Got to the bottom of the "no interrupt"/reset problem. Bootstrap places a rom in memory that re-directs interrupts with a scheme they call pseudo vectors. In earlier testing I wanted to get that rom out of the way so I turned it off. If you try to use interrupts in bootstrap with the rom off, it vectors to the usual spot in the $FFxx space. Since there is the GM flash up there it will run the GM ISR. This was un-planned un-expected operation, but completely the way it works. My bad.
Turned on a bit in HPRIO at $103C to enable the rom and now working as expected. Oh well, there goes three hours. Now, back to looking at the TPU.
Initial look with the scope shows that the interrupt lines up with the start of each low res pulse.
-Tom
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