Thanks. I looked at the handler (I guess both interrupts and exceptions go through the same mechanism?) and tracked down Mario Kart's exception display code: L, Up, Left, Down, Right, R, L, B, A. Press that when you see a white square in the upper left corner (i.e. the game has crashed) and you'll get some info on the screen.
First line is what I'm guessing is a thread ID (always seems to be 5), then the PC at which the exception occurred, then the exception code (as listed in the R4300i manual). Second line is RA, third I don't know (was just zeros for me).
The reset button still appears to work. (For me, it only blanks out the screen and doesn't actually reset the game, even if it's not crashed. Some issue with the CD64 maybe.)
This doesn't work on Mupen64; the code runs, but I guess it just never redraws the screen if the game never finishes its handler.
Using 810DC6FE FFFF shortens the code to simply "press L".
Notice the white square in the corner (looks like the bottom left corner of the "A") that indicates a game crash.
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