177 lines
4.6 KiB
C++
177 lines
4.6 KiB
C++
/* -*- c++ -*- */
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/*
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* construct P25 frames out of raw dibits
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* Copyright 2010, 2011, 2012, 2013 KA1RBI
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*/
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#include <vector>
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#include <stdio.h>
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#include <stdint.h>
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#include "bch.h"
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#include <sys/time.h>
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#include "op25_p25_frame.h"
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#include "p25_framer.h"
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#include "check_frame_sync.h"
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static const int max_frame_lengths[16] = {
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// lengths are in bits, not symbols
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792, // 0 - hdu
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0, 0, // 1, 2 - undef
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144, // 3 - tdu
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0, // 4 - undef
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P25_VOICE_FRAME_SIZE, // 5 - ldu1
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0, // 6 - undef
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720, // 7 - trunking (FIXME: are there systems with longer ones?)
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0, // 8 - undef
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0, // 9 - VSELP "voice PDU"
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P25_VOICE_FRAME_SIZE, // a - ldu2
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0, // b - undef
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962, // c - pdu (triple data block MBT)
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0, 0, // d, e - undef
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432 // f - tdu
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};
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// constructor
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p25_framer::p25_framer(int debug, int msgq_id) :
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d_debug(debug),
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d_msgq_id(msgq_id),
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reverse_p(0),
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nid_syms(0),
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next_bit(0),
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nid_accum(0),
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nac(0),
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duid(0),
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parity(0),
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frame_size_limit(0),
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symbols_received(0),
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frame_body(P25_VOICE_FRAME_SIZE)
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{
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}
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// destructor
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p25_framer::~p25_framer ()
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{
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}
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/*
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* Process the 64 bits after the frame sync, which should be the frame NID
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* 1. verify bch and reject if bch cannot be decoded
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* 2. extract NAC and DUID
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* Returns false if decode failure, else true
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*/
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bool p25_framer::nid_codeword(uint64_t acc) {
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bit_vector cw(64);
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uint64_t save_acc = acc;
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// save the parity lsb, not used by BCH`
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int acc_parity = acc & 1;
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// for bch, split bits into codeword vector (lsb first)
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for (int i = 0; i <= 63; i++) {
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acc >>= 1;
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cw[i] = acc & 1;
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}
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// do bch decode
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int ec = bchDec(cw);
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// load corrected bch bits into acc (msb first)
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acc = 0;
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for (int i = 63; i >= 0; i--) {
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acc |= cw[i];
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acc <<= 1;
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}
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// put the parity lsb back
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acc |= acc_parity;
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// check if bch decode unsuccessful
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if (ec < 0)
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return false;
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bch_errors = ec;
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nid_word = acc; // reconstructed NID
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// extract nac and duid
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nac = (acc >> 52) & 0xfff;
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duid = (acc >> 48) & 0x00f;
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parity = acc_parity;
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return true;
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}
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/*
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* rx_sym: called once per received symbol
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* 1. looks for flags sequences
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* 2. after flags detected (nid_syms > 0), accumulate 64-bit NID word
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* 3. do BCH check on completed NID
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* 4. after valid BCH check (next_bit > 0), accumulate frame data bits
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*
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* Returns true when complete frame received, else false
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*/
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bool p25_framer::rx_sym(uint8_t dibit) {
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struct timeval currtime;
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symbols_received++;
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bool rc = false;
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dibit ^= reverse_p;
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// FIXME assert(dibit >= 0 && dibit <= 3)
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nid_accum <<= 2;
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nid_accum |= dibit;
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if (nid_syms == 12) {
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// ignore status dibit
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nid_accum >>= 2;
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} else if (nid_syms >= 33) {
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// nid completely received
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nid_syms = 0;
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bool bch_rc = nid_codeword(nid_accum);
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if (bch_rc) { // if ok to start accumulating frame data
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next_bit = 48 + 64;
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frame_size_limit = max_frame_lengths[duid];
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if (frame_size_limit <= next_bit)
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// size isn't known a priori -
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// fall back to max. size and wait for next FS
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frame_size_limit = P25_VOICE_FRAME_SIZE;
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}
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}
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if (nid_syms > 0) // if nid accumulation in progress
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nid_syms++; // count symbols in nid
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if(check_frame_sync((nid_accum & P25_FRAME_SYNC_MASK) ^ P25_FRAME_SYNC_MAGIC, 3, 48)) {
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nid_syms = 1;
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}
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if(check_frame_sync((nid_accum & P25_FRAME_SYNC_MASK) ^ P25_FRAME_SYNC_REV_P, 0, 48)) {
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nid_syms = 1;
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reverse_p ^= 0x02; // auto flip polarity reversal
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fprintf(stderr, "Reversed FS polarity detected - autocorrecting\n");
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}
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if(check_frame_sync((nid_accum & P25_FRAME_SYNC_MASK) ^ 0x001050551155LL, 0, 48)) {
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gettimeofday(&currtime, 0);
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fprintf(stderr, "%010lu.%06lu channel %d tuning error -1200\n", currtime.tv_sec, currtime.tv_usec, d_msgq_id);
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}
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if(check_frame_sync((nid_accum & P25_FRAME_SYNC_MASK) ^ 0xFFEFAFAAEEAALL, 0, 48)) {
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gettimeofday(&currtime, 0);
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fprintf(stderr, "%010lu.%06lu channel %d tuning error +1200\n", currtime.tv_sec, currtime.tv_usec, d_msgq_id);
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}
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if(check_frame_sync((nid_accum & P25_FRAME_SYNC_MASK) ^ 0xAA8A0A008800LL, 0, 48)) {
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gettimeofday(&currtime, 0);
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fprintf(stderr, "%010lu.%06lu channel %d tuning error +/- 2400\n", currtime.tv_sec, currtime.tv_usec, d_msgq_id);
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}
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if (next_bit > 0) {
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frame_body[next_bit++] = (dibit >> 1) & 1;
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frame_body[next_bit++] = dibit & 1;
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}
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// dispose of received frame (if exists) and:
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// 1. complete frame is received, or
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// 2. flags is received
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if ((next_bit > 0) && (next_bit >= frame_size_limit || nid_syms > 0)) {
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if (nid_syms > 0) // if this was triggered by FS
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next_bit -= 48; // FS has been added to body - remove it
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p25_setup_frame_header(frame_body, nid_word);
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frame_size = next_bit;
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next_bit = 0;
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rc = true; // set rc indicating frame available
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}
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return rc;
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}
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