;************************************************************************
daptive filter using the LMS instruction                     *
*
;************************************************************************
        .mmregs
 .def begin, N, Beta

N .set 16  ; the LMS adaptive filter will have N taps
REF .set 300h  ; Reference chanel port address
IN .set 100h  ; Input chanel port address
OUT .set 200h  ; Output chanel port address

COUNT .set 2000  ; process .250 seconds of data

REFERENCE    .usect "REF", N        ; allocate space for ref buffer
COEFFICIENTS .usect "FILTER", N     ; allocate space for adaptive filter

 .bss ERROR, 3, 1 ; make sure that these vars on same page
Beta .set ERROR + 1 ; beta is a variable so it can be changed
    ; during processing
INPUT .set ERROR + 2

 .sect  "vectors"        ; set up a reset vector
  B     begin

        .text
        NOP
begin   SSBX    SXM             ; sign extention is on
 SSBX FRCT  ; We are performing Q15*Q15 mult.
    ; Need left shift of one so
    ; Q31 is in accumulator. Turn FRCT on.
 RSBX OVM  ; let the accumulator over flow

 LD #ERROR, DP ; set up data page
 STM #INPUT, AR5 ;
 STM #REFERENCE, AR4 ;
 STM #COUNT, AR6 ; loop counter

 ST #300, Beta ; Beta can be changed during processing
    ; Beta is initialized to .009
 STM #N, BK  ; set the circular buffer size register
 STM #1, AR0  ; load index increment value

LOOP
 STM #COEFFICIENTS, AR3
ADAPT
 LD #0, B  ; clear B
 STM #N-2, BRC ; We will do one tap before start of rptb
 LD ERROR, T ; error(0) = Beta*error(-1)
 RPTBD LMS_END-1
  MPY *AR4, A  ; A = error(-1)*x(-n)
    ; note: past error is used for update
  LMS *AR3, *AR4+0% ; A = A + *AR3<<16 + 2^15
    ; B = B + *AR3 x *AR4

   ST A, *AR3+ ; save filter coefficient
   ||MPY *AR4, A  ; error(-1) * x(-(n-1))
    ; note: past error is used for update
   LMS *AR3, *AR4+0% ; A = A + *AR3<<16 + 2^15
    ; B = B + *AR3 x *AR4

LMS_END
 ST A, *AR3  ; finish up last coefficient update
 ||SUB *AR5, A  ; A = (*AR5)<<16 - B,  the new error
 STH A, ERROR ; save the new error

 PORTW ERROR, OUT ; output the error signal

 LD Beta, T  ; Update the error
 MPY ERROR, A ; A = ERROR(0)*Beta
 STH A, ERROR

 PORTR IN, *AR5 ; EC on this input signal

 BANZD LOOP, *AR6- ;
  PORTR REF, *AR4+0% ; reference signal read

; BANZ takes effect here

DONE B DONE  ; processing complete

        .end