On Thu, 25 Mar 2004, Vintage Computer Festival wrote:
Has anybody
out there written drivers for the WD1793 floppy
disk controller chip? I've been doing that for fun, and have
hit on a very strange problem with the 'read track' command.
It seems to work just fine, returning a stream of bytes that
includes the data for each sector, until it finds a byte with
a value of $29 (or 29H, if you prefer). From that point up
to the next address mark, it gets garbled data. No other data
value seems to have any odd effect. 'Read sector' returns >
the right
data with no weirdness.
The data isn't necesarily aligned on byte boundaries. It's
a bit stream. Back when I used to disassemble track data by
hand, I'd simply do multiple track reads until what I wanted
was byte-aligned, and view with SID or the PDOS equiv.
You could code up a bit stream and look for the sync patterns
and all that and byte align it yourself.
Write current turn off creates glitches in the inter-sector
gaps. It's normal.
If I recall, dumped tracks that were never written often
byte-align. It's been a long time...