2009-11-21
Following on from the previous WIP, we need a reliable method to interpret bit cell data from the measured flux transition timing.
One idea (after some sleep) is to derive data within a context. You might be tempted to think the 4us values are spot on, being very close multiples of 2us. In reality however, they are bit shifts from 3.6us. 1.8us is clearly the real bit cell rate that was used when mastering the disk.
But the shifts always happen after a certain pattern that has been established before, like they should have been eliminated through pre-compensation. Either pre-compensation was not used and what we see is the result after 20 years, or pre-compensation was good enough to reduce the bit shifts to these values in the first place.
Now our thinking is:
Now this might work for any kind of encoding, but it’s not exactly easy to create code that does this efficiently. :)