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

[Andy McFadden <fadden@fadden.com>]

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).

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.  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.

> 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.

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