CLK/Components/Serial/Line.cpp

//
//  SerialPort.cpp
//  Clock Signal
//
//  Created by Thomas Harte on 12/10/2019.
//  Copyright © 2019 Thomas Harte. All rights reserved.
//

#include "Line.hpp"

#include <cassert>
#include <limits>

using namespace Serial;

template <bool include_clock>
void Line<include_clock>::set_writer_clock_rate(const HalfCycles clock_rate) {
	clock_rate_ = clock_rate;
}

template <bool include_clock>
void Line<include_clock>::advance_writer(HalfCycles cycles) {
	if(cycles == HalfCycles(0)) return;

	const auto integral_cycles = cycles.as_integral();
	remaining_delays_ = std::max(remaining_delays_ - integral_cycles, Cycles::IntType(0));
	if(events_.empty()) {
		write_cycles_since_delegate_call_ += integral_cycles;
		if(transmission_extra_) {
			transmission_extra_ -= integral_cycles;
			if(transmission_extra_ <= 0) {
				transmission_extra_ = 0;
				if constexpr (!include_clock) {
					update_delegate(level_);
				}
			}
		}
	} else {
		while(!events_.empty()) {
			if(events_.front().delay <= integral_cycles) {
				cycles -= events_.front().delay;
				write_cycles_since_delegate_call_ += events_.front().delay;
				const auto old_level = level_;

				auto iterator = events_.begin() + 1;
				while(iterator != events_.end() && iterator->type != Event::Delay) {
					level_ = iterator->type == Event::SetHigh;
					if constexpr(include_clock) {
						update_delegate(level_);
					}
					++iterator;
				}
				events_.erase(events_.begin(), iterator);

				if constexpr (!include_clock) {
					if(old_level != level_) {
						update_delegate(old_level);
					}
				}

				// Book enough extra time for the read delegate to be posted
				// the final bit if one is attached.
				if(events_.empty()) {
					transmission_extra_ = minimum_write_cycles_for_read_delegate_bit();
				}
			} else {
				events_.front().delay -= integral_cycles;
				write_cycles_since_delegate_call_ += integral_cycles;
				break;
			}
		}
	}
}

template <bool include_clock>
void Line<include_clock>::write(const bool level) {
	if(!events_.empty()) {
		events_.emplace_back();
		events_.back().type = level ? Event::SetHigh : Event::SetLow;
	} else {
		level_ = level;
		transmission_extra_ = minimum_write_cycles_for_read_delegate_bit();
	}
}

template <bool include_clock>
template <bool lsb_first, typename IntT> void Line<include_clock>::write_internal(
	const HalfCycles cycles,
	int count,
	const IntT levels
) {
	remaining_delays_ += count * cycles.as_integral();

	auto event = events_.size();
	events_.resize(events_.size() + size_t(count)*2);
	while(count--) {
		events_[event].type = Event::Delay;
		events_[event].delay = int(cycles.as_integral());
		IntT bit;
		if constexpr (lsb_first) {
			bit = levels & 1;
			levels >>= 1;
		} else {
			constexpr auto top_bit = IntT(0x80) << ((sizeof(IntT) - 1) * 8);
			bit = levels & top_bit;
			levels <<= 1;
		}

		events_[event+1].type = bit ? Event::SetHigh : Event::SetLow;
		event += 2;
	}
}

template <bool include_clock>
void Line<include_clock>::write(const HalfCycles cycles, const int count, const int levels) {
	write_internal<true, int>(cycles, count, levels);
}

template <bool include_clock>
template <bool lsb_first, typename IntT> void Line<include_clock>::write(const HalfCycles cycles, const IntT value) {
	write_internal<lsb_first, IntT>(cycles, 8 * sizeof(IntT), value);
}

template <bool include_clock>
void Line<include_clock>::reset_writing() {
	remaining_delays_ = 0;
	events_.clear();
}

template <bool include_clock>
bool Line<include_clock>::read() const {
	return level_;
}

template <bool include_clock>
void Line<include_clock>::set_read_delegate(
	ReadDelegate *const delegate,
	[[maybe_unused]] const Storage::Time bit_length
) {
	read_delegate_ = delegate;
	if constexpr (!include_clock) {
		assert(bit_length > Storage::Time(0));
		read_delegate_bit_length_ = bit_length;
		read_delegate_bit_length_.simplify();
		write_cycles_since_delegate_call_ = 0;
	}
}

template <bool include_clock>
void Line<include_clock>::update_delegate(const bool level) {
	// Exit early if there's no delegate, or if the delegate is waiting for
	// zero and this isn't zero.
	if(!read_delegate_) return;

	if constexpr (!include_clock) {
		const int cycles_to_forward = write_cycles_since_delegate_call_;
		write_cycles_since_delegate_call_ = 0;
		if(level && read_delegate_phase_ == ReadDelegatePhase::WaitingForZero) return;

		// Deal with a transition out of waiting-for-zero mode by seeding time left
		// in bit at half a bit.
		if(read_delegate_phase_ == ReadDelegatePhase::WaitingForZero) {
			time_left_in_bit_ = read_delegate_bit_length_;
			time_left_in_bit_.clock_rate <<= 1;
			read_delegate_phase_ = ReadDelegatePhase::Serialising;
		}

		// Forward as many bits as occur.
		Storage::Time time_left(cycles_to_forward, int(clock_rate_.as_integral()));
		const int bit = level ? 1 : 0;
		while(time_left >= time_left_in_bit_) {
			if(!read_delegate_->serial_line_did_produce_bit(this, bit)) {
				read_delegate_phase_ = ReadDelegatePhase::WaitingForZero;
				if(bit) return;
			}

			time_left -= time_left_in_bit_;
			time_left_in_bit_ = read_delegate_bit_length_;
		}
		time_left_in_bit_ -= time_left;
	} else {
		read_delegate_->serial_line_did_produce_bit(this, level);
	}
}

template <bool include_clock>
Cycles::IntType Line<include_clock>::minimum_write_cycles_for_read_delegate_bit() {
	if(!read_delegate_) return 0;
	return 1 + (read_delegate_bit_length_ * unsigned(clock_rate_.as_integral())).template get<int>();
}

//
// Explicitly instantiate the meaningful instances of templates above;
// this class uses templates primarily to keep the interface compact and
// to take advantage of constexpr functionality selection, not so as
// to be generic.
//

template class Serial::Line<true>;
template class Serial::Line<false>;

template void Line<true>::write<true, uint8_t>(HalfCycles, uint8_t);
template void Line<true>::write<false, uint8_t>(HalfCycles, uint8_t);
template void Line<true>::write<true, uint16_t>(HalfCycles, uint16_t);
template void Line<true>::write<false, uint16_t>(HalfCycles, uint16_t);
template void Line<true>::write<true, uint32_t>(HalfCycles, uint32_t);
template void Line<true>::write<false, uint32_t>(HalfCycles, uint32_t);
template void Line<true>::write<true, uint64_t>(HalfCycles, uint64_t);
template void Line<true>::write<false, uint64_t>(HalfCycles, uint64_t);

template void Line<false>::write<true, uint8_t>(HalfCycles, uint8_t);
template void Line<false>::write<false, uint8_t>(HalfCycles, uint8_t);
template void Line<false>::write<true, uint16_t>(HalfCycles, uint16_t);
template void Line<false>::write<false, uint16_t>(HalfCycles, uint16_t);
template void Line<false>::write<true, uint32_t>(HalfCycles, uint32_t);
template void Line<false>::write<false, uint32_t>(HalfCycles, uint32_t);
template void Line<false>::write<true, uint64_t>(HalfCycles, uint64_t);
template void Line<false>::write<false, uint64_t>(HalfCycles, uint64_t);