.title	"IIR3.asm"
	.mmregs
	.def	start
X	.usect	"X",3
Y	.usect	"y",3
B	.usect	"B",3
A	.usect	"A",3
PA0	.set	0
PA1	.set	1
	.data
table:	.word	0		;x(n-2)
	.word	0		;x(n-1)
	.word	0		;y(n-2)
	.word	0		;y(n-1)
	.word	1*32768/10	;B2
	.word	2*32768/10	;B1
	.word	3*32768/10	;B0
	.word	5*32768/10	;A2
	.word	-4*32768/10	;A1
	.text
start:	SSBX	FRCT
	STM	#X,AR1		;傳送初始數據x(n-2),x(n-1)
	RPT	#1
	MVPD	#table,*AR1+
	
	STM	#Y,AR1		;傳送初始數據y(n-2),y(n-1)
	RPT	#1
	MVPD	#table+2,*AR1+
	
	STM	#B,AR1		;傳送系數B2,B1,B0
	RPT	#2
	MVPD	#table+4,*AR1+
	
	STM	#A,AR1		;傳送系數A2,A1
	RPT	#1
	MVPD	#table+7,*AR1+
	
	STM	#X+2,AR2	;輔助寄存器指針初始化
	STM	#A+1,AR3
	STM	#Y+1,AR4
	STM	#B+2,AR5
	STM	#3,BK		;(BK)=3
	STM	#-1,AR0		;(AR0)=-1
IIR:	PORTR	PA1,*AR2	;輸入x(n)
	MPY	*AR2+0%,*AR5+0%,A	;計算前向通道
	MAC	*AR2+0%,*AR5+0%,A
	MAC	*AR2,*AR5+0%,A
	MAC	*AR4+0%,*AR3+0%,A	;計算反饋通道
	MAC	*AR4+0%,*AR3+0%,A
	MAR	*AR3+0%
	STH	A,*AR4			;保存y(n)
	BD	IIR
	PORTW	*AR4,PA0		;輸出y(n)
	.end