dos33fsprogs/pt3_lib/pt3_lib_irq_handler.s

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pt3_irq_handler:
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pt3_irq_smc1:
bit MOCK_6522_T1CL ; clear 6522 interrupt by reading T1C-L ; 4
lda DONE_PLAYING ; 3
beq pt3_play_music ; if song done, don't play music ; 3/2nt
jmp done_pt3_irq_handler ; 3
;============
; 13
pt3_play_music:
; decode a frame of music
jsr pt3_make_frame
; handle song over condition
lda DONE_SONG
beq mb_write_frame ; if not done, continue
lda LOOP ; see if looping
beq move_to_next
pt3_loop_smc:
lda #$d1 ; looping, move to loop location
; non-zero to avoid the temptation
; to merge with following lda #$0
sta current_pattern_smc+1
lda #$0
sta current_line_smc+1
sta current_subframe_smc+1
sta DONE_SONG ; undo the next song
beq done_pt3_irq_handler ; branch always
move_to_next:
; same as "press right"
ldx #$20
jmp quiet_exit
;======================================
; Write frames to Mockingboard
;======================================
; for speed could merge this into
; the decode code
mb_write_frame:
tax ; set up reg count ; 2
;============
; 2
;==================================
; loop through the 14 registers
; reading the value, then write out
;==================================
mb_write_loop:
lda AY_REGISTERS,X ; load register value ; 4
; special case R13. If it is 0xff, then don't update
; otherwise might spuriously reset the envelope settings
cpx #13 ; 2
bne mb_not_13 ; 3/2nt
cmp #$ff ; 2
beq mb_skip_13 ; 3/2nt
;============
; typ 5
mb_not_13:
; address
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pt3_irq_smc2:
stx MOCK_6522_ORA1 ; put address on PA1 ; 4
stx MOCK_6522_ORA2 ; put address on PA2 ; 4
ldy #MOCK_AY_LATCH_ADDR ; latch_address for PB1 ; 2
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pt3_irq_smc3:
sty MOCK_6522_ORB1 ; latch_address on PB1 ; 4
sty MOCK_6522_ORB2 ; latch_address on PB2 ; 4
ldy #MOCK_AY_INACTIVE ; go inactive ; 2
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pt3_irq_smc4:
sty MOCK_6522_ORB1 ; 4
sty MOCK_6522_ORB2 ; 4
; value
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pt3_irq_smc5:
sta MOCK_6522_ORA1 ; put value on PA1 ; 4
sta MOCK_6522_ORA2 ; put value on PA2 ; 4
lda #MOCK_AY_WRITE ; ; 2
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pt3_irq_smc6:
sta MOCK_6522_ORB1 ; write on PB1 ; 4
sty MOCK_6522_ORB1 ; 4
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pt3_irq_smc7:
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sta MOCK_6522_ORB2 ; write on PB2 ; 4
sty MOCK_6522_ORB2 ; 4
;===========
; 56
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:
;=================================
; Finally done with this interrupt
;=================================
done_pt3_irq_handler: