46:48 -06:00
parent c89e855559
commit 015104bd57
1 changed files with 8 additions and 5 deletions
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13
src/apple2.enc.c
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@ -22,6 +22,8 @@
* different byte value that would be literally written to and read from
* the disk media. Apple II's RWTS subroutine would then translate them
* back into data that is useful to the software being run.
*
* Also, since I forget: gcr is short for "group coded recording"
*/
static vm_8bit gcr62[] = {
// 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
@ -219,11 +221,6 @@ apple2_enc_sector(vm_segment *dest, vm_segment *src,
vm_segment_set(dest, doff++, 0xaa);
vm_segment_set(dest, doff++, 0xad);
// Sure... let's just toss in a few self-sync bytes
for (i = 0; i < 6; i++) {
vm_segment_set(dest, doff++, 0xff);
}
// Now we use the gcr table for 6-and-2 encoding to take the XOR'd
// values and represent them as they should be in the destination
// segment. This constitutes the data field of the sector.
@ -292,5 +289,11 @@ apple2_enc_sector_header(vm_segment *seg, int off,
vm_segment_set(seg, off++, 0xaa);
vm_segment_set(seg, off++, 0xeb);
// Write six (exactly six!) self-sync bytes following the epilogue,
// because the Disk II controller/RWTS method expect to find it.
for (int i = 0; i < 6; i++) {
vm_segment_set(seg, off++, 0xff);
}
return off - orig;
}