26 Feb
2012
26 Feb
'12
7:44 p.m.
Hi guys,
Does anyone know what the typical range of floppy and ST506/ST412 drive
track-to-track seek rates is?
I'm finding myself having to modify the seek logic in the DiscFerret to
accommodate the Seagate ST-277R RLL drive, which requires that
buffered-seek pulses be spaced between 8 and 200 microseconds apart. Any
more than that and it assumes you're doing a 'slow' seek at 10ms per step.
A number of hard drives are like that. The worst one I've seen is the
SA4000 (Shugart 14" winchester) where there's an aceptable speed range
for 'buffered seeks' and a slower range for track-at-a-timne seeks. But
if you get between them, the drive will mis-step and end up on the wrong
cylinder. With no warning.
At the moment the DiscFerret's step rates are set up in 250us intervals,
with an 8-bit divider register. Seek rates can be between 250
microseconds and 64 milliseconds in this configuration.
Feeding the ST277R the 250us step pulses... really screws it up. The
drive deasserts READY and SEEK-COMPLETE and seems to freeze up
completely. Hardly unexpected...
If I change the seek clock to 125us, I get a minimum of 125us and a
maximum of 32ms using the same divider.
Is 32ms likely to be enough for even the slowest drives?
The slowest I have seen were some of the full-height 5.25" drives which
had a 30ms seek time, So 32ms would eb OK for those.
Is the problem in providng a greater reage of times the length of the
divider or the numbero f bits needed to sleect the time? If the latter, I
mighty be tempted to have a doubling series onece toy get to, say, 10ms
(that is, have 10, 20, 40, 80 ms only). I can't think that would cause
any problems.
Most single-chipl FSCs only allowed for a few different step rants.
-tony