Software-based floppy disc data separator

On 15/06/10 02:43, Chuck Guzis wrote: No -- the hardware only stores "time since last edge". So the edges are always one "virtual nanosecond" wide. The code extends these to two PLL clock cycles for the DPLL counter reset, and also stores whether there was a data pulse (transition) in the current data window. You could feed the DiscFerret a 5ms long pulse if you liked, the counter would just keep going and the next time the counter was latched into RAM you'd get a reading of 5ms + time_inactive. That is, the time from transition edge to transition edge. Let's say you have this input: a b ------+ +----------+ +-------- | | | | | | | | +---+ +-----+ The data in buf[] is just the time from a to b -- the duty cycle can vary as much as you like, and because T(a-b) is still the same, you'll get the same timing value. -- Phil. classiccmp at philpem.me.uk http://www.philpem.me.uk/