Architecture Overview

The Core Flight System (cFS) is not a monolithic application but a flexible and modular framework built from a collection of distinct components. The main nasa/cFS repository acts as a bundle, integrating these components, which are included as Git submodules.

This modular design is a key architectural principle, allowing missions to select and customize the components they need.

Core Framework Components

These three submodules form the essential core of the cFS framework.

  • cfe (core Flight Executive): This is the heart of cFS. It provides the foundational services required for a flight software system, including:

    • Software Bus (SB) for message-based communication.
    • Executive Services (ES) for application and task management.
    • Event Services (EVS) for logging and event messaging.
    • Table Services (TBL) for managing onboard tables.
    • Time Services (TIME) for timekeeping.
    • File Services (FS) for file system access.

  • osal (Operating System Abstraction Layer): This component provides a consistent API for operating system services like tasks, mutexes, queues, and file systems. By writing applications against the OSAL API instead of a specific OS (like Linux or RTEMS), cFS applications become highly portable across different target platforms.

  • psp (Platform Support Package): This package contains the hardware- and OS-specific implementations required to port cFS to a new target. It handles the low-level details of the board support package (BSP), such as hardware initialization, interrupt handling, and timer configuration.

Lab Applications

This cFS bundle includes a set of "lab" applications that serve as examples and provide basic functionality to make the system executable out-of-the-box.

  • apps/ci_lab: Command Ingest Lab application, responsible for receiving commands from the ground system and publishing them to the Software Bus.
  • apps/to_lab: Telemetry Output Lab application, which subscribes to telemetry messages on the Software Bus and sends them to the ground system.
  • apps/sch_lab: Scheduler Lab application, a simple scheduler that sends periodic "wakeup" messages to other applications, enabling them to run at predefined intervals.
  • apps/sample_app: A template or example application demonstrating the basic structure of a cFS app.

Libraries

Shared libraries can be used by multiple applications.

  • libs/sample_lib: An example of a shared library within the cFS build system.

Tools

The ecosystem includes several host-side tools to support development and operations.

  • tools/cFS-GroundSystem: A Python-based ground system for sending commands to and receiving telemetry from a running cFS instance.
  • tools/elf2cfetbl: A tool to convert ELF file data into a cFS-compatible table file format.
  • tools/tblCRCTool: A utility for calculating CRCs for cFS table files.