[A86] Re: The f'n 86 screen
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[A86] Re: The f'n 86 screen
There is a reason every grayscale interrupt handler has code similiar to the
following:
in a,(3)
bit 1,a
jr z,IntExit
If you are using a grayscale handler, then you can merely halt before
drawing, and it will work fine. In fact, a halt may work no matter what, do
to the possible voodoo magic of the screen refresh tied to the timer
interrupt. No one really knows for sure how it works, but this is the
likely reason that changing the interrupt speed results in weird screen
effects, like doubling. Just because screen updates happen when interrupts
are disabled is meaningless, because the hardware doesn't have to be
connected via the bus.
I don't know why it only happens for a very small screen area. I haven't
ever really looked into it, but instead corrected the problem using known
methods. It could in fact be something entirely different, but it isn't
likely.
> So, how do you know when the vertical refresh is ready? And why does it
only
> happen at a horisontal line about 2 pixels wide?
References: