FileHandlingCfdp Subtopology — Software Design Document (SDD)

The FileHandlingCfdp subtopology packages CFDP-based file-transfer services and on-board file management commonly needed in F´ CCSDS deployments: CFDP file transfer (bidirectional reliable file delivery), on-board file management, and parameter management via filesystem. By providing these as a pre-wired subgraph, integration engineers avoid repetitive wiring and get a consistent, reusable baseline for CFDP operations.

1. Requirements

2. Design & Core Functions

2.1 Instance Summary

2.2 Configuration Hooks inside the Subtopology

• Uses instance properties (IDs, queue sizes, stack sizes, priorities, CPU affinities) defined in FileHandlingCfdpConfig for these static instances (see §4).
• CfdpManager configuration: The cfdpManager instance is configured with a memory allocator in the configComponents phase to allocate the internal CFDP engine.
• PrmDb configuration: The prmDb instance is configured with a parameter file name (PrmDb.dat) and reads parameters during the readParameters phase.

2.3 Required Inputs for Operation

• Rate Groups: Connect scheduler outputs to the run1Hz (1 Hz scheduling) port of cfdpManager to drive CFDP protocol timers and transaction processing.
• Communication/Framing Stack: Wire CFDP PDU ports between FileHandlingCfdp and your COM/framing subtopology (e.g., ComCcsds, FprimeRouter) to complete uplink/downlink paths for CFDP PDUs.
• Buffer Management: Connect buffer allocation/deallocation ports to downstream buffer managers (typically part of your COM subtopology).

[!WARNING] This subtopology is not configured to be secure by default. For backwards compatibility, it intentionally does not configure a load sandbox for prmDb: PRM_LOAD_FILE may load from any absolute path accessible to the process via ground command. Security-conscious deployments must call FileHandlingCfdp::prmDb.configureLoadSandbox(<directory>) from topology setup code (note: prmDb.configure(<file name>) sets the store-file name and is not a load sandbox). Additionally, CFDP file transfers via cfdpManager are not sandboxed: ground-commanded transactions may read or write any path accessible to the process.

2.4 Differences from FileHandling Subtopology

The FileHandlingCfdp subtopology replaces the traditional FileUplink and FileDownlink components with the CFDP-based CfdpManager component:

• CFDP Protocol: Uses the CCSDS File Delivery Protocol (CFDP) for reliable, autonomous file transfer with automatic retry, gap detection, and acknowledgments.
• Bidirectional Transfer: Single component handles both uplink (ground → flight) and downlink (flight → ground) file transfers.
• Class 1 & Class 2: Supports both unacknowledged (Class 1) and acknowledged (Class 2) transfer modes.

2.5 Limitations

Focused on CFDP-based file transfer and on-board file ops only. It does not provide:

• General uplink/downlink routing for non-CFDP traffic
• Framing/deframing services (must be provided by separate framing subtopology)
• Generic command and data handling services (Commands, events, telemetry, etc.)

3. Usage

3.1 Example Usage

topology Flight {
  instance FileHandlingCfdp.Subtopology

  param connections instance FileHandlingCfdp.prmDb

  # Schedule the CFDP manager at 1 Hz (required for protocol timers)
  connections RateGroups {
    rg.RateGroupMemberOut[0] -> FileHandlingCfdp.Subtopology.cfdpManager.run1Hz
  }

  # Wire CFDP PDU data flow to/from communication stack
  connections ComCcsds_FileHandlingCfdp {
    # CFDP Downlink -> ComQueue (PDU egress)
    FileHandlingCfdp.Subtopology.cfdpManager.dataOut[0] -> ComCcsds.Subtopology.bufferQueueIn[ComCcsds.Ports_ComBufferQueue.CFDP]
    ComCcsds.Subtopology.bufferReturnOut[ComCcsds.Ports_ComBufferQueue.CFDP] -> FileHandlingCfdp.Subtopology.cfdpManager.dataReturnIn[0]
    
    # FprimeRouter -> CFDP Uplink (PDU ingress)
    ComCcsds.Subtopology.cfdpUplinkOut -> FileHandlingCfdp.Subtopology.cfdpManager.dataIn[0]
    FileHandlingCfdp.Subtopology.cfdpManager.dataInReturn[0] -> ComCcsds.Subtopology.cfdpUplinkReturnIn
    
    # Buffer allocation for CFDP PDU construction
    FileHandlingCfdp.Subtopology.cfdpManager.bufferAllocate[0] -> ComCcsds.Subtopology.bufferGetIn[ComCcsds.Ports_ComBufferGet.CFDP]
    ComCcsds.Subtopology.bufferDeallocateOut[ComCcsds.Ports_ComBufferGet.CFDP] -> FileHandlingCfdp.Subtopology.cfdpManager.bufferDeallocate[0]
  }
}

3.2 CFDP Configuration

The CFDP manager is configured at runtime via parameters defined in CfdpCfg.fpp (compile-time configuration) and component parameters (runtime configuration):

Compile-time Configuration (CfdpCfg.fpp)

• Number of channels: Cfdp::NumChannels - Number of independent CFDP communication channels (default: 2)
• Number of transactions: Cfdp::NumTransactions - Maximum concurrent CFDP transactions per channel
• Maximum PDU size: Cfdp::MaxPduSize - Maximum size of a single CFDP PDU in bytes
• File path size: Cfdp::MaxFilePathSize - Maximum length of file paths

Runtime Parameters (per channel)

• Local Entity ID: Unique identifier for this CFDP entity
• ACK/NAK limits: Maximum retry attempts for acknowledged transfers
• Timers: ACK timeout and inactivity timeout durations
• Directories: Temporary, failure, and move directories for file operations
• Throttling: Maximum outgoing PDUs per cycle for bandwidth control

See the CfdpManager SDD for detailed configuration options.

4. Configuration

Configure only the instance properties for the static instances owned by the subtopology. All knobs live under: Svc/Subtopologies/FileHandlingCfdp/FileHandlingCfdpConfig/FileHandlingCfdpConfig.fpp. The generated constants header for this module (e.g., FppConstantsAc.hpp) reflects these settings.

4.1 Component properties (FileHandlingCfdpConfig.fpp)

• Base ID — Base identifier for the subtopology; component IDs are offset from this base.
• Queue sizes — Queue depths for cfdpManager, fileManager, prmDb.
• Stack sizes — Task stacks for active components.
• Priorities — RTOS priorities for the active/queued components.
• CPU affinities — Core pinning for active component tasks; defaults to TASK_DEFAULT (no pinning).

These knobs tailor runtime footprint and scheduling without modifying the subtopology wiring.

4.2 Memory Allocation

The cfdpManager component requires a memory allocator to be provided during configuration. The subtopology includes a MallocAllocator instance (Allocation::memAllocator) that is passed to cfdpManager.configure() in the configComponents phase. The allocator is used to dynamically allocate the CFDP engine structure.

5. Traceability Matrix