A92: Strange interrupt behavior
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A92: Strange interrupt behavior
I'm working on the chip8 emulator for the TI-92/92+/89. It requires a delay
timer that runs at 60 Hz, which I implemented with interrupts. This is my
first time working with interrupts. I looked at other people's code and found
out how it works, so I implemented it in mine, and the delay works correctly.
I remembered to back up all registers used in the interrupt function at the
beginning of the function and restore them at the end. However, it causes
random data to be written to the screen and after a few minutes of sitting
there with the random data being written to the screen (along with the normal
data) it will crash with an address error. I am really lost as to why this is
happening, and as I couldn't find a very good reference on interrupts, I
decided to pose the question here. This is my interrupt handler routine:
DelayRegTimer:
movem d0/a0,-(a7)
lea dtimer(PC),a0
move.w (a0),d0
cmp.w #0,d0
beq AfterDec
sub.w #1,d0
move.w d0,(a0)
AfterDec:
movem (a7)+,d0/a0
rte
It is supposed to decrement dtimer if it's not zero, and leave it alone if it
is, and then return to wherever the program was at before. Can you tell me
why this causes the random data to be written to the screen?
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