Re: Apple ][ plus 13 sector! Problems...

[Andy McFadden <fadden@fadden.com>]

Paul Schlyter <pausch@saaf.se> wrote:
>> BTW, I don't believe "Beneath Apple DOS" shows you how to identify
>> self-sync nibbles.  It can be done, though you don't have enough cycles
>> to tell the difference between 9-bit and 10-bit self-sync bytes.
> 
> Except on weird copy protected disk formats, were 9-bit self sync nibbles
> ever used?

DOS 3.2 might have.  I don't remember.  And my books are still packed in
boxes from moving.  (On the bright side, faddensoft.com and nulib.com are
back up now that I have DSL again.)

It certainly doesn't matter in an emulated world unless you're trying to
make copy protected disks work.  However, knowing which bytes are self-sync
is very useful when trying to figure out what's data and what's a gap.

>> If you
>> just look for a large stretch of FF you're in trouble, and if you try to
>> spot address or data field markers you're going to fail on copy-protected
>> discs.  It's easy to write nibble reading and processing code that works
>> *most* of the time, but it's hard to make it work *all* of the time.
> 
> I gues it would be impossible to determine the track start in a way
> which always worked.

You have to over-read and then find the overlap, which appears to be
what the TrackStar imager does.  The variable-length nibble format it
uses is much better than the fixed-length .NIB format.  For the reasons
stated earlier, though, it's hard to do conversions between them unless
the disk is unprotected.  In that case, you just find a data epilog
and break the track there, padding it out with FFs.

> Does SST come with assembler source, or is it binaries only?

I haven't found source.  According to one bit of documentation, the author
bought source for a nibble copier from somebody and modified it.

(And while we're on the subject, I'm still on a quest to find source or
a disassembly for DDD Deluxe 5.x.  It's a bit larger than its predecessors.)

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