CLK/Components/6522/6522.hpp

//
//  6522.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 06/06/2016.
//  Copyright 2016 Thomas Harte. All rights reserved.
//

#pragma once

#include <cstdint>

#include "Implementation/6522Storage.hpp"

#include "../../ClockReceiver/ClockReceiver.hpp"

namespace MOS::MOS6522 {

enum Port {
	A = 0,
	B = 1
};

enum Line {
	One = 0,
	Two = 1
};

/*!
	Provides the mechanism for just-int-time communication from a 6522; the normal use case is to compose a
	6522 and a subclass of PortHandler in order to reproduce a 6522 and its original bus wiring.
*/
class PortHandler {
public:
	/// Requests the current input value of the named port from the port handler.
	uint8_t get_port_input(Port) {
		return 0xff;
	}

	/// Sets the current output value of the named oprt and provides @c direction_mask, indicating which pins are marked as output.
	void set_port_output(Port, [[maybe_unused]] uint8_t value, [[maybe_unused]] uint8_t direction_mask) {}

	/// Sets the current logical output level for the named line on the specified  port.
	void set_control_line_output(Port, Line, [[maybe_unused]] bool value) {}

	/// Sets the current logical value of the interrupt line.
	void set_interrupt_status([[maybe_unused]] bool status) {}

	/// Provides a measure of time elapsed between other calls.
	void run_for(HalfCycles) {}

	/// Receives passed-on flush() calls from the 6522.
	void flush() {}
};

/*!
	Provided as an optional alternative base to @c PortHandler for port handlers; via the delegate pattern adds
	a virtual level of indirection for receiving changes to the interrupt line.
*/
class IRQDelegatePortHandler: public PortHandler {
public:
	class Delegate {
		public:
			/// Indicates that the interrupt status has changed for the IRQDelegatePortHandler provided.
			virtual void mos6522_did_change_interrupt_status(void *irq_delegate) = 0;
	};

	/// Sets the delegate that will receive notification of changes in the interrupt line.
	void set_interrupt_delegate(Delegate *);

	/// Overrides @c PortHandler::set_interrupt_status, notifying the delegate if one is set.
	void set_interrupt_status(bool);

private:
	Delegate *delegate_ = nullptr;
};

/*!
	Implements a template for emulation of the MOS 6522 Versatile Interface Adaptor ('VIA').

	The VIA provides:
		* two timers, each of which may trigger interrupts and one of which may repeat;
		* two digial input/output ports; and
		* a serial-to-parallel shifter.

	Consumers should derive their own curiously-recurring-template-pattern subclass,
	implementing bus communications as required.
*/
template <class BusHandlerT> class MOS6522: public MOS6522Storage {
public:
	MOS6522(BusHandlerT &bus_handler) noexcept : bus_handler_(bus_handler) {}
	MOS6522(const MOS6522 &) = delete;

	/*! Sets a register value. */
	void write(int address, uint8_t value);

	/*! Gets a register value. */
	uint8_t read(int address);

	/*! @returns the bus handler. */
	BusHandlerT &bus_handler();

	/// Sets the input value of the named line and port.
	void set_control_line_input(Port, Line, bool value);

	/// Runs for a specified number of half cycles.
	void run_for(const HalfCycles);

	/// Runs for a specified number of cycles.
	void run_for(const Cycles);

	/// @returns @c true if the IRQ line is currently active; @c false otherwise.
	bool get_interrupt_line() const;

	/// Updates the port handler to the current time and then requests that it flush.
	void flush();

private:
	void do_phase1();
	void do_phase2();
	void shift_in();
	void shift_out();

	BusHandlerT &bus_handler_;
	HalfCycles time_since_bus_handler_call_;

	void access(int address);

	uint8_t get_port_input(Port port, uint8_t output_mask, uint8_t output, uint8_t timer_mask);
	inline void reevaluate_interrupts();

	/// Sets the current intended output value for the port and line;
	/// if this affects the visible output, it will be passed to the handler.
	void set_control_line_output(Port port, Line line, LineState value);
	void evaluate_cb2_output();
	void evaluate_port_b_output();
};

}

#include "Implementation/6522Implementation.hpp"