Re: Anyone got a Torch Z80 disc pack + Perfect Writer?

In message <8d56b8d04e.Matthew@xxxxxxxxxxxxxxxxxxxxxxxxxx>
Matthew Phillips <mnews@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

In message <a9f07ad04e.davehigton@xxxxxxxxxxxxx>
on 8 Apr 2007 Dave Higton wrote:

In message <f5b836d04e.Matthew@xxxxxxxxxxxxxxxxxxxxxxxxxx>
Matthew Phillips <mnews@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

The main problem with CPM disc formats is there was virtually no
standard format. Although the basic principles of the format are the
same, there are several critical parameters which cannot be readily
worked out by exaiming the disc, so CPMFS only supports a limited range
of disc formats at the moment, one of which is the format used by Acorn
CP/M systems. Whether that covers the Torch system I am not sure, as I
have never had an Acorn CP/M system of any kind.

Do you have the CP/M Alteration Guide?

No, would that help? If it is a publication by Digital Research that OEMs
use to guide them on producing the BIOS and fitting CP/M to their systems,
then it would not be of use. What I would need to know are the specific
disc parameters used by a Torch system.

Things like the Block Shift (BLS), Block Mask (BLM), Extend Mask (EXM) and
so on.

The Acorn CP/M format that CPMFS currently supports is 80 track,
double-sided with lowest sector number 0 and ten sectors per track.

BSH = 4
BLM = 15
EXM = 1
PSH = 1
DSM = 195

There seems also to be a skew table involved.

I do have the CP/M Alteration Guide!

BSH = 4 and BLM = 15 determines that BLS = 2048. NB BLS = Block
Size, not Block Shift.

BLS = 2048 and DSM = 195 determines that the disc capacity is
390 KB. If I read correctly, this is the gross capacity
including directory space. This might help us determine DRM.

The "standard" skew factor as far as Digital Research was concerned
was 6, so the translate table from the Alteration Guide is:

XLT0: DB 1, 7, 13, 19, 25, 5, 11, 17, 23, 3, 9, 15, 21,
DB 2, 8, 14, 20, 26, 6, 12, 18, 24, 4, 10, 16, 22

Hope this helps!

Dave
.

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