实验7.1 FIR
;=============================================================
; fir4.asm
;用用循环缓冲区和双操作数寻址方法实现FIR滤波器
;先用matlab,选择80点汉明窗设计一个截止频率为0.2π的低通滤波器
; 本例与前不同的是系数直接引用程序存储器的系数表
;N=5 y(n)=h0*x(n)+h1*x(n-1)+h2*x(n-2)+h3*x(n-3)+h4*x(n-4)
;=============================================================
.title "fir4.asm"
.mmregs
.def start
;分配数据存储区
.bss y,1 ;y
xn .usect "xn",80 ;xn
h .usect "h",80 ;h
PA0 .set 0000H ;数据输出端口
PA1 .set 0001H ;数据输入端口
;参数表
.data
table: .word -7,-18,-24,-22,-9,11,33,48
;已在Matlab中转成十六进制的小数
.word 46,20,-24,-73,-104,-97,-43,49
.word 146,204,187,81,-91,-268,-371,-337
.word -144,162,476,661,603,261,-297,-894
.word -1283,-1222,-562,697,2373,4142,5618,6456
.word 6456,5618,4142,2373,697,-562,-1222,-1283
.word -894,-297,261,603,661,476,162,-144
.word -337,-371,-268,-91,81,187,204,146
.word 49,-43,-97,-104,-73,-24,20,46
.word 48,33,11,-9,-22,-24,-18,-7

start: SSBX FRCT ;小数乘法
;把参数表复制到数据存储区
STM #h,AR1
RPT #79
MVPD #table,*AR1+
;把x(n)-x(n-79)赋始值0
STM #xn,AR1
RPT #79
ST #0,*AR1+

STM #xn+79,AR3 ;x(n-79)---AR3
STM #h+79,AR4 ;h(n-79)---AR4
STM #80,BK ;循环缓冲区大小80
STM #-1,AR0 ;指针调整值-1
LD #xn,DP ;DP指向xn所在页
PORTR PA1,@xn ;输入数据
LD #y,DP ;DP指向y所在页
FIR: RPTZ A,#79 ;进行一次FIR运算
MAC *AR3+0%,*AR4+0%,A;A=(AR3)*(AR4)+A,
AR3=AR3+AR0,AR4=AR4+AR0
STH A,@y ;保存计算结果
PORTW @y,PA0 ;输出结果
BD FIR ;读入下一个数据并进行下一次计算
PORTR PA1,*AR3+0% ;新数据覆盖了最旧的数据