/*
JPC: An x86 PC Hardware Emulator for a pure Java Virtual Machine
Release Version 2.4
A project from the Physics Dept, The University of Oxford
Copyright (C) 2007-2010 The University of Oxford
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:
jpc.sourceforge.net
or the developer website
sourceforge.net/projects/jpc/
Conceived and Developed by:
Rhys Newman, Ian Preston, Chris Dennis
End of licence header
*/
package org.jpc.emulator.motherboard;
import java.io.*;
import org.jpc.emulator.*;
import org.jpc.emulator.memory.PhysicalAddressSpace;
import org.jpc.emulator.processor.Processor;
/**
* I/O Device mapped to port 0x92 that controls the enabled status of the 20th
* address line.
* @author Chris Dennis
*/
public class GateA20Handler extends AbstractHardwareComponent implements IODevice
{
private Processor cpu;
private PhysicalAddressSpace physicalAddressSpace;
private boolean ioportRegistered;
public GateA20Handler()
{
ioportRegistered = false;
cpu = null;
physicalAddressSpace = null;
}
public void loadState(DataInput input) throws IOException
{
ioportRegistered = false;
}
private void setGateA20State(boolean value)
{
physicalAddressSpace.setGateA20State(value);
}
/**
* Writes a byte into the handler. Bit 1 controls the A20 state, if high
* A20 is enabled, if low A20 is disabled. If bit 0 is high then the
* processor will be reset.
* @param address location being written to
* @param data byte value being written
*/
public void ioPortWrite8(int address, int data)
{
setGateA20State((data & 0x02) != 0);
if ((data & 0x01) != 0)
cpu.reset();
}
public void ioPortWrite16(int address, int data)
{
ioPortWrite8(address, data);
}
public void ioPortWrite32(int address, int data)
{
ioPortWrite8(address, data);
}
/**
* Reads a byte from the handler. If A20 is enabled then this will return
* 0x02, else it will return 0x00.
* @param address location being read
* @return byte value read
*/
public int ioPortRead8(int address)
{
return physicalAddressSpace.getGateA20State() ? 0x02 : 0x00;
}
public int ioPortRead16(int address)
{
return ioPortRead8(address) | 0xff00;
}
public int ioPortRead32(int address)
{
return ioPortRead8(address) | 0xffffff00;
}
public int[] ioPortsRequested()
{
return new int[] {0x92};
}
public boolean initialised()
{
return ioportRegistered && (cpu != null) && (physicalAddressSpace != null);
}
public boolean updated()
{
return ioportRegistered && cpu.updated() && physicalAddressSpace.updated();
}
public void updateComponent(HardwareComponent component)
{
if (component instanceof IOPortHandler)
{
((IOPortHandler)component).registerIOPortCapable(this);
ioportRegistered = true;
}
}
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 Processor) && component.initialised())
cpu = (Processor) component;
}
public void reset()
{
ioportRegistered = false;
physicalAddressSpace = null;
cpu = null;
}
}