speaking of 3.5" floppies, is 720K R.I.P.?

On Monday (02/02/2009 at 06:40PM -0800), Chuck Guzis wrote: I have been trying to do this exact thing... simulate 10-hole hard sectored floppies with the 3.5" drive. I'm finding it much more difficult than I expected. It seems that the speed of these drives is not very constant. So, when I trigger off the real index pulse from the drive and then generate very accurately timed pulses simulating the 10 other holes, it appears that they are not lining up with the data some number of rotations later. The result is a high number of soft errors during read back. My simple plan was to just watch for the real index hole from the selected drive and then generate the synthetic ones back to the controller until the drive was deselected. I could see I had a timing problem which I initially blamed on the microcontroller's RC clock (I am using an ATMEL AVR instead of a PIC). So, I improved this in various increments, ending up with a +/- 50ppm osc can and at each increment of improving the stability of the clock, my soft errors INCREASED! I'm now reworking the whole design and I'm going to keep the soft sectored drive always selected, always motor on and continually watch the real index pulses and compute the instantaneous RPM. From that, I'll generate the pseudo index pulses which will hopefully better match the current speed of the drive. The pseudo pulses and all the other drive signals will be externally gated onto the floppy bus since I need to keep the emulating drive always active-- and I want to emulate two drives at the same time. Kind of a pain but I don't see how else to get there now. Any suggestions on what I am missing? Chris