Re: 6502 illegal opcodes questions

[pausch@saaf.se (Paul Schlyter)]

In article <446f7e4c$0$4512$9b4e6d93@newsread2.arcor-online.net>,
Linards Ticmanis  <ticmanis@gmx.de> wrote:

> Paul Schlyter wrote:
> 
>>> IIRC the S-JiffyDOS patch uses illegal opcodes to speed up GCR decoding.
>>> (Jochen, are you reading here and can comment?)
>> 
>> That can also be done without illegal opcodes.  The Apple Pascal RWTS
>> did it, and was able to read all sectors of a floppy on one revolution
>> of the disk -- oncluding GCR decoding on-the-fly.
> 
> But isn't Apple GCR a bit simpler than commodore GCR? Apple's 16-sector 
> format stores three data bytes per four disk bytes (3:4), Commodore gets 
> in four data bytes per five disk bytes (4:5) IIRC.

Dunny about that.  Apple 13-sector format stored 5 data bytes ber 8 disk bytes
(5:8), which was less efficient than (3:4) --- still, the denibblizing code
was a bit longer in the (5:8) case than the (3:4) case.

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