[sebhc] Floppies, archives, and ROMs

[Dave Dunfield]

>Dave wrote (regarding simulating hard-sector pulses with soft-sector 
>diskettes):
>>  - "Remember" the timing for up to four drives, so that after the first
>>    calibration (power on), you can begin inserting hard-sector pulses as 
>>soon
>>    as you see the index pulse (subject to above guard time of course).
>
>The internal drag of a particular floppy might alter the speed slightly, so 
>it might be better to compute the timing from scratch after any insertion.  
>Also remember that insertions can occur while the motor is engaged (even if 
>rude!).  :-)

Unfortunately you can't reliably detect insertions without modifying the drive
(if you are willing to add a lead to *always* watch the write product signal of
all drives, then you could detect when a diskette has been inserted).

As to drag slowing the disk down ... I avoid using disks which have a high
drag, and have not seen much effect with "normal" disks - Unless you modify the
drive to perform insertion detection as noted above, you would have to always
waste the extra revolution every time the drive motors are turned on (note, you
are already wasting up to one revolution while waiting for the index pulse). I
have no idea if the software will tolerate this long a time before index pulses
appear or not.

Also, since I would update the timing on every detection of the index hole, this
would only be a concern if:
  - A disk has just been inserted (no previous accesses)
  - A write is occuring on the first access (read error would just retry)
  - The disk has enough drag to noticably slow the drive motor.

I think that once you have "calibrated", it would be safe to begin sending the
fake index pulses once you have determined that the drive is up to speed and
have seen one index hole - but another big benefit of a microcontroller based
implementation is that you could easily make waiting for two index pulses an
option.

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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