Hello Pete,

Pete Rittwage schrieb:
> Hi guys,
> 
> With the help of "TeaRex" on my forum, I added a simple way to 
> read/write disk images using the index hole sensor built into the 1571. 
>  Through this addition, a revelation occurred.
> 
> We had always assumed (since the 80's) that the Electronic Arts' "fat 
> tracks" protection had 2 tracks (34 and 35) perfectly aligned.  I added 
> the index hole code and wrote out the disk perfectly aligned to track 0 
> and thought it was beaten.  :)
> 
> Well, it turns out this assumption is *not* true.  When reading against 
> the index hole, track 35 is actually skewed back 1/4 track or so on all 
> the original disks.  If I write it back out skewed in this way, it 
> boots.  These were never "FAT" tracks at all, just a specific track skew 
> between two identical copies of a track.

can you poove that observation with my cbmrpm41 tool (currently 
available through OpenCBM CVS only)? Job mode 2 measures out relative 
track synchronization regarding the the relation of two "neighbored" 
sector numbers between the two tracks. You can advise cbmrpm41 which 
sector to choose and also limit the measurement to these two tracks:

     cbmrpm41 -j 2 -b 34 -e 35 -c 2  8

> XEMAG 2.0 (the Activision variety of this protection) is skewed about 
> 1/2 track between 35 and 36 (and some amount between 34 and 35 also that 
> doesn't appear to be checked).
> 
> I noticed years back that this protection boots if the drive motor is 
> slowed down to 298.5 or lower (within reason) no matter what the skew. I 
> guess something about how their timing check is setup allows this to pass.

Please keep the descriptions of the different protection schemes at your 
main site updated. One day each and every feature of the different 
protection schemes may be revealed and well documented.


Womo

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