dos33fsprogs/split_screen/mockingboard.s

; ZP addresses

; 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

; 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


; 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


reset_ay_both:
	;======================
	; Reset Left AY-3-8910
	;======================
reset_ay_left:
	lda	#MOCK_AY_RESET
	sta	MOCK_6522_1_ORB
	lda	#MOCK_AY_INACTIVE
	sta	MOCK_6522_1_ORB

	; AY-3-8913: Wait 5 us
	nop
	nop
	nop
	nop
	nop

	;======================
	; Reset Right AY-3-8910
	;======================
reset_ay_right:
	lda	#MOCK_AY_RESET
	sta	MOCK_6522_2_ORB
	lda	#MOCK_AY_INACTIVE
	sta	MOCK_6522_2_ORB

	; AY-3-8913: Wait 5 us
	nop
	nop
	nop
	nop
	nop

	;=========================
	; Setup initial conditions
	;=========================


	; 7: ENABLE
	ldx	#7
	lda	#$38			; noise disabled, ABC enabled
	sta	MB_VALUE
	jsr	write_ay_both

	rts



	;=========================================
	; Write Right/Left to save value AY-3-8910
	;=========================================
	; register in X
	; value in MB_VALUE

write_ay_both:
	; address
	stx	MOCK_6522_1_ORA		; put address on PA1		; 4
	stx	MOCK_6522_2_ORA		; put address on PA2		; 4
	lda	#MOCK_AY_LATCH_ADDR	; latch_address on PB1		; 2
	sta	MOCK_6522_1_ORB		; latch_address on PB1		; 4
	sta	MOCK_6522_2_ORB		; latch_address on PB2		; 4
	lda	#MOCK_AY_INACTIVE	; go inactive			; 2
	sta	MOCK_6522_1_ORB						; 4
	sta	MOCK_6522_2_ORB						; 4
								;===========
								;        28
	; value
	lda	MB_VALUE						; 3
	sta	MOCK_6522_1_ORA		; put value on PA1		; 4
	sta	MOCK_6522_2_ORA		; put value on PA2		; 4
	lda	#MOCK_AY_WRITE		;				; 2
	sta	MOCK_6522_1_ORB		; write on PB1			; 4
	sta	MOCK_6522_2_ORB		; write on PB2			; 4
	lda	#MOCK_AY_INACTIVE	; go inactive			; 2
	sta	MOCK_6522_1_ORB						; 4
	sta	MOCK_6522_2_ORB						; 4
								;===========
								;        31

	rts								; 6
								;===========
								;       65

	;=======================================
	; 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_ADDRL:MB_ADDRH has address of Mockingboard
	; returns X=0 if not found, X=1 if found

mockingboard_detect_slot4:
	lda	#0
	sta	MB_ADDRL

mb4_detect_loop:	; self-modifying
	lda	#$04	; we're only looking in Slot 4
	ora	#$C0	; make it start with C
	sta	MB_ADDRH
	ldy	#04	; $CX04
	ldx	#02	; 2 tries?
mb4_check_cycle_loop:
	lda	(MB_ADDRL),Y		; timer 6522 (Low Order Counter)
					; count down
	sta	TEMP			; 3 cycles
	lda	(MB_ADDRL),Y		; + 5 cycles = 8 cycles
					; between the two accesses to the timer
	sec
	sbc	TEMP			; subtract to see if we had 8 cycles
	cmp	#$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