[Coco] 1bit hsync nasties....

[Darren A]

On Wed, Jan 22, 2014 at 2:52 PM, Simon Jonassen wrote:

> Well John...
>
> We have a nice litte vector (secondary) at $10c
>
> Which usually holds a jmp $xxxx (somewhere in basic on a cold boot)....
>
> If we hook the hsync (which is 15750 Hz (15625 for pal)) then that jmp
> $xxxx
> gets executed very fast
>
> So that jmp (4 cycles) gets executed 312 / 262 lines (per frame)
>
> 312 * 4cycles = 1248 cycles (you do the math for NTSC)
>
>
And don't forget that on a CoCo 3 the interrupt first goes to $FEF7 which
does an LBRA to $010C. That's 5 more cycles per call on a CoCo 3 than you
get on a CoCo 1/2. Of course you can change that as well.

Darren