/*
	Copyright (c) 1996-1997 Swiss Federal Institute of Technology, 
	Computer Engineering and Networks Laboratory. All rights reserved.

	Written by George Fankhauser <gfa@acm.org>. For more documentation
	please visit http://www.tik.ee.ethz.ch/~gfa.
	
	This device is root counter 2 of the PSX

	
	File:                  $Source: /usr/drwho/vault/cvs/topsy/MipsSim/PSXClock.java,v $
 	Author(s):             G. Fankhauser
 	Affiliation:           ETH Zuerich, TIK
 	Version:               $Revision: 1.2 $
 	Creation Date:         December 1999
 	Last Date of Change:   $Date: 2000/05/08 19:08:27 $      by: $Author: gfa $
	
	
	$Log: PSXClock.java,v $
	Revision 1.2  2000/05/08 19:08:27  gfa
	*** empty log message ***
	
*/

import MemoryRegion;
import ClockErrorException;

public class PSXClock extends MemoryRegion {
	
	final int CLOCKADDRSIZE = 12;
	final int COUNTER0 = 0x00;
	final int COUNTER1 = 0x04;
	final int COUNTER2 = 0x08;

 	static final int CLOCKSPEED = 1;  // if the clock were real
					    // this would be one	
	// ctrl register: sc1 sc0 rw1 rw0 m2 m1 m0 bcd
	
	byte mode = 2;
	int counter = 0;
	int counterInitValue = 0;
	byte control;
	boolean lsb = true;
	
	public PSXClock(int baseAddress) {
		from = baseAddress; 
		to = baseAddress+CLOCKADDRSIZE;
	}
	
	// read/write depends on hi/low byte settings of the control register
	byte readByte(int address) throws ClockErrorException {
	  // must be allowed for use with IDT board :-(
	  // throw new ClockErrorException();
	  return 0;
	}
	
	void writeByte(int address, byte data) throws ClockErrorException {	
		int addr = address - from;
		byte mode = (byte)(0);

		if ((addr == 0) || (addr == 0) || (addr == 0)) {
			writeCountRegister(data);
		}
		else if (addr == 0) {
			if ((data & mode) == mode) {
				control = data;
				lsb = true;
			}
			else {
			    throw new ClockErrorException("mode not supported");
			}
		}
		else {
		  throw new ClockErrorException("invalid address");
		}
	}

	void writeCountRegister(byte data) {
		if (lsb) {
			counterInitValue &= 0x0000ff00;
			counterInitValue |= data;
			lsb = false;
		}
		else {
			int d = data << 8;
			d &= 0x0000ff00;
			counterInitValue &= 0x000000ff;
			counterInitValue |= d;
			counter = counterInitValue;
		}
	}
	
	// System Clock is 33.8688 MHz, timer clock 4.2336
	// to get 100 Hz we divide by 42336
	void checkInterrupt(Processor p) {
		counter -= CLOCKSPEED;
		if (counter <= 1) {
		        //System.out.println("clock hit");
			counter = counterInitValue;
			p.interrupt(0);	// post interrupt #0
		}
	}
}