Re: Making disk images of NorthStar CP/M disks with Catweasel

On Sep 14, 3:59 am, glen herrmannsfeldt <g...@xxxxxxxxxxxxxxxx> wrote:
lync...@xxxxxxxxx wrote:

(snip)

I *think* it would be possible to make a plain "bit dump" of the
arbitrary hard sector floppy disk into the DMK format. However to get
anything useful the specific rules would have to be written to get it
to actually find and decode Vector sectors. It really is not that
hard to do though. My original approach was for two programs: one
that made the raw bit dump of the hard sector disk into the DMK image
format and another which decoded the DMK image into useful NorthStar
sectors and tracks.

I have thought for a while now, someone should connect a floppy
drive to a fast digitizer, such that one could read the data
off a track, and do any desired processing later. That should
be enough to allow for any format with enough documentation.

-- glen

Glen,

That is pretty much exactly what a Catweasel already does. It samples
the floppy disk at various user selectable frequencies and builds an
image of the track somewhat like a digitizing sampler would do for an
audio tape. When you look at the output of the CW you can see the
long and short magnetic transition pulses of an FM signal and the
long, medium, and short pulses of an MFM signal. You see the clock
bits, data bits, noise, preindex marks, preaddress marks, index holes,
sector holes, etc -- whatever is on the disk (or not). I do not think
there is a signal you could generate with a floppy disk drive that the
Catweasel couldn't read!

It is a rather strange way to think about a floppy disk but once I got
my brain around the concept now I wish every FDC was a Catweasel.
They are truly amazing devices. I think they are inexpensive and
invaluable tools in recovering vintage computer data. You can get a
PCI MkIV for $125 US or an ISA MkI for $65 or so. Missing, corrupted,
or erroroneous sectors can't hide their secrets from a Catweasel! I
think it is too bad more people aren't getting them and writing the
decoder software for their favorite vintage formats.

Writing the "raw bit dump" program for hard sector disks is fairly
easy to do. Its the writing the format decoder which is the hard
part. Especially one that is error tolerant and robust. Mine is
taking a while to get to work properly but apparently Jim Battle wrote
one for the PTDOS on the Helios for the SOL 20 which works well.

http://www.sol20.org/ptdos.html

Best of luck with your project and have a nice day!

Andrew Lynch


.

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