(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...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
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/myd...ection.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
Soon to come a detail documentation on this format obtained by reverse engineering (others and me) and discussion with the author.