; Various tests for output filter and DAC.  I used a Nippon Precision Circuits
; SM5813AP dual-channel 8-times oversampling digital filter into a Burr Brown
; PCM1700P dual-channel 18-bit DAC.  The code is very specific to my hardware.
;
; available signals:
;	impulse
;	square
;	triangle
;	sine		(uses twin-integrator harmonic oscillator)
;
; This code is not interrupt driven but simple spins waiting for transmitter
; ready on each sample.
;
;
; written by Quinn Jensen
; home: jensenq@qcj.icon.com
;
include	"ioequ.inc"

	org	p:$0000
	jmp	<start

	org	p:$000C
;ssi	jsr	ssi_int				;go handle SSI interrupt

; data areas

	org	x:$0
i_left	dc	0				;left channel in
i_right	dc	0				;right channel in

	org	p:$40
start

; assign mode

	movec	#$0300,sr			;go to IPL 3

; set up interrupts

;       movep	#0<<13|3<<12|0<<10,x:m_ipr	;put SSI at lev 3, others off

; set system sample rate

	bclr	#6,x:<<m_pbd			;32.55 kHz
	bset	#5,x:<<m_pbd			;
	bclr	#4,x:<<m_pbd			;

; set up SSI

	movep	#2<<13|1<<8,x:m_cra		;16-bit word, 2 time slots
	movep	#0<<15|3<<12|1<<11|1<<9,x:m_crb	;sync,network,enable

	movep	#0,x:m_pcddr			;port C is SSI/SCI
	movep	#$1FF,x:m_pcc			;port C is SSI/SCI

; enable interrupts

;       movec	#0,sr				;lower IPL

	jmp	<impulse			;jump to the desired signal

; impulse

impulse
	move	#>-.5,a

im1
	do	#400,im0
	jsr	<imp
im0     
	neg	a
	jsr	<imp
	neg	a
	jmp	<im1

imp
	jclr	#6,x:m_sr,*			;wait for transmitter ready
	movep	a,x:m_tx
	jclr	#6,x:m_sr,*			;wait for transmitter ready
	movep	a,x:m_tx
	rts

; square wave

square
	move	#>-.1,a

sq1
	do	#200,sq0
	jclr	#6,x:m_sr,*			;wait for transmitter ready
	movep	a,x:m_tx
	jclr	#6,x:m_sr,*			;wait for transmitter ready
	movep	a,x:m_tx
sq0     
	neg	a
	jmp	<sq1


; triangle wave

triangle
	move	#>.010,x0
	move	#>-.9,a

l0      
	do	#90*2,l1
	add	x0,a
	jclr	#6,x:m_sr,*			;wait for transmitter ready
	movep	a,x:m_tx
	jclr	#6,x:m_sr,*			;wait for transmitter ready
	movep	a,x:m_tx
l1
	move	x0,b
	neg	b
	move	b,x0
	jmp	<l0


; sine wave

sine
	move	#>.050,x0			;oscillator freq
	move	#>-.209,a			;initial conditions
	move	#>.2090,b			;

loop
	mac	x0,y0,a
	move	a,y0
	jclr	#6,x:m_sr,*			;wait for transmitter ready
	movep	a,x:m_tx		
	mac	-x0,y0,b
	move	b,y0
	jclr	#6,x:m_sr,*			;wait for transmitter ready
	movep	b,x:m_tx		

	jmp	<loop

	end