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x86?  We ain't got no x86.  We don't NEED no stinking x86!

Ok, I got a bit further with this. It *sometimes* works. I got it going for a few seconds, powered off, back on and it partially showed info on the LCD, powered off completely, wait 10 seconds, powered back on and it's back to no interrupts. I'll keep at it. I'd blame it on my timer values if it wasn't for the factor that when it's not wokring there are no interrupts at all.

This particular design is a 65c02. I was working on two designs at the same time: 6502 and 65816. I finished the '02 first, so got a PCB fabbed just before Christmas. Once I've finished with it, it's back to the 65816 design which does test for VDA & VDA in the CPLD (the one in the '02 and one I the 816 are very similar, but not quite the same). It's been slowed down a bit as I've been learning how to use Kicad over Christmas, so am remaking the 65816 design in there as I won't be restircted to a 160x100mm (an Eagle maximum, restricted by my old license).

Looks like a combination of issues. There are actually IRQs firing, but my Rigol 'scope seems to have a problem displaying the low pulses if I 'zoom out' to see a number of them - sometimes I see none, sometimes I see some if I'm lukcy. If I zoom in to about 20ms and set triggering I will see them.
On top of that I think my LCD busy flag routine also has a timing problem at 16MHz as now that I've updated the 15ms wait routine (I've relaxed it to slightly over 15ms), I get rubbish on the screen. This indicates that the LCD is being successfuly initialised (which uses the T1 timer at the moment as the busy flag doesn't work for that) and then swaps over to using the busy flag and so - rubbish on screen.
Add the two together and it looked like the VIAs were the issue.
Still looking into it, but tomorrow as it's a bit late.