Re: Write Signal on Disk II Question

[Linards Ticmanis <ticmanis@gmx.de>]

ferdimh@gmx.de wrote:

> The problem is that I don't know neither the exact prenibblizing
> scheme nor the usual disk image formats.

There's a copy of "Beneath Apple ProDOS" floating around online which
explains the scheme fairly well in the early chapters. Also you might
look into the disk-handling code of any emulator, as they usually
convert .dsk to nibble data and vice-versa on the fly.

Disk image formats:

.dsk or .do: 35 tracks of 16 sectors of 256 un-nibblized data, sectors
are ordered in the track as DOS numbers them. No file or track headers.

.po: Same, sectors are in the order ProDOS numbers them.

.nib: 35 tracks of $1A00 bytes each, as you read them from the latch. No
headers either. Does not discern between sync and non-sync bytes, and
does not store the exact track lengths, thus there will be some
duplication of data as real tracks are almost always shorter than $1A00
bytes. The track data in the file is not guaranteed to start with the
first sector; it might even start in the middle of a sector. Thus you
should treat the $1A00 bytes of a single track as a circular structure
with wrap-around and then search for the sector you want. The format
does not handle half-track data.

-- 
Linards Ticmanis