CLK/Storage/Disk/Drive.cpp

//
//  Drive.cpp
//  Clock Signal
//
//  Created by Thomas Harte on 25/09/2016.
//  Copyright 2016 Thomas Harte. All rights reserved.
//

#include "Drive.hpp"

#include "Track/UnformattedTrack.hpp"

#include <algorithm>
#include <cassert>
#include <cmath>
#include <chrono>
#include <random>

using namespace Storage::Disk;

Drive::Drive(int input_clock_rate, int revolutions_per_minute, int number_of_heads):
	Storage::TimedEventLoop(input_clock_rate),
	available_heads_(number_of_heads) {
	set_rotation_speed(revolutions_per_minute);

	const auto seed = static_cast<std::default_random_engine::result_type>(std::chrono::system_clock::now().time_since_epoch().count());
	std::default_random_engine randomiser(seed);

	// Get at least 64 bits of random information; rounding is likey to give this a slight bias.
	random_source_ = 0;
	auto half_range = (randomiser.max() - randomiser.min()) / 2;
	for(int bit = 0; bit < 64; ++bit) {
		random_source_ <<= 1;
		random_source_ |= ((randomiser() - randomiser.min()) >= half_range) ? 1 : 0;
	}
}

Drive::Drive(int input_clock_rate, int number_of_heads) : Drive(input_clock_rate, 300, number_of_heads) {}

void Drive::set_rotation_speed(float revolutions_per_minute) {
	// Rationalise the supplied speed so that cycles_per_revolution_ is exact.
	cycles_per_revolution_ = int(0.5f + float(get_input_clock_rate()) * 60.0f / revolutions_per_minute);

	// From there derive the appropriate rotational multiplier and possibly update the
	// count of cycles since the index hole proportionally.
	const float new_rotational_multiplier = float(cycles_per_revolution_) / float(get_input_clock_rate());
	cycles_since_index_hole_ *= new_rotational_multiplier / rotational_multiplier_;
	rotational_multiplier_ = new_rotational_multiplier;
	cycles_since_index_hole_ %= cycles_per_revolution_;
}

Drive::~Drive() {
	if(disk_) disk_->flush_tracks();
}

void Drive::set_disk(const std::shared_ptr<Disk> &disk) {
	if(disk_) disk_->flush_tracks();
	disk_ = disk;
	has_disk_ = !!disk_;

	invalidate_track();
	did_set_disk();
	update_clocking_observer();
}

bool Drive::has_disk() const {
	return has_disk_;
}

ClockingHint::Preference Drive::preferred_clocking() {
	return (!motor_is_on_ || !has_disk_) ? ClockingHint::Preference::None : ClockingHint::Preference::JustInTime;
}

bool Drive::get_is_track_zero() const {
	return head_position_ == HeadPosition(0);
}

void Drive::step(HeadPosition offset) {
	HeadPosition old_head_position = head_position_;
	head_position_ += offset;
	if(head_position_ < HeadPosition(0)) {
		head_position_ = HeadPosition(0);
		if(observer_) observer_->announce_drive_event(drive_name_, Activity::Observer::DriveEvent::StepBelowZero);
	} else {
		if(observer_) observer_->announce_drive_event(drive_name_, Activity::Observer::DriveEvent::StepNormal);
	}

	// If the head moved, flush the old track.
	if(head_position_ != old_head_position) {
		track_ = nullptr;
	}

	// Allow a subclass to react, if desired.
	did_step(head_position_);
}

std::shared_ptr<Track> Drive::step_to(HeadPosition offset) {
	HeadPosition old_head_position = head_position_;
	head_position_ = std::max(offset, HeadPosition(0));

	if(disk_ && head_position_ != old_head_position) {
		track_ = nullptr;
		setup_track();
	}

	return track_;
}

void Drive::set_head(int head) {
	head = std::min(head, available_heads_ - 1);
	if(head != head_) {
		head_ = head;
		track_ = nullptr;
	}
}

int Drive::get_head_count() const {
	return available_heads_;
}

bool Drive::get_tachometer() const {
	// I have made a guess here that the tachometer is a symmetric square wave;
	// if that is correct then around 60 beats per rotation appears to be correct
	// to proceed beyond the speed checks I've so far uncovered.
	constexpr float ticks_per_rotation = 60.0f; // 56 was too low; 64 too high.
	return int(get_rotation() * 2.0f * ticks_per_rotation) & 1;
}

float Drive::get_rotation() const {
	return get_time_into_track();
}

float Drive::get_time_into_track() const {
	// i.e. amount of time since the index hole was seen, as a proportion of a second,
	// converted to a proportion of a rotation.
	return float(cycles_since_index_hole_) / (float(get_input_clock_rate()) * rotational_multiplier_);
}

bool Drive::get_is_read_only() const {
	if(disk_) return disk_->get_is_read_only();
	return true;
}

bool Drive::get_is_ready() const {
	return ready_index_count_ == 2;
}

void Drive::set_motor_on(bool motor_is_on) {
	if(motor_is_on_ != motor_is_on) {
		motor_is_on_ = motor_is_on;

		if(observer_) {
			observer_->set_drive_motor_status(drive_name_, motor_is_on_);
			if(announce_motor_led_) {
				observer_->set_led_status(drive_name_, motor_is_on_);
			}
		}

		if(!motor_is_on) {
			ready_index_count_ = 0;
			if(disk_) disk_->flush_tracks();
		}
		update_clocking_observer();
	}
}

bool Drive::get_motor_on() const {
	return motor_is_on_;
}

bool Drive::get_index_pulse() const {
	return index_pulse_remaining_ > Cycles(0);
}

void Drive::set_event_delegate(Storage::Disk::Drive::EventDelegate *delegate) {
	event_delegate_ = delegate;
}

void Drive::advance(const Cycles cycles) {
	cycles_since_index_hole_ += cycles.as_integral();
	if(event_delegate_) event_delegate_->advance(cycles);
}

void Drive::run_for(const Cycles cycles) {
	// Assumed: the index pulse pulses even if the drive has stopped spinning.
	index_pulse_remaining_ = std::max(index_pulse_remaining_ - cycles, Cycles(0));

	if(motor_is_on_) {
		if(has_disk_) {
			Time zero(0);

			auto number_of_cycles = cycles.as_integral();
			while(number_of_cycles) {
				auto cycles_until_next_event = get_cycles_until_next_event();
				auto cycles_to_run_for = std::min(cycles_until_next_event, number_of_cycles);
				if(!is_reading_ && cycles_until_bits_written_ > zero) {
					auto write_cycles_target = cycles_until_bits_written_.get<Cycles::IntType>();
					if(cycles_until_bits_written_.length % cycles_until_bits_written_.clock_rate) ++write_cycles_target;
					cycles_to_run_for = std::min(cycles_to_run_for, write_cycles_target);
				}

				number_of_cycles -= cycles_to_run_for;
				if(!is_reading_) {
					if(cycles_until_bits_written_ > zero) {
						Storage::Time cycles_to_run_for_time(static_cast<int>(cycles_to_run_for));
						if(cycles_until_bits_written_ <= cycles_to_run_for_time) {
							if(event_delegate_) event_delegate_->process_write_completed();
							if(cycles_until_bits_written_ <= cycles_to_run_for_time)
								cycles_until_bits_written_.set_zero();
							else
								cycles_until_bits_written_ -= cycles_to_run_for_time;
						} else {
							cycles_until_bits_written_ -= cycles_to_run_for_time;
						}
					}
				}
				TimedEventLoop::run_for(Cycles(cycles_to_run_for));
			}
		} else {
			TimedEventLoop::run_for(cycles);
		}
	}
}

// MARK: - Track timed event loop

void Drive::get_next_event(float duration_already_passed) {
	if(!disk_) {
		current_event_.type = Track::Event::IndexHole;
		current_event_.length = 1.0f;
		set_next_event_time_interval((current_event_.length - duration_already_passed) * rotational_multiplier_);
		return;
	}

	// Grab a new track if not already in possession of one. This will recursively call get_next_event,
	// supplying a proper duration_already_passed.
	if(!track_) {
		random_interval_ = 0.0f;
		setup_track();
		return;
	}

	// If gain has now been turned up so as to generate noise, generate some noise.
	if(random_interval_ > 0.0f) {
		current_event_.type = Track::Event::FluxTransition;
		current_event_.length = float(2 + (random_source_&1)) / 1000000.0f;
		random_source_ = (random_source_ >> 1) | (random_source_ << 63);

		if(random_interval_ < current_event_.length) {
			current_event_.length = random_interval_;
			random_interval_ = 0.0f;
		} else {
			random_interval_ -= current_event_.length;
		}
		set_next_event_time_interval(current_event_.length);
		return;
	}

	if(track_) {
		const auto track_event = track_->get_next_event();
		current_event_.type = track_event.type;
		current_event_.length = track_event.length.get<float>();
	} else {
		current_event_.length = 1.0f;
		current_event_.type = Track::Event::IndexHole;
	}

	// Begin a 2ms period of holding the index line pulse active if this is an index pulse event.
	if(current_event_.type == Track::Event::IndexHole) {
		index_pulse_remaining_ = Cycles((get_input_clock_rate() * 2) / 1000);
	}

	// divide interval, which is in terms of a single rotation of the disk, by rotation speed to
	// convert it into revolutions per second; this is achieved by multiplying by rotational_multiplier_
	float interval = std::max((current_event_.length - duration_already_passed) * rotational_multiplier_, 0.0f);

	// An interval greater than 15ms => adjust gain up the point where noise starts happening.
	// Seed that up and leave a 15ms gap until it starts.
	constexpr float safe_gain_period = 15.0f / 1000000.0f;
	if(interval >= safe_gain_period) {
		random_interval_ = interval - safe_gain_period;
		interval = safe_gain_period;
	}

	set_next_event_time_interval(interval);
}

void Drive::process_next_event() {
	if(current_event_.type == Track::Event::IndexHole) {
		if(ready_index_count_ < 2) ready_index_count_++;
		cycles_since_index_hole_ = 0;
	}
	if(
		event_delegate_ &&
		(current_event_.type == Track::Event::IndexHole || is_reading_)
	){
		event_delegate_->process_event(current_event_);
	}
	get_next_event(0.0f);
}

// MARK: - Track management

std::shared_ptr<Track> Drive::get_track() {
	if(disk_) return disk_->get_track_at_position(Track::Address(head_, head_position_));
	return nullptr;
}

void Drive::set_track(const std::shared_ptr<Track> &track) {
	if(disk_) disk_->set_track_at_position(Track::Address(head_, head_position_), track);
}

void Drive::setup_track() {
	track_ = get_track();
	if(!track_) {
		track_ = std::make_shared<UnformattedTrack>();
	}

	float offset = 0.0f;
	const auto track_time_now = get_time_into_track();
	const auto time_found = track_->seek_to(Time(track_time_now)).get<float>();

	// `time_found` can be greater than `track_time_now` if limited precision caused rounding.
	if(time_found <= track_time_now) {
		offset = track_time_now - time_found;
	}

	// Reseed cycles_since_index_hole_; 99.99% of the time it'll still be correct as is,
	// but if the track has rounded one way or the other it may now be very slightly adrift.
	cycles_since_index_hole_ = (int((time_found + offset) * cycles_per_revolution_)) % cycles_per_revolution_;

	get_next_event(offset);
}

void Drive::invalidate_track() {
	random_interval_ = 0.0f;
	track_ = nullptr;
	if(patched_track_) {
		set_track(patched_track_);
		patched_track_ = nullptr;
	}
}

// MARK: - Writing

void Drive::begin_writing(Time bit_length, bool clamp_to_index_hole) {
	// Do nothing if already writing.
	// TODO: cope properly if there's no disk to write to.
	if(!is_reading_ || !disk_) return;

	// Get a copy of the track if that hasn't happened yet.
	if(!track_) {
		setup_track();
	}

	// Store the relevant parameters, and kick off writing.
	is_reading_ = false;
	clamp_writing_to_index_hole_ = clamp_to_index_hole;

	cycles_per_bit_ = Storage::Time(int(get_input_clock_rate())) * bit_length;
	cycles_per_bit_.simplify();

	write_segment_.length_of_a_bit = bit_length / Time(rotational_multiplier_);
	write_segment_.data.clear();

	write_start_time_ = Time(get_time_into_track());
}

void Drive::write_bit(bool value) {
	write_segment_.data.push_back(value);
	cycles_until_bits_written_ += cycles_per_bit_;
}

void Drive::end_writing() {
	// If the user modifies a track, it's scaled up to a "high" resolution and modifications
	// are plotted on top of that.
	//
	// "High" is defined as: two samples per clock relative to an idiomatic
	// 8Mhz disk controller and 300RPM disk speed.
	const size_t high_resolution_track_rate = 3200000;

	if(!is_reading_) {
		is_reading_ = true;

		if(!patched_track_) {
			// Avoid creating a new patched track if this one is already patched
			patched_track_ = std::dynamic_pointer_cast<PCMTrack>(track_);
			if(!patched_track_ || !patched_track_->is_resampled_clone()) {
				Track *const tr = track_.get();
				patched_track_.reset(PCMTrack::resampled_clone(tr, high_resolution_track_rate));
			}
		}
		patched_track_->add_segment(write_start_time_, write_segment_, clamp_writing_to_index_hole_);
		cycles_since_index_hole_ %= cycles_per_revolution_;
		invalidate_track();
	}
}

bool Drive::is_writing() const {
	return !is_reading_;
}

void Drive::set_activity_observer(Activity::Observer *observer, const std::string &name, bool add_motor_led) {
	observer_ = observer;
	announce_motor_led_ = add_motor_led;
	if(observer) {
		drive_name_ = name;

		observer->register_drive(drive_name_);
		observer->set_drive_motor_status(drive_name_, motor_is_on_);

		if(add_motor_led) {
			observer->register_led(drive_name_);
			observer->set_led_status(drive_name_, motor_is_on_);
		}
	}
}