[sebhc] Floppies, archives, and ROMs

[West, Ronald S.]

> 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.

I wouldn't recommend remembering timing rates. The controller's timing
should be dynamic and generate each set of holes based on the dt between the
previous index holes (after the +/-15% test is satisfied). If the next set
are a bit different the controller generates a slightly different timing for
them. This is obviously not the best situation. It would be better if we
could get the real time rotational speed of the spindle, but that isn't
available. We might be able to derrive it from the raw data coming off of
the heads, but that would involve more drastic modifications to the drive in
question. What we are talking about here could be in-line on the back of the
drive, placed on the controller card, or even on the drive electronics.
...lots of flexibility.

Ron


> -----Original Message-----
> From: sebhc at sebhc.org [mailto:sebhc at sebhc.org] On Behalf Of 
> Dave Dunfield
> Sent: Wednesday, February 02, 2005 11:46 AM
> To: sebhc at sebhc.org
> Subject: RE: [sebhc] Floppies, archives, and ROMs
> 
> 
> 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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