CLK/Components/8255/i8255.hpp

//
//  i8255.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 01/08/2017.
//  Copyright 2017 Thomas Harte. All rights reserved.
//

#pragma once

#include <cstdint>

namespace Intel::i8255 {

class PortHandler {
public:
	void set_value([[maybe_unused]] int port, [[maybe_unused]] uint8_t value) {}
	uint8_t get_value([[maybe_unused]] int port) { return 0xff; }
};

// TODO: Modes 1 and 2.
template <class T> class i8255 {
public:
	i8255(T &port_handler) : control_(0), outputs_{0, 0, 0}, port_handler_(port_handler) {}

	/*!
		Stores the value @c value to the register at @c address. If this causes a change in 8255 output
		then the PortHandler will be informed.
	*/
	void write(const int address, const uint8_t value) {
		switch(address & 3) {
			case 0:
				if(!(control_ & 0x10)) {
					// TODO: so what would output be when switching from input to output mode?
					outputs_[0] = value; port_handler_.set_value(0, value);
				}
			break;
			case 1:
				if(!(control_ & 0x02)) {
					outputs_[1] = value; port_handler_.set_value(1, value);
				}
			break;
			case 2:	outputs_[2] = value; port_handler_.set_value(2, value);	break;
			case 3:
				if(value & 0x80) {
					control_ = value;
				} else {
					if(value & 1) {
						outputs_[2] |= 1 << ((value >> 1)&7);
					} else {
						outputs_[2] &= ~(1 << ((value >> 1)&7));
					}
				}
				update_outputs();
			break;
		}
	}

	/*!
		Obtains the current value for the register at @c address. If this provides a reading
		of input then the PortHandler will be queried.
	*/
	uint8_t read(const int address) {
		switch(address & 3) {
			case 0:	return (control_ & 0x10) ? port_handler_.get_value(0) : outputs_[0];
			case 1:	return (control_ & 0x02) ? port_handler_.get_value(1) : outputs_[1];
			case 2:	{
				if(!(control_ & 0x09)) return outputs_[2];
				uint8_t input = port_handler_.get_value(2);
				return ((control_ & 0x01) ?
					(input & 0x0f) :
					(outputs_[2] & 0x0f)) | ((control_ & 0x08) ?
						(input & 0xf0) : (outputs_[2] & 0xf0));
			}
			case 3:	return control_;
		}
		return 0xff;
	}

private:
	void update_outputs() {
		if(!(control_ & 0x10)) port_handler_.set_value(0, outputs_[0]);
		if(!(control_ & 0x02)) port_handler_.set_value(1, outputs_[1]);
		port_handler_.set_value(2, outputs_[2]);
	}

	uint8_t control_;
	uint8_t outputs_[3];
	T &port_handler_;
};

}