This is intended to be enough to start producing something of an output. But something's obviously still broken.

Machines/Electron/Electron.cpp

@@ -12,9 +12,17 @@
 
 using namespace Electron;
 
-Machine::Machine()
+static const int cycles_per_line = 128;
+static const int cycles_per_frame = 312*cycles_per_line;
+static const int crt_cycles_multiplier = 8;
+static const int crt_cycles_per_line = crt_cycles_multiplier * cycles_per_line;
+
+Machine::Machine() :
+	_interruptControl(0),
+	_frameCycles(0),
+	_outputPosition(0)
 {
-	_crt = new Outputs::CRT(128, 312, 1, 1);
+	_crt = new Outputs::CRT(crt_cycles_per_line, 312, 1, 1);
 	_interruptStatus = 0x02;
 	setup6502();
 }
@@ -25,6 +33,8 @@ Machine::~Machine()
 
 unsigned int Machine::perform_bus_operation(CPU6502::BusOperation operation, uint16_t address, uint8_t *value)
 {
+	unsigned int cycles = 1;
+
 	if(address < 32768)
 	{
 		if(isReadOperation(operation))
@@ -34,9 +44,15 @@ unsigned int Machine::perform_bus_operation(CPU6502::BusOperation operation, uin
 		else
 		{
 			_ram[address] = *value;
+
+// TODO: range check on address; a lot of the time the machine will be running code outside of
+// the screen area, meaning that no update is required.
+//			if (address
+			update_display();
 		}
 
-		// TODO: RAM timing
+		// TODO: RAM timing for Modes 0–3
+		cycles += (_frameCycles&1)^1;
 	}
 	else
 	{
@@ -44,7 +60,7 @@ unsigned int Machine::perform_bus_operation(CPU6502::BusOperation operation, uin
 		{
 			if((address & 0xff00) == 0xfe00)
 			{
-				printf("%c: %02x: ", isReadOperation(operation) ? 'r' : 'w', *value);
+//				printf("%c: %02x: ", isReadOperation(operation) ? 'r' : 'w', *value);
 
 				switch(address&0xf)
 				{
@@ -57,18 +73,16 @@ unsigned int Machine::perform_bus_operation(CPU6502::BusOperation operation, uin
 						else
 						{
 							_interruptControl = *value;
+							evaluate_interrupts();
 						}
-						printf("Interrupt status or control\n");
 					break;
 					case 0x1:
 					break;
 					case 0x2:
-						_screenStartAddress = (_screenStartAddress & 0xff00) | ((*value) & 0xe0);
+						_startScreenAddress = (_startScreenAddress & 0xff00) | ((*value) & 0xe0);
-						printf("Screen start address low, now %04x\n", _screenStartAddress);
 					break;
 					case 0x3:
-						_screenStartAddress = (_screenStartAddress & 0x00ff) | (uint16_t)(((*value) & 0x3f) << 8);
+						_startScreenAddress = (_startScreenAddress & 0x00ff) | (uint16_t)(((*value) & 0x3f) << 8);
-						printf("Screen start address high, now %04x\n", _screenStartAddress);
 					break;
 					case 0x4:
 						printf("Cassette\n");
@@ -81,7 +95,13 @@ unsigned int Machine::perform_bus_operation(CPU6502::BusOperation operation, uin
 							{
 								_activeRom = (Electron::ROMSlot)nextROM;
 							}
-							printf("Interrupt clear and paging\n");
+
+							if( (*value)&0x10 ) _interruptStatus &= ~InterruptDisplayEnd;
+							if( (*value)&0x20 ) _interruptStatus &= InterruptRealTimeClock;
+							if( (*value)&0x40 ) _interruptStatus &= InterruptHighToneDetect;
+							evaluate_interrupts();
+
+							// TODO: NMI (?)
 						}
 					break;
 					case 0x6:
@@ -91,7 +111,8 @@ unsigned int Machine::perform_bus_operation(CPU6502::BusOperation operation, uin
 						printf("Misc. control\n");
 					break;
 					default:
-						printf("Palette\n");
+						update_display();
+//						printf("Palette\n");
 					break;
 				}
 			}
@@ -121,7 +142,16 @@ unsigned int Machine::perform_bus_operation(CPU6502::BusOperation operation, uin
 		}
 	}
 
-	return 1;
+	_frameCycles += cycles;
+	if(_frameCycles == cycles_per_frame)
+	{
+		update_display();
+		_frameCycles = 0;
+	}
+	if(_frameCycles == 128*128) signal_interrupt(InterruptRealTimeClock);
+	if(_frameCycles == 284*128) signal_interrupt(InterruptDisplayEnd);
+
+	return cycles;
 }
 
 void Machine::set_rom(ROMSlot slot, size_t length, const uint8_t *data)
@@ -136,3 +166,81 @@ void Machine::set_rom(ROMSlot slot, size_t length, const uint8_t *data)
 
 	memcpy(target, data, std::min((size_t)16384, length));
 }
+
+inline void Machine::signal_interrupt(Electron::Interrupt interrupt)
+{
+	_interruptStatus |= (interrupt << 2);
+	evaluate_interrupts();
+}
+
+inline void Machine::evaluate_interrupts()
+{
+	if(_interruptStatus & _interruptControl)
+	{
+		_interruptStatus |= 1;
+	}
+	set_irq_line(_interruptStatus & 1);
+}
+
+inline void Machine::update_display()
+{
+	const int end_of_hsync = 3 * cycles_per_line;
+
+	if(_frameCycles >= end_of_hsync)
+	{
+		// assert sync for the first three lines of the display
+		if(_outputPosition < end_of_hsync)
+		{
+			_crt->output_sync(end_of_hsync * crt_cycles_multiplier);
+			_outputPosition = end_of_hsync;
+		}
+
+		while(_outputPosition < _frameCycles)
+		{
+			const int current_line = _outputPosition >> 7;
+			const int line_position = _outputPosition & 127;
+
+			// all lines then start with 9 cycles of sync
+			if(!line_position)
+			{
+				_crt->output_sync(9 * crt_cycles_multiplier);
+				_outputPosition += 9;
+			}
+			else
+			{
+				// on lines prior to 28 or after or equal to 284, or on a line that is equal to 8 or 9 modulo 10 in a line-spaced mode,
+				// the line is then definitely blank.
+				if(current_line < 28 || current_line >= 284)
+				{
+					if(line_position == 9)
+					{
+						_crt->output_blank(119 * crt_cycles_multiplier);
+						_outputPosition += 119;
+					}
+				}
+				else
+				{
+					// there are then 15 cycles of blank, 80 cycles of pixels, and 24 further cycles of blank
+					if(line_position == 9)
+					{
+						_crt->output_blank(15 * crt_cycles_multiplier);
+						_outputPosition += 15;
+						_crt->output_data(80 * crt_cycles_multiplier);
+					}
+
+					if(line_position >= 24 && line_position < 104)
+					{
+						// TODO: actually output some pixels, why not?
+						_outputPosition++;
+					}
+
+					if(line_position == 104)
+					{
+						_crt->output_blank(24 * crt_cycles_multiplier);
+						_outputPosition += 24;
+					}
+				}
+			}
+		}
+	}
+}

Machines/Electron/Electron.hpp

@@ -29,6 +29,14 @@ enum ROMSlot: uint8_t {
 	ROMSlotOS
 };
 
+enum Interrupt: uint8_t {
+	InterruptRealTimeClock		= 0x01,
+	InterruptDisplayEnd			= 0x02,
+	InterruptTransmitDataEmpty	= 0x04,
+	InterruptReceiveDataFull	= 0x08,
+	InterruptHighToneDetect		= 0x10
+};
+
 class Machine: public CPU6502::Processor<Machine> {
 
 	public:
@@ -45,10 +53,16 @@ class Machine: public CPU6502::Processor<Machine> {
 	private:
 		uint8_t _os[16384], _basic[16384], _ram[32768];
 		uint8_t _interruptStatus, _interruptControl;
-		uint16_t _screenStartAddress;
 		ROMSlot _activeRom;
 
 		Outputs::CRT *_crt;
+
+		int _frameCycles, _outputPosition;
+		uint16_t _startScreenAddress, _currentScreenAddress;
+
+		inline void update_display();
+		inline void signal_interrupt(Interrupt interrupt);
+		inline void evaluate_interrupts();
 };
 
 }

Processors/6502/CPU6502.hpp

@@ -981,6 +981,16 @@ template <class T> class Processor {
 			_reset_line_is_enabled = active;
 		}
 
+		void set_irq_line(bool active)
+		{
+			// TODO
+		}
+
+		void set_nmi_line(bool active)
+		{
+			// TODO
+		}
+
 		bool is_jammed()
 		{
 			return _is_jammed;