dos33fsprogs/music/chiptune_player/interrupt_handler.s

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;================================
;================================
; 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
TIME_OFFSET EQU 13
interrupt_handler:
; pha ; save A ; 3
; A is saved in $45 by firmware
txa
pha ; save X
tya
pha ; save Y
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; inc $0404 ; debug (flashes char onscreen)
bit $C404 ; clear 6522 interrupt by reading T1C-L ; 4
lda DONE_PLAYING ; 3
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beq mb_play_music ; if song done, don't play music ; 3/2nt
jmp check_keyboard ; 3
;============
; 13
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mb_play_music:
;======================================
; Write frames to Mockingboard
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;======================================
; actually plays frame loaded at end of
; last interrupt, so 20ms behind?
mb_write_frame:
ldx #0 ; set up reg count ; 2
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;============
; 2
;==================================
; loop through the 14 registers
; reading the value, then write out
;==================================
; inlined "write_ay_both" to save up to 156 (12*13) cycles
; unrolled
mb_write_loop:
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lda REGISTER_DUMP,X ; load register value ; 4
cmp REGISTER_OLD,X ; compare with old values ; 4
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beq mb_no_write ; 3/2nt
;=============
; typ 11
; special case R13. If it is 0xff, then don't update
; otherwise might spuriously reset the envelope settings
cpx #13 ; 2
bne mb_not_13 ; 3/2nt
cmp #$ff ; 2
beq mb_skip_13 ; 3/2nt
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;============
; 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
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ldy #MOCK_AY_INACTIVE ; go inactive ; 2
sty MOCK_6522_ORB1 ; 4
sty 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
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sty MOCK_6522_ORB1 ; 4
sta MOCK_6522_ORB2 ; write on PB2 ; 4
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sty MOCK_6522_ORB2 ; 4
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;===========
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; 60
mb_no_write:
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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:
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;=====================================
; 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
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;===================================
; 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
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ldy MB_CHUNK_OFFSET ; get chunk offset ; 3
;=============
; 5
mb_load_loop:
lda (INL),y ; load register value ; 5
sta REGISTER_DUMP,X ; 4
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;============
; 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
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bmi mb_load_loop ; otherwise, loop ; 3/2nt
;============
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; 18
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;=========================================
; if A_COARSE_TONE is $ff then we are done
lda A_COARSE_TONE ; 3
bpl mb_not_done ; 3/2nt
lda #1 ; set done playing ; 2
jmp quiet_exit ; 3
;===========
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; typ 6
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mb_not_done:
;==============================================
; incremement offset. If 0 move to next chunk
;==============================================
increment_offset:
inc MB_CHUNK_OFFSET ; increment offset ; 5
bne back_to_first_reg ; if not zero, done ; 3/2nt
;=====================
; move to next state
;=====================
clc
rol DECODER_STATE ; next state ; 5
; 20 -> 40 -> 80 -> c+00
bcs wraparound_to_a ; 3/2nt
bit DECODER_STATE ;bit7->N bit6->V
bvs back_to_first_reg ; do nothing on B ; 3/2nt
start_c:
lda #1
sta CHUNKSIZE
; setup next three chunks of song
lda #1 ; start decompressing
sta DECOMPRESS_TIME ; outside of handler
jmp back_to_first_reg
wraparound_to_a:
lda #$3
sta CHUNKSIZE
lda #$20
sta DECODER_STATE
sta COPY_TIME ; start copying
lda DECOMPRESS_TIME
beq blah
lda #1
sta DECODE_ERROR
blah:
;==============================
; After 14th reg, reset back to
; read R0 data
;==============================
back_to_first_reg:
lda #0 ; 2
bit DECODER_STATE ; 3
bmi back_to_first_reg_c ; 2nt/3
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bvc back_to_first_reg_a ; 2nt/3
back_to_first_reg_b:
lda #$1 ; offset by 1
back_to_first_reg_a:
clc ; 2
adc #>UNPACK_BUFFER ; in proper chunk 1 or 2 ; 2
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jmp update_r0_pointer ; 3
back_to_first_reg_c:
lda #>(UNPACK_BUFFER+$2A00) ; in linear C area ; 2
update_r0_pointer:
sta INH ; update r0 pointer ; 3
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;=================================
; Finally done with this interrupt
;=================================
done_interrupt:
;=====================
; Update time counter
;=====================
update_time:
inc FRAME_COUNT ; 5
lda FRAME_COUNT ; 3
cmp #50 ; 3
bne done_time ; 3/2nt
lda #$0 ; 2
sta FRAME_COUNT ; 3
update_second_ones:
inc $7d0+TIME_OFFSET+3 ; 6
inc $bd0+TIME_OFFSET+3 ; 6
lda $bd0+TIME_OFFSET+3 ; 4
cmp #$ba ; one past '9' ; 2
bne done_time ; 3/2nt
lda #'0'+$80 ; 2
sta $7d0+TIME_OFFSET+3 ; 4
sta $bd0+TIME_OFFSET+3 ; 4
update_second_tens:
inc $7d0+TIME_OFFSET+2 ; 6
inc $bd0+TIME_OFFSET+2 ; 6
lda $bd0+TIME_OFFSET+2 ; 4
cmp #$b6 ; 6 (for 60 seconds) ; 2
bne done_time ; 3/2nt
lda #'0'+$80 ; 2
sta $7d0+TIME_OFFSET+2 ; 4
sta $bd0+TIME_OFFSET+2 ; 4
update_minutes:
inc $7d0+TIME_OFFSET ; 6
inc $bd0+TIME_OFFSET ; 6
; we don't handle > 9:59 songs yet
done_time:
;=============
; 90 worst
;=================================
; Moved visualization here as a hack
;=================================
;============================
; Visualization
;============================
jsr clear_top
lda RASTERBARS_ON
beq skip_rasters
jsr draw_rasters
skip_rasters:
jsr volume_bars
jsr page_flip
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check_keyboard:
jsr get_key
lda LASTKEY
beq exit_interrupt
cmp #(' '+$80)
bne key_R
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key_space:
lda #$80
eor DONE_PLAYING
jmp quiet_exit
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key_R:
cmp #'R'
bne key_left
lda #$ff
eor RASTERBARS_ON
sta RASTERBARS_ON
jmp done_key
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key_left:
cmp #'A'
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bne key_right
lda #$40
bne quiet_exit
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key_right:
cmp #'D'
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bne done_key
lda #$20
bne quiet_exit
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done_key:
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jmp exit_interrupt
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quiet_exit:
sta DONE_PLAYING
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jsr clear_ay_both
;=====================================
; clear register area
;=====================================
ldx #13 ; 2
lda #0 ; 2
mb_clear_reg:
sta REGISTER_DUMP,X ; clear register value ; 4
sta REGISTER_OLD,X ; clear old values ; 4
dex ; 2
bpl mb_clear_reg ; 2nt/3
exit_interrupt:
; pla ; restore a ; 4
pla
tay ; restore Y
pla
tax ; restore X
lda $45 ; restore A
rti ; return from interrupt ; 6
;============
; typical
; ???? cycles
REGISTER_OLD:
.byte 0,0,0,0,0,0,0,0,0,0,0,0,0,0