Re: DSK to NIB Instruction

["Charlie" <charlied at bboard dot SPAMcom>]

"Andy McFadden" <fadden@fadden.com> wrote in message 
news:4%v2f.1858$Aw.32985@typhoon.sonic.net...
> Paul Schlyter <pausch@saaf.se> wrote:
>> This of course means that the nib image files aren't an accurate
>> representation of the bits on the floppy.  To become more accurate,
>> nib files should really be a bit stream rather than a byte stream,
>> where sync nibbles are stored as 10 instead of 8 bits.  Of course
>> all normal nibbles might then start at any bit within a byte, and
>> the lowest-level processing of the nib file would be much slower
>> (to read one nibble one would usually have to read two bytes from
>> the nib file and then shift and mask these two bytes into the "nibble"
>> byte one wanted to read).
>
> It's actually much simpler than that.  The timing on an Apple II is such
> that you can detect which bytes are sync bytes, but not how large they
> are, unless (a) you can identify your position with great accuracy and
> (b) you can do the timing over a long series of sync bytes.
>
> So unless you're confronted with a scheme that uses both 9-bit and 10-bit
> bytes, all you need is one bit to say "it's a sync byte" and a per-disk
> or per-track flag that says "9 bits" or "10 bits".
>
> All nibble values have the high bit set, so you just store it with the
> high bit clear if it's a sync byte.
>
> With this, and a header that identifies the number of tracks and the
> length of each track, we'd be in much better shape.  The hard part here
> is that we don't have source code for SST, which makes it hard to write
> a tool that creates these disks without reinventing the wheel.
>
> What we *do* have is Disk2FDI.  The FDI format has the exact track length,
> can identify 9-bit vs. 10-bit sync bytes, and so on.  Converting raw .FDI
> to .NIB is vaguely criminal. :-)  There's also no "raw" format for 3.5"
> media, so they always have to be converted to .dsk.

Maybe I'm misunderstanding you but, Disk2FDI is capable of creating raw .FDI 
from 3.5" disks.  A simple two wire cable connecting a fast parallel port to 
the disk controller is necessary but it's an easy modification.  Disk2FDI 
can also create .DC (diskcopy?) images directly from the 3.5" disks.  I do 
it all the time.

One thing though .FDI images of 3.5" disks are very large and can take hours 
to create.

Charlie