dos33fsprogs/music/chiptune_debug/chiptune_tiny.s

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; VMW Minimal Mockingboard Issue Reproducer
; ZP addresses
MB_CHUNK_OFFSET = $94
MB_VALUE = $91
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; left channel
MOCK_6522_1_ORB = $C400 ; 6522 #1 port b data
MOCK_6522_1_ORA = $C401 ; 6522 #1 port a data
MOCK_6522_1_DDRB = $C402 ; 6522 #1 data direction port B
MOCK_6522_1_DDRA = $C403 ; 6522 #1 data direction port A
MOCK_6522_1_T1C_L = $C404 ; 6522 #1 Low-order counter
MOCK_6522_1_T1C_H = $C405 ; 6522 #1 High-order counter
MOCK_6522_1_T1L_L = $C406 ; 6522 #1 Low-order latch
MOCK_6522_1_T1L_H = $C407 ; 6522 #1 High-order latch
MOCK_6522_1_T2C_L = $C408 ; 6522 #1 Timer2 Low-order Latch/Counter
MOCK_6522_1_T2C_H = $C409 ; 6522 #1 Timer2 High-order Latch/Counter
MOCK_6522_1_SR = $C40A ; 6522 #1 Shift Register
MOCK_6522_1_ACR = $C40B ; 6522 #1 Auxiliary Control Register
MOCK_6522_1_PCR = $C40C ; 6522 #1 Peripheral Control Register
MOCK_6522_1_IFR = $C40D ; 6522 #1 Interrupt Flag Register
MOCK_6522_1_IER = $C40E ; 6522 #1 Interrupt Enable Register
MOCK_6522_1_ORAN = $C40F ; 6522 #1 port a data, no handshake
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; right channel
MOCK_6522_2_ORB = $C480 ; 6522 #2 port b data
MOCK_6522_2_ORA = $C481 ; 6522 #2 port a data
MOCK_6522_2_DDRB = $C482 ; 6522 #2 data direction port B
MOCK_6522_2_DDRA = $C483 ; 6522 #2 data direction port A
MOCK_6522_2_T1C_L = $C484 ; 6522 #2 Low-order counter
MOCK_6522_2_T1C_H = $C485 ; 6522 #2 High-order counter
MOCK_6522_2_T1L_L = $C486 ; 6522 #2 Low-order latch
MOCK_6522_2_T1L_H = $C487 ; 6522 #2 High-order latch
MOCK_6522_2_T2C_L = $C488 ; 6522 #2 Timer2 Low-order Latch/Counter
MOCK_6522_2_T2C_H = $C489 ; 6522 #2 Timer2 High-order Latch/Counter
MOCK_6522_2_SR = $C48A ; 6522 #2 Shift Register
MOCK_6522_2_ACR = $C48B ; 6522 #2 Auxiliary Control Register
MOCK_6522_2_PCR = $C48C ; 6522 #2 Peripheral Control Register
MOCK_6522_2_IFR = $C48D ; 6522 #2 Interrupt Flag Register
MOCK_6522_2_IER = $C48E ; 6522 #2 Interrupt Enable Register
MOCK_6522_2_ORAN = $C48F ; 6522 #2 port a data, no handshake
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;=========================
; Init Variables
;=========================
lda #$0
sta MB_CHUNK_OFFSET
;============================
; Init the Mockingboard
;============================
jsr mockingboard_init
jsr reset_ay_both
jsr clear_ay_both
;=========================
; Setup Interrupt Handler
;=========================
; Vector address goes to 0x3fe/0x3ff
lda #<interrupt_handler
sta $03fe
lda #>interrupt_handler
sta $03ff
;============================
; Enable 50Hz clock on 6522
;============================
sei ; disable interrupts just in case
lda #$40 ; Continuous interrupts, don't touch PB7
sta MOCK_6522_1_ACR ; ACR register
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lda #$7F ; clear all interrupt flags
sta MOCK_6522_1_IER ; IER register (interrupt enable)
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lda #$C0
sta MOCK_6522_1_IFR ; IFR: 1100 0000
; clear timer interrupt in flag register
; should we try to clear all?
sta MOCK_6522_1_IER ; IER: 1100 0000, enable timer1 interrupt
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lda #$E7
sta MOCK_6522_1_T1C_L ; write into low-order latch
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lda #$4f
sta MOCK_6522_1_T1C_H ; write into high-order latch,
; load both values into counter
; clear interrupt and start counting
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; 4fe7 / 1e6 = .020s, 50Hz
;=========================
; Setup initial conditions
;=========================
; 5: C CHANNEL COARSE
; ldx #5
; lda #$0 ; always 0
; sta MB_VALUE
; jsr write_ay_both
; 7: ENABLE
ldx #7
lda #$38 ; noise disabled, ABC enabled
sta MB_VALUE
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jsr write_ay_address_right
; 10: C Amplitude
ldx #10
lda #$c ; always volume 12
sta MB_VALUE
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jsr write_ay_address_right
; 4: C CHANNEL FINE
ldx #4
lda #$51
sta MB_VALUE
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jsr write_ay_address_right
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;============================
; Enable 6502 interrupts
;============================
cli ; clear interrupt mask
;============================
; Loop forever
;============================
main_loop:
jmp main_loop
;=========
;routines
;=========
; AY-3-8910 commands on port B
; RESET BDIR BC1
MOCK_AY_RESET = $0 ; 0 0 0
MOCK_AY_INACTIVE = $4 ; 1 0 0
MOCK_AY_READ = $5 ; 1 0 1
MOCK_AY_WRITE = $6 ; 1 1 0
MOCK_AY_LATCH_ADDR = $7 ; 1 1 1
;========================
; Mockingboard Init
;========================
; Initialize the 6522s
; set the data direction for all pins of PortA/PortB to be output
mockingboard_init:
lda #$ff ; all 8 pins output (1), portA
sta MOCK_6522_1_DDRA
sta MOCK_6522_2_DDRA
; only 3 pins output (1), port B
lda #$7
sta MOCK_6522_1_DDRB
sta MOCK_6522_2_DDRB
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rts
reset_ay_both:
;======================
; Reset Left AY-3-8910
;======================
reset_ay_left:
lda #MOCK_AY_RESET
sta MOCK_6522_1_ORB
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lda #MOCK_AY_INACTIVE
sta MOCK_6522_1_ORB
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;======================
; Reset Right AY-3-8910
;======================
reset_ay_right:
lda #MOCK_AY_RESET
sta MOCK_6522_2_ORB
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lda #MOCK_AY_INACTIVE
sta MOCK_6522_2_ORB
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rts
; Write sequence
; Inactive -> Latch Address -> Inactive -> Write Data -> Inactive
;=========================================
; Write Right/Left to save value AY-3-8910
;=========================================
; register in X
; value in MB_VALUE
write_ay_both:
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write_ay_address_left:
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; address
stx MOCK_6522_1_ORA ; put address on PA1 ; 3
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; on AY-3-8913 hold 300ns
nop
lda #MOCK_AY_LATCH_ADDR ; latch_address on PB1 ; 2
sta MOCK_6522_1_ORB ; latch_address on PB1 ; 3
nop
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lda #MOCK_AY_INACTIVE ; go inactive ; 2
sta MOCK_6522_1_ORB ; 3
; on AY-3-8913 hold at least 50ns
nop
write_ay_value_left:
lda MB_VALUE ; 3
sta MOCK_6522_1_ORA ; put value on PA1 ; 3
; AY-3-8913 must hold 50ns
nop
lda #MOCK_AY_WRITE ; ; 2
sta MOCK_6522_1_ORB ; write on PB1 ; 3
; AY-3-8913 must hold 1800ns
nop
nop
nop
nop
nop
lda #MOCK_AY_INACTIVE ; go inactive ; 2
sta MOCK_6522_1_ORB ; 3
; AY-3-8913 must hold 100ns
nop
write_ay_address_right:
; address
stx MOCK_6522_2_ORA ; put address on PA2 ; 3
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; on AY-3-8913 hold 300ns
nop
lda #MOCK_AY_LATCH_ADDR ; latch_address on PB2 ; 2
sta MOCK_6522_2_ORB ; latch_address on PB2 ; 3
nop
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lda #MOCK_AY_INACTIVE ; go inactive ; 2
sta MOCK_6522_2_ORB ; 3
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; on AY-3-8913 hold at least 50ns
nop
write_ay_value_right:
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lda MB_VALUE ; 3
sta MOCK_6522_2_ORA ; put value on PA2 ; 3
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; AY-3-8913 must hold 50ns
nop
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lda #MOCK_AY_WRITE ; ; 2
sta MOCK_6522_2_ORB ; write on PB2 ; 3
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; AY-3-8913 must hold 1800ns
nop
nop
nop
nop
nop
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lda #MOCK_AY_INACTIVE ; go inactive ; 2
sta MOCK_6522_2_ORB ; 3
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; AY-3-8913 must hold 100ns
nop
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rts ; 6
;===========
; 53
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;=======================================
; clear ay -- clear all 14 AY registers
; should silence the card
;=======================================
clear_ay_both:
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ldx #13
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lda #0
sta MB_VALUE
clear_ay_left_loop:
jsr write_ay_both
dex
bpl clear_ay_left_loop
rts
;================================
;================================
; mockingboard interrupt handler
;================================
;================================
interrupt_handler:
pha ; save A ; 3
; Should we save X and Y too?
bit MOCK_6522_1_T1C_L ; clear 6522 interrupt by
; reading T1C-L ; 4
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mb_play_music:
;======================================
; Write frames to Mockingboard
;======================================
; actually plays frame loaded at end of
; last interrupt, so 20ms behind?
mb_write_frame:
ldy MB_CHUNK_OFFSET
; 4: C CHANNEL FINE
lda c_fine,Y
sta MB_VALUE
ldx #4
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jsr write_ay_value_right
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increment_offset:
inc MB_CHUNK_OFFSET ; increment offset
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lda MB_CHUNK_OFFSET
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and #$1 ; reduce number played
; $f = 16
; $3 = 4
; $1 = 2
; $0 = 1
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sta MB_CHUNK_OFFSET
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done_interrupt:
pla ; restore a ; 4
rti ; return from interrupt ; 6
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; 4: C fine frequency
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c_fine:
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.byte $51,$3c,$32,$50, $3d,$32,$50,$3c, $33,$50,$3c,$32,$51,$3c,$32,$50
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