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73 lines
2.0 KiB
C++
73 lines
2.0 KiB
C++
//
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// DigitalPhaseLockedLoop.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 11/07/2016.
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// Copyright © 2016 Thomas Harte. All rights reserved.
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//
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#include "DigitalPhaseLockedLoop.hpp"
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#include <algorithm>
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#include <cstdlib>
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using namespace Storage;
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DigitalPhaseLockedLoop::DigitalPhaseLockedLoop(int clocks_per_bit, size_t length_of_history) :
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clocks_per_bit_(clocks_per_bit),
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phase_(0),
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window_length_(clocks_per_bit),
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offset_history_pointer_(0),
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offset_history_(length_of_history, 0),
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offset_(0) {}
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void DigitalPhaseLockedLoop::run_for(const Cycles &cycles) {
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offset_ += cycles.as_int();
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phase_ += cycles.as_int();
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if(phase_ >= window_length_) {
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int windows_crossed = phase_ / window_length_;
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// check whether this triggers any 0s, if anybody cares
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if(delegate_) {
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if(window_was_filled_) windows_crossed--;
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for(int c = 0; c < windows_crossed; c++)
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delegate_->digital_phase_locked_loop_output_bit(0);
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}
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window_was_filled_ = false;
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phase_ %= window_length_;
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}
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}
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void DigitalPhaseLockedLoop::add_pulse() {
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if(!window_was_filled_) {
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if(delegate_) delegate_->digital_phase_locked_loop_output_bit(1);
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window_was_filled_ = true;
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post_phase_offset(phase_, offset_);
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offset_ = 0;
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}
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}
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void DigitalPhaseLockedLoop::post_phase_offset(int new_phase, int new_offset) {
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offset_history_[offset_history_pointer_] = new_offset;
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offset_history_pointer_ = (offset_history_pointer_ + 1) % offset_history_.size();
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// use an unweighted average of the stored offsets to compute current window size,
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// bucketing them by rounding to the nearest multiple of the base clocks per bit
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int total_spacing = 0;
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int total_divisor = 0;
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for(int offset : offset_history_) {
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int multiple = (offset + (clocks_per_bit_ >> 1)) / clocks_per_bit_;
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if(!multiple) continue;
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total_divisor += multiple;
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total_spacing += offset;
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}
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if(total_divisor) {
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window_length_ = total_spacing / total_divisor;
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}
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int error = new_phase - (window_length_ >> 1);
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// use a simple spring mechanism as a lowpass filter for phase
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phase_ -= (error + 1) >> 1;
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}
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