;***************************************************************
;
;	Stereo Flange for the DSP56001 processor
;	Developed by Quinn Jensen (jensenq@npd.novell.com)
;
;***************************************************************
include 'tdsg.basic.a56'

dot
	org	x:$20

; Sample rate              32.5500 kc         
; 
; Delay time (1-12)         6.0000 ms         
; Depth (1-10)             10.0000
; Speed (1-10)              1.0000
; Regen (1-10)              9.0000
; 
; max depth +/-             6.0000 ms         
; min delay                 1.0000 ms         
; max delay                12.0000 ms         
; 1/2 cycle period          4.5100 s          
; samples per 1/2 cyc  146800.5000
; time delta/samp           0.0817 us         
; offset samp/samp          0.0027
; 
  doff_i equ                               -33
  ddeltaf equ                     0.0026607539
  dspeed_i equ                          146800
  dregen equ                      0.8888888889

delay	equ	$2000
dmax	equ	4096		;125 ms
doff	dc	doff_i    	;current delay distance
	org	y:doff
	dc	0

	org	x:doff+1
ddelta	dc	0		;
	org	y:ddelta
	dc	ddeltaf

	org	x:ddelta+1

dspeed	dc	dspeed_i
dtoggle	dc	0		;
delayout
	dc	0

	org	y:$0

	org	p:dot		;go back to P-space
;
; non-interrupt code
;

hf_init
	move	#delay,r1			;delay line input
 	movec	#dmax-1,m1			;
	move	#doff_i,n1			;distance to output
	rts

;
; fs = 32.552083 kHz
;

hf_comp
	jsr	<saveregs
;
;	output and input mix
;
	clr	a	#.4375,x1		;clr a, get input scale
	clr	b	#.5,y1			;clr b, get output scaler

	move		x:<delayout,y0		;get delay out

	move		#.70,x0			;do regen term
	macr	x0,y0,a
	macr	x0,y0,a

	move		#.75,x0

	macr	y0,x0,b	x:<in_l,x0		;b = .5 * delay, x0=in_l
	macr	x0,y1,b		b,y0       	;b += .5 * in_l, y0=b
	macr	x0,x1,a b,x:<out_l		;a += x1 * in_l, L = b
	move			y0,b		;b = -y0
	neg	b	x:<in_r,x0		;x0 = in_r
	macr	x0,y1,b				;b += .5 * in_r
	macr	x0,x1,a	b,x:<out_r		;R = b, a += x1 * in_r
;
;	delay line in
;
	move		a,x:(r1)+
;
;	delay line length modulation
;
	move		l:<doff,a		;a = current offset
	move		l:<ddelta,x		;x = current delta
	add	x,a
	move		a,l:<doff		;new offset = a + x
	move		a1,n1

	move		x1,b			;save delta for later use

; smoothly transition between delay-line offsets by
; interpolating the current sample with the previous or next
; one depending on whether the delay is currently getting longer or
; shorter.  Otherwise, an obnoxious click results when the offset snaps
; to the next integral value.

	move			y:<doff,a	;compute |frac(doff)|
	lsr	a	#$800000,x0
	or	x0,a	#.5,x1
	move		a1,x0
	mpy	-x0,x1,a
	tst	b		a,y0		;y0 = 0.5 * |frac(doff)|
	jpl	shorter				;on positive delta, the
						;delay is shortening

	move		(r1)-			;get previous sample
	move		x:(r1+n1),x0
	mpy	y0,x0,a	#.5,b			;scale
	sub	y0,b	(r1)+			;compute scale for cur sample
	move			b,y0
	move		x:(r1+n1),x0		;get cur sample
	mac	x0,y0,a				;scale and sum
	jmp	endpan

shorter
	move		x:(r1+n1),x0		;get cur sample
	mpy	y0,x0,a	#.5,b			;scale
	sub	y0,b	(r1)+			;compute scale for next sample
	move			b,y0
	move		x:(r1+n1),x0		;get next sample
	mac	x0,y0,a	(r1)-			;scale and sum
endpan
	move		a,x:<delayout		;store resulting output

; update the triangle wave modulation

	move		x:<dtoggle,a		;decrement toggle count
	move		#>1,x0
	sub	x0,a
	move		a,x:<dtoggle
	jgt	notogg				;time to toggle?
	move		x:<dspeed,x0		;yes, negate delta and reset
	move		l:<ddelta,a
	neg	a	x0,x:<dtoggle
	move		a,l:<ddelta
notogg
bypass
	jsr	<restregs
	rts

	end