filter.asm

基于DSP的自适应滤波器的设计与实现（C54x上实现）的源代码

;****************************************************************
; Function: dlms
; Version: 1.00
; Description: dlms fir filter
;
; Copyright Texas instruments Inc, 1998
;----------------------------------------------------------------
; Revision History:
; 1.00, R. Piedra, 8/31/98 - Original release. Started from code by
; Padma Mallela.
;****************************************************************
    .mmregs
; Far-mode adjustment
    .if __far_mode
offset .set 1 ; far mode uses one extra location for ret addr ll
    .else
offset .set 0
   .endif
   .asg (0), mu_error ; 2*mu*error(i) variable
   .asg (1), save_st1 ; stack description
   .asg (2), save_st0
   .asg (3), save_ar6
   .asg (4), save_ar1
   .asg (5), ret_addr
; x in A
   .asg (6 + offset), arg_h
   .asg (7 + offset), arg_y
   .asg (8 + offset), arg_d
   .asg (9 + offset), arg_des
   .asg (10 + offset), arg_rate
   .asg (11 + offset), arg_nh
   .asg (12 + offset), arg_n
; register usage
; AR0 : circ addr. index
   .asg ar1, ar_count
   .asg ar2, ar_d
   .asg ar3, ar_h
   .asg ar4, ar_des
   .asg ar5, ar_x
   .asg ar6, ar_y
   
   ;*****************************************************************************
   .def _dlms
_dlms:
; Preserve registers
;-------------------
    pshm ar1
    pshm ar6
    PSHM ST0 ; 1 cycle
    PSHM ST1 ; 1 cycle
    RSBX OVA ; 1 cycle
    RSBX OVB ; 1 cycle
; Preserve space for local variables
; ----------------------------------
    frame -1 ; mu_error local var
; Set math and overflow modes
;---------------------------
    ssbx SXM ; sign extension on
    ssbx frct ; fract on
    ld #0,ASM ; clear ASM (used by st||mpy)
     st #0, *sp(mu_error) ; clear error OJO : make argument
;
; Get arguments
;---------------
   stlm a, ar_x ; pointer to x
    mvdk *sp(arg_h),*(ar_h) ; pointer to h
    mvdk *sp(arg_y),*(ar_y) ; pointer to y
    mvdk *sp(arg_d),*(ar_d) ; de-referencing
    mvdk *ar_d,*(ar_d) ; pointer to d
    mvdk *sp(arg_des),*(ar_des) ; for circ addr
    mvdk *sp(arg_n), *(ar_count) ; sample counter
    mar *ar_count- ; ar_count= nsamples-1
     ld *sp(arg_nh),a ; a = nh
; Initialize registers
; --------------------
   stlm a,bk ; bk = circular buffer size = nh
    stm #1,AR0
    sub #03,a
_start:
   stl a, *sp(arg_nh)
; Loop through remaining (n-1) samples
;-------------------------------------
next_sample:
   mvdk *sp(arg_nh),brc
    ld *sp(mu_error), t ; t = 2 * mu * error (i)
    sub b,b ; b = 0
; Loop through (nh-2) taps: compute filter and adapt at = time
; ------------------------------------------------------------
   rptbd lms_end -1
   mpy *ar_d+0%,a ; a = mu_error * x(1)
; point to x(2)
    lms *ar_h, *ar_d ; b = b + h(1) * x(2)
; a = a + h(1)
lms_beg
    st a, *ar_h+0%; ; update h(1)
; point to h(2)
    || mpy *ar_d+0%,a ; a = mu_error * x(2)
; point to x(0)
    lms *ar_h, *ar_d ; b = b + h(2) * x(0)
; a = a + h(2)
lms_end
; Perform 1st tap outside to avoid that the oldest
; sample is over written before updating the h(0) coef
; ----------------------------------------------------
   st a, *ar_h+0% ; update last coef
   || mpy *ar_d+0%,a ; error * x(0)
    mvdd *ar_x+, *ar_d ; new sample --> dbuffer x(0)
    lms *ar_h, *ar_d+0% ; b = b * h(0) * x(1)
; Write output sample
; -------------------
    sth b, *ar_y+
; Compute new error
; ----------------
    st a,*ar_h+0%
    || sub *ar_des+,a ; bh = error(i)= des(i)-y(i)
    banzd next_sample, *ar_count
    mpya *sp(arg_rate) ; b = step_size * error(i)
    sth b, *sp(mu_error) ; save as local variable
; Return
;-------
_end
   .asg ar_h, ar_temp ; ar_h not used any more
   mvdk *sp(arg_d), *(ar_temp)
   mvkd *(ar_d), *ar_temp ; update new ar_d
; Return overflow flag
; --------------------
   ld 0,a
   xc 1,AOV
   ld #1,a
; Adjust stack pointer and restore registers
; ------------------------------------------
   frame +1 ; adjust for local vars
     POPM ST1 ; 1 cycle
     POPM ST0 ; 1 cycle
     popm ar6
     popm ar1
   .if __far_mode
   fretd
   .else
   retd
   .endif
    nop
    nop