Pardon the anglais but is there a reason why you are not using the addx instruction for the various adc instructions? Why cant 'adc_indx' look like:


adc_indx:
moveq.l #0,d0
move.b (a3)+,d0
add.b d3,d0
lea.l 0(a4,d0.l),a0
move.b (a0)+,d1
move.b (a0),-(a7)
move.w (a7)+,d0
move.b d1,d0
lea.l 0(a4,d0.l),a0
move.b (a0),d0
add.b d7,d7 ;maybe set extend flag
addx.b d0,d2 ;Edit: swapped the args
scs d7
svs (a2)
move.b d2,d5 ;N
move.b d2,d6 ;Z
bra.l update_timer

Edit: Changed
move.b d7,d1 ;get carry flag
add.b d1,d1 ;maybe set extend flag

to

add.b d7,d7