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/*
* Copyright (C) 2014 Bastian Bloessl <bloessl@ccs-labs.org>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <iostream>
#include <iomanip>
#define dout debug && std::cout
#define lout log && std::cout
#include "decoder_impl.h"
#include "constants.h"
#include <boost/format.hpp>
using namespace rds;
decoder_impl::decoder_impl(bool log, bool debug) :
log(log),
debug(debug)
{
//set_output_multiple(104); // 1 RDS datagroup = 104 bits
enter_no_sync();
}
void decoder_impl::decode_group(unsigned int *group) {
#define HEX(a) std::hex << std::setfill('0') << std::setw(4) << long(a) << std::dec
for(int i = 0; i < 4; i++) {
dout << " " << HEX(group[i]);
}
dout << std::endl;
}
////////////////////////// HELPER FUNTIONS /////////////////////////
void decoder_impl::enter_no_sync() {
presync = false;
d_state = NO_SYNC;
}
void decoder_impl::enter_sync(unsigned int sync_block_number) {
wrong_blocks_counter = 0;
blocks_counter = 0;
block_bit_counter = 0;
block_number = (sync_block_number + 1) % 4;
group_assembly_started = false;
d_state = SYNC;
}
/* see Annex B, page 64 of the standard */
unsigned int decoder_impl::calc_syndrome(unsigned long message,
unsigned char mlen) {
unsigned long reg = 0;
unsigned int i;
const unsigned long poly = 0x5B9;
const unsigned char plen = 10;
for (i = mlen; i > 0; i--) {
reg = (reg << 1) | ((message >> (i-1)) & 0x01);
if (reg & (1 << plen)) reg = reg ^ poly;
}
for (i = plen; i > 0; i--) {
reg = reg << 1;
if (reg & (1<<plen)) reg = reg ^ poly;
}
return (reg & ((1<<plen)-1)); // select the bottom plen bits of reg
}
int decoder_impl::work (int noutput_items,
const int *in)
{
dout << "RDS data decoder at work: input_items = "
<< noutput_items << ", /104 = "
<< noutput_items / 104 << std::endl;
int i=0,j;
unsigned long bit_distance, block_distance;
unsigned int block_calculated_crc, block_received_crc, checkword,dataword;
unsigned int reg_syndrome;
/* the synchronization process is described in Annex C, page 66 of the standard */
while (i<noutput_items) {
reg=(reg<<1)|in[i]; // reg contains the last 26 rds bits
switch (d_state) {
case NO_SYNC:
reg_syndrome = calc_syndrome(reg,26);
for (j=0;j<5;j++) {
if (reg_syndrome==syndrome[j]) {
if (!presync) {
lastseen_offset=j;
lastseen_offset_counter=bit_counter;
presync=true;
lout << "@@@@@ presync" << std::endl;
}
else {
bit_distance=bit_counter-lastseen_offset_counter;
if (offset_pos[lastseen_offset]>=offset_pos[j]) {
block_distance=offset_pos[j]+4-offset_pos[lastseen_offset];
}
else {
block_distance=offset_pos[j]-offset_pos[lastseen_offset];
}
if ((block_distance*26)!=bit_distance) {
presync=false;
lout << "@@@@@ presync lost " << j << " " <<
block_distance*26 << " " <<
bit_distance << " " <<
std::endl;
}
else {
lout << "@@@@@ Sync State Detected" << std::endl;
enter_sync(j);
}
}
break; //syndrome found, no more cycles
}
}
break;
case SYNC:
/* wait until 26 bits enter the buffer */
if (block_bit_counter<25) block_bit_counter++;
else {
good_block=false;
dataword=(reg>>10) & 0xffff;
block_calculated_crc=calc_syndrome(dataword,16);
checkword=reg & 0x3ff;
/* manage special case of C or C' offset word */
if (block_number==2) {
block_received_crc=checkword^offset_word[block_number];
if (block_received_crc==block_calculated_crc)
good_block=true;
else {
block_received_crc=checkword^offset_word[4];
if (block_received_crc==block_calculated_crc)
good_block=true;
else {
wrong_blocks_counter++;
good_block=false;
}
}
}
else {
block_received_crc=checkword^offset_word[block_number];
if (block_received_crc==block_calculated_crc)
good_block=true;
else {
wrong_blocks_counter++;
good_block=false;
lout << "@@@@@ CRC " <<
std::hex << std::setfill('0') << std::setw(4) <<
block_received_crc << " " <<
std::hex << std::setfill('0') << std::setw(4) <<
block_calculated_crc << std::dec << std::endl;
}
}
/* done checking CRC */
if (block_number==0 && good_block) {
group_assembly_started=true;
group_good_blocks_counter=1;
}
if (group_assembly_started) {
if (!good_block) group_assembly_started=false;
else {
group[block_number]=dataword;
group_good_blocks_counter++;
}
if (group_good_blocks_counter==5) decode_group(group);
}
block_bit_counter=0;
block_number=(block_number+1) % 4;
blocks_counter++;
/* 1187.5 bps / 104 bits = 11.4 groups/sec, or 45.7 blocks/sec */
if (blocks_counter==50) {
if (wrong_blocks_counter>35) {
lout << "@@@@@ Lost Sync (Got " << wrong_blocks_counter
<< " bad blocks on " << blocks_counter
<< " total)" << std::endl;
enter_no_sync();
} else {
lout << "@@@@@ Still Sync-ed (Got " << wrong_blocks_counter
<< " bad blocks on " << blocks_counter
<< " total)" << std::endl;
}
blocks_counter=0;
wrong_blocks_counter=0;
}
}
break;
default:
d_state=NO_SYNC;
break;
}
i++;
bit_counter++;
}
return noutput_items;
}
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