.mmregs
	
	.def  fir_init		;initialize FIR filter
	.def  fir_task		;perform FIR filtering
	
	
	
;FIR緩沖
		.data
_fir_size	.word 0x41
_fir_size1  .word 0x40
_fir_data_addr  .word 0
_fir_coff_addr  .word 0

		.sect "fir_coff"
;FIR系數表緩沖
fir_coff_table:   	;zx it must be placed in bit bound
		.word 00000H,0FFEDH
		.word 0FFE2H,0FFE7H,00000H,00024H,0003FH
		.word 00036H,00000H,0FFB1H,0FF79H,0FF8FH
		.word 00000H,0009EH,00105H,000D7H,00000H
		.word 0FEE0H,0FE2BH,0FE82H,00000H,001FCH
		.word 0033FH,002AAH,00000H,0FC4FH,0F9BAH
		.word 0FA8BH,00000H,0096DH,0143AH,01CCBH
		.word 0200EH,01CCBH,0143AH,0096DH,00000H
		.word 0FA8BH,0F9BAH,0FC4FH,00000H,002AAH
		.word 0033FH,001FCH,00000H,0FE82H,0FE2BH
		.word 0FEE0H,00000H,000D7H,00105H,0009EH
		.word 00000H,0FF8FH,0FF79H,0FFB1H,00000H
		.word 00036H,0003FH,00024H,00000H,0FFE7H
		.word 0FFE2H,0FFEDH,00000H

;FIR數據緩沖
d_data_buffer   .usect   "fir_bfr",256	;zx it must be placed in bit bound.Q15
	
	
	.text
;--------------------------------------
;初始化FIR濾波器
;--------------------------------------
fir_init:
			; 初始化濾波器狀態
			STM     d_data_buffer,AR4
			RPT     #255
			ST      #0,*AR4+
FIR_coff:
			; 以_fir_data_addr保存FIR數據指針
			LD      *(_fir_size1),A
			ADD     #d_data_buffer,A
			STL     A,*(_fir_data_addr)
			; 以_fir_coff_addr保存FIR系數表指針
			ST      #fir_coff_table,*(_fir_coff_addr)
			RET
		
			
;This subroutine performs FIR filtering using MAC instruction.
;accumulator A (filter output) = h(n)*x(n-i) for i = 0,1...15
;------------------------------------------
;實現FIR濾波
;輸入：以A保存輸入數據
;輸出: 以A保存輸出數據
;------------------------------------------
fir_task:
			SSBX     OVM
			SSBX     FRCT
			NOP
			NOP
			STM      #1,AR0
			LD       *(_fir_size),B
			STLM     B,BK
			;STM     #K_FIR_BFFR,BK			;FIR circular bffr value
			;LD      *INBUF_P+,A				;load the input value
			LD       *(_fir_coff_addr),B
			NOP
			STLM     B,AR2
			NOP
			NOP
			LD       *(_fir_data_addr),B
			NOP
			STLM     B,AR3
			NOP
			NOP
			
fir_filter:
			STL      A,*AR3+%			;replace oldest sample with newest sample
			LD       #0,A
			NOP
			NOP
			RPT      *(_fir_size1)
			MAC      *AR2+0%,*AR3+0%,A  ;filtering
			NOP
			NOP
			LDM      AR2,B
			NOP
			STL      B,*(_fir_coff_addr)
			LDM      AR3,B
			NOP
			STL      B,*(_fir_data_addr)				
fir_filter_loop
			RET
		.end