Hard-sector discs -- how many sectors?

Chuck Guzis wrote: That's easy. The hard-sector support is basically a state machine that bolts onto the start/stop detector. There are four standard trigger modes (immediate, time-delayed, index-pulse and MFM Sync). When the track-mark detector is enabled, an additional state is added to the trigger FSM -- essentially it waits for a single track mark, then carries on waiting for whatever you told it to wait for. So if you program the trigger unit like this: * Start Event = HSTMD + Index Pulse * Start Count = 1 * Stop Event = Index Pulse * Stop Count = 2 What you'll get is this: t i j j I I I I I I I I ... S-----------P S=start, P=stop, -= acquisition zone. t = track mark detected, i = index after track mark, j = index pulses By changing the start and stop counts, you can read any of the 32 sectors individually, or read the entire disc in one shot (the index pulses are stored as part of the timing data, which allows the data to be separated into sectors after it's read). The write module works in a similar way -- it's an FSM that executes single-byte instructions. A byte with a 1 in the MSB waits <byte[6:0]> clock cycles, then writes a transition. A byte with a 0 can execute one of a number of micro-instructions (00nnnnnn is "wait N, don't write", 01000000 is "stop now", and there are a few others for "wait for track mark" and "wait for next index pulse"). The real pain is going to be *testing* all this stuff. I might end up tying a 4046 PLL and a counter to a 3.5" drive to make a "fake hard-sector" drive, just to test the HSTMD... -- Phil. classiccmp at philpem.me.uk http://www.philpem.me.uk/