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Re: Track reading (Sedoric / FDC)

Posted: Sat Jan 05, 2019 2:02 pm
by christian
Unlike Sedoric, there is no information stored on the disk because FTDOS does not permit to adjust the disk geometry.
So the format is always: 2 sides x 41 tracks x 17 sectors x 256 bytes. (with Jasmin 2)

Re: Track reading (Sedoric / FDC)

Posted: Sat Jan 05, 2019 3:49 pm
by Symoon
Hey thanks a lot, very valuable information ;)

Re: Track reading (Sedoric / FDC)

Posted: Sat Jan 05, 2019 7:32 pm
by Symoon
Interestingly, Omniflop lists 4 different formats for Jasmin:
40x17 340kB
41x17 348.5kB
42x17 357kB
They have been provided by ChloƩ so I suspect I should ask for details on the other forum!

Re: Track reading (Sedoric / FDC)

Posted: Sat Jan 05, 2019 8:18 pm
by iss
This is from Jasmin manual, not very informative...
jas-man.png

Re: Track reading (Sedoric / FDC)

Posted: Sun Jan 06, 2019 10:00 am
by Symoon
Thanks. I suspect the differences are with the user available tracks (would the system be present on the disk or not).
Or maybe small differences betwenn the (apparently) many different FTDOS versions.

Re: Track reading (Sedoric / FDC)

Posted: Tue Jan 08, 2019 8:35 pm
by Symoon
One mystery solved: the Nibble manual explains how it deals with track mode.
It actually reads the whole track first, keeping in memory each of the sectors ID positions. Then it reads each sector, and puts them in place of the ones that were read in track mode... "Because of the bad quality of track reading".

That's how there are much less $C2 in Nibble "track+sector" reading ;)

Re: Track reading (Sedoric / FDC)

Posted: Wed Jan 09, 2019 9:08 am
by iss
This makes sense - first to use whole track reading just to get the "description" of the track (i.e. number of sectors and their size) and then to read every sector individually. Very interesting! :)

Re: Track reading (Sedoric / FDC)

Posted: Mon Jan 13, 2020 4:56 pm
by ThomH
I've just discovered possibly the most egregious of false sync situations:

On track 41, the ID mark for any normally-written floppy will be [sync] A1 * 3, FB 29. The final nine bits of that sequence are 000101001, which MFM encodes to: 01 01 00 10 00 10 01 00 1x, i.e. the C2 sync followed by 00 1x.

So a read track is essentially guaranteed always to lose synchronisation when reading addresses on track 41.