Operation Of The Eccp; Figure 14-3.Eccp Operation Sequence - Lucent Technologies DSP1617 Information Manual

Information Manual
April 1998

14.4 Operation of the ECCP

To operate the ECCP, the user first programs its mode of operation by setting the control register (ECON), setting
the traceback length register (TBLR), and appropriately initializing the present state accumulated costs. The com-
plete Viterbi decoding operation is achieved by the following steps: recursively loading the received symbols into
the ECCP; executing the ECCP with an UpdateMLSE, an UpdateConv, or a TraceBack instruction; and, finally,
unloading the decoded symbol from the ECCP. The operation of the ECCP is captured in the signal flow diagram in
Figure 14-3.
YES
NEW
NO
ADAPTED
CHANNEL
?
TL = TBLR
FETCH MINIMUM COST INDEX
CALCULATE
REVERSED PATH
TL = TL – 1
NO IS
TL = 0?
IS
YES
TRACEBACK
INSTR.
?
DECREMENT
TBLR BY ONE
OUTPUT
DECODED SYMBOL
Lucent Technologies Inc.
DSP1611/17/18/27/28/29 DIGITAL SIGNAL PROCESSOR
DSP PROGRAMS ECCP
DSP LOADS CHANNEL/GENERATING
POLYNOMIALS INTO THE ECCP
DSP LOADS RECEIVED
SYMBOLS INTO THE ECCP
UPDATE INSTRUCTION
YES
NO
VITERBI
DECODING
COMPLETE
ALL
SYMBOLS
DECODED
Figure 14-3. ECCP Operation Sequence
DRAFT COPY
Error Correction Coprocessor (DSP1618/28 Only)
DSP EXECUTES
YES
?
NO
SET K = 0
CALCULATE BRANCH METRIC
FOR BOTH STATE TRANSITIONS TO K
CALCULATE ACCUMULATED COST
FOR STATE TRANSITIONS TO K
SELECT MINIMUM ACCUMULATED
COST AS SURVIVOR PATH
UPDATE MINIMUM COST INDEX
STORE SURVIVOR PATH
INCREMENT
K BY ONE
IS
NO YES
(C – 1)
K < 2 – 1
?
5-4502
14-7