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

[pausch@saaf.se (Paul Schlyter)]

In article <rEyKc.2980$54.38387@typhoon.sonic.net>,
Andy McFadden  <fadden@fadden.com> wrote:

> Paul Schlyter <pausch@saaf.se> wrote:
>> One possible way would be if someone wrote an "ADT for NIB files".
>> To read a physical disk and convert it to a .NIB file would be almost
>> trivial:
>> 
>> 1. Identify the beginning of the track -- the best way is probably to
>> locate the largest block of FF self-sync nibbles.
>> 
>> 2. Start there and read the entire track (a certain number of nibbles,
>> this number is the same for all 5.25" GCR disks).  Reading a nibble
>> is very easy -- "Beneath Apple DOS" explains how to do it, and the
>> code is availabine within RWTS as well -- it's just a few bytes long).
>> 
>> 3. Send the nibbles over the serial line, and let the PC side store
>> the data in the .NIB file.
> 
> That's what SST is for.  It reads the disk in image format and records it
> on two 16-sector floppies, which you ADT over.  You then run SST in an
> emulator to recombine the two images into a single .NIB image (or you can
> use a feature in the CiderPress tools to do it).

Yes I know about SST, but I always thought it was a very awkward way to transfer
a disk to a .NIB file image.  But if I desperately wanted to transfer some
13-sector disk image I'd probably do it.

> I transferred a 13-sector copy-protected Castle Wolfenstein image using
> this approach.  Once it's in .NIB format you can use CiderPress to look
> at or extract the files.  (The Wolfenstein screen shot on the web site
> came straight off the copy-protected 13-sector .NIB file.)
> 
> 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?

> 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.

>> To do it the other way, i.e. transfer a .NIB file to a physical Apple
>> II disk, is considerably harder.
> 
> Actually, it's exactly the same process with SST, just going the other
> direction.
>
>> Also note that an "ADT for NIB files" would have no error checking.
>> If some nibble is misread from the disk, there'll be no way to
>> check for that.
> 
> You could, of course, convert the .NIB image to a .DSK image, perhaps
> using some tool that runs under Windows and warns you if any sectors
> failed to convert. :-)  Only works on non- or mildly-protected discs.
> 
> SST is available for download; check the newsgroup FAQ.

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

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