[Coco] cache sector 0? related question

[Aaron Wolfe]

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.