The Apple II MouseCard IRQ is Synced to Vertical Blanking After All
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Summary
While conducting research into why there was extensive screen flickering when using the (emulated) Apple II MouseCard in the MAME (Multiple Arcade Machine Emulator) Apple II system, Colin Leroy-Mira reportedly discovered that only the emulation suffered from these issues, with no such phenomenon happening when using real (PAL or NTSC) hardware.
It was alleged that the MouseCard lacked the functionality to sync with the system’s vertical blanking (VBL) while creating images, a claim that was dismissed; instead, it was established that the card synched with the VBL precisely as described in The Friendly Manual, with the card’s firmware subsequently run by the system’s CPU, which signals when to sync with the card.
