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Atari ST protections - Printable Version

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Atari ST protections - admin - 11-04-2013

It's been a really long time since I looked at Atari ST stuff. Back when I wrote the last version of the Copy II 64/128 with Central Point Software I also tinkered with Copy II ST coding a little bit. I seem to recall the ST uses the WD177x floppy controller, so we were limited in what we could actually do.

Can someone chime in and let us know the titles of some of the most difficult to copy programs that were released for the ST?

Also, I want to support any of disk image formats that people want, so please voice your opinion on formats should be supported. Thanks!


RE: Atari ST protections - DrCoolZic - 12-19-2013

(11-04-2013, 11:08 PM)admin Wrote: Can someone chime in and let us know the titles of some of the most difficult to copy programs that were released for the ST?
Humm many titles are indeed difficult to reproduce but lets start with one: Turrican.

Turrican uses a protection called “no flux area”. This is somewhat a misnomer as in fact this is created by sending very close transitions to the write head, but this result in reading no flux transition in a specific area (no clock no data!). As the WD1772 is not capable to return the extracted “clock” value from the MFM input stream a trick is used: we have a second overlapping sector (aka sector within sector) that is shifted by a half cell value. Reading both sector result in reading data and clock bytes and therefore allow to check that there is indeed no transitions detected by the FDC. More information here
http://www.sarnau.info/atari:protection_turrican and here http://www.atari-forum.com/viewtopic.php?f=47&t=22195 and here http://www.atari-forum.com/viewtopic.php?f=47&t=19948&start=25#p189968
       
In order for your board to reproduce this protection it will have to write a “relatively high frequency” signal to fool the read channel … If need more info I can publish one chapter of an upcoming doc Smile

For description of protection used on Atari you should go to my page here http://info-coach.fr/atari/software/preservation.php and read my doc http://info-coach.fr/atari/documents/mydoc/Atari-Copy-Protection.pdf
I am rewriting this document in light of experiment I did with other disk flux transition recorders … soon to come

Quote:Also, I want to support any of disk image formats that people want, so please voice your opinion on formats should be supported. Thanks!
For protected game your best bet is the Pasti / STX format http://pasti.fxatari.com/. Problem is that there is no official description of the format Sad
Soon to come a detail documentation on this format obtained by reverse engineering (others and me) and discussion with the author.


RE: Atari ST protections - admin - 12-19-2013

Thanks for the info. I do not believe in the "no flux area" theory. There are flux transitions always returned by the drives. Some drives return a pretty reliable version of the magnetic data, and some are so-so. Using a logic analyzer, you can record the flux transitions and compare them with what the drives return. In the case of the Panasonic JU-256A216P drives, the flux transitions returned equal the time that passes as the disk spins, even if its many milliseconds long. Typically, the time is broken into maximum blocks of around 25,000us. So, even though there is a portion of the disk where there were no deliberate flux transitions written, the magnetic data is still changing due to the magnetic field of adjacent tracks. The AGC is cranked up extremely high when this occurs and the data is clocked correctly. Some Epson drives return short-long-short-long bit cell periods during these times.

For SuperCard Pro, it does not matter as these protections are duplicated without needing to do anything but write the data back as it is read. Although I have not tried Turrican, I have reproduced what you call "no flux areas" manually without any issues and duplicated those by reading and re-writing the data using the SuperCard Pro analyzer. I will see if I can find an original Turrican just to verify it works.