On Mon, 1 Feb 2021, Al Kossow wrote:
Imagedisk, even though it spends way too much time with the heads
spinning on the media at least does real-time retries. the problem is
you also need to be able to stop and assemble a complete image by
splicing together multiple partial attempts.
Well, isn't that logical? ;-)
I do this with my Linux implementation of IMD, and I do this with my
floppy version of the mfmreader: immediately abort an operation when there
are noises coming from the media, clean, restart at one/two cylinders
before the forced abort, etc. and then "splice" together the individual
read attempts.
You can't do real-time retries when reading at the flux level if you have
no idea of the format. So often, it's better to sample a disk several
times in case that the later processing reveals bad sectors. So often
enough you can get an error free image produced from several samples.
The toughest part of course is the "PLL" that you need in software to lock
to the bit rate.
Christian
