s6_iir.sa

dsp6713开发板的许多例程.对入门特别有用

***********************************************************************
*         Copyright (C) 1996-2001 Texas Instruments Incorporated
*                      All Rights Reserved
*         IIR6 ASSEMBLY OPTIMIZER SOURCE - Example 6-45
*         From Programmer's Guide
***********************************************************************
********* ASSEMBLY OPTIMIZER CODE: *******************

        .def _iir_sa

_iir_sa: .cproc  x, y, c1, c2, c3

        .reg    xi, xi1, yi1
        .reg	p0, p1, p2, s0, s1, cntr
        .no_mdep
 
        MVK     100,cntr        ; cntr = 100
        LDH	.D2	*y++,yi1        ; yi+1

LOOP:   .trip 100
        LDH	.D1	  *x++,xi       ; xi
        MPY	.M1	  c1,xi,p0      ; c1 * xi
        LDH	.D1	  *x,xi1        ; xi+1
        MPY	.M1X  c2,xi1,p1     ; c2 * xi+1
        ADD	.L1	  p0,p1,s0      ; c1 * xi + c2 * xi+1
        MPY	.M2X  c3,yi1,p2     ; c3 * yi
        ADD	.L2X  s0,p2,s1      ; c1 * xi + c2 * xi+1 + c3 * yi
        SHR	.S2	  s1,15,yi1     ; yi+1
        STH	.D2	  yi1,*y++      ; store yi+1
[cntr]  SUB	.L1	  cntr,1,cntr   ; decrement loop counter
[cntr]  B	.S1	  LOOP          ; branch to loop

        .endproc