DSP56300 datasheet(104/108 Pages) FREESCALE

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C-12

Viterbi Decoder Implementation

24-Bit Algorithm Program Listing

;********POSTPROCESSING, FLUSH ENCODER BACK TO 0****

; ASSUMES that there are an odd number of bytes of data!!!

; This will need redoing if the number of data bytes is even.

; THESE SETUPS SHOULD ACCOMODATE ENCODERS OF 5 TO 8 BITS.

; ENCBITS-1 PREPROCESSED, 152 IN MAIN LOOP DONE

; SO WE HAVE 24-ENCBITS+1 BITS LEFT.

; WE DO ENCODER FLUSHING FOR #ENCBITS-1 BITS. SO WE HAVE

; (24-ENCBITS+1) - ENCBITS+1 DO DO BEFORE FLUSHING.

; NEXT, WE PROCESS THE ENCODER FLUSH BITS, STOPPING TO STORE

; PATHS AS NEEDED. WE STORE AFTER 16 BITS PROCESSED SO THIS MEANS

; STORE PATHS AFTER 24-2*ENCBITS+2 (from nonflush) +16-(24-2*ENCBITS+2)

; (these are the additional flush bits needed before storing paths).

; FINALLY, WE FINISH OUT THE DATA. THE BITS REMAINING ARE:

; 24-ENCBITS+1-(24-2*ENCBITS+2)-(16-(24-2*ENCBITS+2))

; = 8-ENCBITS+1.

;

; FOR THIS EXAMPLE, WE NONFLUSH PROCESS

; 14 MORE BITS, THEN FLUSH 2, STORE PATH, THEN FLUSH

; THE LAST THREE TO STATE 0.

; LAST 14 NONFLUSH BITS---

;**********************************************************************

#24-(2*ENCBITS)+2,LAST14

FindMetrics

ACS

;

LAST14

;

ENCODER FLUSH-----

;

move

#>NUMSTATES/2,n5

;flush, process 16,8, 4, then 2,

;

then 1 state

#16-(24-(2*ENCBITS)+2),FLSH;process 2 of last five bits to get

;

next to last byte

FindMetrics

ACSFlush

;

ACS

FLSH

STOREPATHS#NUMSTATES/8

;

FLUSH THE LAST THREE BITS------

;

#8-ENCBITS+1,FLSH3

;process last 3 bits to get last

;

byte

FindMetrics

ACSFlush

;

ACS

FLSH3

;

TRACEBACK

;

FINISH

nop

Example C-1

24-bit Algorithm Program Listing (Continued)

Freescale Semiconductor, Inc.

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