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Yet another POCSAG bugfix (multi-batch messages are not cut anymore)

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Added BCH ECC functions for checking, error correction and encoding
This commit is contained in:
furrtek 2017-02-06 20:32:33 +00:00
parent 98f89a84bb
commit 24abe4b427
9 changed files with 627 additions and 64 deletions
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115
firmware/common/pocsag.cpp
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@ -23,13 +23,10 @@
#include "pocsag.hpp"
#include "baseband_api.hpp"
#include "portapack.hpp"
#include "portapack_persistent_memory.hpp"
using namespace portapack;
#include "string_format.hpp"
#include "utility.hpp"
namespace pocsag {
@ -48,12 +45,118 @@ std::string flag_str(PacketFlag packetflag) {
case PacketFlag::NORMAL: return "OK";
case PacketFlag::IDLE: return "IDLE";
case PacketFlag::TIMED_OUT: return "TIMED OUT";
case PacketFlag::TOO_LONG: return "TOO LONG";
default: return "";
}
}
bool decode_batch(const POCSAGPacket& batch, POCSAGState * const state) {
void insert_BCH(BCHCode& BCH_code, uint32_t * codeword) {
uint32_t parity = 0;
int data[21];
int bit;
int * bb;
size_t c;
for (c = 0; c < 21; c++) {
bit = (((*codeword) << c) & 0x80000000U) ? 1 : 0;
if (bit) parity++;
data[c] = bit;
}
bb = BCH_code.encode(data);
// Make sure ECC bits are cleared
(*codeword) &= 0xFFFFF801;
for (c = 0; c < 10; c++) {
bit = bb[c];
(*codeword) |= (bit << (10 - c));
if (bit) parity++;
}
// Even parity
(*codeword) |= (parity & 1);
}
void pocsag_encode(
BCHCode& BCH_code, const std::string text, const uint32_t address,
std::vector<uint32_t>& codewords) {
size_t b, c, address_slot;
size_t bit_idx, char_idx = 0;
uint32_t codeword;
char ascii_char;
size_t text_size = text.size();
// Preamble
for (b = 0; b < (POCSAG_PREAMBLE_LENGTH / 32); b++) {
codewords.push_back(0xAAAAAAAA);
}
// Address
codeword = (address & 0x1FFFF8U) << 13;
address_slot = (address & 7) * 2;
// Function
codeword = 3 << 11;
insert_BCH(BCH_code, &codeword);
// Address batch
codewords.push_back(POCSAG_SYNCWORD);
for (c = 0; c < 16; c++) {
if (c == address_slot)
codewords.push_back(codeword);
else
codewords.push_back(POCSAG_IDLEWORD);
}
codeword = 0;
bit_idx = 20 + 11;
// Messages batch(es)
do {
codewords.push_back(POCSAG_SYNCWORD);
for (c = 0; c < 16; c++) {
// Fill up 20 bits
do {
bit_idx -= 7;
if (char_idx < text_size)
ascii_char = text[char_idx] & 0x7F;
else
ascii_char = 0; // Padding
// Bottom's up
ascii_char = (ascii_char & 0xF0) >> 4 | (ascii_char & 0x0F) << 4; // *6543210 -> 3210*654
ascii_char = (ascii_char & 0xCC) >> 2 | (ascii_char & 0x33) << 2; // 3210*654 -> 103254*6
ascii_char = (ascii_char & 0xAA) >> 2 | (ascii_char & 0x55); // 103254*6 -> *0123456
codeword |= (ascii_char << bit_idx);
char_idx++;
} while (bit_idx > 11);
codeword &= 0x7FFFF800; // Trim data
codeword |= 0x80000000; // Message type
insert_BCH(BCH_code, &codeword);
codewords.push_back(codeword);
if (bit_idx != 11) {
bit_idx = 20 + bit_idx;
codeword = ascii_char << bit_idx;
} else {
bit_idx = 20 + 11;
codeword = 0;
}
}
} while (char_idx < text_size);
}
bool pocsag_decode_batch(const POCSAGPacket& batch, POCSAGState * const state) {
uint32_t codeword;
char ascii_char;
std::string output_text = "";
@ -67,7 +170,7 @@ bool decode_batch(const POCSAGPacket& batch, POCSAGState * const state) {
if (!(codeword & 0x80000000U)) {
// Address codeword
if (state->mode == STATE_CLEAR) {
if (codeword != POCSAG_IDLE) {
if (codeword != POCSAG_IDLEWORD) {
state->function = (codeword >> 11) & 3;
state->address = (codeword >> 10) & 0x1FFFF8U; // 18 MSBs are transmitted
state->mode = STATE_HAVE_ADDRESS;