174 lines
2.7 KiB
ArmAsm
174 lines
2.7 KiB
ArmAsm
;================================
|
|
;================================
|
|
; mockingboard interrupt handler
|
|
;================================
|
|
;================================
|
|
; On Apple II/6502 the interrupt handler jumps to address in 0xfffe
|
|
; This is in the ROM, which saves the registers
|
|
; on older IIe it saved A to $45 (which could mess with DISK II)
|
|
; newer IIe doesn't do that.
|
|
; It then calculates if it is a BRK or not (which trashes A)
|
|
; Then it sets up the stack like an interrupt and calls 0x3fe
|
|
|
|
; Note: the IIc is much more complicated
|
|
; its firmware tries to decode the proper source
|
|
; based on various things, including screen hole values
|
|
; we bypass that by switching out ROM and replacing the
|
|
; $fffe vector with this, but that does mean we have
|
|
; to be sure status flag and accumulator set properly
|
|
|
|
interrupt_handler:
|
|
php ; save status flags
|
|
cld ; clear decimal mode
|
|
pha ; save A ; 3
|
|
; A is saved in $45 by firmware
|
|
txa
|
|
pha ; save X
|
|
tya
|
|
pha ; save Y
|
|
|
|
; inc $0404 ; debug (flashes char onscreen)
|
|
|
|
|
|
ay3_irq_handler:
|
|
bit MOCK_6522_T1CL ; clear 6522 interrupt by reading T1C-L ; 4
|
|
|
|
; see if still counting down
|
|
lda SONG_COUNTDOWN
|
|
bpl done_update_song
|
|
|
|
try_again:
|
|
ldy SONG_OFFSET
|
|
set_notes_loop:
|
|
|
|
; see if hit end
|
|
lda (SONG_L),Y
|
|
cmp #$C0
|
|
bne all_ok
|
|
|
|
; if at end, loop
|
|
|
|
loop_forever:
|
|
; jmp loop_forever
|
|
|
|
lda #0
|
|
sta SONG_OFFSET
|
|
|
|
; lda #<peasant_song
|
|
; sta SONG_L
|
|
; lda #>peasant_song
|
|
; sta SONG_H
|
|
|
|
|
|
beq try_again ; bra
|
|
all_ok:
|
|
|
|
; see if note
|
|
|
|
tax
|
|
and #$C0
|
|
cmp #$C0
|
|
beq handle_timing
|
|
|
|
note_only:
|
|
txa
|
|
; CCOONNNN -- c=channel, o=octave, n=note
|
|
; TODO: OONNNNCC instead?
|
|
|
|
lsr
|
|
lsr
|
|
lsr
|
|
lsr
|
|
sta octave_smc+1
|
|
lsr
|
|
and #$FE
|
|
sta out_smc+1
|
|
|
|
txa
|
|
|
|
and #$3F
|
|
|
|
tax
|
|
lda frequency_lookup_low,X
|
|
sty y_smc+1
|
|
out_smc:
|
|
ldx #$00
|
|
jsr ay3_write_reg ; trashes A/Y
|
|
|
|
; set coarse note A
|
|
; hack: if octave=0 (C2) then coarse=1
|
|
; else coarse=0
|
|
|
|
inx
|
|
octave_smc:
|
|
lda #$dd
|
|
and #$3 ; if 0 then 1
|
|
; if 1,2,3 then 0
|
|
bne blah0
|
|
blah1:
|
|
lda #1
|
|
bne blah_blah
|
|
blah0:
|
|
lda #0
|
|
blah_blah:
|
|
|
|
jsr ay3_write_reg ; trashes A/Y
|
|
|
|
y_smc:
|
|
ldy #0
|
|
iny
|
|
|
|
; bne not_wrap2 ; assume less than 256 bytes
|
|
; inc SONG_H
|
|
;not_wrap2:
|
|
bne set_notes_loop ; bra
|
|
|
|
handle_timing:
|
|
; was timing
|
|
|
|
txa
|
|
|
|
and #$3f
|
|
sta SONG_COUNTDOWN
|
|
iny
|
|
sty SONG_OFFSET
|
|
bne not_wrap1
|
|
|
|
inc SONG_H
|
|
|
|
not_wrap1:
|
|
|
|
done_update_song:
|
|
dec SONG_COUNTDOWN
|
|
|
|
|
|
;=================================
|
|
; Finally done with this interrupt
|
|
;=================================
|
|
|
|
done_ay3_irq_handler:
|
|
|
|
pla
|
|
tay ; restore Y
|
|
pla
|
|
tax ; restore X
|
|
pla ; restore a ; 4
|
|
|
|
; on II+/IIe (but not IIc) we need to do this?
|
|
interrupt_smc:
|
|
lda $45 ; restore A
|
|
plp ; restore flags
|
|
|
|
rti ; return from interrupt ; 6
|
|
|
|
;============
|
|
; typical
|
|
; ???? cycles
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|