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Add SDD for ComCcsds subtopology (#4128)
* Create SDD for ComCcsds subtopology * Update Svc/Subtopologies/ComCcsds/docs/sdd.md Co-authored-by: Thomas Boyer-Chammard <[email protected]> * Update Svc/Subtopologies/ComCcsds/docs/sdd.md Co-authored-by: Thomas Boyer-Chammard <[email protected]> * Update Svc/Subtopologies/ComCcsds/docs/sdd.md Co-authored-by: Thomas Boyer-Chammard <[email protected]> * Revise CCSDS subtopology entries and limitations Updated descriptions for CCSDS subtopologies and clarified limitations. --------- Co-authored-by: Thomas Boyer-Chammard <[email protected]>
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‎Svc/Subtopologies/ComCcsds/docs/sdd.md‎

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# ComCcsds (CCSDS Framing) Subtopology — Software Design Document (SDD)
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The **ComCcsds subtopologies** implement F´’s **CCSDS** communications stack for framing/deframing on the flight side. There are **two variants** in the same module:
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1. 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
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2. A variant that **expects an external implementation of [`Svc.ComInterface`](https://fprime.jpl.nasa.gov/latest/docs/reference/communication-adapter-interface/)** provided by the deployment.
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Both variants provide the standard **router + ComQueue + CCSDS framers/deframers** path and are tuned through **ComCcsdsConfig** instance properties.
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> [!IMPORTANT]
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> `ComCcsds` provides framing/deframing for CCSDS SpacePackets inside TM/TC data transfer frames.
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---
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## 1. Requirements
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| ID | Description | Validation |
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| ---------------- | -------------------------------------------------------------------------------------------------------------- | ---------- |
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| SVC-COMCCSDS-001 | Provide a **CCSDS framer** to convert COM buffers into CCSDS frames for downlink. | Inspection |
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| SVC-COMCCSDS-002 | Provide a **CCSDS deframing path** to parse incoming CCSDS frames into COM buffers for uplink. | Inspection |
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| SVC-COMCCSDS-003 | Provide an F´ **router** to route deframed packets (e.g., commands/files) into the flight software. | Inspection |
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| SVC-COMCCSDS-004 | Provide a **subtopology variant that supplies `Svc::ComStub`** designed to connect to a ByteStream driver. | Inspection |
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| SVC-COMCCSDS-005 | Provide a **subtopology variant that expects an external `Svc::ComInterface`** supplied by the deployment. | Inspection |
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| SVC-COMCCSDS-006 | Support **configurable instance properties** (IDs, queue sizes, stack sizes, priorities) via `ComCcsdsConfig`. | Inspection |
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---
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## 2. Design & Core Functions
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### 2.1 Instance Summary
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| Instance name | Type (Svc/Drv) | Kind | Purpose (core function) |
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| --------------------- | ------------------------------- | ------- | ----------------------------------------------------------------------------------------------- |
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| `fprimeRouter` | `Svc.FprimeRouter` | Passive | Routes deframed packets (e.g., commands/files) into the flight software. |
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| `comQueue` | `Svc.ComQueue` | Active | Queues categorized COM data for framing (telemetry, events, file, etc.); exposes `run`. |
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| `spacePacketFramer` | `Svc.Ccsds.SpacePacketFramer` | Passive | Builds **CCSDS Space Packets** from COM buffers (downlink step 1). |
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| `framer` | `Svc.Ccsds.TmFramer` | Passive | Builds **CCSDS TM Transfer Frames** from space packets and sends to the link (downlink step 2). |
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| `spacePacketDeframer` | `Svc.Ccsds.SpacePacketDeframer` | Passive | Deframes F Prime data from **CCSDS Space Packets** (uplink step 2). |
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| `tcDeframer` | `Svc.Ccsds.tcFramer` | Passive | Deframes **CCSDS Space Packets** from **CCSDS TM Transfer Frames** (uplink step 1). |
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| `frameAccumulator` | `Svc.FrameAccumulator` | Passive | Collects bytes from the link and emits complete frames/packets for deframing (uplink path). |
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| `comStub` | `Svc.ComStub` | Passive | (Variant A only) Implementation of `Svc.ComInterface`, adapting a `Drv::ByteStreamDriverModel`. |
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> **Two variants:**
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> **A. “With ComStub”:** Subtopology **includes** `Svc::ComStub` and exposes **ByteStream** ports to your driver.
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> **B. “With External ComInterface”:** Subtopology **does not include** `Svc::ComStub`; you **provide** one in the deployment.
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### 2.2 Required Inputs for Operation
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* **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.
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* **Transport Endpoint:**
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* **Variant A:** Wire **ByteStream send/recv** between your **`Drv::ByteStreamDriverModel`** and the subtopology’s **`ComStub`**.
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* **Variant B:** Provide your own **`Svc::ComInterface`** and wire it to the **CCSDS framer/deframer ports** in the subtopology.
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* **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`**.
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### 2.3 Limitations
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These subtopologies focus on the **CCSDS framing and deframing setup** and does not provide wider CDH.
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---
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## 3. Usage
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Below are **two usage patterns**, one for each variant. Replace identifiers/ports with the **exact names in `ComCcsds.fpp`**.
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### 3.1 Variant A — ComCcsds **with** `Svc::ComStub` (expects a ByteStream driver)
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```fpp
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topology Flight {
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import ComCcsds.Subtopology
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instance comDriver: <ByteStreamDriverInterface>
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# (A1) Schedule ComQueue telemetry downlink (optional)
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connections RateGroups {
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rg.RateGroupMemberOut[0] -> ComCcsds.comQueue.run
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}
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# (A2) Wire ByteStream driver <-> ComStub supplied by the subtopology
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connections Link {
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comDriver.$recv -> ComCcsds.comStub.drvReceiveIn
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ComCcsds.comStub.drvReceiveReturnOut -> comDriver.recvReturnIn
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ComCcsds.comStub.drvSendOut -> comDriver.$send
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comDriver.ready -> ComCcsds.comStub.drvConnected
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}
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}
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```
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> [!TIP]
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> `ComCcsds.commsBufferManager` can be reused if the `ByteStreamDriver` requires buffer management.
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### 3.2 Variant B — ComCcsds **without** `Svc::ComStub`
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```fpp
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topology Flight {
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import ComCcsds.FramingSubtopology
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# (B1) Provide your own ComInterface
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instance radio: <YourComInterface>
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# (B2) Schedule ComQueue
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connections RateGroups {
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rg.RateGroupMemberOut[0] -> ComCcsds.comQueue.run
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}
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# (B3) Wire your ComInterface between the driver and the ComCcsds framer/deframer
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connections Link {
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# Downlink: TM framer -> your ComInterface
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ComCcsds.framer.dataOut -> radio.dataIn
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radio.dataReturnOut -> ComCcsds.framer.dataReturnIn
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radio.comStatusOut -> ComCcsds.framer.comStatusIn
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# Uplink: your ComInterface -> frame accumulator
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radio.dataOut -> ComCcsds.frameAccumulator.dataIn
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ComCcsds.frameAccumulator.dataReturnOut -> radio.dataReturnIn
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}
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}
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```
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---
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## 4. Configuration
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> Configure **only the instance properties** owned by the ComCcsds subtopologies. All knobs live under:
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> `Svc/Subtopologies/ComCcsds/ComCcsdsConfig/ComCcsdsConfig.fpp`
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### 4.1 Component properties (`ComCcsdsConfig.fpp`)
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* **Base ID** — Base identifier for the subtopologies; instance IDs are offset from this base.
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* **Queue sizes** — Depths for **`ComQueue`** and any other active/queued elements defined by the subtopology.
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* **Stack sizes** — Task stack allocations for active components (if any beyond `ComQueue`).
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* **Priorities** — RTOS priorities for active/queued components as applicable.
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### 4.2 Buffer Manager Bin Configuration
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`module BuffMgr` provides constants for the bins configured for `commsBufferManager`.
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---
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## 5. Traceability Matrix
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| Requirement ID | Satisfied by (instance/type) |
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| ---------------- | -------------------------------------------------------------------------------------- |
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| SVC-COMCCSDS-001 | `spacePacketFramer` — `Svc.Ccsds.SpacePacketFramer`, `tmFramer` — `Svc.Ccsds.TmFramer` |
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| SVC-COMCCSDS-002 | `frameAccumulator` — `Svc.FrameAccumulator` |
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| SVC-COMCCSDS-003 | `fprimeRouter` — `Svc.FprimeRouter` |
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| SVC-COMCCSDS-004 | `Subtopology` (variant including `Svc.ComStub`) |
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| SVC-COMCCSDS-005 | `FramingSubtopology` (variant expecting external `Svc.ComInterface`) |
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| SVC-COMCCSDS-006 | `ComCcsdsConfig` module |
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