Steven Seagal wrote: DrCoolZic wrote:
Just discovered this thread
very interesting despite the fact that there are a lot of incorrect information about fuzzy bits, bit decoding, and NFA
I'm interested in correct information about fuzzy bits at any rate, that's the only part that is so so in Steem's support of SCP.
I do not want to reopen a sterile discussion about fuzzy bits as everybody stays on his position: Jim thinks that it can always be detected in one revolution, Jeff / IFW and myself believe this is wrong. The definition of fuzzy bits (as per patent definition) is read multiple time (the patent says three times) the data and compare: if different ==> fuzzy.
In general it is possible to predict that some transitions will never produce fuzzy bits but not the opposite. For example totally out of band transitions will not generate fuzzy bits if placed correctly.
With only one revolution you may try to play some tricks (simulate seed rotation variation) but I am not sure this will work in all cases.
As you mention in this thread the fuzzy bits of type Dungeon master requires to have a relatively good DPLL to be detected correctly.
But excellent job as usual Mr Seagal
Not sure? did you fix the Jupiter master drive hard to decode sync sequence?
No special fix is needed for reading.
As said the first part of importance to decode correctly information, and especially fuzzy bits, is the DPLL process on input transitions (conversion from flux transitions to bits)
The second important part is of course correctly decoding these bits into bytes. The state machines inside WD1772 are not always intuitive! One difficult part is the decoding of sync marks. Here you need at least two information:
- the actual sync character received (so for example you can check for a sequence of 3 A1) and
- the output of the shift register
because as you know actually both do not match in many cases.
For example the traditional 3 "A1" sequence does result in the detection of 3 4489 but the shift regiter gives 14 A1 A1.
In the case of Jupiter masterdrive and others there is a hard to decode sequence (Thanks to IFW to provide the correct state machine) of C2 followed by A1 that decode as C2 0B (On an Atari you provide 29 f5 f7 f7 to the write track command) this is explained here http://www.atari-forum.com/viewtopic.ph ... 72#p265938
If you are reading it correctly this mean congratulation you did the right thing (i.e. the right state machine)
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