tuwien.auto.calimero.link.medium.PL132Ack Maven / Gradle / Ivy
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/*
Calimero 2 - A library for KNX network access
Copyright (c) 2006, 2011 B. Malinowsky
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
Linking this library statically or dynamically with other modules is
making a combined work based on this library. Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.
As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under terms
of your choice, provided that you also meet, for each linked independent
module, the terms and conditions of the license of that module. An
independent module is a module which is not derived from or based on
this library. If you modify this library, you may extend this exception
to your version of the library, but you are not obligated to do so. If
you do not wish to do so, delete this exception statement from your
version.
*/
package tuwien.auto.calimero.link.medium;
/**
* Raw acknowledgment frame on PL132 communication medium.
*
* The acknowledgment on PL132 medium is handled using the frame checksum of the
* corresponding request frame.
* A positive acknowledgment frame contains the sequence of bits received in the FCS field
* of the corresponding L-data request. A negative acknowledgment contains the bitwise
* complement of the checksum received with the L-data request.
*
* @author B. Malinowsky
*/
public class PL132Ack extends RawAckBase
{
/**
* Negative acknowledgment type, reception buffer is full.
*
*
* @see #getAckType()
*/
public static final int FULL = 0x100;
/**
* The kind of acknowledgment is unknown, because no checksum from the request frame
* is available for comparison, or the delivered checksum in the ack-frame is invalid.
*
*
* @see #getAckType()
*/
public static final int UNKNOWN_ACK = 0x200;
private final int fcs;
/**
* Creates a new PL132 acknowledgment frame out of a byte array.
*
* The acknowledgment type returned for the created frame is always
* {@link PL132Ack#UNKNOWN_ACK}, since no checksum of the corresponding request frame
* is supplied. Use {@link #getChecksum()} to determine the type of acknowledgment.
*
* @param data byte array containing the acknowledgment frame
* @param offset start offset of frame structure in data, offset >= 0
*/
public PL132Ack(final byte[] data, final int offset)
{
final int hi = data[offset] & 0xff;
fcs = hi << 8 | data[offset + 1] & 0xff;
ack = UNKNOWN_ACK;
}
/**
* Creates a new PL132 acknowledgment frame out of a byte array.
*
*
* @param data byte array containing the acknowledgment frame
* @param offset start offset of frame structure in data, offset >= 0
* @param requestChecksum checksum of the corresponding request frame
*/
public PL132Ack(final byte[] data, final int offset, final int requestChecksum)
{
final int hi = data[offset] & 0xff;
fcs = hi << 8 | data[offset + 1] & 0xff;
if (fcs == requestChecksum)
ack = ACK;
else if ((~fcs & 0xffff) == requestChecksum)
ack = FULL;
else
ack = UNKNOWN_ACK;
}
/**
* Returns the checksum contained in this acknowledgment frame.
*
*
* @return checksum as unsigned 16 bit value
*/
public final int getChecksum()
{
return fcs;
}
/* (non-Javadoc)
* @see tuwien.auto.calimero.link.medium.RawAckBase#toString()
*/
public String toString()
{
return ack == ACK ? "ACK" : ack == FULL ? "FULL" : "unknown ack";
}
}