SS/80 Exerciser

[magore]

Given that I was not 100% not sure how teledisk encoded and managed with errors I have been rereading documents and I have been working through teledisk_loader.c (the main teledisk decoder) to examine the decoding process more carefully. I have rewritten much of teledisk_loader.c and now plan to merge it into my td02lif.c wrapper. It will be much easier to patch up bad tracks with missing or bogus sectors.

I noticed while doing this rewrite that images created by the old TELEDISK dos program did not store CRC values for the sector header information itself at all - just a 1 byte CRC for the much larger sector data. The 1 byte data CRC makes no sense - the lack of checking the CRC for the sector header is a bug. They used 2 byte CRC with the teledisk comment and 1 or 0 bytes for most of everything else. The smaller size vs 2 byte CRC would only save a few percent on image sizes. Well perhaps this may reflect as to why we can have broken teledisk images with no hint as to how.

Fortunately I can do a number of sanity checks - verify we have all of the sectors on all tracks.
Eliminate all sectors whose size does not match those on the track 0. Parse the LIF data while reading and stop after the last record - not at the end of disk, etc...

I hope to have my updated code on github in a few days...