[Coco] IRQ question

[Glen Hewlett]

Hi All,

I need some help from a CoCo3 IRQ expert.

I thought I had this figured out but something is not right with my IRQ setting for my Pac Man transcode project.  I’ve gotten to the first attract mode and the animation is running about 1/4 the speed of the real machine.  I was getting worried it was a problem with the CPU not being fast enough but it looks like the IRQ just isn’t kicking in at the correct time.  It seems to update the IRQ on the CoCo 3 every 4 frames and not when the VBLANK occurs at least according to MAME in debug mode.  What I need is it to be triggered on every VBLANK or (VSYNC)

On Pac man hardware the IRQ kicks in approximately 60 times a second and using MAME debugger option I can see it in action, every IRQ it does is one frame.  On the CoCo 3 under MAME debugger running my code it seems to kick in around every 4th frame and definitely not when the beamy is at 241 like pac man shows under MAME debug mode.  I know MAME might not be perfect but there is definitely something wrong with my IRQ settings.  I’ve setup the following code for my IRQ thinking it should trigger on the VBORD, is this the same as VBLANK?

        LDA     #%00110100              *
        STA     $FF01                   * HSYNC IRQ Disabled, IRQ Polarity Flag falling Edge, Data Direction Normal, Select Line LSB = 0, HSYNC Flag = 0
        STA     $FF03                   * VSYNC IRQ Disabled, IRQ Polarity Flag falling Edge, Data Direction Normal, Select Line MSB = 0, VSYNC Flag = 0
        STA     $FF21                   * CONTROL OF CD FIRQ* TO CPU DISABLED, IRQ Polarity Falling Edge of CD, CD Flag off
        STA     $FF23                   * CONTROL OF Cart FIRQ* TO CPU DISABLED, IRQ Polarity Falling Edge of Cart, Cart Flag off

        LDA     #%01101100              *
        STA     $FF90                   * CoCo 3 Mode, MMU Enabled, GIME IRQ Enabled, GIME FIRQ Disabled, Vector RAM at FEXX enabled, Standard SCS Normal, ROM Map 16k Int, 16k Ext
        LDA     #%00000000              *
        STA     $FF91                   * Mem Type 64k chips, 63.695 usec timer, MMU Task 0 - $FFA0-$FFA7
		
        LDA     #%10000000              *
        STA     $FF98                   * Graphics mode, Colour output, 60 hz, max vertical res

        LDA     #%00001000              * $08
        STA     $FF92                   * Enable only the Vertical Border Sync (VBORD) Interrupt

The IRQ routine itself is big… Other then running normal code I’m only doing the following in the IRQ routine itself:
IRQ starts…
	No special code here

At the end of the IRQ I have:
	LDA	$FF92                  * Reading this makes the IRQ enabled again
	RTI

Does the above look OK for setting the IRQ to hit 60 times a second on the VBLANK signal?  If so then maybe the CoCo 3 just isn’t fast enough to run my Pac Man translated code.  :(

Thanks for looking,
Glen