Merge pull request #18 from TomHarte/Vic-20

Adds basic NTSC VIC-20 emulation.
2025-01-27 06:35:04 +00:00 · 2016-06-14 18:20:06 -04:00 · 2016-06-14 18:20:06 -04:00 · 8c82f6ae37
commit 8c82f6ae37
parent ebaad920a8 a2a6e3c818
29 changed files with 1523 additions and 90 deletions
--- a/.gitignore
+++ b/.gitignore
@ -18,8 +18,8 @@ DerivedData
 *.xcuserstate
 .DS_Store

-# Exclude Electron ROMs
-OSBindings/Mac/Clock Signal/Resources/Electron/*
+# Exclude system ROMs
+ROMImages/*

 # CocoaPods
 #
--- a/Components/6522/6522.cpp
+++ b/Components/6522/6522.cpp
@ -0,0 +1,12 @@
+//
+//  6522.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 06/06/2016.
+//  Copyright © 2016 Thomas Harte. All rights reserved.
+//
+
+#include "6522.hpp"
+
+using namespace MOS;
+
--- a/Components/6522/6522.hpp
+++ b/Components/6522/6522.hpp
@ -0,0 +1,233 @@
+//
+//  6522.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 06/06/2016.
+//  Copyright © 2016 Thomas Harte. All rights reserved.
+//
+
+#ifndef _522_hpp
+#define _522_hpp
+
+#include <cstdint>
+#include <cstdio>
+
+namespace MOS {
+
+class MOS6522Delegate {
+	public:
+		virtual void mos6522_did_change_interrupt_status(void *mos6522) = 0;
+};
+
+template <class T> class MOS6522 {
+	private:
+		enum InterruptFlag: uint8_t {
+			CA2ActiveEdge	= 1 << 0,
+			CA1ActiveEdge	= 1 << 1,
+			ShiftRegister	= 1 << 2,
+			CB2ActiveEdge	= 1 << 3,
+			CB1ActiveEdge	= 1 << 4,
+			Timer2			= 1 << 5,
+			Timer1			= 1 << 6,
+		};
+
+	public:
+		void set_register(int address, uint8_t value)
+		{
+			address &= 0xf;
+//			printf("6522 %p: %d <- %02x\n", this, address, value);
+			switch(address)
+			{
+				case 0x0:
+					_registers.output[1] = value;
+					static_cast<T *>(this)->set_port_output(1, value);	// TODO: handshake
+				break;
+				case 0x1:
+					_registers.output[0] = value;
+					static_cast<T *>(this)->set_port_output(0, value);	// TODO: handshake
+				break;
+				case 0xf:
+					// No handshake, so write directly
+					_registers.output[0] = value;
+					static_cast<T *>(this)->set_port_output(0, value);
+				break;
+
+				case 0x2:
+					_registers.data_direction[1] = value;
+				break;
+				case 0x3:
+					_registers.data_direction[0] = value;
+				break;
+
+				// Timer 1
+				case 0x6:	case 0x4:	_registers.timer_latch[0] = (_registers.timer_latch[0]&0xff00) | value;	break;
+				case 0x5:	case 0x7:
+					_registers.timer_latch[0] = (_registers.timer_latch[0]&0x00ff) | (uint16_t)(value << 8);
+					_registers.interrupt_flags &= ~InterruptFlag::Timer1;
+					if(address == 0x05)
+					{
+						_registers.timer[0] = _registers.timer_latch[0];
+						_timer_is_running[0] = true;
+					}
+					reevaluate_interrupts();
+				break;
+
+				// Timer 2
+				case 0x8:	_registers.timer_latch[1] = value;	break;
+				case 0x9:
+					_registers.interrupt_flags &= ~InterruptFlag::Timer2;
+					_registers.timer[1] = _registers.timer_latch[1] | (uint16_t)(value << 8);
+					_timer_is_running[1] = true;
+					reevaluate_interrupts();
+				break;
+
+				// Shift
+				case 0xa:	_registers.shift = value;				break;
+
+				// Control
+				case 0xb: _registers.auxiliary_control = value;		break;
+				case 0xc: _registers.peripheral_control = value;	break;
+
+				// Interrupt control
+				case 0xd:
+					_registers.interrupt_flags &= ~value;
+					reevaluate_interrupts();
+				break;
+				case 0xe:
+					if(value&0x80)
+						_registers.interrupt_enable |= value;
+					else
+						_registers.interrupt_enable &= ~value;
+					reevaluate_interrupts();
+				break;
+			}
+		}
+
+		uint8_t get_register(int address)
+		{
+			address &= 0xf;
+//			printf("6522 %p: %d\n", this, address);
+			switch(address)
+			{
+//				case 0x0:	return (_registers.auxiliary_control & 0x40) ? _registers.input[1] : static_cast<T *>(this)->get_port_input(1);
+				case 0x0:	return _registers.output[1];//static_cast<T *>(this)->get_port_input(1);
+				case 0xf:	// TODO: handshake, latching
+				case 0x1:	return static_cast<T *>(this)->get_port_input(0);
+
+				case 0x2:	return _registers.data_direction[1];
+				case 0x3:	return _registers.data_direction[0];
+
+				// Timer 1
+				case 0x4:
+					_registers.interrupt_flags &= ~InterruptFlag::Timer1;
+					reevaluate_interrupts();
+				return _registers.timer[0] & 0x00ff;
+				case 0x5:	return _registers.timer[0] >> 8;
+				case 0x6:	return _registers.timer_latch[0] & 0x00ff;
+				case 0x7:	return _registers.timer_latch[0] >> 8;
+
+				// Timer 2
+				case 0x8:
+					_registers.interrupt_flags &= ~InterruptFlag::Timer2;
+					reevaluate_interrupts();
+				return _registers.timer[1] & 0x00ff;
+				case 0x9:	return _registers.timer[1] >> 8;
+
+				case 0xa:	return _registers.shift;
+
+				case 0xb:	return _registers.auxiliary_control;
+				case 0xc:	return _registers.peripheral_control;
+
+				case 0xd:	return _registers.interrupt_flags | (get_interrupt_line() ? 0x80 : 0x00);
+				case 0xe:	return _registers.interrupt_enable | 0x80;
+			}
+
+			return 0xff;
+		}
+
+		void set_control_line_input(int port, int line, bool value)
+		{
+		}
+
+		void run_for_cycles(unsigned int number_of_cycles)
+		{
+			_registers.timer[0] -= number_of_cycles;
+			_registers.timer[1] -= number_of_cycles;
+
+			if(!_registers.timer[1] && _timer_is_running[1])
+			{
+				_timer_is_running[1] = false;
+				_registers.interrupt_flags |= InterruptFlag::Timer2;
+				reevaluate_interrupts();
+			}
+
+			if(!_registers.timer[0] && _timer_is_running[0])
+			{
+				_registers.interrupt_flags |= InterruptFlag::Timer1;
+				reevaluate_interrupts();
+
+				// TODO: reload shouldn't occur for a further 1.5 cycles
+				if(_registers.auxiliary_control&0x40)
+					_registers.timer[0] = _registers.timer_latch[0];
+				else
+					_timer_is_running[0] = false;
+			}
+			// TODO: lots of other status effects
+		}
+
+		bool get_interrupt_line()
+		{
+			uint8_t interrupt_status = _registers.interrupt_flags & _registers.interrupt_enable & 0x7f;
+			return !!interrupt_status;
+		}
+
+		void set_delegate(MOS6522Delegate *delegate)
+		{
+			_delegate = delegate;
+		}
+
+		MOS6522() :
+			_timer_is_running{false, false},
+			_last_posted_interrupt_status(false)
+		{}
+
+	private:
+		// Intended to be overwritten
+		uint8_t get_port_input(int port)				{	return 0xff;	}
+		void set_port_output(int port, uint8_t value)	{}
+
+		// Delegate and communications
+		MOS6522Delegate *_delegate;
+		bool _last_posted_interrupt_status;
+		inline void reevaluate_interrupts()
+		{
+			bool new_interrupt_status = get_interrupt_line();
+			if(new_interrupt_status != _last_posted_interrupt_status)
+			{
+				_last_posted_interrupt_status = new_interrupt_status;
+				if(_delegate) _delegate->mos6522_did_change_interrupt_status(this);
+			}
+		}
+
+		// The registers
+		struct Registers {
+			uint8_t output[2], input[2], data_direction[2];
+			uint16_t timer[2], timer_latch[2];
+			uint8_t shift;
+			uint8_t auxiliary_control, peripheral_control;
+			uint8_t interrupt_flags, interrupt_enable;
+
+			// "A  low  reset  (RES)  input  clears  all  R6522  internal registers to logic 0"
+			Registers() :
+				output{0, 0}, input{0, 0}, data_direction{0, 0},
+				auxiliary_control(0), peripheral_control(0),
+				interrupt_flags(0), interrupt_enable(0) {}
+		} _registers;
+
+		// Internal state other than the registers
+		bool _timer_is_running[2];
+};
+
+}
+
+#endif /* _522_hpp */
--- a/Components/6560/6560.cpp
+++ b/Components/6560/6560.cpp
@ -0,0 +1,440 @@
+//
+//  6560.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 05/06/2016.
+//  Copyright © 2016 Thomas Harte. All rights reserved.
+//
+
+#include "6560.hpp"
+
+using namespace MOS;
+
+MOS6560::MOS6560() :
+	_crt(new Outputs::CRT::CRT(65*4, 4, Outputs::CRT::NTSC60, 1)),
+	_horizontal_counter(0),
+	_vertical_counter(0),
+	_cycles_since_speaker_update(0),
+	_is_odd_frame(false)
+{
+	_crt->set_composite_sampling_function(
+		"float composite_sample(usampler2D texID, vec2 coordinate, vec2 iCoordinate, float phase, float amplitude)"
+		"{"
+			"uint c = texture(texID, coordinate).r;"
+			"float y = float(c >> 4) / 4.0;"
+			"uint yC = c & 15u;"
+			"float phaseOffset = 6.283185308 * float(yC) / 16.0;"
+
+//			"float chroma = step(mod(phase + phaseOffset + 0.785398163397448, 6.283185308), 3.141592654);"
+			"float chroma = cos(phase + phaseOffset);"
+			"return mix(y, step(yC, 14) * chroma, amplitude);"
+		"}");
+
+	// set up colours table
+	// 0
+	// 2, 6, 9, B,
+	// 4, 5, 8, A, C, E
+	// 3, 7, D, F
+	// 1
+	uint8_t luminances[16] = {		// range is 0–4
+		0, 4, 1, 3, 2, 2, 1, 3,
+		2, 1, 2, 1, 2, 3, 2, 3
+	};
+//	uint8_t pal_chrominances[16] = {	// range is 0–15; 15 is a special case meaning "no chrominance"
+//		15, 15, 5, 13, 2, 10, 0, 8,
+//		6, 7, 5, 13, 2, 10, 0, 8,
+//	};
+	uint8_t ntsc_chrominances[16] = {
+		15, 15, 2, 10, 4, 12, 6, 14,
+		0, 8, 2, 10, 4, 12, 6, 14,
+	};
+	for(int c = 0; c < 16; c++)
+	{
+		_colours[c] = (uint8_t)((luminances[c] << 4) | ntsc_chrominances[c]);
+	}
+
+	// show only the centre
+	_crt->set_visible_area(_crt->get_rect_for_area(16, 237, 11*4, 55*4, 4.0f / 3.0f));
+	_speaker.set_input_rate(255681.75);	// assuming NTSC; clock rate / 4
+}
+
+void MOS6560::set_register(int address, uint8_t value)
+{
+	address &= 0xf;
+	_registers[address] = value;
+	switch(address)
+	{
+		case 0x0:
+			_interlaced = !!(value&0x80);
+			_first_column_location = value & 0x7f;
+		break;
+
+		case 0x1:
+			_first_row_location = value;
+		break;
+
+		case 0x2:
+			_number_of_columns = value & 0x7f;
+			_video_matrix_start_address = (uint16_t)((_video_matrix_start_address & 0x3c00) | ((value & 0x80) << 2));
+		break;
+
+		case 0x3:
+			_number_of_rows = (value >> 1)&0x3f;
+			_tall_characters = !!(value&0x01);
+		break;
+
+		case 0x5:
+			_character_cell_start_address = (uint16_t)((value & 0x0f) << 10);
+			_video_matrix_start_address = (uint16_t)((_video_matrix_start_address & 0x0200) | ((value & 0xf0) << 6));
+		break;
+
+		case 0xa:
+		case 0xb:
+		case 0xc:
+		case 0xd:
+			update_audio();
+			_speaker.set_control(address - 0xa, value);
+		break;
+
+		case 0xe:
+			update_audio();
+			_auxiliary_colour = _colours[value >> 4];
+			_speaker.set_volume(value & 0xf);
+		break;
+
+		case 0xf:
+			if(_this_state == State::Border)
+			{
+				output_border(_cycles_in_state * 4);
+				_cycles_in_state = 0;
+			}
+			_invertedCells = !!((value >> 3)&1);
+			_borderColour = _colours[value & 0x07];
+			_backgroundColour = _colours[value >> 4];
+		break;
+
+		// TODO: audio, primarily
+
+		default:
+		break;
+	}
+}
+
+uint8_t MOS6560::get_register(int address)
+{
+	address &= 0xf;
+	switch(address)
+	{
+		default: return _registers[address];
+		case 0x03: return (uint8_t)(_vertical_counter << 7) | (_registers[3] & 0x7f);
+		case 0x04: return (_vertical_counter >> 1) & 0xff;
+	}
+}
+
+void MOS6560::output_border(unsigned int number_of_cycles)
+{
+	uint8_t *colour_pointer = _crt->allocate_write_area(1);
+	if(colour_pointer) *colour_pointer = _borderColour;
+	_crt->output_level(number_of_cycles);
+}
+
+uint16_t MOS6560::get_address()
+{
+	_cycles_since_speaker_update++;
+
+	_horizontal_counter++;
+	if(_horizontal_counter == 65)
+	{
+		_horizontal_counter = 0;
+		_vertical_counter++;
+		_column_counter = -1;
+
+		if(_vertical_counter == (_interlaced ? (_is_odd_frame ? 262 : 263) : 261))
+		{
+			_is_odd_frame ^= true;
+			_vertical_counter = 0;
+			_row_counter = -1;
+		}
+
+		if(_row_counter >= 0)
+		{
+			_row_counter++;
+			if(_row_counter == _number_of_rows*(_tall_characters ? 16 : 8)) _row_counter = -1;
+		}
+		else if(_vertical_counter == _first_row_location * 2)
+		{
+			_video_matrix_line_address_counter = _video_matrix_start_address;
+			_row_counter = 0;
+		}
+	}
+
+	if(_column_counter >= 0)
+	{
+		_column_counter++;
+		if(_column_counter == _number_of_columns*2)
+		{
+			_column_counter = -1;
+			if((_row_counter&(_tall_characters ? 15 : 7)) == (_tall_characters ? 15 : 7))
+			{
+				_video_matrix_line_address_counter = _video_matrix_address_counter;
+			}
+		}
+	}
+	else if(_horizontal_counter == _first_column_location)
+	{
+		_column_counter = 0;
+		_video_matrix_address_counter = _video_matrix_line_address_counter;
+	}
+
+	// determine output state; colour burst and sync timing are currently a guess
+	if(_horizontal_counter > 61) _this_state = State::ColourBurst;
+	else if(_horizontal_counter > 57) _this_state = State::Sync;
+	else
+	{
+		_this_state = (_column_counter >= 0 && _row_counter >= 0) ? State::Pixels : State::Border;
+	}
+
+	// apply vertical sync
+	if(
+		(_vertical_counter < 3 && (_is_odd_frame || !_interlaced)) ||
+		(_interlaced &&
+			(
+				(_vertical_counter == 0 && _horizontal_counter > 32) ||
+				(_vertical_counter == 1) || (_vertical_counter == 2) ||
+				(_vertical_counter == 3 && _horizontal_counter <= 32)
+			)
+		))
+		_this_state = State::Sync;
+
+	// update the CRT
+	if(_this_state != _output_state)
+	{
+		switch(_output_state)
+		{
+			case State::Sync:			_crt->output_sync(_cycles_in_state * 4);										break;
+			case State::ColourBurst:	_crt->output_colour_burst(_cycles_in_state * 4, _is_odd_frame ? 128 : 0, 0);	break;
+			case State::Border:			output_border(_cycles_in_state * 4);											break;
+			case State::Pixels:			_crt->output_data(_cycles_in_state * 4, 1);										break;
+		}
+		_output_state = _this_state;
+		_cycles_in_state = 0;
+
+		pixel_pointer = nullptr;
+		if(_output_state == State::Pixels)
+		{
+			pixel_pointer = _crt->allocate_write_area(260);
+		}
+	}
+	_cycles_in_state++;
+
+	// compute the address
+	if(_this_state == State::Pixels)
+	{
+		/*
+			Per http://tinyvga.com/6561 :
+
+			The basic video timing is very simple.  For
+			every character the VIC-I is about to display, it first fetches the
+			character code and colour, then the character appearance (from the
+			character generator memory).  The character codes are read on every
+			raster line, thus making every line a "bad line".  When the raster
+			beam is outside of the text window, the videochip reads from $001c for
+			most time.  (Some videochips read from $181c instead.)  The address
+			occasionally varies, but it might also be due to a flaky bus.  (By
+			reading from unconnected address space, such as $9100-$910f, you can
+			read the data fetched by the videochip on the previous clock cycle.)
+		*/
+		if(_column_counter&1)
+		{
+			return _character_cell_start_address + (_character_code*(_tall_characters ? 16 : 8)) + (_row_counter&(_tall_characters ? 15 : 7));
+		}
+		else
+		{
+			uint16_t result = _video_matrix_address_counter;
+			_video_matrix_address_counter++;
+			return result;
+		}
+	}
+
+	return 0x1c;
+}
+
+void MOS6560::set_graphics_value(uint8_t value, uint8_t colour_value)
+{
+	// TODO: this isn't correct, as _character_value will be
+	// accessed second, then output will roll over. Probably it's
+	// correct (given the delays upstream) to output all 8 on an &1
+	// and to adjust the signalling to the CRT above?
+	if(_this_state == State::Pixels)
+	{
+		if(_column_counter&1)
+		{
+			_character_value = value;
+
+			if(pixel_pointer)
+			{
+				uint8_t cell_colour = _colours[_character_colour & 0x7];
+				if(!(_character_colour&0x8))
+				{
+					pixel_pointer[0] = ((_character_value >> 7)&1) ? cell_colour : _backgroundColour;
+					pixel_pointer[1] = ((_character_value >> 6)&1) ? cell_colour : _backgroundColour;
+					pixel_pointer[2] = ((_character_value >> 5)&1) ? cell_colour : _backgroundColour;
+					pixel_pointer[3] = ((_character_value >> 4)&1) ? cell_colour : _backgroundColour;
+					pixel_pointer[4] = ((_character_value >> 3)&1) ? cell_colour : _backgroundColour;
+					pixel_pointer[5] = ((_character_value >> 2)&1) ? cell_colour : _backgroundColour;
+					pixel_pointer[6] = ((_character_value >> 1)&1) ? cell_colour : _backgroundColour;
+					pixel_pointer[7] = ((_character_value >> 0)&1) ? cell_colour : _backgroundColour;
+				}
+				else
+				{
+					uint8_t colours[4] = {_backgroundColour, _borderColour, cell_colour, _auxiliary_colour};
+					pixel_pointer[0] =
+					pixel_pointer[1] = colours[(_character_value >> 6)&3];
+					pixel_pointer[2] =
+					pixel_pointer[3] = colours[(_character_value >> 4)&3];
+					pixel_pointer[4] =
+					pixel_pointer[5] = colours[(_character_value >> 2)&3];
+					pixel_pointer[6] =
+					pixel_pointer[7] = colours[(_character_value >> 0)&3];
+				}
+				pixel_pointer += 8;
+			}
+		}
+		else
+		{
+			_character_code = value;
+			_character_colour = colour_value;
+		}
+	}
+}
+
+void MOS6560::update_audio()
+{
+	_speaker.run_for_cycles(_cycles_since_speaker_update >> 2);
+	_cycles_since_speaker_update &= 3;
+}
+
+#pragma mark - Audio
+
+MOS6560Speaker::MOS6560Speaker() :
+	_volume(0),
+	_control_registers{0, 0, 0, 0},
+	_shift_registers{0, 0, 0, 0},
+	_counters{2, 1, 0, 0}	// create a slight phase offset for the three channels
+{
+}
+
+void MOS6560Speaker::set_volume(uint8_t volume)
+{
+	_volume = volume;
+}
+
+void MOS6560Speaker::set_control(int channel, uint8_t value)
+{
+	_control_registers[channel] = value;
+}
+
+// Source: VICE. Not original.
+static uint8_t noise_pattern[] = {
+	0x07, 0x1e, 0x1e, 0x1c, 0x1c, 0x3e, 0x3c, 0x38, 0x78, 0xf8, 0x7c, 0x1e, 0x1f, 0x8f, 0x07, 0x07,
+	0xc1, 0xc0, 0xe0, 0xf1, 0xe0, 0xf0, 0xe3, 0xe1, 0xc0, 0xe0, 0x78, 0x7e, 0x3c, 0x38, 0xe0, 0xe1,
+	0xc3, 0xc3, 0x87, 0xc7, 0x07, 0x1e, 0x1c, 0x1f, 0x0e, 0x0e, 0x1e, 0x0e, 0x0f, 0x0f, 0xc3, 0xc3,
+	0xf1, 0xe1, 0xe3, 0xc1, 0xe3, 0xc3, 0xc3, 0xfc, 0x3c, 0x1e, 0x0f, 0x83, 0xc3, 0xc1, 0xc1, 0xc3,
+	0xc3, 0xc7, 0x87, 0x87, 0xc7, 0x0f, 0x0e, 0x3c, 0x7c, 0x78, 0x3c, 0x3c, 0x3c, 0x38, 0x3e, 0x1c,
+	0x7c, 0x1e, 0x3c, 0x0f, 0x0e, 0x3e, 0x78, 0xf0, 0xf0, 0xe0, 0xe1, 0xf1, 0xc1, 0xc3, 0xc7, 0xc3,
+	0xe1, 0xf1, 0xe0, 0xe1, 0xf0, 0xf1, 0xe3, 0xc0, 0xf0, 0xe0, 0xf8, 0x70, 0xe3, 0x87, 0x87, 0xc0,
+	0xf0, 0xe0, 0xf1, 0xe1, 0xe1, 0xc7, 0x83, 0x87, 0x83, 0x8f, 0x87, 0x87, 0xc7, 0x83, 0xc3, 0x83,
+	0xc3, 0xf1, 0xe1, 0xc3, 0xc7, 0x81, 0xcf, 0x87, 0x03, 0x87, 0xc7, 0xc7, 0x87, 0x83, 0xe1, 0xc3,
+	0x07, 0xc3, 0x87, 0x87, 0x07, 0x87, 0xc3, 0x87, 0x83, 0xe1, 0xc3, 0xc7, 0xc3, 0x87, 0x87, 0x8f,
+	0x0f, 0x87, 0x87, 0x0f, 0xcf, 0x1f, 0x87, 0x8e, 0x0e, 0x07, 0x81, 0xc3, 0xe3, 0xc1, 0xe0, 0xf0,
+	0xe0, 0xe3, 0x83, 0x87, 0x07, 0x87, 0x8e, 0x1e, 0x0f, 0x07, 0x87, 0x8f, 0x1f, 0x07, 0x87, 0xc1,
+	0xf0, 0xe1, 0xe1, 0xe3, 0xc7, 0x0f, 0x03, 0x8f, 0x87, 0x0e, 0x1e, 0x1e, 0x0f, 0x87, 0x87, 0x0f,
+	0x87, 0x1f, 0x0f, 0xc3, 0xc3, 0xf0, 0xf8, 0xf0, 0x70, 0xf1, 0xf0, 0xf0, 0xe1, 0xf0, 0xe0, 0x78,
+	0x7c, 0x78, 0x7c, 0x70, 0x71, 0xe1, 0xe1, 0xc3, 0xc3, 0xc7, 0x87, 0x1c, 0x3c, 0x3c, 0x1c, 0x3c,
+	0x7c, 0x1e, 0x1e, 0x1e, 0x1c, 0x3c, 0x78, 0xf8, 0xf8, 0xe1, 0xc3, 0x87, 0x1e, 0x1e, 0x3c, 0x3e,
+	0x0f, 0x0f, 0x87, 0x1f, 0x8e, 0x0f, 0x0f, 0x8e, 0x1e, 0x1e, 0x1e, 0x1e, 0x0f, 0x0f, 0x8f, 0x87,
+	0x87, 0xc3, 0x83, 0xc1, 0xe1, 0xc3, 0xc1, 0xc3, 0xc7, 0x8f, 0x0f, 0x0f, 0x0f, 0x0f, 0x83, 0xc7,
+	0xc3, 0xc1, 0xe1, 0xe0, 0xf8, 0x3e, 0x3c, 0x3c, 0x3c, 0x3c, 0x3c, 0x78, 0x3e, 0x1e, 0x1e, 0x1e,
+	0x0f, 0x0f, 0x0f, 0x1e, 0x0e, 0x1e, 0x1e, 0x0f, 0x0f, 0x87, 0x1f, 0x87, 0x87, 0x1c, 0x3e, 0x1f,
+	0x0f, 0x0f, 0x8e, 0x3e, 0x0e, 0x3e, 0x1e, 0x1c, 0x3c, 0x7c, 0xfc, 0x38, 0x78, 0x78, 0x38, 0x78,
+	0x70, 0xf8, 0x7c, 0x1e, 0x3c, 0x3c, 0x30, 0xf1, 0xf0, 0x70, 0x70, 0xe0, 0xf8, 0xf0, 0xf8, 0x78,
+	0x78, 0x71, 0xe1, 0xf0, 0xe3, 0xc1, 0xf0, 0x71, 0xe3, 0xc7, 0x87, 0x8e, 0x3e, 0x0e, 0x1e, 0x3e,
+	0x0f, 0x07, 0x87, 0x0c, 0x3e, 0x0f, 0x87, 0x0f, 0x1e, 0x3c, 0x3c, 0x38, 0x78, 0xf1, 0xe7, 0xc3,
+	0xc3, 0xc7, 0x8e, 0x3c, 0x38, 0xf0, 0xe0, 0x7e, 0x1e, 0x3e, 0x0e, 0x0f, 0x0f, 0x0f, 0x03, 0xc3,
+	0xc3, 0xc7, 0x87, 0x1f, 0x0e, 0x1e, 0x1c, 0x3c, 0x3c, 0x0f, 0x07, 0x07, 0xc7, 0xc7, 0x87, 0x87,
+	0x8f, 0x0f, 0xc0, 0xf0, 0xf8, 0x60, 0xf0, 0xf0, 0xe1, 0xe3, 0xe3, 0xc3, 0xc3, 0xc3, 0x87, 0x0f,
+	0x87, 0x8e, 0x1e, 0x1e, 0x3f, 0x1e, 0x0e, 0x1c, 0x3c, 0x7e, 0x1e, 0x3c, 0x38, 0x78, 0x78, 0x78,
+	0x38, 0x78, 0x3c, 0xe1, 0xe3, 0x8f, 0x1f, 0x1c, 0x78, 0x70, 0x7e, 0x0f, 0x87, 0x07, 0xc3, 0xc7,
+	0x0f, 0x1e, 0x3c, 0x0e, 0x0f, 0x0e, 0x1e, 0x03, 0xf0, 0xf0, 0xf1, 0xe3, 0xc1, 0xc7, 0xc0, 0xe1,
+	0xe1, 0xe1, 0xe1, 0xe0, 0x70, 0xe1, 0xf0, 0x78, 0x70, 0xe3, 0xc7, 0x0f, 0xc1, 0xe1, 0xe3, 0xc3,
+	0xc0, 0xf0, 0xfc, 0x1c, 0x3c, 0x70, 0xf8, 0x70, 0xf8, 0x78, 0x3c, 0x70, 0xf0, 0x78, 0x70, 0x7c,
+	0x7c, 0x3c, 0x38, 0x1e, 0x3e, 0x3c, 0x7e, 0x07, 0x83, 0xc7, 0xc1, 0xc1, 0xe1, 0xc3, 0xc3, 0xc3,
+	0xe1, 0xe1, 0xf0, 0x78, 0x7c, 0x3e, 0x0f, 0x1f, 0x07, 0x8f, 0x0f, 0x83, 0x87, 0xc1, 0xe3, 0xe3,
+	0xc3, 0xc3, 0xe1, 0xf0, 0xf8, 0xf0, 0x3c, 0x7c, 0x3c, 0x0f, 0x8e, 0x0e, 0x1f, 0x1f, 0x0e, 0x3c,
+	0x38, 0x78, 0x70, 0x70, 0xf0, 0xf0, 0xf8, 0x70, 0x70, 0x78, 0x38, 0x3c, 0x70, 0xe0, 0xf0, 0x78,
+	0xf1, 0xf0, 0x78, 0x3e, 0x3c, 0x0f, 0x07, 0x0e, 0x3e, 0x1e, 0x3f, 0x1e, 0x0e, 0x0f, 0x87, 0x87,
+	0x07, 0x0f, 0x07, 0xc7, 0x8f, 0x0f, 0x87, 0x1e, 0x1e, 0x1f, 0x1e, 0x1e, 0x3c, 0x1e, 0x1c, 0x3e,
+	0x0f, 0x03, 0xc3, 0x81, 0xe0, 0xf0, 0xfc, 0x38, 0x3c, 0x3e, 0x0e, 0x1e, 0x1c, 0x7c, 0x1e, 0x1f,
+	0x0e, 0x3e, 0x1c, 0x78, 0x78, 0x7c, 0x1e, 0x3e, 0x1e, 0x3c, 0x1f, 0x0f, 0x1f, 0x0f, 0x0f, 0x8f,
+	0x1c, 0x3c, 0x78, 0xf8, 0xf0, 0xf8, 0x70, 0xf0, 0x78, 0x78, 0x3c, 0x3c, 0x78, 0x3c, 0x1f, 0x0f,
+	0x07, 0x86, 0x1c, 0x1e, 0x1c, 0x1e, 0x1e, 0x1f, 0x03, 0xc3, 0xc7, 0x8e, 0x3c, 0x3c, 0x1c, 0x18,
+	0xf0, 0xe1, 0xc3, 0xe1, 0xc1, 0xe1, 0xe3, 0xc3, 0xc3, 0xe3, 0xc3, 0x83, 0x87, 0x83, 0x87, 0x0f,
+	0x07, 0x07, 0xe1, 0xe1, 0xe0, 0x7c, 0x78, 0x38, 0x78, 0x78, 0x3c, 0x1f, 0x0f, 0x8f, 0x0e, 0x07,
+	0x0f, 0x07, 0x83, 0xc3, 0xc3, 0x81, 0xf0, 0xf8, 0xf1, 0xe0, 0xe3, 0xc7, 0x1c, 0x3e, 0x1e, 0x0f,
+	0x0f, 0xc3, 0xf0, 0xf0, 0xe3, 0x83, 0xc3, 0xc7, 0x07, 0x0f, 0x0f, 0x0f, 0x0f, 0x0f, 0x07, 0x87,
+	0x0f, 0x0f, 0x0e, 0x0f, 0x0f, 0x1e, 0x0f, 0x0f, 0x87, 0x87, 0x87, 0x8f, 0xc7, 0xc7, 0x83, 0x83,
+	0xc3, 0xc7, 0x8f, 0x87, 0x07, 0xc3, 0x8e, 0x1e, 0x38, 0x3e, 0x3c, 0x38, 0x7c, 0x1f, 0x1c, 0x38,
+	0x3c, 0x78, 0x7c, 0x1e, 0x1c, 0x3c, 0x3f, 0x1e, 0x0e, 0x3e, 0x1c, 0x3c, 0x1f, 0x0f, 0x07, 0xc3,
+	0xe3, 0x83, 0x87, 0x81, 0xc1, 0xe3, 0xcf, 0x0e, 0x0f, 0x1e, 0x3e, 0x1e, 0x1f, 0x0f, 0x8f, 0xc3,
+	0x87, 0x0e, 0x03, 0xf0, 0xf0, 0x70, 0xe0, 0xe1, 0xe1, 0xc7, 0x8e, 0x0f, 0x0f, 0x1e, 0x0e, 0x1e,
+	0x1f, 0x1c, 0x78, 0xf0, 0xf1, 0xf1, 0xe0, 0xf1, 0xe1, 0xe1, 0xe0, 0xe0, 0xf1, 0xc1, 0xf0, 0x71,
+	0xe1, 0xc3, 0x83, 0xc7, 0x83, 0xe1, 0xe1, 0xf8, 0x70, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0x70, 0xf8,
+	0x70, 0x70, 0x61, 0xe0, 0xf0, 0xe1, 0xe0, 0x78, 0x71, 0xe0, 0xf0, 0xf8, 0x38, 0x1e, 0x1c, 0x38,
+	0x70, 0xf8, 0x60, 0x78, 0x38, 0x3c, 0x3f, 0x1f, 0x0f, 0x1f, 0x0f, 0x1f, 0x87, 0x87, 0x83, 0x87,
+	0x83, 0xe1, 0xe1, 0xf0, 0x78, 0xf1, 0xf0, 0x70, 0x38, 0x38, 0x70, 0xe0, 0xe3, 0xc0, 0xe0, 0xf8,
+	0x78, 0x78, 0xf8, 0x38, 0xf1, 0xe1, 0xe1, 0xc3, 0x87, 0x87, 0x0e, 0x1e, 0x1f, 0x0e, 0x0e, 0x0f,
+	0x0f, 0x87, 0xc3, 0x87, 0x07, 0x83, 0xc0, 0xf0, 0x38, 0x3c, 0x3c, 0x38, 0xf0, 0xfc, 0x3e, 0x1e,
+	0x1c, 0x1c, 0x38, 0x70, 0xf0, 0xf1, 0xe0, 0xf0, 0xe0, 0xe0, 0xf1, 0xe3, 0xe0, 0xe1, 0xf0, 0xf0,
+	0x78, 0x7c, 0x78, 0x3c, 0x78, 0x78, 0x38, 0x78, 0x78, 0x78, 0x78, 0x70, 0xe3, 0x83, 0x83, 0xe0,
+	0xc3, 0xc1, 0xe1, 0xc1, 0xc1, 0xc1, 0xe3, 0xc3, 0xc7, 0x1e, 0x0e, 0x1f, 0x1e, 0x1e, 0x0f, 0x0f,
+	0x0e, 0x0e, 0x0e, 0x07, 0x83, 0x87, 0x87, 0x0e, 0x07, 0x8f, 0x0f, 0x0f, 0x0f, 0x0e, 0x1c, 0x70,
+	0xe1, 0xe0, 0x71, 0xc1, 0x83, 0x83, 0x87, 0x0f, 0x1e, 0x18, 0x78, 0x78, 0x7c, 0x3e, 0x1c, 0x38,
+	0xf0, 0xe1, 0xe0, 0x78, 0x70, 0x38, 0x3c, 0x3e, 0x1e, 0x3c, 0x1e, 0x1c, 0x70, 0x3c, 0x38, 0x3f,
+};
+
+#define shift(r) _shift_registers[r] = (uint8_t)((_shift_registers[r] << 1) | (((_shift_registers[r]^0x80)&_control_registers[r]) >> 7));
+#define increment(r) _shift_registers[r] = (_shift_registers[r]+1)%8191;
+#define update(r, m, up) _counters[r]++; if((_counters[r] >> m) == 0x7f) { up(r); _counters[r] = _control_registers[r]&0x7f; }
+
+void MOS6560Speaker::get_samples(unsigned int number_of_samples, int16_t *target)
+{
+	for(unsigned int c = 0; c < number_of_samples; c++)
+	{
+		update(0, 2, shift);
+		update(1, 1, shift);
+		update(2, 0, shift);
+		update(3, 1, increment);
+
+		target[c] = (
+			(_shift_registers[0]&1) +
+			(_shift_registers[1]&1) +
+			(_shift_registers[2]&1) +
+			((noise_pattern[_shift_registers[3] >> 3] >> (_shift_registers[3]&7))&(_control_registers[3] >> 7)&1)
+		) * _volume * 700;
+	}
+}
+
+void MOS6560Speaker::skip_samples(unsigned int number_of_samples)
+{
+	for(unsigned int c = 0; c < number_of_samples; c++)
+	{
+		update(0, 2, shift);
+		update(1, 1, shift);
+		update(2, 0, shift);
+		update(3, 1, increment);
+	}
+}
+
+#undef shift
+#undef increment
+#undef update
--- a/Components/6560/6560.hpp
+++ b/Components/6560/6560.hpp
@ -0,0 +1,86 @@
+//
+//  6560.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 05/06/2016.
+//  Copyright © 2016 Thomas Harte. All rights reserved.
+//
+
+#ifndef _560_hpp
+#define _560_hpp
+
+#include "../../Outputs/CRT/CRT.hpp"
+#include "../../Outputs/Speaker.hpp"
+
+namespace MOS {
+
+class MOS6560Speaker: public ::Outputs::Filter<MOS6560Speaker> {
+	public:
+		MOS6560Speaker();
+
+		void set_volume(uint8_t volume);
+		void set_control(int channel, uint8_t value);
+
+		void get_samples(unsigned int number_of_samples, int16_t *target);
+		void skip_samples(unsigned int number_of_samples);
+
+	private:
+		unsigned int _counters[4];
+		uint8_t _shift_registers[4];
+		uint8_t _control_registers[4];
+		uint8_t _volume;
+};
+
+class MOS6560 {
+	public:
+		MOS6560();
+		Outputs::CRT::CRT *get_crt() { return _crt.get(); }
+		Outputs::Speaker *get_speaker() { return &_speaker; }
+
+		uint16_t get_address();
+		void set_graphics_value(uint8_t value, uint8_t colour_value);
+
+		void synchronise() { update_audio(); }
+
+		void set_register(int address, uint8_t value);
+		uint8_t get_register(int address);
+
+	private:
+		std::unique_ptr<Outputs::CRT::CRT> _crt;
+		MOS6560Speaker _speaker;
+
+		bool _interlaced, _tall_characters;
+		uint8_t _first_column_location, _first_row_location;
+		uint8_t _number_of_columns, _number_of_rows;
+		uint16_t _character_cell_start_address, _video_matrix_start_address;
+		uint8_t _backgroundColour, _borderColour, _auxiliary_colour;
+		bool _invertedCells;
+
+		int _horizontal_counter, _vertical_counter;
+
+		int _column_counter, _row_counter;
+		uint16_t _video_matrix_address_counter, _video_matrix_line_address_counter;
+
+		enum State {
+			Sync, ColourBurst, Border, Pixels
+		} _this_state, _output_state;
+		unsigned int _cycles_in_state;
+
+		uint8_t _character_code, _character_colour, _character_value;
+
+		uint8_t *pixel_pointer;
+
+		uint8_t _registers[16];
+		uint8_t _colours[16];
+
+		bool _is_odd_frame;
+
+		void output_border(unsigned int number_of_cycles);
+
+		unsigned int _cycles_since_speaker_update;
+		void update_audio();
+};
+
+}
+
+#endif /* _560_hpp */
--- a/Machines/Atari2600/Atari2600.cpp
+++ b/Machines/Atari2600/Atari2600.cpp
@ -69,7 +69,7 @@ void Machine::setup_output(float aspect_ratio)
 			"uint iPhase = (c >> 4);"

 			"float phaseOffset = 6.283185308 * float(iPhase - 1u) / 13.0;"
-			"return (float(y) / 14.0) * (1.0 - amplitude) + step(1, iPhase) * amplitude * cos(phase + phaseOffset);"
+			"return mix(float(y) / 14.0, step(1, iPhase) * cos(phase + phaseOffset), amplitude);"
 		"}");
 	_crt->set_output_device(Outputs::CRT::Television);

@ -89,7 +89,7 @@ void Machine::switch_region()
 			"uint direction = iPhase & 1u;"
 			"float phaseOffset = float(7u - direction) + (float(direction) - 0.5) * 2.0 * float(iPhase >> 1);"
 			"phaseOffset *= 6.283185308 / 12.0;"
-			"return (float(y) / 14.0) * (1.0 - amplitude) + step(4, (iPhase + 2u) & 15u) * amplitude * cos(phase + phaseOffset);"
+			"return mix(float(y) / 14.0, step(4, (iPhase + 2u) & 15u) * cos(phase + phaseOffset), amplitude);"
 		"}");
 	_crt->set_new_timing(228, 312, Outputs::CRT::ColourSpace::YUV, 228, 1);

--- a/Machines/Vic-20/Vic20.cpp
+++ b/Machines/Vic-20/Vic20.cpp
@ -0,0 +1,136 @@
+//
+//  Vic20.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 04/06/2016.
+//  Copyright © 2016 Thomas Harte. All rights reserved.
+//
+
+#include "Vic20.hpp"
+
+#include <algorithm>
+
+using namespace Vic20;
+
+Machine::Machine() :
+	_rom(nullptr)
+{
+	_userPortVIA.set_delegate(this);
+	_keyboardVIA.set_delegate(this);
+	set_reset_line(true);
+}
+
+Machine::~Machine()
+{
+	delete[] _rom;
+}
+
+unsigned int Machine::perform_bus_operation(CPU6502::BusOperation operation, uint16_t address, uint8_t *value)
+{
+	set_reset_line(false);
+
+	// run the phase-1 part of this cycle, in which the VIC accesses memory
+	uint16_t video_address = _mos6560->get_address();
+	uint8_t video_value = 0xff; // TODO
+	if(!(video_address&0x2000))
+	{
+		video_value = _characterROM[video_address & 0x0fff];
+	}
+	else
+	{
+		video_address &= 0x1fff;
+		if(video_address < sizeof(_userBASICMemory)) video_value = _userBASICMemory[video_address];
+		else if(video_address >= 0x1000 && video_address < 0x2000) video_value = _screenMemory[video_address&0x0fff];
+	}
+	_mos6560->set_graphics_value(video_value, _colorMemory[video_address & 0x03ff]);
+
+	// run the phase-2 part of the cycle, which is whatever the 6502 said it should be
+	if(isReadOperation(operation))
+	{
+		*value = read_memory(address);
+		if((address&0xfff0) == 0x9000)
+		{
+			*value = _mos6560->get_register(address - 0x9000);
+		}
+		else if((address&0xfff0) == 0x9110)
+		{
+			*value = _userPortVIA.get_register(address - 0x9110);
+		}
+		else if((address&0xfff0) == 0x9120)
+		{
+			*value = _keyboardVIA.get_register(address - 0x9120);
+		}
+	}
+	else
+	{
+		uint8_t *ram = ram_pointer(address);
+		if(ram) *ram = *value;
+		else if((address&0xfff0) == 0x9000)
+		{
+			_mos6560->set_register(address - 0x9000, *value);
+		}
+		else if((address&0xfff0) == 0x9110)
+		{
+			_userPortVIA.set_register(address - 0x9110, *value);
+		}
+		else if((address&0xfff0) == 0x9120)
+		{
+			_keyboardVIA.set_register(address - 0x9120, *value);
+		}
+	}
+
+	_userPortVIA.run_for_cycles(1);
+	_keyboardVIA.run_for_cycles(1);
+	return 1;
+}
+
+#pragma mark - 6522 delegate
+
+void Machine::mos6522_did_change_interrupt_status(void *mos6522)
+{
+	bool irq = _userPortVIA.get_interrupt_line() || _keyboardVIA.get_interrupt_line();
+	set_irq_line(irq);
+}
+
+#pragma mark - Setup
+
+void Machine::setup_output(float aspect_ratio)
+{
+	_mos6560 = std::unique_ptr<MOS::MOS6560>(new MOS::MOS6560());
+}
+
+void Machine::set_rom(ROMSlot slot, size_t length, const uint8_t *data)
+{
+	uint8_t *target = nullptr;
+	size_t max_length = 0x2000;
+	switch(slot)
+	{
+		case ROMSlotKernel:		target = _kernelROM;							break;
+		case ROMSlotCharacters:	target = _characterROM;	max_length = 0x1000;	break;
+		case ROMSlotBASIC:		target = _basicROM;								break;
+	}
+
+	if(target)
+	{
+		size_t length_to_copy = std::min(max_length, length);
+		memcpy(target, data, length_to_copy);
+	}
+}
+
+void Machine::add_prg(size_t length, const uint8_t *data)
+{
+	if(length > 2)
+	{
+		_rom_address = (uint16_t)(data[0] | (data[1] << 8));
+		_rom_length = (uint16_t)(length - 2);
+		if(_rom_address >= 0x1000 && _rom_address+_rom_length < 0x2000)
+		{
+			memcpy(&_screenMemory[_rom_address - 0x1000], &data[2], length - 2);
+		}
+		else
+		{
+			_rom = new uint8_t[length - 2];
+			memcpy(_rom, &data[2], length - 2);
+		}
+	}
+}
--- a/Machines/Vic-20/Vic20.hpp
+++ b/Machines/Vic-20/Vic20.hpp
@ -0,0 +1,151 @@
+//
+//  Vic20.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 04/06/2016.
+//  Copyright © 2016 Thomas Harte. All rights reserved.
+//
+
+#ifndef Vic20_hpp
+#define Vic20_hpp
+
+#include "../../Processors/6502/CPU6502.hpp"
+#include "../../Components/6560/6560.hpp"
+#include "../../Components/6522/6522.hpp"
+#include "../CRTMachine.hpp"
+
+namespace Vic20 {
+
+enum ROMSlot {
+	ROMSlotKernel,
+	ROMSlotBASIC,
+	ROMSlotCharacters,
+};
+
+
+#define key(line, mask) (((mask) << 3) | (line))
+
+enum Key: uint16_t {
+	Key2		= key(7, 0x01),		Key4		= key(7, 0x02),		Key6			= key(7, 0x04),		Key8		= key(7, 0x08),
+	Key0		= key(7, 0x10),		KeyDash		= key(7, 0x20),		KeyHome			= key(7, 0x40),		KeyF7		= key(7, 0x80),
+	KeyQ		= key(6, 0x01),		KeyE		= key(6, 0x02),		KeyT			= key(6, 0x04),		KeyU		= key(6, 0x08),
+	KeyO		= key(6, 0x10),		KeyAt		= key(6, 0x20),		KeyUp			= key(6, 0x40),		KeyF5		= key(6, 0x80),
+	KeyCBM		= key(5, 0x01),		KeyS		= key(5, 0x02),		KeyF			= key(5, 0x04),		KeyH		= key(5, 0x08),
+	KeyK		= key(5, 0x10),		KeyColon	= key(5, 0x20),		KeyEquals		= key(5, 0x40),		KeyF3		= key(5, 0x80),
+	KeySpace	= key(4, 0x01),		KeyZ		= key(4, 0x02),		KeyC			= key(4, 0x04),		KeyB		= key(4, 0x08),
+	KeyM		= key(4, 0x10),		KeyFullStop	= key(4, 0x20),		KeyRShift		= key(4, 0x40),		KeyF1		= key(4, 0x80),
+	KeyRunStop	= key(3, 0x01),		KeyLShift	= key(3, 0x02),		KeyX			= key(3, 0x04),		KeyV		= key(3, 0x08),
+	KeyN		= key(3, 0x10),		KeyComma	= key(3, 0x20),		KeySlash		= key(3, 0x40),		KeyDown		= key(3, 0x80),
+	KeyControl	= key(2, 0x01),		KeyA		= key(2, 0x02),		KeyD			= key(2, 0x04),		KeyG		= key(2, 0x08),
+	KeyJ		= key(2, 0x10),		KeyL		= key(2, 0x20),		KeySemicolon	= key(2, 0x40),		KeyRight	= key(2, 0x80),
+	KeyLeft		= key(1, 0x01),		KeyW		= key(1, 0x02),		KeyR			= key(1, 0x04),		KeyY		= key(1, 0x08),
+	KeyI		= key(1, 0x10),		KeyP		= key(1, 0x20),		KeyAsterisk		= key(1, 0x40),		KeyReturn	= key(1, 0x80),
+	Key1		= key(0, 0x01),		Key3		= key(0, 0x02),		Key5			= key(0, 0x04),		Key7		= key(0, 0x08),
+	Key9		= key(0, 0x10),		KeyPlus		= key(0, 0x20),		KeyGBP			= key(0, 0x40),		KeyDelete	= key(0, 0x80),
+};
+
+class UserPortVIA: public MOS::MOS6522<UserPortVIA> {
+};
+
+class KeyboardVIA: public MOS::MOS6522<KeyboardVIA> {
+	public:
+		void set_key_state(Key key, bool isPressed) {
+			if(isPressed)
+				_columns[key & 7] &= ~(key >> 3);
+			else
+				_columns[key & 7] |= (key >> 3);
+		}
+
+		void clear_all_keys() {
+			memset(_columns, 0xff, sizeof(_columns));
+		}
+
+		// to satisfy MOS::MOS6522
+		uint8_t get_port_input(int port) {
+			if(!port) {
+				uint8_t result = 0xff;
+				for(int c = 0; c < 8; c++)
+				{
+					if(!(_activation_mask&(1 << c)))
+						result &= _columns[c];
+				}
+				return result;
+			}
+
+			return 0xff;
+		}
+
+		void set_port_output(int port, uint8_t value) {
+			if(port)
+				_activation_mask = value;
+		}
+
+		KeyboardVIA() {
+			clear_all_keys();
+		}
+	private:
+		uint8_t _columns[8];
+		uint8_t _activation_mask;
+};
+
+class Machine: public CPU6502::Processor<Machine>, public CRTMachine::Machine, public MOS::MOS6522Delegate {
+	public:
+		Machine();
+		~Machine();
+
+		void set_rom(ROMSlot slot, size_t length, const uint8_t *data);
+		void add_prg(size_t length, const uint8_t *data);
+		void set_key_state(Key key, bool isPressed) { _keyboardVIA.set_key_state(key, isPressed); }
+		void clear_all_keys() { _keyboardVIA.clear_all_keys(); }
+
+		// to satisfy CPU6502::Processor
+		unsigned int perform_bus_operation(CPU6502::BusOperation operation, uint16_t address, uint8_t *value);
+		void synchronise() { _mos6560->synchronise(); }
+
+		// to satisfy CRTMachine::Machine
+		virtual void setup_output(float aspect_ratio);
+		virtual void close_output() {}
+		virtual Outputs::CRT::CRT *get_crt() { return _mos6560->get_crt(); }
+		virtual Outputs::Speaker *get_speaker() { return _mos6560->get_speaker(); }
+		virtual void run_for_cycles(int number_of_cycles) { CPU6502::Processor<Machine>::run_for_cycles(number_of_cycles); }
+
+		// to satisfy MOS::MOS6522::Delegate
+		virtual void mos6522_did_change_interrupt_status(void *mos6522);
+
+	private:
+		uint8_t _characterROM[0x1000];
+		uint8_t _basicROM[0x2000];
+		uint8_t _kernelROM[0x2000];
+
+		uint8_t *_rom;
+		uint16_t _rom_address, _rom_length;
+
+		uint8_t _userBASICMemory[0x0400];
+		uint8_t _screenMemory[0x1000];
+		uint8_t _colorMemory[0x0400];
+
+		inline uint8_t *ram_pointer(uint16_t address) {
+			if(address < sizeof(_userBASICMemory)) return &_userBASICMemory[address];
+			if(address >= 0x1000 && address < 0x2000) return &_screenMemory[address&0x0fff];
+			if(address >= 0x9400 && address < 0x9800) return &_colorMemory[address&0x03ff];	// TODO: make this 4-bit
+			return nullptr;
+		}
+
+		inline uint8_t read_memory(uint16_t address) {
+			uint8_t *ram = ram_pointer(address);
+			if(ram) return *ram;
+			else if(address >= 0x8000 && address < 0x9000) return _characterROM[address&0x0fff];
+			else if(address >= 0xc000 && address < 0xe000) return _basicROM[address&0x1fff];
+			else if(address >= 0xe000) return _kernelROM[address&0x1fff];
+			else if(address >= _rom_address && address < _rom_address+_rom_length) return _rom[address - _rom_address];
+			return 0xff;
+		}
+
+		std::unique_ptr<MOS::MOS6560> _mos6560;
+		UserPortVIA _userPortVIA;
+		KeyboardVIA _keyboardVIA;
+};
+
+}
+
+#endif /* Vic20_hpp */
--- a/Signal.xcodeproj/project.pbxproj
+++ b/Signal.xcodeproj/project.pbxproj
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 				4B55CE521C3B7ABF0093A61B /* CSElectron.h */,
 				4B55CE531C3B7ABF0093A61B /* CSElectron.mm */,
+				4BC9DF461D04565200F44158 /* CSKeyboardMachine.h */,
 				4B55CE4C1C3B3BDA0093A61B /* CSMachine.h */,
 				4B55CE4D1C3B3BDA0093A61B /* CSMachine.mm */,
 				4B55CE4F1C3B78A80093A61B /* CSMachine+Subclassing.h */,
+				4B886FF31D03B61E004291C3 /* CSVic20.h */,
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 			);
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 				4B2E2D931C399D1200138695 /* ElectronDocument.xib */,
 				4B55CE5E1C3B7D960093A61B /* MachineDocument.swift */,
+				4B73C7191D036BD90074D992 /* Vic20Document.swift */,
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 			);
 			path = Documents;
 			sourceTree = "<group>";
@ -848,6 +866,15 @@
 			path = Formats;
 			sourceTree = "<group>";
 		};
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+				4B886FF01D03B517004291C3 /* Vic20.cpp */,
+				4B886FF11D03B517004291C3 /* Vic20.hpp */,
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+		};
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@ -1127,6 +1154,7 @@
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 				4BB73EB51B587A5100552FC2 /* Clock SignalTests */,
 				4BB73EC01B587A5100552FC2 /* Clock SignalUITests */,
+				4BC9DF4A1D04691600F44158 /* Components */,
 				4BB73EDC1B587CA500552FC2 /* Machines */,
 				4B366DFD1B5C165F0026627B /* Outputs */,
 				4BB73EDD1B587CA500552FC2 /* Processors */,
@ -1191,9 +1219,10 @@
 		4BB73EDC1B587CA500552FC2 /* Machines */ = {
 			isa = PBXGroup;
 			children = (
+				4B046DC31CFE651500E9E45E /* CRTMachine.hpp */,
 				4B2E2D961C3A06EC00138695 /* Atari2600 */,
 				4B2E2D9E1C3A070900138695 /* Electron */,
-				4B046DC31CFE651500E9E45E /* CRTMachine.hpp */,
+				4B886FF61D03B632004291C3 /* Vic-20 */,
 			);
 			name = Machines;
 			path = ../../Machines;
@ -1238,24 +1267,42 @@
 			path = Shaders;
 			sourceTree = "<group>";
 		};
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+			children = (
+				4BC9DF4B1D04691600F44158 /* 6522 */,
+				4BC9DF4C1D04691600F44158 /* 6560 */,
+			);
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+			path = ../../Components;
+			sourceTree = "<group>";
+		};
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+			isa = PBXGroup;
+			children = (
+				4BCA98C11D065CA20062F44C /* 6522.cpp */,
+				4BCA98C21D065CA20062F44C /* 6522.hpp */,
+			);
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+			sourceTree = "<group>";
+		};
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+			isa = PBXGroup;
+			children = (
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+				4BC9DF4E1D04691600F44158 /* 6560.hpp */,
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+			sourceTree = "<group>";
+		};
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 			isa = PBXGroup;
 			children = (
-				4BE5F85B1C3E1C2500C43F01 /* Electron */,
+				4BC9DF441D044FCA00F44158 /* ROMImages */,
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 			sourceTree = "<group>";
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-				4BCB70B41C947DDC005B1712 /* plus1.rom in Resources */,
 				4BB73EA71B587A5100552FC2 /* Atari2600Document.xib in Resources */,
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-				4BE5F85E1C3E1C2500C43F01 /* basic.rom in Resources */,
+				4BC9DF451D044FCA00F44158 /* ROMImages in Resources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
@ -1663,18 +1709,23 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
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+				4B73C71A1D036BD90074D992 /* Vic20Document.swift in Sources */,
 				4BBF99181C8FBA6F0075DAFB /* TextureTarget.cpp in Sources */,
 				4BC76E691C98E31700E6EF73 /* FIRFilter.cpp in Sources */,
 				4B55CE5F1C3B7D960093A61B /* MachineDocument.swift in Sources */,
+				4BCA98C31D065CA20062F44C /* 6522.cpp in Sources */,
 				4B69FB441C4D941400B5F0AA /* TapeUEF.cpp in Sources */,
 				4BBF99141C8FBA6F0075DAFB /* CRTInputBufferBuilder.cpp in Sources */,
 				4B2409551C45AB05004DA684 /* Speaker.cpp in Sources */,
@ -1736,6 +1787,14 @@
 			path = ..;
 			sourceTree = "<group>";
 		};
+		4B73C71B1D036C030074D992 /* Vic20Document.xib */ = {
+			isa = PBXVariantGroup;
+			children = (
+				4B73C71C1D036C030074D992 /* Base */,
+			);
+			name = Vic20Document.xib;
+			sourceTree = "<group>";
+		};
 		4BB73EA51B587A5100552FC2 /* Atari2600Document.xib */ = {
 			isa = PBXVariantGroup;
 			children = (
--- a/Signal/Base.lproj/Atari2600Document.xib
+++ b/Signal/Base.lproj/Atari2600Document.xib
@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
-<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="9532" systemVersion="15E65" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
+<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="9532" systemVersion="15F34" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
    <dependencies>
        <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="9532"/>
    </dependencies>
--- a/Signal/Base.lproj/Vic20Document.xib
+++ b/Signal/Base.lproj/Vic20Document.xib
@ -0,0 +1,42 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="9532" systemVersion="15F34" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
+    <dependencies>
+        <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="9532"/>
+    </dependencies>
+    <objects>
+        <customObject id="-2" userLabel="File's Owner" customClass="Atari2600Document" customModule="Clock_Signal" customModuleProvider="target">
+            <connections>
+                <outlet property="openGLView" destination="DEG-fq-cjd" id="Gxs-2u-n7B"/>
+                <outlet property="window" destination="xOd-HO-29H" id="JIz-fz-R2o"/>
+            </connections>
+        </customObject>
+        <customObject id="-1" userLabel="First Responder" customClass="FirstResponder"/>
+        <customObject id="-3" userLabel="Application" customClass="NSObject"/>
+        <window title="Window" allowsToolTipsWhenApplicationIsInactive="NO" autorecalculatesKeyViewLoop="NO" oneShot="NO" releasedWhenClosed="NO" showsToolbarButton="NO" visibleAtLaunch="NO" animationBehavior="default" id="xOd-HO-29H" userLabel="Window">
+            <windowStyleMask key="styleMask" titled="YES" closable="YES" miniaturizable="YES" resizable="YES"/>
+            <windowCollectionBehavior key="collectionBehavior" fullScreenPrimary="YES"/>
+            <windowPositionMask key="initialPositionMask" leftStrut="YES" rightStrut="YES" topStrut="YES" bottomStrut="YES"/>
+            <rect key="contentRect" x="133" y="235" width="400" height="300"/>
+            <rect key="screenRect" x="0.0" y="0.0" width="1366" height="768"/>
+            <value key="minSize" type="size" width="228" height="171"/>
+            <view key="contentView" id="gIp-Ho-8D9">
+                <rect key="frame" x="0.0" y="0.0" width="400" height="300"/>
+                <autoresizingMask key="autoresizingMask"/>
+                <subviews>
+                    <openGLView useAuxiliaryDepthBufferStencil="NO" allowOffline="YES" wantsBestResolutionOpenGLSurface="YES" translatesAutoresizingMaskIntoConstraints="NO" id="DEG-fq-cjd" customClass="CSOpenGLView">
+                        <rect key="frame" x="0.0" y="0.0" width="400" height="300"/>
+                    </openGLView>
+                </subviews>
+                <constraints>
+                    <constraint firstItem="DEG-fq-cjd" firstAttribute="centerX" secondItem="gIp-Ho-8D9" secondAttribute="centerX" id="ES5-nL-N3h"/>
+                    <constraint firstItem="DEG-fq-cjd" firstAttribute="height" secondItem="gIp-Ho-8D9" secondAttribute="height" id="YoB-qI-LFX"/>
+                    <constraint firstItem="DEG-fq-cjd" firstAttribute="centerY" secondItem="gIp-Ho-8D9" secondAttribute="centerY" id="d5Y-3a-CEI"/>
+                    <constraint firstItem="DEG-fq-cjd" firstAttribute="width" secondItem="gIp-Ho-8D9" secondAttribute="width" id="mYS-bH-DST"/>
+                </constraints>
+            </view>
+            <connections>
+                <outlet property="delegate" destination="-2" id="0bl-1N-x8E"/>
+            </connections>
+        </window>
+    </objects>
+</document>
--- a/Signal/ClockSignal-Bridging-Header.h
+++ b/Signal/ClockSignal-Bridging-Header.h
@ -3,8 +3,11 @@
 //

 #import "CSMachine.h"
+#import "CSKeyboardMachine.h"
+
 #import "CSAtari2600.h"
 #import "CSElectron.h"
+#import "CSVic20.h"

 #import	"CSOpenGLView.h"
 #import "AudioQueue.h"
--- a/Signal/Documents/Atari2600Document.swift
+++ b/Signal/Documents/Atari2600Document.swift
@ -26,17 +26,9 @@ class Atari2600Document: MachineDocument {
 	}

 	override var windowNibName: String? {
-		// Returns the nib file name of the document
-		// If you need to use a subclass of NSWindowController or if your document supports multiple NSWindowControllers, you should remove this property and override -makeWindowControllers instead.
 		return "Atari2600Document"
 	}

-	override func dataOfType(typeName: String) throws -> NSData {
-		// Insert code here to write your document to data of the specified type. If outError != nil, ensure that you create and set an appropriate error when returning nil.
-		// You can also choose to override fileWrapperOfType:error:, writeToURL:ofType:error:, or writeToURL:ofType:forSaveOperation:originalContentsURL:error: instead.
-		throw NSError(domain: NSOSStatusErrorDomain, code: unimpErr, userInfo: nil)
-	}
-
 	override func readFromData(data: NSData, ofType typeName: String) throws {
 		atari2600.setROM(data)
 	}
--- a/Signal/Documents/ElectronDocument.swift
+++ b/Signal/Documents/ElectronDocument.swift
@ -20,16 +20,18 @@ class ElectronDocument: MachineDocument {
 		return NSSize(width: 11.0, height: 10.0)
 	}

+	private func rom(name: String) -> NSData? {
+		return dataForResource(name, ofType: "rom", inDirectory: "ROMImages/Electron")
+	}
+
 	override func windowControllerDidLoadNib(aController: NSWindowController) {
 		super.windowControllerDidLoadNib(aController)

 		self.intendedCyclesPerSecond = 2000000

-		if let osPath = NSBundle.mainBundle().pathForResource("os", ofType: "rom") {
-			self.electron.setOSROM(NSData(contentsOfFile: osPath)!)
-		}
-		if let basicPath = NSBundle.mainBundle().pathForResource("basic", ofType: "rom") {
-			self.electron.setBASICROM(NSData(contentsOfFile: basicPath)!)
+		if let os = rom("os"), basic = rom("basic") {
+			self.electron.setOSROM(os)
+			self.electron.setBASICROM(basic)
 		}

 		establishStoredOptions()
@ -57,8 +59,8 @@ class ElectronDocument: MachineDocument {
 	}

 	override func readFromData(data: NSData, ofType typeName: String) throws {
-		if let plus1Path = NSBundle.mainBundle().pathForResource("plus1", ofType: "rom") {
-			electron.setROM(NSData(contentsOfFile: plus1Path)!, slot: 12)
+		if let plus1ROM = rom("plus1") {
+			electron.setROM(plus1ROM, slot: 12)
 		}
 		electron.setROM(data, slot: 15)
 	}
@ -93,25 +95,4 @@ class ElectronDocument: MachineDocument {
 		electron.useTelevisionOutput = (displayType == 1)
 		self.displayTypeButton.selectItemAtIndex(displayType)
 	}
-
-	// MARK: NSWindowDelegate
-	func windowDidResignKey(notification: NSNotification) {
-		electron.clearAllKeys()
-	}
-
-	// MARK: CSOpenGLViewResponderDelegate
-	override func keyDown(event: NSEvent) {
-		electron.setKey(event.keyCode, isPressed: true)
-	}
-
-	override func keyUp(event: NSEvent) {
-		electron.setKey(event.keyCode, isPressed: false)
-	}
-
-	override func flagsChanged(newModifiers: NSEvent) {
-		electron.setKey(VK_Shift, isPressed: newModifiers.modifierFlags.contains(.ShiftKeyMask))
-		electron.setKey(VK_Control, isPressed: newModifiers.modifierFlags.contains(.ControlKeyMask))
-		electron.setKey(VK_Command, isPressed: newModifiers.modifierFlags.contains(.CommandKeyMask))
-		electron.setKey(VK_Option, isPressed: newModifiers.modifierFlags.contains(.AlternateKeyMask))
-	}
 }
--- a/Signal/Documents/MachineDocument.swift
+++ b/Signal/Documents/MachineDocument.swift
@ -48,9 +48,11 @@ class MachineDocument: NSDocument, CSOpenGLViewDelegate, CSOpenGLViewResponderDe
 		// establish and provide the audio queue, taking advice as to an appropriate sampling rate
 		let maximumSamplingRate = AudioQueue.preferredSamplingRate()
 		let selectedSamplingRate = self.machine().idealSamplingRateFromRange(NSRange(location: 0, length: NSInteger(maximumSamplingRate)))
-		audioQueue = AudioQueue(samplingRate: Float64(selectedSamplingRate))
-		self.machine().audioQueue = self.audioQueue
-		self.machine().setAudioSamplingRate(selectedSamplingRate)
+		if selectedSamplingRate > 0 {
+			audioQueue = AudioQueue(samplingRate: Float64(selectedSamplingRate))
+			self.machine().audioQueue = self.audioQueue
+			self.machine().setAudioSamplingRate(selectedSamplingRate)
+		}
 	}

 	override func close() {
@ -95,6 +97,15 @@ class MachineDocument: NSDocument, CSOpenGLViewDelegate, CSOpenGLViewResponderDe
 		lastTime = time
 	}

+	// MARK: Utilities for children
+	func dataForResource(name : String, ofType type: String, inDirectory directory: String) -> NSData? {
+		if let path = NSBundle.mainBundle().pathForResource(name, ofType: type, inDirectory: directory) {
+			return NSData(contentsOfFile: path)
+		}
+
+		return nil
+	}
+
 	// MARK: CSOpenGLViewDelegate
 	func runForNumberOfCycles(numberOfCycles: Int32) {
 		if actionLock.tryLock() {
@ -110,8 +121,36 @@ class MachineDocument: NSDocument, CSOpenGLViewDelegate, CSOpenGLViewResponderDe
 		}
 	}

-	// MARK: CSOpenGLViewResponderDelegate
-	func keyDown(event: NSEvent) {}
-	func keyUp(event: NSEvent) {}
-	func flagsChanged(newModifiers: NSEvent) {}
+	// MARK: NSDocument overrides
+	override func dataOfType(typeName: String) throws -> NSData {
+		throw NSError(domain: NSOSStatusErrorDomain, code: unimpErr, userInfo: nil)
+	}
+
+	// MARK: Key forwarding
+	private func withKeyboardMachine(action: (CSKeyboardMachine) -> ()) {
+		if let keyboardMachine = self.machine() as? CSKeyboardMachine {
+			action(keyboardMachine)
+		}
+	}
+
+	func windowDidResignKey(notification: NSNotification) {
+		self.withKeyboardMachine { $0.clearAllKeys() }
+	}
+
+	func keyDown(event: NSEvent) {
+		self.withKeyboardMachine { $0.setKey(event.keyCode, isPressed: true) }
+	}
+
+	func keyUp(event: NSEvent) {
+		self.withKeyboardMachine { $0.setKey(event.keyCode, isPressed: false) }
+	}
+
+	func flagsChanged(newModifiers: NSEvent) {
+		self.withKeyboardMachine {
+			$0.setKey(VK_Shift, isPressed: newModifiers.modifierFlags.contains(.ShiftKeyMask))
+			$0.setKey(VK_Control, isPressed: newModifiers.modifierFlags.contains(.ControlKeyMask))
+			$0.setKey(VK_Command, isPressed: newModifiers.modifierFlags.contains(.CommandKeyMask))
+			$0.setKey(VK_Option, isPressed: newModifiers.modifierFlags.contains(.AlternateKeyMask))
+		}
+	}
 }
--- a/Signal/Documents/Vic20Document.swift
+++ b/Signal/Documents/Vic20Document.swift
@ -0,0 +1,47 @@
+//
+//  Vic20Document.swift
+//  Clock Signal
+//
+//  Created by Thomas Harte on 04/06/2016.
+//  Copyright © 2016 Thomas Harte. All rights reserved.
+//
+
+import Foundation
+
+class Vic20Document: MachineDocument {
+
+	private lazy var vic20 = CSVic20()
+	override func machine() -> CSMachine! {
+		return vic20
+	}
+
+	// MARK: NSDocument overrides
+	override init() {
+		super.init()
+		self.intendedCyclesPerSecond = 1022727
+		// TODO: or 1108405 for PAL; see http://www.antimon.org/dl/c64/code/stable.txt
+
+		if let kernel = rom("kernel-ntsc"), basic = rom("basic"), characters = rom("characters-english") {
+			vic20.setKernelROM(kernel)
+			vic20.setBASICROM(basic)
+			vic20.setCharactersROM(characters)
+		}
+	}
+
+	override class func autosavesInPlace() -> Bool {
+		return true
+	}
+
+	override var windowNibName: String? {
+		return "Vic20Document"
+	}
+
+	// MARK: machine setup
+	private func rom(name: String) -> NSData? {
+		return dataForResource(name, ofType: "bin", inDirectory: "ROMImages/Vic20")
+	}
+
+	override func readFromData(data: NSData, ofType typeName: String) throws {
+		vic20.setPRG(data)
+	}
+}
--- a/OSBindings/Mac/Clock
+++ b/OSBindings/Mac/Clock
@ -74,6 +74,20 @@
 			<key>NSDocumentClass</key>
 			<string>$(PRODUCT_MODULE_NAME).ElectronDocument</string>
 		</dict>
+		<dict>
+			<key>CFBundleTypeExtensions</key>
+			<array>
+				<string>prg</string>
+			</array>
+			<key>CFBundleTypeName</key>
+			<string>Vic-20 Cartridge</string>
+			<key>CFBundleTypeRole</key>
+			<string>Viewer</string>
+			<key>LSTypeIsPackage</key>
+			<integer>0</integer>
+			<key>NSDocumentClass</key>
+			<string>$(PRODUCT_MODULE_NAME).Vic20Document</string>
+		</dict>
 	</array>
 	<key>CFBundleExecutable</key>
 	<string>$(EXECUTABLE_NAME)</string>
--- a/Signal/Wrappers/AudioQueue.m
+++ b/Signal/Wrappers/AudioQueue.m
@ -10,7 +10,7 @@
@import AudioToolbox;

 #define AudioQueueNumAudioBuffers	4
-#define AudioQueueStreamLength		1024
+#define AudioQueueStreamLength		4096
 #define AudioQueueBufferLength		512

 enum {
--- a/Signal/Wrappers/CSElectron.h
+++ b/Signal/Wrappers/CSElectron.h
@ -6,19 +6,16 @@
 //  Copyright © 2016 Thomas Harte. All rights reserved.
 //

-#include "CSMachine.h"
-#import "KeyCodes.h"
+#import "CSMachine.h"
+#import "CSKeyboardMachine.h"

-@interface CSElectron : CSMachine
+@interface CSElectron : CSMachine <CSKeyboardMachine>

 - (void)setOSROM:(nonnull NSData *)rom;
 - (void)setBASICROM:(nonnull NSData *)rom;
 - (void)setROM:(nonnull NSData *)rom slot:(int)slot;
 - (BOOL)openUEFAtURL:(nonnull NSURL *)URL;

- (void)setKey:(uint16_t)key isPressed:(BOOL)isPressed;
- (void)clearAllKeys;
-
@property (nonatomic, assign) BOOL useFastLoadingHack;
@property (nonatomic, assign) BOOL useTelevisionOutput;

--- a/Signal/Wrappers/CSKeyboardMachine.h
+++ b/Signal/Wrappers/CSKeyboardMachine.h
@ -0,0 +1,16 @@
+//
+//  CSKeyboardMachine.h
+//  Clock Signal
+//
+//  Created by Thomas Harte on 05/06/2016.
+//  Copyright © 2016 Thomas Harte. All rights reserved.
+//
+
+#import "KeyCodes.h"
+
+@protocol CSKeyboardMachine <NSObject>
+
+- (void)setKey:(uint16_t)key isPressed:(BOOL)isPressed;
+- (void)clearAllKeys;
+
+@end
--- a/Signal/Wrappers/CSMachine.h
+++ b/Signal/Wrappers/CSMachine.h
@ -14,8 +14,8 @@

 - (void)runForNumberOfCycles:(int)numberOfCycles;

- (int)idealSamplingRateFromRange:(NSRange)range;
- (void)setAudioSamplingRate:(int)samplingRate;
+- (float)idealSamplingRateFromRange:(NSRange)range;
+- (void)setAudioSamplingRate:(float)samplingRate;

 - (void)setView:(CSOpenGLView *)view aspectRatio:(float)aspectRatio;
 - (void)drawViewForPixelSize:(CGSize)pixelSize onlyIfDirty:(BOOL)onlyIfDirty;
--- a/Signal/Wrappers/CSMachine.mm
+++ b/Signal/Wrappers/CSMachine.mm
@ -36,25 +36,25 @@ struct SpeakerDelegate: public Outputs::Speaker::Delegate {
 	}];
 }

- (int)idealSamplingRateFromRange:(NSRange)range {
+- (float)idealSamplingRateFromRange:(NSRange)range {
 	@synchronized(self) {
 		Outputs::Speaker *speaker = self.machine->get_speaker();
 		if(speaker)
 		{
-			return speaker->get_ideal_clock_rate_in_range((int)range.location, (int)(range.location + range.length));
+			return speaker->get_ideal_clock_rate_in_range((float)range.location, (float)(range.location + range.length));
 		}
-		return (int)range.location;
+		return 0;
 	}
 }

- (void)setAudioSamplingRate:(int)samplingRate {
+- (void)setAudioSamplingRate:(float)samplingRate {
 	@synchronized(self) {
 		_speakerDelegate.machine = self;
 		[self setSpeakerDelegate:&_speakerDelegate sampleRate:samplingRate];
 	}
 }

- (BOOL)setSpeakerDelegate:(Outputs::Speaker::Delegate *)delegate sampleRate:(int)sampleRate {
+- (BOOL)setSpeakerDelegate:(Outputs::Speaker::Delegate *)delegate sampleRate:(float)sampleRate {
 	@synchronized(self) {
 		Outputs::Speaker *speaker = self.machine->get_speaker();
 		if(speaker)
@ -88,5 +88,4 @@ struct SpeakerDelegate: public Outputs::Speaker::Delegate {
 	self.machine->get_crt()->draw_frame((unsigned int)pixelSize.width, (unsigned int)pixelSize.height, onlyIfDirty ? true : false);
 }

-
@end
--- a/Signal/Wrappers/CSVic20.h
+++ b/Signal/Wrappers/CSVic20.h
@ -0,0 +1,19 @@
+//
+//  CSVic20.h
+//  Clock Signal
+//
+//  Created by Thomas Harte on 04/06/2016.
+//  Copyright © 2016 Thomas Harte. All rights reserved.
+//
+
+#import "CSMachine.h"
+#import "CSKeyboardMachine.h"
+
+@interface CSVic20 : CSMachine <CSKeyboardMachine>
+
+- (void)setKernelROM:(nonnull NSData *)rom;
+- (void)setBASICROM:(nonnull NSData *)rom;
+- (void)setCharactersROM:(nonnull NSData *)rom;
+- (void)setPRG:(nonnull NSData *)prg;
+
+@end
--- a/Signal/Wrappers/CSVic20.mm
+++ b/Signal/Wrappers/CSVic20.mm
@ -0,0 +1,122 @@
+//
+//  CSVic20.m
+//  Clock Signal
+//
+//  Created by Thomas Harte on 04/06/2016.
+//  Copyright © 2016 Thomas Harte. All rights reserved.
+//
+
+#import "CSVic20.h"
+
+#import "Vic20.hpp"
+
+@implementation CSVic20 {
+	Vic20::Machine _vic20;
+}
+
+- (CRTMachine::Machine * const)machine {
+	return &_vic20;
+}
+
+- (void)setROM:(nonnull NSData *)rom slot:(Vic20::ROMSlot)slot {
+	_vic20.set_rom(slot, rom.length, (const uint8_t *)rom.bytes);
+}
+
+- (void)setKernelROM:(nonnull NSData *)rom {
+	[self setROM:rom slot:Vic20::ROMSlotKernel];
+}
+
+- (void)setBASICROM:(nonnull NSData *)rom {
+	[self setROM:rom slot:Vic20::ROMSlotBASIC];
+}
+
+- (void)setCharactersROM:(nonnull NSData *)rom {
+	[self setROM:rom slot:Vic20::ROMSlotCharacters];
+}
+
+- (void)setPRG:(nonnull NSData *)prg {
+	_vic20.add_prg(prg.length, (const uint8_t *)prg.bytes);
+}
+
+- (void)setKey:(uint16_t)key isPressed:(BOOL)isPressed {
+	static NSDictionary<NSNumber *, NSNumber *> *vicKeysByKeys = @{
+		@(VK_ANSI_1):	@(Vic20::Key::Key1),	@(VK_ANSI_2):	@(Vic20::Key::Key2),
+		@(VK_ANSI_3):	@(Vic20::Key::Key3),	@(VK_ANSI_4):	@(Vic20::Key::Key4),
+		@(VK_ANSI_5):	@(Vic20::Key::Key5),	@(VK_ANSI_6):	@(Vic20::Key::Key6),
+		@(VK_ANSI_7):	@(Vic20::Key::Key7),	@(VK_ANSI_8):	@(Vic20::Key::Key8),
+		@(VK_ANSI_9):	@(Vic20::Key::Key9),	@(VK_ANSI_0):	@(Vic20::Key::Key0),
+
+		@(VK_ANSI_Q):	@(Vic20::Key::KeyQ),	@(VK_ANSI_W):	@(Vic20::Key::KeyW),
+		@(VK_ANSI_E):	@(Vic20::Key::KeyE),	@(VK_ANSI_R):	@(Vic20::Key::KeyR),
+		@(VK_ANSI_T):	@(Vic20::Key::KeyT),	@(VK_ANSI_Y):	@(Vic20::Key::KeyY),
+		@(VK_ANSI_U):	@(Vic20::Key::KeyU),	@(VK_ANSI_I):	@(Vic20::Key::KeyI),
+		@(VK_ANSI_O):	@(Vic20::Key::KeyO),	@(VK_ANSI_P):	@(Vic20::Key::KeyP),
+		@(VK_ANSI_A):	@(Vic20::Key::KeyA),	@(VK_ANSI_S):	@(Vic20::Key::KeyS),
+		@(VK_ANSI_D):	@(Vic20::Key::KeyD),	@(VK_ANSI_F):	@(Vic20::Key::KeyF),
+		@(VK_ANSI_G):	@(Vic20::Key::KeyG),	@(VK_ANSI_H):	@(Vic20::Key::KeyH),
+		@(VK_ANSI_J):	@(Vic20::Key::KeyJ),	@(VK_ANSI_K):	@(Vic20::Key::KeyK),
+		@(VK_ANSI_L):	@(Vic20::Key::KeyL),	@(VK_ANSI_Z):	@(Vic20::Key::KeyZ),
+		@(VK_ANSI_X):	@(Vic20::Key::KeyX),	@(VK_ANSI_C):	@(Vic20::Key::KeyC),
+		@(VK_ANSI_V):	@(Vic20::Key::KeyV),	@(VK_ANSI_B):	@(Vic20::Key::KeyB),
+		@(VK_ANSI_N):	@(Vic20::Key::KeyN),	@(VK_ANSI_M):	@(Vic20::Key::KeyM),
+
+		@(VK_Space):			@(Vic20::Key::KeySpace),
+		@(VK_Return):			@(Vic20::Key::KeyReturn),
+		@(VK_Delete):			@(Vic20::Key::KeyDelete),
+		@(VK_ANSI_Comma):		@(Vic20::Key::KeyComma),
+		@(VK_ANSI_Period):		@(Vic20::Key::KeyFullStop),
+		@(VK_ANSI_Minus):		@(Vic20::Key::KeyDash),
+		@(VK_ANSI_Equal):		@(Vic20::Key::KeyEquals),
+		@(VK_ANSI_Semicolon):	@(Vic20::Key::KeyColon),
+		@(VK_ANSI_Quote):		@(Vic20::Key::KeySemicolon),
+		@(VK_ANSI_Slash):		@(Vic20::Key::KeySlash),
+		@(VK_Option):			@(Vic20::Key::KeyCBM),
+		@(VK_Control):			@(Vic20::Key::KeyControl),
+
+		@(VK_F1):	@(Vic20::Key::KeyF1),	@(VK_F3):	@(Vic20::Key::KeyF3),
+		@(VK_F5):	@(Vic20::Key::KeyF5),	@(VK_F7):	@(Vic20::Key::KeyF7),
+
+		@(VK_ANSI_Grave):			@(Vic20::Key::KeyLeft),
+		@(VK_Tab):					@(Vic20::Key::KeyRunStop),
+		@(VK_ANSI_LeftBracket):		@(Vic20::Key::KeyAt),
+		@(VK_ANSI_RightBracket):	@(Vic20::Key::KeyAsterisk),
+		@(VK_ANSI_Backslash):		@(Vic20::Key::KeyUp),
+
+		@(VK_RightArrow):			@(Vic20::Key::KeyRight),
+		@(VK_DownArrow):			@(Vic20::Key::KeyDown),
+	};
+
+	// Not yet mapped:
+	//	KeyHome
+	//	KeyPlus
+	//	KeyGBP
+
+	@synchronized(self) {
+		switch(key)
+		{
+			default: {
+				NSNumber *targetKey = vicKeysByKeys[@(key)];
+				if(targetKey)
+				{
+					_vic20.set_key_state((Vic20::Key)targetKey.integerValue, isPressed);
+				}
+				else
+					NSLog(@"Unmapped: %02x", key);
+			} break;
+
+			case VK_Shift:
+				// Yuck
+				_vic20.set_key_state(Vic20::Key::KeyLShift, isPressed);
+				_vic20.set_key_state(Vic20::Key::KeyRShift, isPressed);
+			break;
+		}
+	}
+}
+
+- (void)clearAllKeys {
+	@synchronized(self) {
+		_vic20.clear_all_keys();
+	}
+}
+
+@end
--- a/Outputs/CRT/CRT.cpp
+++ b/Outputs/CRT/CRT.cpp
@ -377,6 +377,10 @@ Outputs::CRT::Rect CRT::get_rect_for_area(int first_line_after_sync, int number_
 	unsigned int horizontal_scan_period = _horizontal_flywheel->get_scan_period();
 	unsigned int horizontal_retrace_period = horizontal_period - horizontal_scan_period;

+	// make sure that the requested range is visible
+	if(first_cycle_after_sync < horizontal_retrace_period) first_cycle_after_sync = (int)horizontal_retrace_period;
+	if(first_cycle_after_sync + number_of_cycles > horizontal_scan_period) number_of_cycles = (int)(horizontal_scan_period - (unsigned)first_cycle_after_sync);
+
 	float start_x = (float)((unsigned)first_cycle_after_sync - horizontal_retrace_period) / (float)horizontal_scan_period;
 	float width = (float)number_of_cycles / (float)horizontal_scan_period;

@ -384,6 +388,13 @@ Outputs::CRT::Rect CRT::get_rect_for_area(int first_line_after_sync, int number_
 	unsigned int vertical_period = _vertical_flywheel->get_standard_period();
 	unsigned int vertical_scan_period = _vertical_flywheel->get_scan_period();
 	unsigned int vertical_retrace_period = vertical_period - vertical_scan_period;
+
+	// make sure that the requested range is visible
+//	if((unsigned)first_line_after_sync * horizontal_period < vertical_retrace_period)
+//		first_line_after_sync = (vertical_retrace_period + horizontal_period - 1) / horizontal_period;
+//	if((first_line_after_sync + number_of_lines) * horizontal_period > vertical_scan_period)
+//		number_of_lines = (int)(horizontal_scan_period - (unsigned)first_cycle_after_sync);
+
 	float start_y = (float)(((unsigned)first_line_after_sync * horizontal_period) - vertical_retrace_period) / (float)vertical_scan_period;
 	float height = (float)((unsigned)number_of_lines * horizontal_period) / vertical_scan_period;

--- a/Outputs/CRT/Internals/CRTOpenGL.cpp
+++ b/Outputs/CRT/Internals/CRTOpenGL.cpp
@ -334,6 +334,7 @@ void OpenGLOutputBuilder::draw_frame(unsigned int output_width, unsigned int out

 	glActiveTexture(pixel_accumulation_texture_unit);
 	framebuffer->bind_texture();
+//	compositeTexture->bind_texture();
 	framebuffer->draw((float)output_width / (float)output_height);

 	_fence = glFenceSync(GL_SYNC_GPU_COMMANDS_COMPLETE, 0);
--- a/Outputs/Speaker.hpp
+++ b/Outputs/Speaker.hpp
@ -24,7 +24,7 @@ class Speaker {
 				virtual void speaker_did_complete_samples(Speaker *speaker, const int16_t *buffer, int buffer_size) = 0;
 		};

-		int get_ideal_clock_rate_in_range(int minimum, int maximum)
+		float get_ideal_clock_rate_in_range(float minimum, float maximum)
 		{
 			// return exactly the input rate if possible
 			if(_input_cycles_per_second >= minimum && _input_cycles_per_second <= maximum) return _input_cycles_per_second;
@ -36,7 +36,7 @@ class Speaker {
 			return maximum;
 		}

-		void set_output_rate(int cycles_per_second, int buffer_size)
+		void set_output_rate(float cycles_per_second, int buffer_size)
 		{
 			_output_cycles_per_second = cycles_per_second;
 			if(_buffer_size != buffer_size)
@ -58,7 +58,7 @@ class Speaker {
 			_delegate = delegate;
 		}

-		void set_input_rate(int cycles_per_second)
+		void set_input_rate(float cycles_per_second)
 		{
 			_input_cycles_per_second = cycles_per_second;
 			set_needs_updated_filter_coefficients();
@ -74,7 +74,7 @@ class Speaker {
 		bool _coefficients_are_dirty;
 		Delegate *_delegate;

-		int _input_cycles_per_second, _output_cycles_per_second;
+		float _input_cycles_per_second, _output_cycles_per_second;

 		void set_needs_updated_filter_coefficients()
 		{
@ -181,7 +181,7 @@ template <class T> class Filter: public Speaker {
 			}
 			else
 			{
-				_number_of_taps = (_input_cycles_per_second + _output_cycles_per_second) / _output_cycles_per_second;
+				_number_of_taps = (int)ceilf((_input_cycles_per_second + _output_cycles_per_second) / _output_cycles_per_second);
 				_number_of_taps *= 2;
 				_number_of_taps |= 1;
 			}
@ -190,7 +190,7 @@ template <class T> class Filter: public Speaker {
 			_buffer_in_progress_pointer = 0;

 			_stepper = std::unique_ptr<SignalProcessing::Stepper>(new SignalProcessing::Stepper((uint64_t)_input_cycles_per_second, (uint64_t)_output_cycles_per_second));
-			_filter = std::unique_ptr<SignalProcessing::FIRFilter>(new SignalProcessing::FIRFilter((unsigned int)_number_of_taps, (unsigned int)_input_cycles_per_second, 0.0, (float)_output_cycles_per_second / 2.0f, SignalProcessing::FIRFilter::DefaultAttenuation));
+			_filter = std::unique_ptr<SignalProcessing::FIRFilter>(new SignalProcessing::FIRFilter((unsigned int)_number_of_taps, (float)_input_cycles_per_second, 0.0, (float)_output_cycles_per_second / 2.0f, SignalProcessing::FIRFilter::DefaultAttenuation));

 			_input_buffer = std::unique_ptr<int16_t>(new int16_t[_number_of_taps]);
 			_input_buffer_depth = 0;
--- a/ROMImages/Electron/readme.txt
+++ b/ROMImages/Electron/readme.txt
@ -0,0 +1,16 @@
+ROM files would ordinarily go here; the copyright status of these is uncertain so they have not been included in this repository.
+
+Expected files:
+
+basic.rom
+os.rom
+plus1.rom
+
+Likely to be desired in the future:
+
+adfs.rom
+ADFS-E00_1.rom
+ADFS-E00_2.rom
+DFSE00r3.rom
+ElectronExpansionRomPresAP2-v1.23.rom
+os300.rom
--- a/ROMImages/Vic20/readme.txt
+++ b/ROMImages/Vic20/readme.txt
@ -0,0 +1,17 @@
+ROM files would ordinarily go here; the copyright status of these is uncertain so they have not been included in this repository.
+
+Expected files:
+
+basic.bin
+characters-english.bin
+kernel-ntsc.rom
+
+Likely to be desired in the future:
+
+characters-danish.bin
+characters-japanese.bin
+characters-swedish.bin
+kernel-danish.bin
+kernel-japanese.bin
+kernel-pal.bin
+kernel-swedish.bin