;; This example shows another way to handle the interrupts by hitting the hardware ;; directly. ;; ;; There are 6 interrupts per screen, one of which is triggered 2 HSYNCs after the start ;; of the VSYNC signal. We can use this to syncronise our interrupts. ;; ;; We first need to synchronise with the VSYNC, we can then enable our interrupts. ;; We now know exactly the order the interrupts will come and we can have 1 function for ;; each. org &4000 start: di ;; disable interrupts im 1 ;; Z80 interrupt mode (z80 calls to &0038 for each interrupt) ld a,&c3 ;; Z80 JP instruction ld hl,int_fn ;; we always call this function for interrupt ld (&0038),a ;; write JP instruction ld (&0039),hl ;; write address ei ;; delay loop: jp loop ;;-------------------------------------------------------------------------------------------- ;; this is synchronised to happen 2 HSYNCs after VSYNC int_fn: push af push hl push bc ;; in vsync? ld b,&f5 in a,(c) rra jr nc,int_fn_not_vsync ;; in vsync. ;; reset counter xor a jp int_fn_handle int_fn_not_vsync: ld a,(counter) inc a int_fn_handle: ;; counter is the number of the interrupt function ;; to execute ;; ;; multiply this by 3 to find JP in table to use ;; ;; then execute the function ld (counter),a ld l,a add a,a ;; x2 add a,l ;; x3 add a,int_functions AND 255 ld l,a ld a,int_functions/256 adc a,0 ld h,a call call_hl pop bc pop hl pop af ei reti call_hl: jp (hl) counter: defb 0 int_functions: jp int1 jp int2 jp int3 jp int4 jp int5 jp int6 int1: ret int2: ret int3: ret int4: ret int5: ret int6: ret end start