|(5) Timer channel 0 interrupt routine
Clear the status register flag to stop the interrupt signal.
Read COUNT and, if it is not 0, decrement it by one and store
the value in COUNT and end.
If COUNT is 0, increment MUSIC_ADRS by two to address the next
If the next tone is H'FFFF (iteration of the last tone), stop
timer ch0 and reset MUSIC_ADRS to the same initial value as set in the
main routine. Reset the COUNT address to 0.
If the next sound is not H'FFFF (iteration of the last sound),
start timer ch0 and store the sound data length (R0L) at the COUNT
If the read value is H'FFFF(rest), stop timer ch3 to suppress
Restore the registers from the stack and return from the interrupt