/*
    Copyright (c) 1996-1998 Swiss Federal Institute of Technology, 
    Computer Engineering and Networks Laboratory. All rights reserved.

    Written by David Schweikert <schweikert@acm.org>. For more documentation
    please visit http://www.tik.ee.ethz.ch/~gfa.
    
    Ethernet device simulation using Ethertap device under Linux 2.1.x.
    Based on UART.java by George Fankhauser <gfa@acm.org>.

	File:                  $Source: /usr/drwho/vault/cvs/topsy/MipsSim/Ethertap.java,v $
 	Affiliation:           ETH Zuerich, TIK
 	Version:               $Revision: 1.1 $
 	Creation Date:         December 1996
 	Last Date of Change:   $Date: 2000/04/05 14:33:15 $      by: $Author: gfa $
	
	
	$Log: Ethertap.java,v $
	Revision 1.1  2000/04/05 14:33:15  gfa
	*** empty log message ***
	

*/

import java.io.*;
import java.net.*;
import java.util.*;

/* 
   I don't know how the real ethernet devices are memory mapped.
   I have tried to do it as simple as possible.
   
   - Memory layout (bytes):

         Offset  Description
   ------------  ---------------------------------
      0 (0x000)  Status
      4 (0x001)  Control
     16 (0x010)  Hardware Address (read only), 6 bytes
     32 (0x020)  Data In length (short)
     36 (0x024)  Data In  (device -> OS)
   2048 (0x800)  Data Out length (short)
   2052 (0x804)  Data Out (OS -> device)


   - Control register (8 bit):
   
   Offset (bit)  Description
   ------------  --------------------------------
        0 (LSM)  Send data  (SD)
	1        Data read  (DR)


   - Status register (8 bit):

   Offset (bit)  Description
   ------------  --------------------------------
        0 (LSM)  Received data (RD)

Send protocol: fill data, SD->1
Recv protocol: RD=1? -> read data -> DR=1
	
*/
  


public final class Ethertap extends MemoryRegion {
	final static int INTERRUPT_NR = 2;
	
	final static int ADDRSIZE = 4096; // max. frame len: 1518 bytes
	final static int STATUS_REGISTER = 0x000;
	final static int CONTROL_REGISTER = 0x004;
	final static int HW_ADDRESS = 0x010;
	final static int RX_SIZE = 0x020;
	final static int RX_DATA = 0x024;
	final static int RX_END  = 0x7FF;
	final static int TX_SIZE = 0x800;
	final static int TX_DATA = 0x804;
	final static int TX_END  = 0xFFF;
	
	final static byte SEND_MASK = 0x01; // Control register
	final static byte READ_MASK = 0x02;
	final static byte RECV_MASK = 0x01; // Status register

        InputStream  in;
	OutputStream out;

	public Ethertap(int baseAddress, int port) {
		try {
			Socket s = new Socket(InetAddress.getLocalHost(), port);
			in = s.getInputStream();
			out = s.getOutputStream();
		}
		catch (IOException e) {
			System.out.print(e.getClass().getName()+
					 " ("+e.getMessage()+")\n");
			System.out.println("Ethertap: couldn't connect to Ethertap server.");
		}		
		from = baseAddress; 
		to = baseAddress+ADDRSIZE;
		memory = new byte[ADDRSIZE];

		// Initialize HW address
		memory[HW_ADDRESS]   = 0x01;
		memory[HW_ADDRESS+1] = 0x02;
		memory[HW_ADDRESS+2] = 0x03;
		memory[HW_ADDRESS+3] = 0x04;
		memory[HW_ADDRESS+4] = 0x05;
		memory[HW_ADDRESS+5] = 0x06;
	}

	void writePacket() throws BusErrorException {
		try {
			short len = super.readShort(TX_SIZE+from);
			//System.out.println("Ethertap: sending packet (" + len + ")");
			out.write(memory,TX_DATA,len);
		}
		catch (IOException e) {
			System.out.print(e.getClass().getName()+
					 " ("+e.getMessage()+")\n");
			System.out.println("Ethertap: couldn't send to Ethertap server.");
		}
	}
	
	byte readByte(int address) throws BusErrorException {
		int offset = address-from;

		if (offset >= ADDRSIZE) throw new BusErrorException();
		
		//System.out.println("Ethertap: device memory read: " + (address-from));
		return memory[offset]; // why not 'return super.readByte(address)' ?
	}
	
	short readShort(int address) throws BusErrorException {
		if(address-from >= ADDRSIZE) throw new BusErrorException();
		//System.out.println("Ethertap: device memory read: " + (address-from));
		return super.readShort(address);
	}
	
	int readInt(int address) throws BusErrorException {
		if(address-from >= ADDRSIZE) throw new BusErrorException();
		//System.out.println("Ethertap: device memory read: " + (address-from) +
		//		   " [" + Integer.toHexString(super.readInt(address)) + "]");
		return super.readInt(address);
	}
	
	
	void writeByte(int address, byte data) throws BusErrorException {	
		if(out == null) return;
		
		int offset = address-from;
		
		if (offset != CONTROL_REGISTER && (offset < TX_SIZE || offset > TX_END))
			throw new BusErrorException();
		
		memory[offset] = data;
		
		if (offset == CONTROL_REGISTER) {
			if ((data & SEND_MASK) != 0) {
				writePacket();
				memory[offset] ^= SEND_MASK; // clear send
			} else if ((data & READ_MASK) != 0) {
				memory[STATUS_REGISTER] &= ~RECV_MASK;
				memory[offset] ^= READ_MASK; // clear read
			}
		}
	}
	
	void checkInterrupt(Processor p) throws IOException {
		if(in == null) return;
		try {
			if (in.available() > 0) {
				if ((memory[STATUS_REGISTER] & RECV_MASK) == 0) {
					int len = in.read(memory, RX_DATA, RX_END-RX_DATA);
					//System.out.println("Ethertap: Got " + len + " bytes!");
					super.writeShort(RX_SIZE+from, (short) len);
					memory[STATUS_REGISTER] |= RECV_MASK;
					p.interrupt(INTERRUPT_NR);
				} else {
					byte b[];
					b = new byte[2000];
					System.out.println("*** Ethertap: Packets overflow! Discarding packet.");
					in.read(b);
				}
			}
		}
		catch (Exception e) {
			System.out.print(e.getClass().getName()+
						" ("+e.getMessage()+")\n");
			System.out.println("Ethertap: couldn't receive from Ethertap server.");
		}
	}
}	
	
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