; TMS320C54x assembly language code
; FIR filter with symmetric filter coefficients
; An even number of filter coefficients is assumed
; Addresses:  a6 input buffer, a7 output buffer
;   a4 array with x[n-4], x[n-3], x[n-2], x[n-1] for N = 8
;   a5 array with x[n-5], x[n-6], x[n-7], x[n-8] for N = 8
; Modulo addressing prevents need to reinitialize regs each sample
; Example taken from the C54x Applications Guide, pages 4-7 and 4-8.
firtask:
	ld	#firDP,dp		; initialize data page pointer
	stm	#frameSize-1,brc	; compute 256 outputs
	rptbd	firloop-1
	stm	#N/2,bk			; FIR circular buffer size
	ld	*ar6+,b			; load input value to accumulator b
	mvdd	*ar4,*a5+0%		; move old x[n-N/2] to new x[n-N/2-1]
	stl	b,*ar4%			; replace oldest sample with newest
	add	*a4+0%,*a5+0%,a		; a = x[n] + x[n-N/2-1]
	rptz	b,#(N/2-1)		; zero accumulator b, do N/2-1 taps
	firs	*ar4+0%,*ar5+0%,coeffs	; b += a * h[i], do next a
	mar	*+a4(2)%		; to load the next newest sample
	mar	*ar5+%			; position for x[n-N/2] sample 
	sth	b,*ar7+
firloop:	ret