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.. _library_ccsds_packetization:

ccsds_packetization

The ccsds_packetization library provides the inverse service-layer helpers to the existing ccsds_packet_services library.

This first implementation slice covers:

  • fitting packet streams into TM and AOS packet-service regions
  • preserving partially emitted packet bytes across frame boundaries
  • tracking queued packets per frame type, spacecraft identifier, and virtual channel identifier
  • generating idle packets deliberately when there is remaining frame capacity
  • reporting explicit packetization events for buffered fragments and generated idle packets

Representation

Packetizer state is represented using the compound term:

::

packetizer_state(Channels)

Where Channels is a list of terms of the form:

::

packetizer_channel(FrameType, SpacecraftId, VirtualChannelId, PendingBytes, QueuedPackets)

Where:

  • FrameType is either tm or aos
  • SpacecraftId is the keyed spacecraft identifier
  • VirtualChannelId is the keyed virtual channel identifier
  • PendingBytes is a list of packet bytes already started in an earlier frame but not yet fully emitted
  • QueuedPackets is a list of complete ccsds_packet(...) terms waiting to be packetized for that keyed channel

    Idle packets are generated as telemetry packets using APID 2047, standalone sequence flags, the requested sequence count, a zero-filled secondary header of the requested length, and zero-filled user data.

Packetization

To get the initial packetizer state:

::

| ?- ccsds_packetization::initial_state(State).

To inspect the currently buffered pending bytes and queued packets:

::

| ?- ccsds_packetization::pending_packets(packetizer_state([packetizer_channel(tm, 42, 3, [0x22,0x33], [ccsds_packet(0,0,0,1,3,7,none,[0x44])])]), PendingPackets).

To packetize packets into a TM transfer frame:

::

| ?- ccsds_packetization::packetize_tm_packets(tm_transfer_frame(0, 42, 3, 0, 16, 32, 0, 0, 0, 3, 2047, none, [0,0,0,0,0,0,0], none, none), 0, packetizer_state([]), [ccsds_packet(0, 0, 0, 0, 3, 0, none, [0x42])], UpdatedFrame, UpdatedState).

When the input TM frame already carries a fecf/1 term, packetize_tm_packets/6-7 refresh it from the updated frame bytes. Frames with none keep none.

To packetize packets into an AOS transfer frame:

::

| ?- ccsds_packetization::packetize_aos_packets(aos_transfer_frame(1, 42, 3, 16, signaling_field(0,0,0,0), none, [0,0,0,0,0,0,0,0,0], none, none), 0, packetizer_state([]), [ccsds_packet(0, 0, 0, 0, 3, 0, none, [0x42])], UpdatedFrame, UpdatedState).

When the input AOS frame already carries a fecf/1 term, packetize_aos_packets/6-7 refresh it from the updated frame bytes. Frames with none keep none.

To packetize packets across a sequence of TM transfer frames:

::

| ?- ccsds_packetization::packetize_tm_frames([Frame1, Frame2], 0, packetizer_state([]), Packets, UpdatedFrames, RemainingPackets, UpdatedState).

Events

The richer single-frame and multi-frame packetization predicates return event lists using the terms:

::

buffered_packet_fragment(FrameType, SpacecraftId, VirtualChannelId, PendingBytes) generated_idle_packet(FrameType, SpacecraftId, VirtualChannelId, Packet)

Where:

  • buffered_packet_fragment/4 reports trailing packet bytes buffered for the next frame
  • generated_idle_packet/4 reports an idle packet synthesized to consume remaining frame capacity

Idle packets

To generate a telemetry idle packet with APID 2047:

::

| ?- ccsds_packetization::generate_idle_packet(0, 7, 2, Packet).

API documentation

Open the `../../apis/library_index.html#ccsds_packetization <../../apis/library_index.html#ccsds_packetization>`__ link in a web browser.

Loading

To load all entities in this library, load the loader.lgt file:

::

| ?- logtalk_load(ccsds_packetization(loader)).

Testing

To test this library predicates, load the tester.lgt file:

::

| ?- logtalk_load(ccsds_packetization(tester)).