dos33fsprogs/chiptune_debug/chiptune_tiny.s
2018-06-13 12:17:10 -04:00

260 lines
5.2 KiB
ArmAsm

; VMW Minimal Mockingboard Issue Reproducer
; ZP addresses
MB_CHUNK_OFFSET = $94
MB_VALUE = $91
;=========================
; 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 $C40B ; ACR register
lda #$7F ; clear all interrupt flags
sta $C40E ; IER register (interrupt enable)
lda #$C0
sta $C40D ; IFR: 1100, enable interrupt on timer one oflow
sta $C40E ; IER: 1100, enable timer one interrupt
lda #$E7
sta $C404 ; write into low-order latch
lda #$4f
sta $C405 ; write into high-order latch,
; load both values into counter
; clear interrupt and start counting
; 4fe7 / 1e6 = .020s, 50Hz
;==================
; load first song
;==================
;============================
; Enable 6502 interrupts
;============================
cli ; clear interrupt mask
;============================
; Loop forever
;============================
main_loop:
jmp main_loop
;=========
;routines
;=========
; left speaker
MOCK_6522_ORB1 = $C400 ; 6522 #1 port b data
MOCK_6522_ORA1 = $C401 ; 6522 #1 port a data
MOCK_6522_DDRB1 = $C402 ; 6522 #1 data direction port B
MOCK_6522_DDRA1 = $C403 ; 6522 #1 data direction port A
; right speaker
MOCK_6522_ORB2 = $C480 ; 6522 #2 port b data
MOCK_6522_ORA2 = $C481 ; 6522 #2 port a data
MOCK_6522_DDRB2 = $C482 ; 6522 #2 data direction port B
MOCK_6522_DDRA2 = $C483 ; 6522 #2 data direction port A
; 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 output (1)
sta MOCK_6522_DDRB1
sta MOCK_6522_DDRA1
sta MOCK_6522_DDRB2
sta MOCK_6522_DDRA2
rts
reset_ay_both:
;======================
; Reset Left AY-3-8910
;======================
reset_ay_left:
lda #MOCK_AY_RESET
sta MOCK_6522_ORB1
lda #MOCK_AY_INACTIVE
sta MOCK_6522_ORB1
;======================
; Reset Right AY-3-8910
;======================
reset_ay_right:
lda #MOCK_AY_RESET
sta MOCK_6522_ORB2
lda #MOCK_AY_INACTIVE
sta MOCK_6522_ORB2
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:
; address
stx MOCK_6522_ORA1 ; put address on PA1 ; 3
stx MOCK_6522_ORA2 ; put address on PA2 ; 3
lda #MOCK_AY_LATCH_ADDR ; latch_address on PB1 ; 2
sta MOCK_6522_ORB1 ; latch_address on PB1 ; 3
sta MOCK_6522_ORB2 ; latch_address on PB2 ; 3
lda #MOCK_AY_INACTIVE ; go inactive ; 2
sta MOCK_6522_ORB1 ; 3
sta MOCK_6522_ORB2 ; 3
; value
lda MB_VALUE ; 3
sta MOCK_6522_ORA1 ; put value on PA1 ; 3
sta MOCK_6522_ORA2 ; put value on PA2 ; 3
lda #MOCK_AY_WRITE ; ; 2
sta MOCK_6522_ORB1 ; write on PB1 ; 3
sta MOCK_6522_ORB2 ; write on PB2 ; 3
lda #MOCK_AY_INACTIVE ; go inactive ; 2
sta MOCK_6522_ORB1 ; 3
sta MOCK_6522_ORB2 ; 3
rts ; 6
;===========
; 53
;=======================================
; clear ay -- clear all 14 AY registers
; should silence the card
;=======================================
clear_ay_both:
ldx #13
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 $C404 ; clear 6522 interrupt by reading T1C-L ; 4
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
ldx #4
; lda #$51
lda c_fine,Y
sta MB_VALUE
jsr write_ay_both
; 5: C CHANNEL COARSE
ldx #5
lda #$0 ; always 0
sta MB_VALUE
jsr write_ay_both
; 7: ENABLE
ldx #7
lda #$38 ; noise disabled, ABC enabled
sta MB_VALUE
jsr write_ay_both
; 10: C Amplitude
ldx #10
lda #$c ; always volume 12
sta MB_VALUE
jsr write_ay_both
increment_offset:
inc MB_CHUNK_OFFSET ; increment offset
lda MB_CHUNK_OFFSET
and #$f
sta MB_CHUNK_OFFSET
done_interrupt:
pla ; restore a ; 4
rti ; return from interrupt ; 6
; 4: C fine
c_fine:
.byte $51,$3c,$32,$50,$3d,$32,$50,$3c, $33,$50,$3c,$32,$51,$3c,$32,$50