CCSDS and CSP Headers¶

Many missions prefix their telemetry and telecommands with a standard header. Two common ones are CCSDS Space Packets and the CubeSat Space Protocol (CSP); other standard and mission-specific headers exist but are not covered here. PyMDB ships ready-made helpers for CCSDS and CSP, in the yamcs.pymdb.ccsds and yamcs.pymdb.csp modules. Each helper adds the header parameters, an abstract telemetry container and an abstract command to a system, and returns handles to everything it created — so your own packets and commands can extend them.

These helpers are also worth reading as source code: they are compact, idiomatic examples of container/command inheritance, and a template for writing an equivalent helper for a mission-specific header.

CCSDS Space Packets¶

ccsds.add_ccsds_header(system) models the 6-byte primary header of CCSDS 133.0-B-1. It returns a CcsdsHeader named tuple with:

Field	Contents
`tm_container`	Abstract container `ccsds_space_packet` with the primary header
`tm_version`, `tm_type`, `tm_secondary_header`, `tm_apid`	`ParameterMember` references into the header, ready for use in conditions
`tc_command`	Abstract command `ccsds_space_packet` encoding the header
`tc_secondary_header`, `tc_apid`	The command’s free arguments

Telemetry packets extend tm_container and identify themselves by APID (and other fields as needed):

import yamcs.pymdb as Y
from yamcs.pymdb import ccsds

spacecraft = Y.System("Spacecraft")
header = ccsds.add_ccsds_header(spacecraft)

eps_hk = Y.Container(
    system=spacecraft,
    name="eps_hk",
    base=header.tm_container,
    condition=Y.eq(header.tm_apid, 101),
    entries=[
        # payload fields, positioned after the primary header
    ],
)

Commands extend tc_command, typically through an intermediate abstract command that pins the APID once and adds a mission-specific field such as a command ID:

command_id = Y.IntegerArgument(name="command_id", signed=False,
                               encoding=Y.uint16_t)

project_command = Y.Command(
    system=spacecraft,
    name="MyProjectPacket",
    abstract=True,
    base=header.tc_command,
    assignments={
        header.tc_secondary_header.name: "NotPresent",
        header.tc_apid.name: 101,
    },
    arguments=[command_id],
)

reboot = Y.Command(
    system=spacecraft,
    name="Reboot",
    base=project_command,
    assignments={command_id.name: 1},
)

In the generated command, the sequence count and packet length fields are zeroed fixed-value entries: Yamcs fills them in during link post-processing.

CubeSat Space Protocol¶

csp.add_csp_header(system, ids=None, prefix="csp_") models the 32-bit CSP 1.x header, with its priority, source/destination addresses and ports, and the HMAC/XTEA/RDP/CRC flags.

ids: Optional list of (address, name) pairs, in the same format as enumeration choices (see Parameters). When given, the source and destination fields become enumerations instead of plain integers, so Yamcs displays node names.
prefix: Prefix for all generated names (default csp_), allowing several header sets in one system.

The returned CspHeader named tuple exposes the telemetry container (tm_container), the abstract command (tc_container), and each individual parameter and argument (tm_pri, tm_src, tm_dst, tm_dport, tm_sport, flag parameters, and the tc_* equivalents).

import yamcs.pymdb as Y

satellite = Y.System("MySat")
csp = Y.csp.add_csp_header(satellite, ids=[
    (1, "UHF Radio"),
    (3, "FC"),
    (4, "EPS"),
])

eps_telemetry = Y.Container(
    system=satellite,
    name="eps_telemetry",
    base=csp.tm_container,
    condition=Y.all_of(
        Y.eq(csp.tm_src, "EPS"),
        Y.eq(csp.tm_dport, 7),
    ),
)

As with CCSDS, commands derive from csp.tc_container, assigning the destination address and port per subsystem or service.

The returned handles are ordinary PyMDB objects and can be adjusted after the call — for example setting csp.tc_src.default to the ground station’s own address, or filling in choices on the address fields later, once the node list is assembled.