9 Dec
2003
9 Dec
'03
2:45 p.m.
On Tue, 9 Dec 2003, Eric Smith wrote:
The part of the ST-506 disk emulation that's of
most concern to me is
whether anything needs to be done about write precompensation. The
controller shifts the pulses on write to compensate for the peak
shifts that happen on magnetic media when flux changes are recorded
close together. If the emulated drive does not emulate the peak shift,
the read data timing will be further from the nominal timings that that
the controller expects. This will affect the controller's data
separator PLL. I'm guessing that it won't be enough to cause
reads to fail MOST of the time, but it will reduce the timing margins
enough to that it could potentially cause occasional soft errors.
Right, one option would be for the emulator to have a FM, MFM or RLL front end
and actually decode the bitstream. Then the write-precomp could be undone...
Peter Wallace