Tim's own version of the Catweasel/Compaticard/whatever

This approach to reading and interpreting data recorded on a floppy is very sound, though it might be a bit tricky to interpret. It will almost surely guarantee that you can duplicate the diskette, and quite precisely. However, to that end, if 8" diskettes are on your list of targets, you should oversample 16x so that you can deal in a fairly standard way with the write precompensation. You won't see it on reads, hopefully, but you definitely will want to generate appropriate offsets for writing when you set about to duplicate a diskette. For quite some time I've tried to persuade Eric Smith, who's quite knowledgable about programming the SCENIX SX processor, to write some firmware that would create, functionally, a FDC chip out of one of these ultra-fast single-chippers. The sampling and passing to an external micro for buffering would have to be done by the SX, but since it would function as a FDC, it could get away with relying on an outside master controller to take the sampled data and store it in memory. Data would then be processed to reduce its size prior to archival and would also require pre-write processing to expand it to its 16x or perhaps even 32x oversampled format to generate adequate sufficiently fine resolution for proper write-precompensation. Back when the discussion was about archiving old floppy disk contents, there was considerable discussion how to read and replicate existing FD's. At that time I suggested the methodology in which I have the most confidence, i.e. oversampling at a rate compatible with normal write precomp and subsequently reducing the sample resolution with software. The fact is that it's not difficult to sample and store the signal from the FDD. Interpreting it in light of the modulation, data format, data rate, etc, is quite involved, but certainly achievable, though someone has to undertake to write the code with which to accomplish this. Having the entire diskette sampled as has been suggested, a track at a time means that one's computer can, at its own pace, reduce, interpret, reformat, etc, the data prior to writing it to a duplicate. The reformatting of the data into its original format offers the advantage of phase coherency between sectors so the PLL on the controller doesn't have to shift phase between sectors. That will make the job easy in a case where the PLL has, over time, drifted off its nominal data rate. More importantly, however, the data can be reclaimed and error-corrections made, that are not possible with the FDC. Sampling circuits are quite straighforward and don't need much software to operate them, particularly if they're put in parallel with the FDC. The FDC can be used to direct the headload and seek operations and, in fact, the FDC can tell whether a given sector was recovered correctly, thereby lending confidence to the notion that the data sampled in that particular pass was completely readable. There are, IIRC, 10416 byte-times, nominally in an 8" FD track at MFM. at 16x ovrsampling, that's a fair amount of data. While there are a number of 256Kx8 SRAMS out there, they're not likely to be lying in the corner unused. I recommend, therefore that such a circuit be devised with DRAMS. Those are available on one of those PC-video cards in the bottom drawer, that you don't use any longer. I doubt it will take any longer than 30 minutes to design an adequate sampling circuit readable from a PC's parallel port in EPP mode. In about a week, I may have time to do that and build it up. If somebody's got the time an is willing to take on the coding burden to prove/disprove this notion, I'd be willing to fabricate the circuit and send it to whoever is willing to do the coding. Dick ----- Original Message ----- From: <CLASSICCMP(a)trailing-edge.com> To: <CLASSICCMP(a)classiccmp.org> Sent: Tuesday, July 04, 2000 7:03 AM Subject: Tim's own version of the Catweasel/Compaticard/whatever formats.) overkill uses and/or