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From: D Finnigan <dog_cow@macgui.com>
Newsgroups: comp.sys.apple2
Subject: Re: DOS 3.2, 3.3 and ProDOS GCR in RWTS
Date: Mon, 11 Jan 2016 19:34:55 -0000 (UTC)
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fadden wrote:
> On Sunday, January 10, 2016 at 9:59:57 PM UTC-8, awanderin wrote:
>> [...]
>> >> FWIW, you can find the CiderPress implementation of 6&2 and 5&3
>> >> encoding here:
>> >> https://github.com/fadden/ciderpress/blob/master/diskimg/Nibble.cpp
>> >
>> > Thank you!  I see that you wrote it for both 6x2 and 5x3.  Not to
>> > sound helpless, but I really don't know how to implement this program.
>> > Obviously it's a language, I presume Basic.  Step by step, how can I
>> > make this run?
> 
> http://a2ciderpress.com/
> 
> The code is written in C++.
> 
> FWIW, if you:
>  - set Edit > Preferences > Disk Images > Confirm disk image format
>  - open a DOS 3.2 disk image (.nib) with Tools > Disk sector viewer
> 
> you can choose to view each track as sectors or nibbles.  Might be handy
> for seeing both forms of each track.
> 
> 
>> Do you have the book, Beneath Apple DOS?  It's available on-line as a
>> PDF and it describes the 5&3 decoding in sufficient detail that you
>> should be able to implement in Excel.  You figured out 6&2 so 5&3 is
>> really conceptually the same but the details differ.
> 
> FWIW, I vaguely recall disassembling the DOS 3.2 RWTS code to figure out
> 5&3 encoding, because the Beneath Apple DOS explanation was insufficient,
> and I wasn't able to locate a working implementation (back in 2003).
>

OpenEmulator also has a decoder for DOS 3.2's 5&3 encoding. And DOS 3.3 too.

https://code.google.com/p/openemulator/source/browse/trunk/libdiskimage/DIApple525DiskStorage.cpp