Added overflow-flag setting logic and ensured disk ROM gets through regardless of ROM/disk installation order.

Machines/Commodore/1540/C1540.cpp

@@ -39,6 +39,10 @@ void Machine::set_serial_bus(std::shared_ptr<::Commodore::Serial::Bus> serial_bu
 
 unsigned int Machine::perform_bus_operation(CPU6502::BusOperation operation, uint16_t address, uint8_t *value)
 {
+//	static bool log = false;
+//	if(operation == CPU6502::BusOperation::ReadOpcode) printf("%04x\n", address);
+//	if(operation == CPU6502::BusOperation::ReadOpcode && (address == 0xf3be)) log = true;
+//	if(operation == CPU6502::BusOperation::ReadOpcode && log) printf("%04x\n", address);
 //	if(operation == CPU6502::BusOperation::ReadOpcode && (address >= 0xF556 && address <= 0xF56D)) printf("%04x\n", address);
 //	if(operation == CPU6502::BusOperation::ReadOpcode && (address == 0xE887)) printf("A: %02x\n", get_value_of_register(CPU6502::Register::A));
 
@@ -123,8 +127,14 @@ void Machine::process_input_bit(int value, unsigned int cycles_since_index_hole)
 	{
 		_driveVIA.set_data_input((uint8_t)_shift_register);
 		_bit_window_offset = 0;
+		if(_driveVIA.get_should_set_overflow())
+		{
+			set_overflow_line(true);
 		}
 	}
+	else
+		set_overflow_line(false);
+}
 
 // the 1540 does not recognise index holes
 void Machine::process_index_hole()	{}

Machines/Commodore/1540/C1540.hpp

@@ -132,6 +132,16 @@ class DriveVIA: public MOS::MOS6522<DriveVIA>, public MOS::MOS6522IRQDelegate {
 			_port_a = value;
 		}
 
+		bool get_should_set_overflow() {
+			return _should_set_overflow;
+		}
+
+		void set_control_line_output(Port port, Line line, bool value) {
+			if(port == Port::A && line == Line::Two) {
+				_should_set_overflow = value;
+			}
+		}
+
 		void set_port_output(Port port, uint8_t value, uint8_t direction_mask) {
 			if(port)
 			{
@@ -147,6 +157,7 @@ class DriveVIA: public MOS::MOS6522<DriveVIA>, public MOS::MOS6522IRQDelegate {
 
 	private:
 		uint8_t _port_b, _port_a;
+		bool _should_set_overflow;
 };
 
 /*!

Machines/Commodore/Vic-20/Vic20.cpp

@@ -169,6 +169,11 @@ void Machine::set_rom(ROMSlot slot, size_t length, const uint8_t *data)
 				_c1540->set_rom(data);
 				_c1540->run_for_cycles(2000000);	// pretend it booted a couple of seconds ago
 			}
+			else
+			{
+				_driveROM.reset(new uint8_t[length]);
+				memcpy(_driveROM.get(), data, length);
+			}
 		return;
 	}
 
@@ -221,6 +226,13 @@ void Machine::set_disk(std::shared_ptr<Storage::Disk> disk)
 
 	// hand it the disk
 	_c1540->set_disk(disk);
+
+	// install the ROM if it was previously set
+	if(_driveROM)
+	{
+		_c1540->set_rom(_driveROM.get());
+		_driveROM.reset();
+	}
 }
 
 #pragma mark - Typer

Machines/Commodore/Vic-20/Vic20.hpp

@@ -287,6 +287,7 @@ class Machine:
 		uint8_t _screenMemory[0x1000];
 		uint8_t _colorMemory[0x0400];
 		uint8_t _junkMemory[0x0400];
+		std::unique_ptr<uint8_t> _driveROM;
 
 		uint8_t *_videoMemoryMap[16];
 		uint8_t *_processorReadMemoryMap[64];

Processors/6502/CPU6502.hpp

@@ -472,6 +472,7 @@ template <class T> class Processor {
 		bool _ready_line_is_enabled;
 
 		bool _irq_line_is_enabled, _irq_request_history;
+		bool _nmi_line_is_enabled, _set_overflow_line_is_enabled;
 
 		/*!
 			Gets the program representing an RST response.
@@ -549,7 +550,10 @@ template <class T> class Processor {
 			_interruptFlag(Flag::Interrupt),
 			_s(0),
 			_nextBusOperation(BusOperation::None),
-			_interrupt_requests(InterruptRequestFlags::PowerOn)
+			_interrupt_requests(InterruptRequestFlags::PowerOn),
+			_irq_line_is_enabled(false),
+			_nmi_line_is_enabled(false),
+			_set_overflow_line_is_enabled(false)
 		{
 			// only the interrupt flag is defined upon reset but get_flags isn't going to
 			// mask the other flags so we need to do that, at least
@@ -1237,6 +1241,19 @@ template <class T> class Processor {
 			_irq_line_is_enabled = active;
 		}
 
+		/*!
+			Sets the current level of the set overflow line.
+
+			@param active @c true if the line is logically active; @c false otherwise.
+		*/
+		inline void set_overflow_line(bool active)
+		{
+			// a leading edge will set the overflow flag
+			if(active && !_set_overflow_line_is_enabled)
+				_overflowFlag = Flag::Overflow;
+			_set_overflow_line_is_enabled = active;
+		}
+
 		/*!
 			Sets the current level of the NMI line.
 
@@ -1245,7 +1262,9 @@ template <class T> class Processor {
 		inline void set_nmi_line(bool active)
 		{
 			// NMI is edge triggered, not level
-			_interrupt_requests |= (active ? InterruptRequestFlags::NMI : 0);
+			if(active && !_nmi_line_is_enabled)
+				_interrupt_requests |= InterruptRequestFlags::NMI;
+			_nmi_line_is_enabled = active;
 		}
 
 		/*!