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POCSAGRX.cpp
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POCSAGRX.cpp
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/*
* Copyright (C) 2009-2017 by Jonathan Naylor G4KLX
* Copyright (C) 2018 by Andy Uribe CA6JAU
*
* 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 2 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, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#include "Config.h"
#include "Globals.h"
#include "POCSAGRX.h"
#include "Utils.h"
const uint8_t FSC_BIT_START_ERRS = 2U;
const uint8_t MAX_FSC_BIT_RUN_ERRS = 3U;
const unsigned int MAX_FSC_FRAMES = 4U;
const uint8_t BIT_MASK_TABLE[] = {0x80U, 0x40U, 0x20U, 0x10U, 0x08U, 0x04U, 0x02U, 0x01U};
#define WRITE_BIT1(p,i,b) p[(i)>>3] = (b) ? (p[(i)>>3] | BIT_MASK_TABLE[(i)&7]) : (p[(i)>>3] & ~BIT_MASK_TABLE[(i)&7])
CPOCSAGRX::CPOCSAGRX() :
m_prev(false),
m_state(POCSAGRXS_NONE),
m_bitBuffer(0x00U),
m_buffer(),
m_bufferPtr(0U),
m_lostCount(0U)
{
}
void CPOCSAGRX::reset()
{
m_prev = false;
m_state = POCSAGRXS_NONE;
m_bitBuffer = 0x00U;
m_bufferPtr = 0U;
m_lostCount = 0U;
}
void CPOCSAGRX::databit(bool bit)
{
if (m_state == POCSAGRXS_NONE)
processNone(bit);
else
processData(bit);
}
void CPOCSAGRX::processNone(bool bit)
{
m_bitBuffer <<= 1;
if (bit)
m_bitBuffer |= 0x01U;
// Fuzzy matching of the data sync bit sequence
if (countBits32((m_bitBuffer & POCSAG_FSC_MASK) ^ POCSAG_FSC_WORD) <= FSC_BIT_START_ERRS) {
for (uint8_t i = 0U; i < POCSAG_FSC_BYTES; i++)
m_buffer[i] = POCSAG_FSC[i];
m_lostCount = MAX_FSC_FRAMES;
m_bufferPtr = POCSAG_FSC_BITS;
m_state = POCSAGRXS_DATA;
io.setDecode(true);
}
}
void CPOCSAGRX::processData(bool bit)
{
m_bitBuffer <<= 1;
if (bit)
m_bitBuffer |= 0x01U;
WRITE_BIT1(m_buffer, m_bufferPtr, bit);
m_bufferPtr++;
if (m_bufferPtr >= (POCSAG_FSC_BITS - 2U) && m_bufferPtr <= (POCSAG_FSC_BITS + 2U)) {
// Fuzzy matching of the data sync bit sequence
if (countBits32((m_bitBuffer & POCSAG_FSC_MASK) ^ POCSAG_FSC_WORD) <= MAX_FSC_BIT_RUN_ERRS) {
m_lostCount = MAX_FSC_FRAMES;
m_bufferPtr = POCSAG_FSC_BITS;
io.setDecode(true);
}
}
if (m_bufferPtr == POCSAG_FRAME_LENGTH_BITS) {
m_lostCount--;
io.setDecode(false);
m_bufferPtr = 0U;
if (m_lostCount == 0U) {
m_state = POCSAGRXS_NONE;
pocsagDec.setIdle();
} else
pocsagDec.addData(m_buffer);
}
}