ccsds

The ccsds library implements predicates for parsing and generating CCSDS (Consultative Committee for Space Data Systems) Space Packets following the CCSDS 133.0-B-2 standard (Space Packet Protocol).

Reference documentation:

• https://public.ccsds.org/Pubs/133x0b2e1.pdf

• https://jastoolbox.sandia.gov/topic/communication-specification/jas-packets/ccsds-telecommand-and-telemetry-format-packet-standard/

Packet Structure

A CCSDS Space Packet consists of:

1. Primary Header (6 bytes):

   • Version Number (3 bits) - Always 000 for Space Packets

   • Packet Type (1 bit) - 0=Telemetry, 1=Telecommand

   • Secondary Header Flag (1 bit) - 0=absent, 1=present

   • Application Process ID (APID) (11 bits) - 0-2047

   • Sequence Flags (2 bits) - 00=continuation, 01=first, 10=last, 11=standalone

   • Packet Sequence Count (14 bits) - 0-16383

   • Packet Data Length (16 bits) - Number of octets in data field minus 1

2. User Data Field - Variable length payload

Representation

Packets are represented using the compound term:

ccsds_packet(Version, Type, SecHeaderFlag, APID, SeqFlags, SeqCount, SecHeader, UserData)

Where:

• Version is an integer (0-7, typically 0)

• Type is an integer (0=telemetry, 1=telecommand)

• SecHeaderFlag is an integer (0 or 1)

• APID is an integer (0-2047)

• SeqFlags is an integer (0-3)

• SeqCount is an integer (0-16383)

• SecHeader is either none or secondary_header(Bytes) where Bytes is a list of bytes

• UserData is a list of bytes

Note that the DataLength field from the wire format is not stored in the term representation as it can be computed from SecHeader and UserData. The data_length/2 accessor predicate computes and returns this value when needed.

Parsing

The parse/2 predicate accepts a source term as its first argument. The source can be file(File), stream(Stream), or bytes(Bytes). All source types return a list of packets for uniformity.

To parse packets from a list of bytes:

| ?- ccsds::parse(bytes([0x08, 0x01, 0xC0, 0x00, 0x00, 0x03, 0xDE, 0xAD, 0xBE, 0xEF]), Packets).
Packets = [ccsds_packet(0, 0, 1, 1, 3, 0, none, [222, 173, 190, 239])]
yes

To parse packets from a binary file:

| ?- ccsds::parse(file('telemetry.bin'), Packets).

To parse packets from a binary stream:

| ?- ccsds::parse(stream(Stream), Packets).

When the packets include a secondary header, the secondary header length must be known. In this case, use the ccsds(SecondaryHeaderLength) object instead of the ccsds object. For example, to parse packets with a secondary header of 6 bytes:

| ?- ccsds(6)::parse(bytes([0x08, 0x01, 0xC0, 0x00, 0x00, 0x07, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0xAA, 0xBB]), Packets).

Generating

The generate/2 predicate accepts a sink term as its first argument and a list of packet terms as the second argument. The sink can be file(File), stream(Stream), or bytes(Bytes).

To generate bytes from a list of packet terms:

| ?- ccsds::generate(bytes(Bytes), [ccsds_packet(0, 0, 1, 1, 3, 0, none, [0xDE, 0xAD, 0xBE, 0xEF])]).
Bytes = [8, 1, 192, 0, 0, 3, 222, 173, 190, 239]
yes

To write the bytes generated from a list of packet terms to a binary file:

| ?- ccsds::generate(file('output.bin'), Packets).

To write the bytes generated from a list of packet terms to a binary stream:

| ?- ccsds::generate(stream(Stream), Packets).

Accessor Predicates

The library provides convenient accessor predicates for extracting packet fields:

| ?- ccsds::apid(Packet, APID).

% Returns telemetry or telecommand
| ?- ccsds::type(Packet, Type).

% Returns continuation, first, last, or standalone
| ?- ccsds::sequence_flags(Packet, Flags).

% Returns the secondary header as a list of bytes or none
| ?- ccsds::secondary_header(Packet, SecHeader).

% Returns the secondary header time as a cuc_time(Coarse, Fine) term or fails if no time is available
| ?- ccsds::secondary_header_time(Packet, Time).

| ?- ccsds::user_data(Packet, Data).

% Returns the packet data length (computed from secondary header and user data)
| ?- ccsds::data_length(Packet, Length).

Types and arbitrary generators

The library includes a ccsds_types category that provides ccsds_packet and ccsds_packet(SecondaryHeaderLength) types and arbitrary generators for CCSDS packets. For example:

| ?- type::check(ccsds_packet, Bytes).

| ?- type::arbitrary(ccsds_packet(42), Bytes).

It also provides a ccsds_packets(N) and ccsds_packets(SecondaryHeaderLength, N) types for generating a list with N packets. For example:

| ?- type::arbitrary(ccsds_packets(10), Bytes).

| ?- type::check(ccsds_packets(42, 10), Bytes).

For a term representation of a packet, use the ccsds_packet_term and ccsds_packet_term(SecondaryHeaderLength) types and arbitrary generators. For example:

| ?- type::check(ccsds_packet_term, Packet).

| ?- type::arbitrary(ccsds_packet_term(42), Packet).

API documentation

Open the ../../apis/library_index.html#ccsds link in a web browser.

Loading

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

| ?- logtalk_load(ccsds(loader)).

Testing

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

| ?- logtalk_load(ccsds(tester)).

To test the performance of the library parsing predicates, load the tester_performance.lgt file:

| ?- logtalk_load(ccsds(tester_performance)).