[Coco] Help with speeding up sprite rendering

[William Astle]

On 2017-03-17 01:35 PM, Glen Hewlett wrote:
> The code below doesn’t work on the latest MAME (0.183) but it does work on a real CoCo3.  I have a feeling that MAME doesn’t handle turning off all the interrupts very well.  Maybe it’s me, I’ll have to investigate this more as I’ve been using MAME to test my code for the last six months and this is the first time I’ve had an issue with it.

I don't see any issues with your code.

It might be that you're getting a spurious interrupt in MAME after 
disabling the GIME IRQ. Reading FF92 immediately after disabling 
everything would clear that.

I have a couple of suggestions that may improve the routine speed.

You shouldn't need to clear FF92. It should also remember which 
interrupt flags are enabled when you re-enable the IRQ in FF90. You 
might want to try that on the real CC3. It will shave a few cycles off 
the routine if you don't have to set FF92.

Also, you don't need to save CC unless you need to preserve the carry 
flag for some reason. Everything else that actually matters is clobbered 
by LDA and STA on the way out anyway, or can simply be set explicitly on 
the way out. You said this was during your IRQ handler? In that case, 
you can just do an "orcc #$10" before you reset FF90 to make sure IRQ is 
disabled. No need to do the save/load dance with CC. (load/store + TFR 
is quite slow compared to orcc or andcc) If you do need to restore the 
state of the interrupt flags to an unknown state at the end, then the 
load/store business makes sense. Otherwise, it's using up CPU time for 
no real benefit.

Also, is DP always the same when that code runs? If so, you can just 
reset it directly instead of the save/load dance. That means only one 
"load + TFR" to reset DP. If DP changes unpredictably, then what you're 
doing does make sense.