Package org.yamcs.tctm

Class IssPacketPreprocessor

java.lang.Object

org.yamcs.tctm.AbstractPacketPreprocessor

org.yamcs.tctm.CcsdsPacketPreprocessor

org.yamcs.tctm.IssPacketPreprocessor

All Implemented Interfaces:

PacketPreprocessor

public class IssPacketPreprocessor
extends CcsdsPacketPreprocessor

This implements CCSDS packets as used in ISS (International Space Station).
Primary header (specified by CCSDS 133.0-B-1):

• packet version number (3 bits)
• packet type (1 bit)
• secondary header flag (1 bit)
• application process ID (11 bits)
• sequence flags (2 bits)
• packet sequence count (14 bits)

Secondary header (specific to ISS):

• coarse time (32 bits)
• fine time (8 bits)
• time id(2 bits)
• checksum indicator (1 bit)
• spare (1 bit)
• packet type (4 bits)
• packet ID(32 bits)

If the checksum indicator is 1, the packet is terminated by a two bytes checksum.
This class is effectively making use of the following fields (all the other ones are ignored):

• application process ID(APID) and packet sequence count: used to detect the discontinuity in packets as well as to form the unique key (used to not store duplicates)
• coarse time and fine time: used to derive the timestamp of the packet
• checksum indicator: used to know to compute and verify or not the checksum

The checksum used can be one of

• 16-SUM (default): running sum on each two bytes - the packet has to contain an even number of bytes
• CRC-16-CCIIT: CRC with the generator polynomial x^16 + x^12 + x^5 + 1

Nested Class Summary

Nested classes/interfaces inherited from class org.yamcs.tctm.AbstractPacketPreprocessor

AbstractPacketPreprocessor.TimeDecoderType, AbstractPacketPreprocessor.TimeEpochs

Field Summary

Fields inherited from class org.yamcs.tctm.AbstractPacketPreprocessor

byteOrder, checkForSequenceDiscontinuity, CONFIG_KEY_BYTE_ORDER, CONFIG_KEY_CHECK_SEQUENCE, CONFIG_KEY_ERROR_DETECTION, CONFIG_KEY_TCO_SERVICE, CONFIG_KEY_TIME_ENCODING, customEpoch, customEpochIncludeLeapSecond, errorDetectionCalculator, ETYPE_CORRUPTED_PACKET, eventProducer, log, tcoService, timeDecoder, timeEpoch, timeService, useLocalGenerationTime

Constructor Summary

Constructors

Constructor	Description
IssPacketPreprocessor(String yamcsInstance)
IssPacketPreprocessor(String yamcsInstance, YConfiguration config)

Method Summary

Modifier and Type	Method	Description
TmPacket	process(TmPacket tmPacket)	Processes the packet and returns it.

Methods inherited from class org.yamcs.tctm.CcsdsPacketPreprocessor

checkSequence

Methods inherited from class org.yamcs.tctm.AbstractPacketPreprocessor

checkForSequenceDiscontinuity, checkForSequenceDiscontinuity, getByteOrder, getDefaultDecoderType, getErrorDetectionWordCalculator, setRealtimePacketTime, shiftFromEpoch, verifyCrc

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface org.yamcs.tctm.PacketPreprocessor

process

Constructor Details

IssPacketPreprocessor

public IssPacketPreprocessor(String yamcsInstance)

IssPacketPreprocessor

public IssPacketPreprocessor(String yamcsInstance,
 YConfiguration config)

Method Details

process

public TmPacket process(TmPacket tmPacket)

Description copied from interface: PacketPreprocessor

Processes the packet and returns it.

What this function does is project depended. However, we expect that the generation time and sequence count are filled in.

Can return null if the packet is to be ignored.

Parameters:

tmPacket - - the packet that has to be processed

Returns:

the processed packet