Yes, the Apple II MouseCard IRQ Is Synced to the VBL

A little technical post to document something that was apparently not obvious to everybody. I recently questioned myself and others in the Apple II dev community about the Apple II MouseCard, its interrupts, and their synchronisation with the Apple II vertical blanking. Documentation about the card states that the IRQ is synchronised to the VBL: I wondered a lot about this, stemming from the fact that under MAME emulation, my Shufflepuck game flickered a lot, whereas in real life, it was very cleanly rendered. Of course in my real life, I can test it on an Apple //c, which doesn’t exactly have a MouseCard but a compatible mouse firmware, and also it’s a PAL Apple, so it’s running at 50Hz and not 60. When I want to test if my drawing is fast enough for 60Hz Apple II, I have to waste 3250 cycles before starting to draw. How I waste cycles to make sure my game doesn’t flicker on NTSC machines So I could not do the exact tests I wanted, and I had to ask nice people to test on their NTS ... Read full article.