[Coco] Re: RETRIEVE utility...
Amardeep S Chana
vxlzneo02 at sneakemail.com
Fri Jan 23 08:11:56 EST 2004
"Torsten Dittel" <Torsten at Dittel.info> wrote in
message news:4010FA68.7A1EBD8D at Dittel.info...
> I was playing around with RETRIEVE on some unreadable disks and was
> analyzing its behaviour. It looks like after a read error it isn't
> trying to seek to track 0 and position the head to the damaged track
> again. But I guess this could help with some tracking problems. I wonder
> if it's possible to execute a "Read Track" command which would read the
> whole track. A software could analyze that data and try to extract the
> logical information from that (I made that on the CoCo).
> Any comments?
The "read track" command on a 765 core disk controller is just a "multiple
read sector" command. If you can't read the sectors one by one, you won't
be able to read them with read track. However... there is a clever trick
that can be used to simulate a classic read track:
1. Find out the first physical sector number on the track.
2. Read it with a sector size of 8192 bytes (supported by the more modern
3. Ignore the CRC read error.
4. The data you will have is the entire track after the first data address
mark, plus some repeated data past the index mark as it comes around again.
5. As in all raw read track cases, you'll need to do bit shifts until you
recognize valid data for all sectors other than the first one due to write
splices throwing byte alignments off.
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