82 lines
1.9 KiB
C++
82 lines
1.9 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, 2014 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 <sys/time.h>
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#include "p25p2_framer.h"
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#include "check_frame_sync.h"
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// constructor
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p25p2_framer::p25p2_framer() :
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d_reverse_p(0),
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d_next_bit(0),
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d_in_sync(0),
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nid_accum(0),
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symbols_received(0),
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d_frame_body(P25P2_BURST_SIZE)
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{
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}
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// destructor
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p25p2_framer::~p25p2_framer ()
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{
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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 p25p2_framer::rx_sym(uint8_t dibit) {
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bool rc = false;
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symbols_received++;
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dibit ^= d_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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int found=0;
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if(check_frame_sync((nid_accum & P25P2_FRAME_SYNC_MASK) ^ P25P2_FRAME_SYNC_MAGIC, 4, 40)) {
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found = 1;
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}
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else if(check_frame_sync((nid_accum & P25P2_FRAME_SYNC_MASK) ^ P25P2_FRAME_SYNC_REV_P, 0, 40)) {
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found = 1;
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d_reverse_p ^= 0x02; // auto flip polarity reversal
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fprintf(stderr, "TDMA: Reversed FS polarity detected - autocorrecting\n");
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}
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if (found) {
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uint64_t accum = P25P2_FRAME_SYNC_MAGIC;
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for (int i=0; i < 40; i++) {
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d_frame_body[39 - i] = accum & 1;
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accum = accum >> 1;
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}
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d_next_bit = 40;
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d_in_sync = 10; // renew allowance
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return false;
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}
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if (d_in_sync) {
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d_frame_body[d_next_bit++] = (dibit >> 1) & 1;
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d_frame_body[d_next_bit++] = dibit & 1;
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// dispose of received frame (if exists) and complete frame is received
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if (d_next_bit >= P25P2_BURST_SIZE) {
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rc = true; // set rc indicating frame available
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d_in_sync--; // each frame reduces allowance
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d_next_bit = 0;
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}
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}
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return rc;
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}
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