dos33fsprogs/chiptune_debug/interrupt_handler.s

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;================================
;================================
; mockingboard interrupt handler
;================================
;================================
interrupt_handler:
pha ; save A ; 3
; Should we save X and Y too?
.ifdef NOIRQ
.else
bit $C404 ; clear 6522 interrupt by reading T1C-L ; 4
.endif
mb_play_music:
;======================================
; Write frames to Mockingboard
;======================================
; actually plays frame loaded at end of
; last interrupt, so 20ms behind?
mb_write_frame:
ldx #0 ; set up reg count ; 2
;============
; 2
;==================================
; loop through the 14 registers
; reading the value, then write out
;==================================
; inlined "write_ay_both" to save up to 156 (12*13) cycles
; unrolled
mb_write_loop:
lda REGISTER_DUMP,X ; load register value ; 4
cmp REGISTER_OLD,X ; compare with old values ; 4
beq mb_no_write ; 3/2nt
;=============
; typ 11
; special case R13. If it is 0xff, then don't update
; otherwise might spuriously reset the envelope settings
cpx #13 ; 2
bne mb_not_13 ; 3/2nt
cmp #$ff ; 2
beq mb_skip_13 ; 3/2nt
;============
; typ 5
mb_not_13:
; address
stx MOCK_6522_ORA1 ; put address on PA1 ; 4
stx MOCK_6522_ORA2 ; put address on PA2 ; 4
lda #MOCK_AY_LATCH_ADDR ; latch_address for PB1 ; 2
sta MOCK_6522_ORB1 ; latch_address on PB1 ; 4
sta MOCK_6522_ORB2 ; latch_address on PB2 ; 4
lda #MOCK_AY_INACTIVE ; go inactive ; 2
sta MOCK_6522_ORB1 ; 4
sta MOCK_6522_ORB2 ; 4
; value
lda REGISTER_DUMP,X ; load register value ; 4
sta MOCK_6522_ORA1 ; put value on PA1 ; 4
sta MOCK_6522_ORA2 ; put value on PA2 ; 4
lda #MOCK_AY_WRITE ; ; 2
sta MOCK_6522_ORB1 ; write on PB1 ; 4
sta MOCK_6522_ORB2 ; write on PB2 ; 4
lda #MOCK_AY_INACTIVE ; go inactive ; 2
sta MOCK_6522_ORB1 ; 4
sta MOCK_6522_ORB2 ; 4
;===========
; 62
mb_no_write:
inx ; point to next register ; 2
cpx #14 ; if 14 we're done ; 2
bmi mb_write_loop ; otherwise, loop ; 3/2nt
;============
; 7
mb_skip_13:
;=====================================
; Copy registers to old
;=====================================
ldx #13 ; 2
mb_reg_copy:
lda REGISTER_DUMP,X ; load register value ; 4
sta REGISTER_OLD,X ; compare with old values ; 4
dex ; 2
bpl mb_reg_copy ; 2nt/3
;=============
; 171
;===================================
; Load all 14 registers in advance
;===================================
; note, assuming not cross page boundary, not any slower
; then loading from zero page?
mb_load_values:
ldx #0 ; set up reg count ; 2
ldy MB_CHUNK_OFFSET ; get chunk offset ; 3
;=============
; 5
mb_load_loop:
lda (INL),y ; load register value ; 5
sta REGISTER_DUMP,X ; 4
;============
; 9
;====================
; point to next page
;====================
clc ; point to next interleaved ; 2
lda INH ; page by adding CHUNKSIZE (3/1); 3
adc CHUNKSIZE ; 3
sta INH ; 3
inx ; point to next register ; 2
cpx #14 ; if 14 we're done ; 2
bmi mb_load_loop ; otherwise, loop ; 3/2nt
;============
; 18
;==============================================
; incremement offset. If 0 move to next chunk
;==============================================
increment_offset:
inc MB_CHUNK_OFFSET ; increment offset ; 5
lda #0 ; 2
clc ; 2
adc #>UNPACK_BUFFER ; in proper chunk 1 or 2 ; 2
sta INH ; update r0 pointer ; 3
;=================================
; Finally done with this interrupt
;=================================
done_interrupt:
pla ; restore a ; 4
.ifdef NOIRQ
rts
.else
rti ; return from interrupt ; 6
.endif
REGISTER_OLD:
.byte 0,0,0,0,0,0,0,0,0,0,0,0,0,0