Made an attempt to eliminate creeping tape processing accuracy misses, which implied factoring out the GCM and LCD functions, which I then felt didn't really amount to signal processing.

NumberTheory/Factors.cpp

@@ -0,0 +1,34 @@
+//
+//  Factors.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 29/07/2016.
+//  Copyright © 2016 Thomas Harte. All rights reserved.
+//
+
+#include "Factors.hpp"
+
+unsigned int NumberTheory::greatest_common_divisor(unsigned int a, unsigned int b)
+{
+	if(a < b)
+	{
+		unsigned int swap = b;
+		b = a;
+		a = swap;
+	}
+
+	while(1) {
+		if(!a) return b;
+		if(!b) return a;
+
+		unsigned int remainder = a%b;
+		a = b;
+		b = remainder;
+	}
+}
+
+unsigned int NumberTheory::least_common_multiple(unsigned int a, unsigned int b)
+{
+	unsigned int gcd = greatest_common_divisor(a, b);
+	return (a*b) / gcd;
+}

NumberTheory/Factors.hpp

@@ -0,0 +1,17 @@
+//
+//  Factors.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 29/07/2016.
+//  Copyright © 2016 Thomas Harte. All rights reserved.
+//
+
+#ifndef Factors_hpp
+#define Factors_hpp
+
+namespace NumberTheory {
+	unsigned int greatest_common_divisor(unsigned int a, unsigned int b);
+	unsigned int least_common_multiple(unsigned int a, unsigned int b);
+}
+
+#endif /* Factors_hpp */

OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj

@@ -314,6 +314,7 @@
 		4BB299F71B587D8400A49093 /* txan in Resources */ = {isa = PBXBuildFile; fileRef = 4BB298EB1B587D8400A49093 /* txan */; };
 		4BB299F81B587D8400A49093 /* txsn in Resources */ = {isa = PBXBuildFile; fileRef = 4BB298EC1B587D8400A49093 /* txsn */; };
 		4BB299F91B587D8400A49093 /* tyan in Resources */ = {isa = PBXBuildFile; fileRef = 4BB298ED1B587D8400A49093 /* tyan */; };
+		4BB697C71D4B558F00248BDF /* Factors.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BB697C51D4B558F00248BDF /* Factors.cpp */; };
 		4BB73EA21B587A5100552FC2 /* AppDelegate.swift in Sources */ = {isa = PBXBuildFile; fileRef = 4BB73EA11B587A5100552FC2 /* AppDelegate.swift */; };
 		4BB73EA71B587A5100552FC2 /* Atari2600Document.xib in Resources */ = {isa = PBXBuildFile; fileRef = 4BB73EA51B587A5100552FC2 /* Atari2600Document.xib */; };
 		4BB73EA91B587A5100552FC2 /* Assets.xcassets in Resources */ = {isa = PBXBuildFile; fileRef = 4BB73EA81B587A5100552FC2 /* Assets.xcassets */; };
@@ -700,6 +701,8 @@
 		4BB298EB1B587D8400A49093 /* txan */ = {isa = PBXFileReference; lastKnownFileType = file; path = txan; sourceTree = "<group>"; };
 		4BB298EC1B587D8400A49093 /* txsn */ = {isa = PBXFileReference; lastKnownFileType = file; path = txsn; sourceTree = "<group>"; };
 		4BB298ED1B587D8400A49093 /* tyan */ = {isa = PBXFileReference; lastKnownFileType = file; path = tyan; sourceTree = "<group>"; };
+		4BB697C51D4B558F00248BDF /* Factors.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = Factors.cpp; path = ../../NumberTheory/Factors.cpp; sourceTree = "<group>"; };
+		4BB697C61D4B558F00248BDF /* Factors.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; name = Factors.hpp; path = ../../NumberTheory/Factors.hpp; sourceTree = "<group>"; };
 		4BB73E9E1B587A5100552FC2 /* Clock Signal.app */ = {isa = PBXFileReference; explicitFileType = wrapper.application; includeInIndex = 0; path = "Clock Signal.app"; sourceTree = BUILT_PRODUCTS_DIR; };
 		4BB73EA11B587A5100552FC2 /* AppDelegate.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AppDelegate.swift; sourceTree = "<group>"; };
 		4BB73EA61B587A5100552FC2 /* Base */ = {isa = PBXFileReference; lastKnownFileType = file.xib; name = Base; path = Base.lproj/Atari2600Document.xib; sourceTree = "<group>"; };
@@ -1291,6 +1294,15 @@
 			path = "Wolfgang Lorenz 6502 test suite";
 			sourceTree = "<group>";
 		};
+		4BB697C81D4B559300248BDF /* NumberTheory */ = {
+			isa = PBXGroup;
+			children = (
+				4BB697C51D4B558F00248BDF /* Factors.cpp */,
+				4BB697C61D4B558F00248BDF /* Factors.hpp */,
+			);
+			name = NumberTheory;
+			sourceTree = "<group>";
+		};
 		4BB73E951B587A5100552FC2 = {
 			isa = PBXGroup;
 			children = (
@@ -1300,6 +1312,7 @@
 				4BB73EC01B587A5100552FC2 /* Clock SignalUITests */,
 				4BC9DF4A1D04691600F44158 /* Components */,
 				4BB73EDC1B587CA500552FC2 /* Machines */,
+				4BB697C81D4B559300248BDF /* NumberTheory */,
 				4B366DFD1B5C165F0026627B /* Outputs */,
 				4BB73EDD1B587CA500552FC2 /* Processors */,
 				4BB73E9F1B587A5100552FC2 /* Products */,
@@ -1876,6 +1889,7 @@
 				4BC9DF4F1D04691600F44158 /* 6560.cpp in Sources */,
 				4BBF99151C8FBA6F0075DAFB /* CRTOpenGL.cpp in Sources */,
 				4B0CCC451C62D0B3001CAC5F /* CRT.cpp in Sources */,
+				4BB697C71D4B558F00248BDF /* Factors.cpp in Sources */,
 				4B55CE591C3B7D360093A61B /* ElectronDocument.swift in Sources */,
 				4B4DC82B1D2C27A4003C5BF8 /* SerialBus.cpp in Sources */,
 				4BC3B74F1CD194CC00F86E85 /* Shader.cpp in Sources */,

SignalProcessing/Stepper.hpp

@@ -13,11 +13,25 @@
 
 namespace SignalProcessing {
 
+/*!
+	Allows a repeating action running at an input rate to determine how many times it should
+	trigger an action that runs at an unrelated output rate; therefore it allows something with one
+	clock to sample something with another.
+
+	Uses a Bresenham-like error term internally for full-integral storage with no drift.
+*/
 class Stepper
 {
 	public:
+		/*!
+			Establishes a stepper with a one-to-one conversion rate.
+		*/
 		Stepper() : Stepper(1,1) {}
 
+		/*!
+			Establishes a stepper that will receive steps at the @c input_rate and dictate the number
+			of steps that should be taken at the @c output_rate.
+		*/
 		Stepper(uint64_t output_rate, uint64_t input_rate) :
 			accumulated_error_(0),
 			input_rate_(input_rate),
@@ -26,6 +40,11 @@ class Stepper
 			adjustment_up_((int64_t)(output_rate % input_rate) << 1),
 			adjustment_down_((int64_t)input_rate << 1) {}
 
+		/*!
+			Advances one step at the input rate.
+
+			@returns the number of output steps.
+		*/
 		inline uint64_t step()
 		{
 			uint64_t update = whole_step_;
@@ -38,11 +57,34 @@ class Stepper
 			return update;
 		}
 
+		/*!
+			Advances by @c number_of_steps steps at the input rate.
+
+			@returns the number of output steps.
+		*/
+		inline uint64_t step(uint64_t number_of_steps)
+		{
+			uint64_t update = whole_step_ * number_of_steps;
+			accumulated_error_ += adjustment_up_ * (int64_t)number_of_steps;
+			if(accumulated_error_ > 0)
+			{
+				update += 1 + (uint64_t)(accumulated_error_ / adjustment_down_);
+				accumulated_error_ = (accumulated_error_ % adjustment_down_) - adjustment_down_;
+			}
+			return update;
+		}
+
+		/*!
+			@returns the output rate.
+		*/
 		inline uint64_t get_output_rate()
 		{
 			return output_rate_;
 		}
 
+		/*!
+			@returns the input rate.
+		*/
 		inline uint64_t get_input_rate()
 		{
 			return input_rate_;

Storage/Disk/DiskDrive.cpp

@@ -12,13 +12,48 @@ using namespace Storage;
 
 DiskDrive::DiskDrive(unsigned int clock_rate, unsigned int revolutions_per_minute) :
 	_clock_rate(clock_rate),
-	_revolutions_per_minute(revolutions_per_minute) {}
+	_revolutions_per_minute(revolutions_per_minute),
+	_head_position(0) {}
 
 void DiskDrive::set_expected_bit_length(Time bit_length)
 {
 	_bit_length = bit_length;
 }
 
+void DiskDrive::set_disk(std::shared_ptr<Disk> disk)
+{
+	_disk = disk;
+//	_track.reset();
+}
+
+bool DiskDrive::has_disk()
+{
+	return (bool)_disk;
+}
+
+bool DiskDrive::get_is_track_zero()
+{
+	return _head_position == 0;
+}
+
+void DiskDrive::step(int direction)
+{
+	_head_position = std::max(_head_position + direction, 0);
+	_track = _disk->get_track_at_position((unsigned int)_head_position);
+}
+
 void DiskDrive::digital_phase_locked_loop_output_bit(int value)
 {
+	process_input_bit(value, _cycles_since_index_hole);
+}
+
+void DiskDrive::run_for_cycles(unsigned int number_of_cycles)
+{
+	if(has_disk())
+	{
+		while(number_of_cycles--)
+		{
+
+		}
+	}
 }

Storage/Disk/DiskDrive.hpp

@@ -11,6 +11,7 @@
 
 #include "Disk.hpp"
 #include "DigitalPhaseLockedLoop.hpp"
+#include "../../SignalProcessing/Stepper.hpp"
 
 namespace Storage {
 
@@ -40,6 +41,20 @@ class DiskDrive: public DigitalPhaseLockedLoop::Delegate {
 		Time _bit_length;
 		unsigned int _clock_rate;
 		unsigned int _revolutions_per_minute;
+
+		std::shared_ptr<DigitalPhaseLockedLoop> _pll;
+		std::shared_ptr<Disk> _disk;
+		std::shared_ptr<Track> _track;
+		int _head_position;
+		unsigned int _cycles_since_index_hole;
+
+		void install_track();
+
+		struct {
+			Track::Event current_event;
+			std::unique_ptr<SignalProcessing::Stepper> pulse_stepper;
+			uint32_t time_into_pulse;
+		} _input;
 };
 
 }

Storage/Disk/PCMTrack.cpp

@@ -7,34 +7,10 @@
 //
 
 #include "PCMTrack.hpp"
+#include "../../NumberTheory/Factors.hpp"
 
 using namespace Storage;
 
-unsigned int greatest_common_divisor(unsigned int a, unsigned int b)
-{
-	if(a < b)
-	{
-		unsigned int swap = b;
-		b = a;
-		a = swap;
-	}
-
-	while(1) {
-		if(!a) return b;
-		if(!b) return a;
-
-		unsigned int remainder = a%b;
-		a = b;
-		b = remainder;
-	}
-}
-
-unsigned int least_common_multiple(unsigned int a, unsigned int b)
-{
-	unsigned int gcd = greatest_common_divisor(a, b);
-	return (a*b) / gcd;
-}
-
 PCMTrack::PCMTrack(std::vector<PCMSegment> segments)
 {
 	_segments = std::move(segments);
@@ -87,7 +63,7 @@ void PCMTrack::fix_length()
 	_track_clock_rate = _segments[0].length_of_a_bit.clock_rate;
 	for(size_t c = 1; c < _segments.size(); c++)
 	{
-		_track_clock_rate = least_common_multiple(_track_clock_rate, _segments[c].length_of_a_bit.clock_rate);
+		_track_clock_rate = NumberTheory::least_common_multiple(_track_clock_rate, _segments[c].length_of_a_bit.clock_rate);
 	}
 
 	// therby determine the total length, storing it to next_event as the track-total divisor

Storage/Tape/Tape.cpp

@@ -7,6 +7,7 @@
 //
 
 #include "Tape.hpp"
+#include "../../NumberTheory/Factors.hpp"
 
 using namespace Storage;
 
@@ -22,6 +23,8 @@ TapePlayer::TapePlayer(unsigned int input_clock_rate) :
 void TapePlayer::set_tape(std::shared_ptr<Storage::Tape> tape)
 {
 	_tape = tape;
+	_input.pulse_stepper.reset();
+
 	get_next_pulse();
 }
 
@@ -32,7 +35,18 @@ bool TapePlayer::has_tape()
 
 void TapePlayer::get_next_pulse()
 {
-	_input.time_into_pulse = 0;
+	unsigned int previous_clock_rate = 0;
+
+	// figure out how much time has been run since the last bit ended
+	if(_input.pulse_stepper == nullptr)
+		_input.time_into_pulse = 0;
+	else
+	{
+		_input.time_into_pulse -= _input.current_pulse.length.length;
+		previous_clock_rate = _input.current_pulse.length.clock_rate;
+	}
+
+	// get the new pulse
 	if(_tape)
 		_input.current_pulse = _tape->get_next_pulse();
 	else
@@ -41,6 +55,24 @@ void TapePlayer::get_next_pulse()
 		_input.current_pulse.length.clock_rate = 1;
 		_input.current_pulse.type = Storage::Tape::Pulse::Zero;
 	}
+
+	// if there was any time left over, map into the new time base
+	if(_input.pulse_stepper && _input.time_into_pulse)
+	{
+		// simplify the quotient
+		unsigned int common_divisor = NumberTheory::greatest_common_divisor(_input.time_into_pulse, previous_clock_rate);
+		_input.time_into_pulse /= common_divisor;
+		previous_clock_rate /= common_divisor;
+
+		// build a quotient that is the sum of the time overrun plus the incoming time and adjust the time overrun
+		// to be in terms of the new quotient
+		unsigned int denominator = NumberTheory::least_common_multiple(previous_clock_rate, _input.current_pulse.length.clock_rate);
+		_input.current_pulse.length.length *= denominator / _input.current_pulse.length.clock_rate;
+		_input.current_pulse.length.clock_rate = denominator;
+		_input.time_into_pulse *= denominator / previous_clock_rate;
+	}
+
+	// adjust stepper if required
 	if(_input.pulse_stepper == nullptr || _input.current_pulse.length.clock_rate != _input.pulse_stepper->get_output_rate())
 	{
 		_input.pulse_stepper.reset(new SignalProcessing::Stepper(_input.current_pulse.length.clock_rate, _input_clock_rate));
@@ -51,13 +83,10 @@ void TapePlayer::run_for_cycles(unsigned int number_of_cycles)
 {
 	if(has_tape())
 	{
-		while(number_of_cycles--)
+		_input.time_into_pulse += (unsigned int)_input.pulse_stepper->step(number_of_cycles);
+		while(_input.time_into_pulse >= _input.current_pulse.length.length)
 		{
-			_input.time_into_pulse += (unsigned int)_input.pulse_stepper->step();
-			while(_input.time_into_pulse >= _input.current_pulse.length.length)
-			{
-				run_for_input_pulse();
-			}
+			run_for_input_pulse();
 		}
 	}
 }
@@ -66,4 +95,5 @@ void TapePlayer::run_for_input_pulse()
 {
 	process_input_pulse(_input.current_pulse);
 	get_next_pulse();
+	_input.time_into_pulse = 0;
 }