finally got some time to poke around with the scope.
Sure enough, it's firing IRQ6, the Video interrupt, then throwing the exception.
So I'm speculating it's getting to the point where it clears vsyncen, which lets the vsync signal though UI6 pal, which turns into IRQ6, which goes through the GLUchip, VIA2 throws the IRQ line, but the vsync interrupt handler isn't there...
From what I can figure, the vsync handler also deals with reading ADB and moving the mouse pointer which explains the lack of pointer or ability to reset pram from the keyboard.. ADB circuits seem just fine, polling away cheerfully until you hit a key...
Only sign of unusual signals I've found are some stray noise on D22 once the exception is thrown..
I guess it's diagnostic mode from here and knockup a serial I/F to something..??
Has anyone had a situation where the PAL's go 'soft' in the '30 and the timing goes astray??
Sure enough, it's firing IRQ6, the Video interrupt, then throwing the exception.
So I'm speculating it's getting to the point where it clears vsyncen, which lets the vsync signal though UI6 pal, which turns into IRQ6, which goes through the GLUchip, VIA2 throws the IRQ line, but the vsync interrupt handler isn't there...
From what I can figure, the vsync handler also deals with reading ADB and moving the mouse pointer which explains the lack of pointer or ability to reset pram from the keyboard.. ADB circuits seem just fine, polling away cheerfully until you hit a key...
Only sign of unusual signals I've found are some stray noise on D22 once the exception is thrown..
I guess it's diagnostic mode from here and knockup a serial I/F to something..??
Has anyone had a situation where the PAL's go 'soft' in the '30 and the timing goes astray??