brokenpacketizer.java

这是无线传感器网络用的操作系统tinyos-1.1.0,未来的世界将是它呵

// $Id: BrokenPacketizer.java,v 1.7.2.2 2003/08/18 22:09:43 cssharp Exp $

/*									tab:4
 * "Copyright (c) 2000-2003 The Regents of the University  of California.  
 * All rights reserved.
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 * Permission to use, copy, modify, and distribute this software and its
 * documentation for any purpose, without fee, and without written agreement is
 * hereby granted, provided that the above copyright notice, the following
 * two paragraphs and the author appear in all copies of this software.
 * 
 * IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY FOR
 * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT
 * OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF THE UNIVERSITY OF
 * CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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 * THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
 * ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATION TO
 * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS."
 *
 * Copyright (c) 2002-2003 Intel Corporation
 * All rights reserved.
 *
 * This file is distributed under the terms in the attached INTEL-LICENSE     
 * file. If you do not find these files, copies can be found by writing to
 * Intel Research Berkeley, 2150 Shattuck Avenue, Suite 1300, Berkeley, CA, 
 * 94704.  Attention:  Intel License Inquiry.
 */
package net.tinyos.packet;

import net.tinyos.util.Crc;
import net.tinyos.message.*;
import java.io.*;

/**
 * A packet source for the old, broken mote-PC protocol. Requires a
 * ByteSource for low-level I/O
 */
public class BrokenPacketizer extends AbstractSource {
    final static int SYNC_BYTE = 0x7e;
    private int packetSize;

    ByteSource io;

    /**
     * Packetizers are built using the makeXXX methods in BuildSource
     */
    BrokenPacketizer(String name, int packetSize, ByteSource io) {
	super(name + "," + packetSize);
	this.packetSize = packetSize;
	this.io = io;
    }

    protected void openSource() throws IOException {
	io.open();
    }

    protected void closeSource() {
        io.close();
    }

    protected byte[] readSourcePacket() throws IOException {
	byte[] packet = new byte[packetSize];
	int count = 0;

	do {
	    while (count < packetSize) {
		byte b = io.readByte();

		// Rather broken form of sync
		if (count == 0 && b != SYNC_BYTE)
		    continue;
		packet[count++] = b;
	    }
	    // Drop packets where the crc field is not 1
	} while (packet[packetSize - TOSMsg.size_crc()] != 1);

	return collapsePacket(packet);
    }

    protected boolean writeSourcePacket(byte[] packet) throws IOException {
	io.writeBytes(expandPacket(packet, packetSize));
	return true;
    }

    public static byte[] collapsePacket(byte[] oldPacket) throws IOException {
	// Make a PacketSource-format byte array from the full packet
	int size = (oldPacket[lengthOffset] & 0xff) + dataOffset;
	if (size > oldPacket.length)
	    throw new IOException("TOS_Msg length is too long for packet");
	byte[] psPacket = new byte[size];
	System.arraycopy(oldPacket, 0, psPacket, 0, size);

	return psPacket;
    }

    public static byte[] expandPacket(byte[] psPacket, int packetSize) {
	// Make a full TOS_Msg from the PacketSource-format byte array
	TOSMsg tmsg = new TOSMsg(packetSize);
	tmsg.dataSet(psPacket, 0, 0, psPacket.length);
	tmsg.set_crc(Crc.calc(tmsg.dataGet(), tmsg.get_length() + dataOffset));
	return tmsg.dataGet();
    }
}