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PUS Command Postprocessor

A postprocessor for handling ECSS PUS commands, according to ECSS-E-ST-70-41C.

This postprocessor will set the length and sequence count in the CCSDS primary header. If configured, it can also calculate a checksum.

Class Name

org.yamcs.pus.PusCommandPostprocessor

Configuration Options

seqCounterName (string)

Name of a shared CCSDS sequence counter. By default each link maintains its own per-APID sequence counter independently of all other links. When two or more links specify the same seqCounterName they share a single per-APID counter, so the target receives a continuous sequence across those links.

If not specified, the counter is local to this link.

errorDetection (map)

If specified, a checksum is appended at the end of each command. Detailed below.

timeEncoding (map)

Configures how the release time is encoded in the generated TC[11,4] command (see the pus11 option below). Sub-keys: implicitPfield (boolean, default true), pfield (integer) and pfieldCont (integer, default -1). If not specified, an implicit CUC P-field of 0x2e is used.

tcoService (string)

Name of a TCO service. When set, the release time written in the TC[11,4] command is the on-board time obtained from that service instead of the raw UTC value.

pus11Crc (boolean)

If true (the default) the generated TC[11,4] command carries a trailing CRC.

pus11Apid (integer)

APID to use for the generated TC[11,4] command. If -1 (the default) the APID of the wrapped command is reused.

pus11 (map)

Enables the PUS 11 time-based scheduling support. Detailed below.

embeddedTcCrc (boolean)

If true, a checksum (computed with the errorDetection algorithm) is appended to each TC packet embedded into a command, see Embedded TC packets below. Default: true if errorDetection is configured, false otherwise. Setting it to true without errorDetection is a configuration error.

PUS 11 time-based scheduling

A command issued with the pus11ScheduleAt command option (a timestamp) is not sent as-is; instead it is embedded into a TC[11,4] insert activities into the time-based schedule request that releases it on board at the requested time.

The pus11 map configures the optional sub-schedule and scheduling group identifiers that are written into that request. Each sub-section is independent: when it is present the corresponding field is written into the TC[11,4] command and the matching command option is registered so operators can override the value per command; when it is absent neither the field nor the option exist.

subScheduleId (map)

bytes (integer, 1..8, default 1): width of the sub-schedule id field. default (integer, default 0): value used when the pus11SubScheduleId command option is not set.

groupId (map)

bytes (integer, 1..8, default 1): width of the scheduling group id field. default (integer, default 0): value used when the pus11GroupId command option is not set.

sourceId (integer)

Source id written in the secondary header of the generated TC[11,4] command. Default 0.

Example:

commandPostprocessorClassName: org.yamcs.pus.PusCommandPostprocessor
commandPostprocessorArgs:
    errorDetection:
        type: CRC-16-CCIIT
    pus11:
        subScheduleId: { bytes: 1, default: 1 }
        groupId: { bytes: 1, default: 1 }

Embedded TC packets

Some commands carry complete TC packets as arguments, for example a manually built TC[11,4] insert activities into the time-based schedule or TC[22,4], where each activity is a TC packet. To have these packets processed like top-level commands, annotate the binary argument type with the Yamcs:EmbeddedTc ancillary data:

<BinaryArgumentType name="EmbeddedTcType">
    <AncillaryDataSet>
        <AncillaryData name="Yamcs:EmbeddedTc"/>
    </AncillaryDataSet>
    <BinaryDataEncoding>
        <SizeInBits><FixedValue>-1</FixedValue></SizeInBits>
    </BinaryDataEncoding>
</BinaryArgumentType>

The postprocessor finds the annotated values using the argument locations recorded when the command is encoded. The type can be used for a top-level argument but also as member of an aggregate inside an array, such as a list of activities. For each embedded packet, in the order in which they appear in the command, the postprocessor:

  • fills in the CCSDS packet length;

  • fills in the CCSDS sequence count, using the counter of the embedded packet's APID. The value is published in the command history as ccsds-seqcount:<argument path>, for example ccsds-seqcount:activities[1].tc;

  • if embeddedTcCrc is set, appends the checksum. The command grows by 2 bytes per embedded packet; the entries following an embedded packet are shifted accordingly.

The embedded packets can thus be entered with zero sequence count and length, and without checksum. The outer command gets its length, sequence count and checksum afterwards, as usual.

The SCOS-2000 MIB loader (yamcs-scos2k) annotates the command parameters with (PTC, PFC) = (12, 1) this way.

Limitations:

  • the embedded packet has to be byte aligned.

  • when the checksum is appended, the binary encoding must allow the size to change: either a size of -1 (all the bytes of the value) or a leading size tag (which is updated). With a fixed size or a dynamic size (given by another argument) the command fails.

  • entries located at an absolute position (referenceLocation="containerStart") after an embedded packet are not shifted.

Error Detection sub-configuration

type (string)

Required. Can take one of the values:

  • 16-SUM: calculates a 16 bits checksum over the entire packet which has to contain an even number of bytes. This checksum is used in Columbus/ISS data.

  • CRC-16-CCIIT: standard CRC algorithm used in PUS and also in CCSDS standards for frame encoding.

  • ISO-16: specified in PUS as alternative to CRC-16-CCIIT.

  • NONE: no error detection will be used, this is the default if the errorDetection map is not present.

initialValue (integer)

Used when the type is CRC-16-CCIIT to specify the initial value used for the algorithm. Default: 0xFFFF.

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