4 Jul
2000
4 Jul
'00
4:46 p.m.
What I was getting at was that,
while the CatWeasel seems to work OK for some things, and, in fact, quite a
few, it probably doesn't read/write hard sectored disks
On reading, the Catweasel has a mode where the high order bit of each
sample byte gives the state of the index/sector hole sensor. This should
be great for reading hard sectored disks. On writing, you have to write
a whole track at a time, but it should work OK to compute where the sector
holes ought to be, construct a track of the right length, and write it
out starting at the index hole.
and it probably
doesn't allow minute adjustment sector-by-sector of the data on the diskette
in order to make the format and the data fields within it all
clock-coherent.
I don't see why not, but maybe I don't understand this point. Maybe you're
saying that 14.161 MHz isn't a high enough sample rate...? That seems
unlikely to me.
It was my suggestion that the device be supported
with
software to allow not only that data be extracted from the bitwise
oversampled data recorded as in Tim's buffer, but also that software be
generated to permit the data to be reduced, essentially, to just the data in
the data fields with some set of information (which was TBD when I last
looked) implying the nature of the format in which it was recorded.
Further, it was to be able to write the data into any known format,
including known formats not supported by the controller available to the
user.
This sounds great. My suggestion is that the next step should be to work
on defining the necessary data formats and writing the software, using
the Catweasel (or Tim's board, for that matter) as the hardware base.
It doesn't seem necessary to get bogged down in designing more hardware
first.
The Catweasel may be a good model to keep in mind, but
the comment about
bits moving around over time does give me pause.
That comment had nothing to do with the Catweasel specifically. What
I've observed is that when reading old 8" disks, some look as though they
were written with way too little write-precompensation. I was speculating
that there was enough precomp initially, but that the bits have moved
over time. I might have been completely wrong about that; maybe there
was not enough precomp initially, but the original data separator circuits
were good enough to read the disks anyway. In any case, you'd see the
same thing with Tim's board or any sampling-based hardware.
I simply mean that the Catweasel and Tim's
buffer/sampler board are two
shots at two different targets. There's little point in comparing them
unless the overlap more than they appear to do in the writing I've seen up
to now.
They are exactly the same *hardware* approach, except that the Catweasel
has an ISA interface and Tim's has a parallel port interface. The *software*
that comes with the Catweasel is not the software you're proposing, but
that software hasn't been written yet for Tim's board either. If it looks
like a duck and quacks like a duck, we can make duck soup from it even
if the person who raised it was more interested in duck eggs.
Tim Mann tim.mann(a)compaq.com http://www.tim-mann.org
Compaq Computer Corporation, Systems Research Center, Palo Alto, CA