dos33fsprogs/games/monkey/mockingboard.s

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2020-09-17 05:12:40 +00:00
; Mockingboad programming:
; + Has two 6522 I/O chips connected to two AY-3-8910 chips
; + Optionally has some speech chips controlled via the outport on the AY
; + Often in slot 4
; TODO: how to auto-detect?
; References used:
; http://macgui.com/usenet/?group=2&id=8366
; 6522 Data Sheet
; AY-3-8910 Data Sheet
;========================
; Mockingboard card
; Essentially two 6522s hooked to the Apple II bus
; Connected to AY-3-8910 chips
; PA0-PA7 on 6522 connected to DA0-DA7 on AY
; PB0 on 6522 connected to BC1
; PB1 on 6522 connected to BDIR
; PB2 on 6522 connected to RESET
; 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 Left AY-3-8910
;======================
reset_ay_both:
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 #14
lda #0
sta MB_VALUE
clear_ay_left_loop:
jsr write_ay_both
dex
bpl clear_ay_left_loop
rts
;=======================================
; Detect a Mockingboard card in Slot4
;=======================================
; Based on code from the French Touch "Pure Noise" Demo
; Attempts to time an instruction sequence with a 6522
;
; MB_ADDR_L:MB_ADDR_H has address of Mockingboard
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; returns X=0 if not found, X=1 if found
mockingboard_detect_slot4:
lda #0
sta MB_ADDR_L
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mb4_detect_loop: ; self-modifying
lda #$04 ; we're only looking in Slot 4
ora #$C0 ; make it start with C
sta MB_ADDR_H
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ldy #04 ; $CX04
ldx #02 ; 2 tries?
mb4_check_cycle_loop:
lda (MB_ADDR_L),Y ; timer 6522 (Low Order Counter)
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; count down
sta TEMP ; 3 cycles
lda (MB_ADDR_L),Y ; + 5 cycles = 8 cycles
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; between the two accesses to the timer
sec
sbc TEMP ; subtract to see if we had 8 cycles
cmp #$f8 ; -8
bne mb4_not_in_this_slot
dex ; decrement, try one more time
bne mb4_check_cycle_loop ; loop detection
inx ; Mockingboard found (X=1)
done_mb4_detect:
rts ; return
mb4_not_in_this_slot:
ldx #00
beq done_mb4_detect