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89 lines
2.2 KiB
C++
89 lines
2.2 KiB
C++
//
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// HalfDuplexSerial.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 20/03/2024.
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// Copyright © 2024 Thomas Harte. All rights reserved.
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//
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#pragma once
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namespace Archimedes {
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/// Models a half-duplex serial link between two parties, framing bytes with one start bit and two stop bits.
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struct HalfDuplexSerial {
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static constexpr uint16_t ShiftMask = 0b1111'1110'0000'0000;
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/// Enqueues @c value for output.
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void output(int party, uint8_t value) {
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parties_[party].output_count = 11;
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parties_[party].input = 0x7ff;
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parties_[party].output = uint16_t((value << 1) | ShiftMask);
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}
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/// @returns The last observed input.
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uint8_t input(int party) const {
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return uint8_t(parties_[party].input >> 1);
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}
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static constexpr uint8_t Receive = 1 << 0;
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static constexpr uint8_t Transmit = 1 << 1;
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/// @returns A bitmask of events that occurred during the last shift.
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uint8_t events(int party) {
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const auto result = parties_[party].events;
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parties_[party].events = 0;
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return result;
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}
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bool is_outputting(int party) const {
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return parties_[party].output_count != 11;
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}
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/// Updates the shifters on both sides of the serial link.
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void shift() {
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const uint16_t next = parties_[0].output & parties_[1].output & 1;
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for(int c = 0; c < 2; c++) {
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if(parties_[c].output_count) {
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--parties_[c].output_count;
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if(!parties_[c].output_count) {
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parties_[c].events |= Transmit;
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parties_[c].input_count = -1;
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}
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parties_[c].output = (parties_[c].output >> 1) | ShiftMask;
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} else {
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// Check for a start bit.
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if(parties_[c].input_count == -1 && !next) {
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parties_[c].input_count = 0;
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}
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// Shift in if currently observing.
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if(parties_[c].input_count >= 0 && parties_[c].input_count < 11) {
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parties_[c].input = uint16_t((parties_[c].input >> 1) | (next << 10));
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++parties_[c].input_count;
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if(parties_[c].input_count == 11) {
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parties_[c].events |= Receive;
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parties_[c].input_count = -1;
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}
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}
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}
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}
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}
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private:
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struct Party {
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int output_count = 0;
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int input_count = -1;
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uint16_t output = 0xffff;
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uint16_t input = 0;
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uint8_t events = 0;
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} parties_[2];
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};
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static constexpr int IOCParty = 0;
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static constexpr int KeyboardParty = 1;
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}
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