ComCcsds (CCSDS Framing) Subtopology — Software Design Document (SDD)

The ComCcsds subtopologies implement F´’s CCSDS communications stack for framing/deframing on the flight side. There are two variants in the same module:

A variant that supplies a Svc::ComStub implementation of Svc.ComInterface and expects to be wired to a Drv::ByteStreamDriverModel (TCP/UDP/UART, etc.), and
A variant that expects an external implementation of Svc.ComInterface provided by the deployment.

Both variants provide the standard router + ComQueue + CCSDS framers/deframers path and are tuned through ComCcsdsConfig instance properties.

Important

ComCcsds provides framing/deframing for CCSDS SpacePackets inside TM/TC data transfer frames.

1. Requirements

ID	Description	Validation
SVC-COMCCSDS-001	Provide a CCSDS framer to convert COM buffers into CCSDS frames for downlink.	Inspection
SVC-COMCCSDS-002	Provide a CCSDS deframing path to parse incoming CCSDS frames into COM buffers for uplink.	Inspection
SVC-COMCCSDS-003	Provide an F´ router to route deframed packets (e.g., commands/files) into the flight software.	Inspection
SVC-COMCCSDS-004	Provide a subtopology variant that supplies `Svc::ComStub` designed to connect to a ByteStream driver.	Inspection
SVC-COMCCSDS-005	Provide a subtopology variant that expects an external `Svc::ComInterface` supplied by the deployment.	Inspection
SVC-COMCCSDS-006	Support configurable instance properties (IDs, queue sizes, stack sizes, priorities) via `ComCcsdsConfig`.	Inspection

2. Design & Core Functions

2.1 Instance Summary

Instance name	Type (Svc/Drv)	Kind	Purpose (core function)
`fprimeRouter`	`Svc.FprimeRouter`	Passive	Routes deframed packets (e.g., commands/files) into the flight software.
`comQueue`	`Svc.ComQueue`	Active	Queues categorized COM data for framing (telemetry, events, file, etc.); exposes `run`.
`spacePacketFramer`	`Svc.Ccsds.SpacePacketFramer`	Passive	Builds CCSDS Space Packets from COM buffers (downlink step 1).
`framer`	`Svc.Ccsds.TmFramer`	Passive	Builds CCSDS TM Transfer Frames from space packets and sends to the link (downlink step 2).
`spacePacketDeframer`	`Svc.Ccsds.SpacePacketDeframer`	Passive	Deframes F Prime data from CCSDS Space Packets (uplink step 2).
`tcDeframer`	`Svc.Ccsds.tcFramer`	Passive	Deframes CCSDS Space Packets from CCSDS TM Transfer Frames (uplink step 1).
`frameAccumulator`	`Svc.FrameAccumulator`	Passive	Collects bytes from the link and emits complete frames/packets for deframing (uplink path).
`comStub`	`Svc.ComStub`	Passive	(Variant A only) Implementation of `Svc.ComInterface`, adapting a `Drv::ByteStreamDriverModel`.

Two variants: A. “With ComStub”: Subtopology includes Svc::ComStub and exposes ByteStream ports to your driver. B. “With External ComInterface”: Subtopology does not include Svc::ComStub; you provide one in the deployment.

2.2 Required Inputs for Operation

Rate Groups: Connect a rate group to comQueue.run. This is not required for the subtopology to function, but defines the rate at which ComQueue will send telemetry.
Transport Endpoint:
Variant A: Wire ByteStream send/recv between your Drv::ByteStreamDriverModel and the subtopology’s ComStub.
Variant B: Provide your own Svc::ComInterface and wire it to the CCSDS framer/deframer ports in the subtopology.
Flight-side hookups: Wire the router outputs (commands/files) into your CDH stack (e.g., command dispatcher, file uplink), and feed packet sources (telemetry/events/file downlink) into comQueue.

2.3 Limitations

These subtopologies focus on the CCSDS framing and deframing setup and does not provide wider CDH.

3. Usage

Below are two usage patterns, one for each variant. Replace identifiers/ports with the exact names in ComCcsds.fpp.

3.1 Variant A — ComCcsds with `Svc::ComStub` (expects a ByteStream driver)

topology Flight {
  import ComCcsds.Subtopology

instance comDriver: <ByteStreamDriverInterface>

# (A1) Schedule ComQueue telemetry downlink (optional)
  connections RateGroups {
    rg.RateGroupMemberOut[0] -> ComCcsds.comQueue.run
  }

  # (A2) Wire ByteStream driver <-> ComStub supplied by the subtopology
  connections Link {
    comDriver.$recv                        -> ComCcsds.comStub.drvReceiveIn
    ComCcsds.comStub.drvReceiveReturnOut   -> comDriver.recvReturnIn
    ComCcsds.comStub.drvSendOut            -> comDriver.$send
    comDriver.ready                        -> ComCcsds.comStub.drvConnected
  }
}

Tip

ComCcsds.commsBufferManager can be reused if the ByteStreamDriver requires buffer management.

3.2 Variant B — ComCcsds without `Svc::ComStub`

topology Flight {
  import ComCcsds.FramingSubtopology

  # (B1) Provide your own ComInterface
  instance radio: <YourComInterface>

  # (B2) Schedule ComQueue
  connections RateGroups {
    rg.RateGroupMemberOut[0] -> ComCcsds.comQueue.run
  }

  # (B3) Wire your ComInterface between the driver and the ComCcsds framer/deframer
  connections Link {
    # Downlink: TM framer -> your ComInterface
    ComCcsds.framer.dataOut         -> radio.dataIn
    radio.dataReturnOut               -> ComCcsds.framer.dataReturnIn
    radio.comStatusOut                -> ComCcsds.framer.comStatusIn

    # Uplink: your ComInterface -> frame accumulator
    radio.dataOut                     -> ComCcsds.frameAccumulator.dataIn
    ComCcsds.frameAccumulator.dataReturnOut -> radio.dataReturnIn
  }
}

4. Configuration

Configure only the instance properties owned by the ComCcsds subtopologies. All knobs live under: Svc/Subtopologies/ComCcsds/ComCcsdsConfig/ComCcsdsConfig.fpp

4.1 Component properties (`ComCcsdsConfig.fpp`)

Base ID — Base identifier for the subtopologies; instance IDs are offset from this base.
Queue sizes — Depths for ComQueue and any other active/queued elements defined by the subtopology.
Stack sizes — Task stack allocations for active components (if any beyond ComQueue).
Priorities — RTOS priorities for active/queued components as applicable.

4.2 Buffer Manager Bin Configuration

module BuffMgr provides constants for the bins configured for commsBufferManager.

5. Traceability Matrix

Requirement ID	Satisfied by (instance/type)
SVC-COMCCSDS-001	`spacePacketFramer` — `Svc.Ccsds.SpacePacketFramer`, `tmFramer` — `Svc.Ccsds.TmFramer`
SVC-COMCCSDS-002	`frameAccumulator` — `Svc.FrameAccumulator`
SVC-COMCCSDS-003	`fprimeRouter` — `Svc.FprimeRouter`
SVC-COMCCSDS-004	`Subtopology` (variant including `Svc.ComStub`)
SVC-COMCCSDS-005	`FramingSubtopology` (variant expecting external `Svc.ComInterface`)
SVC-COMCCSDS-006	`ComCcsdsConfig` module