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Packet Types

Regular Packets​

Most packets defined in COSMOS are "regular packets". These are standard command and telemetry packets that flow through interfaces. Regular telemetry packets are identified at the interface level and then the identified raw packets flow through Redis streams for additional processing like decomutation and logging.

LATEST​

LATEST is a special packet name that can be used in place of an actual packet name when retrieving telemetry. It returns the most recently received value of a telemetry item across all packets that contain it. This is useful in systems where the same telemetry item appears in multiple packets, potentially at different rates.

For example, assume the target INST has two packets: PACKET1 and PACKET2. Both packets have a telemetry item called TEMP.

# Get the value of TEMP from the most recently received PACKET1
value = tlm("INST PACKET1 TEMP")
# Get the value of TEMP from the most recently received PACKET2
value = tlm("INST PACKET2 TEMP")
# Get the value of TEMP from whichever packet (PACKET1 or PACKET2) was received most recently
value = tlm("INST LATEST TEMP")

LATEST works by comparing the PACKET_TIMESECONDS timestamp of each packet containing the requested item in the Current Value Table (CVT) and selecting the one with the newest timestamp.

LATEST can be used with:

note

LATEST cannot be used with methods that operate on entire packets such as get_tlm_packet or get_tlm_buffer since those require a specific packet name. If an item only exists in a single packet, LATEST still works but is equivalent to using the packet name directly.

Subpackets​

Subpackets are marked with the keyword SUBPACKET. Subpackets exist inside of regular packets and are identified and broken out during decom processing by a SUBPACKETIZER Python/Ruby class. Subpackets are used for channelized telemetry and for multi-sampled telemetry points in a regular packet. They can also be used for any content that may or may not be present in the parent packet. Note: because subpackets exist inside of regular packets, there is no "raw" version of a subpacket ie. the raw subpacket is part of its parent regular packet.

Virtual Packets​

VIRTUAL packets are used to define structures that can be used inside of regular packets or subpackets. Virtual packets are not identified by either interfaces or subpacketizers, and generally contain no ID fields (though they can).

The STRUCTURE and APPEND_STRUCTURE keywords can be used to add the fields from a virtual packet to a regular packet or subpacket.

Packets marked VIRTUAL are also automatically marked HIDDEN and DISABLED.

Hidden Packets​

HIDDEN packets are regular packets that are intentionally hidden from packet chooser widgets and from code completion. Hidden command packets can still be sent from scripts. Hidden telemetry packet data can still be used in TlmViewer screens.

Disabled Packets​

DISABLED packets are the same as hidden, except disabled command packets also cannot be sent. The disable_cmd and enable_cmd api methods can be used to temporarily make a command disabled or enabled.

Hazardous Packets​

HAZARDOUS command packets will present the user with an "Are You Sure?" message before being sent. Using cmd_no_hazardous_check can be used to avoid this popup for automated scripts.

Hazardous commands also require additional approval if Critical Commanding is enabled in COSMOS Enterprise.

Restricted Packets​

RESTRICTED command packets require additional approval if Critical Commanding is enabled in COSMOS Enterprise.

Note that restricted packets don't cause an "Are You Sure?" dialog.