[sebhc] Floppies, archives, and ROMs

Dave Dunfield dave04a at dunfield.com
Wed Feb 2 10:46:08 CST 2005


At 11:26 02/02/2005 -0500, you wrote:
>Can't the problem of detecting a new disk be solved by limiting the range of
>the uController generating the "holes?" If the index holes get more than
>+/-10 to 15% away from the 300RPM spec then the controller quits generating
>holes. 
>
>This way if the operator removes a disk (however rude or not) then the
>system will start generating holes when the new disk gets close to 300RPM. I
>also thought about doing this but never had the time. Have been working on
>an IDE board for about a year now too but work, home & college classes have
>kept me from continuing. I guess its the same for everyone. Fun stuff
>allways seems to come last.

I'm not worried about what happen if you remove a disk while it is being
accessed - I don't do that, and I think it's entirely reasonable that
removing the disk while it is being accessed with this adapter present
could cause a disk error, given that removing the disk while it is being
accessed WITHOUT this adapter present is also very likelt to cause a
disk error.

Putting the disk in with the drive running is likely to come up to speed
faster than it it is inserted when the drive has to start from completely
stopped. Obviously the controller should stop generating holes if it sees
a really long index pulse (ie: no diskette at all in the drive while selected).
Once it seen a normal index pulse again it can resume.

The original question was regarding what would happen if you removed a disk
(while the drive was idle) and replaced it with a disk that had more "drag",
thus slowing the drive ... My suggestion to remember the drive timing after
the first calibration as long as power is on could cause the holes to be
too fast, if a subsequent disk drags down the motor. This event could not
be detected by monitoring the index pulse, because the drive is not selected
during idle, so the index pulse is not available to the controller.

(Since the drive motor is servo controlled, a disk that drags enough to slow
 it is going be a problem with or without this controller - I have a habit of
 watching the strobe disk of drives on the bench when they are active, and I
 have not seen drive speed variations with disks, except in extream cases
 where the disk was obviously defective]

Regards,
Dave
-- 
dave04a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools: www.dunfield.com
com             Collector of vintage computing equipment:
                http://www.parse.com/~ddunfield/museum/index.html


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