DSP56300 datasheet(48/108 Pages) FREESCALE

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3-20

Viterbi Decoder Implementation

Expanding the Viterbi Algorithm

Memory Organization

The path metric/path memory must start on a 0 mod 2*NUMSTATES boundary for the

modulo addressing to work properly. In addition, the Branch metric storage BRY must

start on a 0 mod NUMSTATES/2 boundary to operate correctly. Finally, the storage of

the input data must be paired in X and Y memory, because we do long moves to get the

decoder input data pairs into the branch metric calculation.

Example 3-8

Memory Organization Code

;**********************MEMORY ORGANIZATION****************************

;

MOST OF THE MEMORY LOCATION IS IMPORTANT--THE FIRST TWO

;

LABELS OF THE X AND Y DATA MEMORY ARE PAIRED AND MUST

;

BE CO LOCATED (AT THE SAME ADDRESSES).

IN ADDITION, STATE1

;

AND STATE2 MUST BE LOCATED ON A 0 MOD 2*NUMSTATES BOUNDARY,

;

BRY MUST BE ON A 0 MOD NUMSTATES/2 BOUNDARY.

;

X and Y memory for input data must be paired --GOOD LUCK.....

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

;

org

x:$0

STATE1

$0ff,$0,$0,$0,$0,$0,$0,$0,0,0,0,0,0,0,0,0

$0,$0,$0,$0,$0,$0,$0,$0,0,0,0,0,0,0,0,0

STATE2

$0ff,$0,$0,$0,$0,$0,$0,$0,0,0,0,0,0,0,0,0

$0,$0,$0,$0,$0,$0,$0,$0,0,0,0,0,0,0,0,0

;

PATHOUT DS

NUMSTATES*(NUMINPUTS/8+1)

INDATA

;THIS DATA ENCODES

;$1234,$5678,$9abc,$4973,$7925,$3491,$ad43,$ff21,$7ebb,$0100,$00 ;....

;I didnÕt include the test data in this listing...

org

y:$0

PATH1

$0,$0,$0,$0,$0,$0,$0,$0,0,0,0,0,0,0,0,0

PATH2

$0,$0,$0,$0,$0,$0,$0,$0,0,0,0,0,0,0,0,0

BRY

DSM

NUMSTATES/2

DECOUT

NUMINPUTS/8

org

y:@cvs(y,INDATA)

YDATA

$a000,$a000,$a000,$6000;....

Freescale Semiconductor, Inc.

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