/*
    JPC: A x86 PC Hardware Emulator for a pure Java Virtual Machine
    Release Version 2.0

    A project from the Physics Dept, The University of Oxford

    Copyright (C) 2007 Isis Innovation Limited

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License version 2 as published by
    the Free Software Foundation.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License along
    with this program; if not, write to the Free Software Foundation, Inc.,
    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 
    Details (including contact information) can be found at: 

    www.physics.ox.ac.uk/jpc
*/

package org.jpc.emulator.motherboard;

import org.jpc.emulator.processor.*;
import org.jpc.emulator.memory.*;
import org.jpc.emulator.HardwareComponent;

public class GateA20Handler implements IOPortCapable, HardwareComponent
{
    private Processor cpu;
    private PhysicalAddressSpace physicalAddressSpace;
    private LinearAddressSpace linearAddressSpace;
    private boolean ioportRegistered;

    public GateA20Handler()
    {
	ioportRegistered = false;
	cpu = null;
        physicalAddressSpace = null;
    }

    private void setGateA20State(boolean value)
    {
	physicalAddressSpace.setGateA20State(value);
    }

    public void ioPortWriteByte(int address, int data)
    {
	setGateA20State((data & 0x02) != 0);
	if ((data & 0x01) != 0)
	    cpu.reset();
    }
    public void ioPortWriteWord(int address, int data)
    {
	ioPortWriteByte(address, data);
    }
    public void ioPortWriteLong(int address, int data)
    {
	ioPortWriteWord(address, data);
    }

    public int ioPortReadByte(int address)
    {
	return physicalAddressSpace.getGateA20State() ? 0x02 : 0x00;
    }
    public int ioPortReadWord(int address)
    {
	return ioPortReadByte(address) | 0xff00;
    }
    public int ioPortReadLong(int address)
    {
	return ioPortReadWord(address) | 0xffff0000;
    }

    public int[] ioPortsRequested()
    {
	return new int[] {0x92};
    }

    public boolean initialised()
    {
	return ioportRegistered && (cpu != null) && (physicalAddressSpace != null) && (linearAddressSpace != null);
    }

    public void acceptComponent(HardwareComponent component)
    {
	if ((component instanceof IOPortHandler) && component.initialised()) 
        {
	    ((IOPortHandler)component).registerIOPortCapable(this);
	    ioportRegistered = true;
	}

	if (component instanceof PhysicalAddressSpace) 
	    physicalAddressSpace = (PhysicalAddressSpace)component;

	if (component instanceof LinearAddressSpace) 
	    linearAddressSpace = (LinearAddressSpace)component;

        if ((component instanceof Processor) && component.initialised()) 
            cpu = (Processor) component;
    }

    public void reset()
    {
	ioportRegistered = false;
        physicalAddressSpace = null;
        linearAddressSpace = null;
	cpu = null;
    }
}
