DSP56300 datasheet(85/108 Pages) FREESCALE

85 / 108 page

Extended Algorithm Program Listing

Viterbi Decoder Implementation

B-7

;***********************ACSFlush Macro****************************

;

FUNCTION: This routine is very similar to the ACS macro, except that

;

the encoding shift register is now flushing back to 0.

;

This means that only the upper paths are taken, halving

;

the number of states we need to update.

The ACS code is

;

modified so that we don't compute the lower paths. In

;

addition, state storage is modified so that survivor

;

paths are stored in consecutive memory locations.

;

Survivors are even states on the first pass, then

;

every fourth state, etc.

;

INPUTS:

;

r2 should point to the beginning of the branch metric table

;

r5 should point to the latest path metric for state 0

;

r4 should point to the storage location for updated state 0

;

n5 should be the number of input states/2 to process

;

n5 is halved each time this macro is invoked

;

OUTPUTS:

;

Updated path metrics/paths stored in XY memory

;

REGISTERS USED:

;

a,b,y01,r2,n2,r3,n3,r4,r5,n5 r2 unchanged (modulo req'd)

;

SA------NSA

;

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

ACSFlush macro

;**

move

#BRY,r2

;r2 points to branch metrics

move

r5,r3

;save r5 to init r4 later

move

r4,n3

;save r4 to init r5 later

move

l:(r2)+n2,y

;get first branch metrics

move

l:(r5)+n5,a

;load 1st metric/path pair

;

n5,_NextStage

;update each state

add

y0,a

l:(r5)-n5,b

;updt met,load next pair

add

y1,b

l:(r2)+n2,y

;updt met,ld nxt br met

max

a,b

(r5)+

;sel surv,save met,inc st ptr

move

l:(r5)+n5,a

;ld next pair

vsl

b,0,l:(r4)+

;end 2nd half

_NextStage

move

n5,b

;recall flush count, loop count

asr

n2,a

;divide it by 2,prep double branch jump

move

n3,r5

move

b,n5

;storage for flush count

asl

(r2)-n2

;reinit branch ptr

move

r3,r4

move

a,n2

;next pass, skip more branches

endm

Example B-1

Extended Algorithm Program Listing (Continued)

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

DSP56300 датащи(PDF) 85 Page - Freescale Semiconductor, Inc

DSP56300 датащи(HTML) 85 Page - Freescale Semiconductor, Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

датащи скачать

ссылки URL