On Thu, Sep 23, 1999 at 10:46:55PM +0100, Andrew Collier wrote: > Actually you mean "pop hl; ei; nop; ret"
> We know that the interrupt line stays active for a lot longer than this > code will take to execute. Fooey. Well, you knew how to fix it anyway. :o) > Unfortunately it now means we spin round the interrupt handler for a > hundred t-states or so But we know pretty much exactly how many, since I measured it that time. > >If the screen is off we expect an answer in the region of 5989. > Frame interrupt -> Frame Interrupt > Mode 2 - 4, Screen on : 5049 > Mode 1 , Screen on : 4291 > Mode 3 - 4, Screen off : 5983 Well that wasn't a bad estimate, the difference being 6*20 = 120 cycles. > Frame interrupt -> Line Interrupt @ 0 (I'm assuming gives 60 lines of border) > Modes 2 - 4 : 1298 (screen off or on gives same result) > Mode 1 : 1015 That instantly tells us that there is contention in the top border. It looks like there may be more contention on the main screen, but calculations will have to be done. One possibility which must now be false is that mode 1 always restricts access to once every 8 cycles. imc
