[Coco] cache sector 0? related question

[Gene Heskett]

On Saturday 25 January 2014 13:08:54 Aaron Wolfe did opine:

> On Sat, Jan 25, 2014 at 12:38 PM, Gene Heskett <gheskett at wdtv.com> wrote:
> > On Saturday 25 January 2014 12:30:32 Aaron Wolfe did opine:
> >> Here's another one for the experts:
> >> 
> >> Is the area in LSN0 that actually contains data ever bigger than 64
> >> bytes? NitrOS9 docs show PD.OPT section is from 0x20 to 0x3F...
> >> then.. nothing?  Of course I ask because 64 bytes is much easier to
> >> deal with than 256.. but don't want to misunderstand something.
> > 
> > Your images are blank beyond $3F?  Every one I have ever looked at had
> > a copy of the $20 byte PD.OPT section there, copied in from from the
> > drive tables of the disk it was formatted in.  There is another,
> > differently defined byte at $42 (IIRC, see the PD.OPT section of the
> > L2 RBF docs) that I have had to change manually, and which reflects
> > the track density capability of that drive. Similar, but not
> > identical to the byte at $10. So you should have valid data up to and
> > including $5F in LSN0.
> > 
> > If you don't, I think we have a problem.
> 
> I looked too quickly, there is indeed data starting at 0x40 on these
> images. I'm not finding what it is supposed to be exactly in the
> Nitros9 tech reference but I'll keep looking and check the os9 books
> too.  Looks like the last non-zero byte on every image I check is
> 0x68, a "1" all by himself.  Maybe 128 bytes would cover it (of course
> with an abort in place for any disk that it didn't cover) but I better
> find docs that match what's found in nature first.
> 
Its confusing, but look at the PD.OPT section.  I penned in the offsets in 
the margin of my copy as they exist in LSN0.  IIRC they start at $3F & 
should run to $5E (IIRC)
> --
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Cheers, Gene
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