void usercb (void cb(void));

Sets routine called as part of MTX BASIC interrupt processing. By default this routine
will be called every 8ms. If CTC channel 0 is re =programmed to pass through VDP
interrupts, then the routine will be called every 20ms. If a direct callback on CTC channel 0 is defined, then BASIC interrupt processing, including this callback will not be processed.

cb =Routine to be called (NULL to remove callback).

Include file: mtxint.h