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/* -*- c++ -*- */
/*
* construct P25 frames out of raw dibits
* Copyright 2010, 2011, 2012, 2013, 2014 KA1RBI
*/
#include <vector>
#include <stdio.h>
#include <stdint.h>
#include <sys/time.h>
#include <p25p2_framer.h>
#include "check_frame_sync.h"
// constructor
p25p2_framer::p25p2_framer() :
d_reverse_p(0),
d_next_bit(0),
d_in_sync(0),
nid_accum(0),
symbols_received(0),
d_frame_body(P25P2_BURST_SIZE)
{
}
// destructor
p25p2_framer::~p25p2_framer ()
{
}
/*
* rx_sym: called once per received symbol
* 1. looks for flags sequences
* 2. after flags detected (nid_syms > 0), accumulate 64-bit NID word
* 3. do BCH check on completed NID
* 4. after valid BCH check (next_bit > 0), accumulate frame data bits
*
* Returns true when complete frame received, else false
*/
bool p25p2_framer::rx_sym(uint8_t dibit) {
bool rc = false;
symbols_received++;
dibit ^= d_reverse_p;
// FIXME assert(dibit >= 0 && dibit <= 3)
nid_accum <<= 2;
nid_accum |= dibit;
int found=0;
if(check_frame_sync((nid_accum & P25P2_FRAME_SYNC_MASK) ^ P25P2_FRAME_SYNC_MAGIC, 4, 40)) {
found = 1;
}
else if(check_frame_sync((nid_accum & P25P2_FRAME_SYNC_MASK) ^ P25P2_FRAME_SYNC_REV_P, 0, 40)) {
found = 1;
d_reverse_p ^= 0x02; // auto flip polarity reversal
fprintf(stderr, "TDMA: Reversed FS polarity detected - autocorrecting\n");
}
if (found) {
uint64_t accum = P25P2_FRAME_SYNC_MAGIC;
for (int i=0; i < 40; i++) {
d_frame_body[39 - i] = accum & 1;
accum = accum >> 1;
}
d_next_bit = 40;
d_in_sync = 10; // renew allowance
return false;
}
if (d_in_sync) {
d_frame_body[d_next_bit++] = (dibit >> 1) & 1;
d_frame_body[d_next_bit++] = dibit & 1;
// dispose of received frame (if exists) and complete frame is received
if (d_next_bit >= P25P2_BURST_SIZE) {
rc = true; // set rc indicating frame available
d_in_sync--; // each frame reduces allowance
d_next_bit = 0;
}
}
return rc;
}
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