portapack-mayhem/firmware/baseband/phase_detector.hpp
2016-04-11 11:50:03 -07:00

69 lines
2.1 KiB
C++

/*
* Copyright (C) 2016 Jared Boone, ShareBrained Technology, Inc.
*
* This file is part of PortaPack.
*
* 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, 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; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/
#ifndef __PHASE_DETECTOR_HPP__
#define __PHASE_DETECTOR_HPP__
#include <cstdint>
#include <cstddef>
#include <cmath>
class PhaseDetectorEarlyLateGate {
public:
using history_t = uint32_t;
using symbol_t = bool;
using error_t = int;
struct result_t {
symbol_t symbol;
error_t error;
};
constexpr PhaseDetectorEarlyLateGate(
const float samples_per_symbol
) : late_mask { (1U << static_cast<size_t>(std::ceil(samples_per_symbol / 2))) - 1 },
early_mask { late_mask << static_cast<size_t>(std::floor(samples_per_symbol / 2)) },
sample_bit { static_cast<size_t>(std::floor(samples_per_symbol / 2)) }
{
}
result_t operator()(const history_t symbol_history) const {
// history = ...0111, early
// history = ...1110, late
const symbol_t symbol = (symbol_history >> sample_bit) & 1;
const int late_side = __builtin_popcount(symbol_history & late_mask);
const int early_side = __builtin_popcount(symbol_history & early_mask);
const int lateness = late_side - early_side;
const int direction = lateness; //std::min(std::max(lateness, -1), 1);
const error_t error = direction;
return { symbol, error };
}
private:
const history_t late_mask;
const history_t early_mask;
const size_t sample_bit;
};
#endif/*__PHASE_DETECTOR_HPP__*/