I can only imagine it was making sure an nmi only occured once per frame. They could have used the irq line on the cartridge slot to clock the nmi flip flop, although during a game that could occur more frequently. But then there is no telling what a game is going to do to the keyboard matrix either. It would seem that disabling interrupts would prevent the button from operating. It should also be possible to disable nmi using the cia and use the cpu to read fff9/fffa, if $de is returned then the button was pressed. Disable irq too and you can clock the flip flop manually, probably as fast as you want. On 05/10/2022 22:16, groepaz_at_gmx.net wrote: > So it is indeed waiting for "not in system NMI". Seems odd - i wonder > what > kind of scenario they had in mind that would be solved by this. >Received on 2022-10-06 16:03:50
Archive generated by hypermail 2.3.0.