diff options
Diffstat (limited to 'roms/7seg_counter_irq_timer_start_stop.asm')
| -rw-r--r-- | roms/7seg_counter_irq_timer_start_stop.asm | 170 |
1 files changed, 170 insertions, 0 deletions
diff --git a/roms/7seg_counter_irq_timer_start_stop.asm b/roms/7seg_counter_irq_timer_start_stop.asm new file mode 100644 index 0000000..3c7aed5 --- /dev/null +++ b/roms/7seg_counter_irq_timer_start_stop.asm @@ -0,0 +1,170 @@ +PORTA = $6001 +DDRA = $6003 +T1LCL = $6004 +T1LCH = $6005 +ACR = $600b +PCR = $600c +IFR = $600d +IER = $600e + +SER = %00000001 +RCLK = %00000010 +SRCLK = %00000100 + +INTERVAL = 33 ; increase counter 3 times per scond +WAIT_INTERVAL = 99 ; wait one second on button press + +CURRENT = $0 ; current counter +VISIBLE = $1 ; visible counter (as last printed to the 7-segment display) +TICKS = $2 ; internal ticks counter (on overflow increment counter) +RUNNING = $3 ; if counter is running or stopped +COUNTER = $4 ; counter, increment on button press, show only shortly when button pressed + + .org #$f800 + +reset: + sei ; disallow interrupts during initialization + + ldx #$FF ; initialize call stack to $1FF + txs + + lda #%11000010 ; enable CA1 and timer1 interrupts + sta IER + lda #$0 ; negative edge triggering + sta PCR + + lda ACR + and #$7F + ora #%01000000 ; setup timer for free running timer1, no PB7 + sta ACR + + lda #%00000111 ; set output on 7seg control pins of PORTA + sta DDRA + + lda #$0 ; initialize 8-bit counter and tick counter + sta CURRENT + lda #$FF ; the visible counter is different at init, so we force + sta VISIBLE ; the drawing of the initial value + lda #INTERVAL + sta TICKS + lda #$FF + sta RUNNING + + lda #$0 ; initialize button press counter + sta COUNTER + + lda #$0F ; initialize counter of VIA timer1 ($270f = 9999 at 1MHz) + sta T1LCL + lda #$27 + sta T1LCH + + cli ; allow interrupts now + +mainloop: ; main loop, just print value of counter + sei + lda CURRENT + cmp VISIBLE + cli + beq mainloop + jsr print7seg ; update value + sei + lda CURRENT + sta VISIBLE + cli + jmp mainloop + +print7seg: + ldy #$8 ; 8 bits to shift +loop7seg: + rol a + bcc zerobit ; C=0, bang a zero to SER +onebit: + ldx #(SER) ; C=1, bang a one to SER + stx PORTA + ldx #(SER | SRCLK) + stx PORTA + ldx #(SER) + stx PORTA + jmp next +zerobit: + ldx #$0 ; C=0, bang a zero to SER + stx PORTA + ldx #SRCLK + stx PORTA + ldx #$0 + stx PORTA + jmp next +next: + dey + bne loop7seg + rol a ; restore A register +output: + ldx #0 ; bang RCLK to store output in latch + stx PORTA + ldx #RCLK + stx PORTA + ldx #0 + stx PORTA + rts + +nmi: + rti + +irq: + pha ; save state + txa + pha + tya + pha + lda IFR ; check interrupt register of VIA + bpl irq_done ; bit 7 set? if not, not an interrupt of the VIA + asl ; bit 6 in sign (timer1) + bmi timer1 + asl ; bit 5 in sign (timer2, unused) + asl ; bit 4 in sign (cb1, unused) + asl ; bit 3 in sign (cb2, unused) + asl ; bit 2 in sign (shift, unused) + asl ; bit 1 in sign (CA1) + bmi ca1 + asl ; bit 0 in sign (CA2, unused) + jmp irq_done ; no more interrupt to handle from VIA + +timer1: + bit T1LCL ; clear timer1 interrupt + lda #$FF + cmp RUNNING + bne irq_done + +tick: + dec TICKS + bne irq_done + lda #INTERVAL + sta TICKS + inc CURRENT ; increment internal counter + jmp irq_done + +ca1: + lda RUNNING ; toggle running flag + eor #$FF + sta RUNNING + inc COUNTER + lda COUNTER + sta CURRENT + lda #WAIT_INTERVAL + sta TICKS + bit PORTA ; clear CA1 interrupt (button press) + jmp irq_done + +irq_done: + pla + tay + pla + tax + pla + cli + rti + + .org #$fffa + .word nmi + .word reset + .word irq |