On Thu, 9 Feb 2012, Michael J. Mahon wrote:
That's what the Zip Chip does with speaker and joystick access, but it also slows down for Disk ][ access, since it won't work with a real disk unless it's running at exactly 1MHz.
It's the Apple IIgs that slows down on Disk II access - "motor on" ($C0x9) is the key.
ZipChip simply does about 50 msec slow down after I/O access. For normal disk I/O that will be re-triggered constantly by the nibble read ($C0xC) polling loop, but a longer than ~50 msec delay will be broken.
http://www.bootzero.com/forum/viewtopic.php?f=3&t=12 http://www.bootzero.com/forum/viewtopic.php?f=3&t=15I guess that they choose ~50 msec to not interfere with disk stepper. Of course a track-synchronized copy protection might fail with ZipChip if it has track-to-track delay of more than ~50 msec.
Same goes for sound - if you have longer than ~50 msec pause/rest, tempo becomes wrong.
Same goes for any I/O that is separated by longer than ~50 msec lack of I/O activity.