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https://github.com/f4exb/sdrangel.git
synced 2025-02-03 09:44:01 -05:00
BFM demod: added RDS decoder class
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f4exb
parent
5761330365
commit
14f72bae8a
@ -5,6 +5,7 @@ set(bfm_SOURCES
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bfmdemodgui.cpp
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bfmplugin.cpp
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rdsdemod.cpp
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rdsdecoder.cpp
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)
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set(bfm_HEADERS
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@ -12,6 +13,7 @@ set(bfm_HEADERS
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bfmdemodgui.h
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bfmplugin.h
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rdsdemod.h
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rdsdecoder.h
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)
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set(bfm_FORMS
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254
plugins/channel/bfm/rdsdecoder.cpp
Normal file
254
plugins/channel/bfm/rdsdecoder.cpp
Normal file
@ -0,0 +1,254 @@
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///////////////////////////////////////////////////////////////////////////////////
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// Copyright (C) 2015 F4EXB //
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// written by Edouard Griffiths //
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// //
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// This program is free software; you can redistribute it and/or modify //
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// it under the terms of the GNU General Public License as published by //
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// the Free Software Foundation as version 3 of the License, or //
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// //
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// This program is distributed in the hope that it will be useful, //
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// but WITHOUT ANY WARRANTY; without even the implied warranty of //
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the //
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// GNU General Public License V3 for more details. //
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// //
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// You should have received a copy of the GNU General Public License //
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// along with this program. If not, see <http://www.gnu.org/licenses/>. //
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///////////////////////////////////////////////////////////////////////////////////
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#include <QDebug>
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#include "rdsdecoder.h"
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const unsigned int RDSDecoder::offset_pos[5] = {0,1,2,3,2};
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const unsigned int RDSDecoder::offset_word[5] = {252,408,360,436,848};
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const unsigned int RDSDecoder::syndrome[5] = {383,14,303,663,748};
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RDSDecoder::RDSDecoder()
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{
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m_reg = 0;
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m_sync = NO_SYNC;
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m_presync = false;
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m_lastseenOffsetCounter = 0;
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m_bitCounter = 0;
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m_lastseenOffset = 0;
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m_wrongBlocksCounter = 0;
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m_blocksCounter = 0;
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m_blockBitCounter = 0;
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m_blockNumber = 0;
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m_groupAssemblyStarted = false;
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m_sync = SYNC;
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m_groupGoodBlocksCounter = 0;
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m_wrongBlocksCounter = 0;
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m_goodBlock = false;
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}
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RDSDecoder::~RDSDecoder()
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{
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}
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void RDSDecoder::frameSync(bool bit)
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{
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unsigned int reg_syndrome;
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unsigned long bit_distance, block_distance;
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unsigned int block_calculated_crc, block_received_crc, checkword, dataword;
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m_reg = (m_reg<<1) | bit;
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switch (m_sync)
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{
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case NO_SYNC:
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reg_syndrome = calc_syndrome(m_reg,26);
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for (int j = 0; j < 5; j++)
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{
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if (reg_syndrome == syndrome[j])
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{
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if (!m_presync)
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{
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m_lastseenOffset = j;
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m_lastseenOffsetCounter = m_bitCounter;
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m_presync=true;
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}
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else
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{
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bit_distance = m_bitCounter - m_lastseenOffsetCounter;
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if (offset_pos[m_lastseenOffset] >= offset_pos[j])
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{
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block_distance = offset_pos[j] + 4 - offset_pos[m_lastseenOffset];
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}
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else
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{
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block_distance = offset_pos[j] - offset_pos[m_lastseenOffset];
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}
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if ((block_distance*26)!=bit_distance)
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{
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m_presync = false;
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}
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else
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{
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qDebug("RDSDecoder::frameSync: Sync State Detected");
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enter_sync(j);
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}
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}
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break; //syndrome found, no more cycles
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}
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}
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break;
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case SYNC:
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// wait until 26 bits enter the buffer
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if (m_blockBitCounter < 25)
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{
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m_blockBitCounter++;
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}
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else
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{
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m_goodBlock = false;
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dataword = (m_reg>>10) & 0xffff;
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block_calculated_crc = calc_syndrome(dataword, 16);
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checkword = m_reg & 0x3ff;
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// manage special case of C or C' offset word
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if (m_blockNumber == 2)
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{
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block_received_crc = checkword ^ offset_word[m_blockNumber];
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if (block_received_crc==block_calculated_crc)
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{
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m_goodBlock = true;
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}
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else
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{
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block_received_crc=checkword^offset_word[4];
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if (block_received_crc==block_calculated_crc)
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{
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m_goodBlock = true;
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}
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else
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{
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m_wrongBlocksCounter++;
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m_goodBlock = false;
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}
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}
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}
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else
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{
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block_received_crc = checkword ^ offset_word[m_blockNumber];
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if (block_received_crc==block_calculated_crc)
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{
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m_goodBlock = true;
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}
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else
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{
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m_wrongBlocksCounter++;
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m_goodBlock = false;
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}
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}
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//done checking CRC
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if (m_blockNumber == 0 && m_goodBlock)
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{
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m_groupAssemblyStarted = true;
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m_groupGoodBlocksCounter = 1;
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}
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if (m_groupAssemblyStarted)
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{
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if (!m_goodBlock)
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{
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m_groupAssemblyStarted = false;
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}
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else
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{
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m_group[m_blockNumber] = dataword;
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m_groupGoodBlocksCounter++;
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}
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if (m_groupGoodBlocksCounter == 5)
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{
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//decode_group(group); TODO: pass on to the group parser
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}
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}
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m_blockBitCounter = 0;
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m_blockNumber = (m_blockNumber + 1) % 4;
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m_blocksCounter++;
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// 1187.5 bps / 104 bits = 11.4 groups/sec, or 45.7 blocks/sec
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if (m_blocksCounter == 50)
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{
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if (m_wrongBlocksCounter > 35)
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{
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qDebug() << "RDSDecoder::frameSync: Lost Sync (Got " << m_wrongBlocksCounter
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<< " bad blocks on " << m_blocksCounter
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<< " total)";
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enter_no_sync();
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}
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else
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{
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qDebug() << "RDSDecoder::frameSync: Still Sync-ed (Got " << m_wrongBlocksCounter
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<< " bad blocks on " << m_blocksCounter
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<< " total)";
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}
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m_blocksCounter = 0;
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m_wrongBlocksCounter = 0;
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}
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}
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break;
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default:
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break;
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}
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m_bitCounter++;
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}
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////////////////////////// HELPER FUNTIONS /////////////////////////
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void RDSDecoder::enter_sync(unsigned int sync_block_number)
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{
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m_wrongBlocksCounter = 0;
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m_blocksCounter = 0;
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m_blockBitCounter = 0;
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m_blockNumber = (sync_block_number + 1) % 4;
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m_groupAssemblyStarted = false;
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m_sync = SYNC;
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}
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void RDSDecoder::enter_no_sync()
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{
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m_presync = false;
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m_sync = NO_SYNC;
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}
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/**
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* see Annex B, page 64 of the standard
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*/
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unsigned int RDSDecoder::calc_syndrome(unsigned long message, unsigned char mlen)
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{
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unsigned long reg = 0;
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unsigned int i;
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const unsigned long poly = 0x5B9;
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const unsigned char plen = 10;
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for (i = mlen; i > 0; i--)
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{
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reg = (reg << 1) | ((message >> (i-1)) & 0x01);
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if (reg & (1 << plen)) reg = reg ^ poly;
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}
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for (i = plen; i > 0; i--)
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{
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reg = reg << 1;
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if (reg & (1<<plen)) {
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reg = reg ^ poly;
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}
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}
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return (reg & ((1<<plen)-1)); // select the bottom plen bits of reg
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}
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59
plugins/channel/bfm/rdsdecoder.h
Normal file
59
plugins/channel/bfm/rdsdecoder.h
Normal file
@ -0,0 +1,59 @@
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///////////////////////////////////////////////////////////////////////////////////
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// Copyright (C) 2015 F4EXB //
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// written by Edouard Griffiths //
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// //
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// This program is free software; you can redistribute it and/or modify //
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// it under the terms of the GNU General Public License as published by //
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// the Free Software Foundation as version 3 of the License, or //
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// //
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// This program is distributed in the hope that it will be useful, //
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// but WITHOUT ANY WARRANTY; without even the implied warranty of //
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the //
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// GNU General Public License V3 for more details. //
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// //
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// You should have received a copy of the GNU General Public License //
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// along with this program. If not, see <http://www.gnu.org/licenses/>. //
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///////////////////////////////////////////////////////////////////////////////////
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#ifndef PLUGINS_CHANNEL_BFM_RDSDECODER_H_
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#define PLUGINS_CHANNEL_BFM_RDSDECODER_H_
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class RDSDecoder
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{
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public:
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RDSDecoder();
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~RDSDecoder();
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void frameSync(bool bit);
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protected:
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unsigned int calc_syndrome(unsigned long message, unsigned char mlen);
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void enter_sync(unsigned int sync_block_number);
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void enter_no_sync();
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private:
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unsigned long m_reg;
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enum { NO_SYNC, SYNC } m_sync;
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bool m_presync;
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unsigned long m_lastseenOffsetCounter;
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unsigned long m_bitCounter;
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unsigned char m_lastseenOffset;
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unsigned int m_blockBitCounter;
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unsigned int m_wrongBlocksCounter;
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unsigned int m_blocksCounter;
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unsigned int m_groupGoodBlocksCounter;
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unsigned char m_blockNumber;
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bool m_groupAssemblyStarted;
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bool m_goodBlock;
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unsigned int m_group[4];
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/* see page 59, Annex C, table C.1 in the standard
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* offset word C' has been put at the end */
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static const unsigned int offset_pos[5];
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static const unsigned int offset_word[5];
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static const unsigned int syndrome[5];
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};
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#endif /* PLUGINS_CHANNEL_BFM_RDSDECODER_H_ */
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