Rationale

Rationale behind Lodestar.

The greatest driver behind this project is the lack of a fast and accessible library for applying control theoretic concepts on real-life (embedded) systems. While platforms such as ROS1 are popular in robotics, people working with applications that require real-time viable code and thread safety are often compelled to write their own solutions, with propiertary implementations being the norm, and a single unified solution is left to be desired.

With this in mind, I set out to develop a unified and approachable control library, with the explicit intention to make it as real-time viable as possible while maintaining code transparency and providing a flexible API2.

For more information, please check out our paper on arXiv entitled “Lodestar: An Integrated Embedded Real-Time Control Engine”.

Core Principles

Lodestar is built on the following core principles:

  1. Firm real-time first:
    • Memory demands should be known at compile-time, minimum/no dynamic memory allocation/paging.
    • Dynamically and statically allocated objects should share a common API.
    • Exceptions should be thrown with care; status-based fallbacks are preferred.
    • Processes should be timed, with fallback mechanisms and deadline violation reporting.
  2. Wide platform support:
    • Maintain minimum demands should be imposed on compiled libraries, preferring header-only libraries instead.
    • Use only ISO/ANSI C++11 features.
    • Make full use of POSIX3 RT (real-time) mechanisms (pthreads, sigactions, etc.).
  3. Flexible interfacing and extension:
    • Extendible, documented, and transparent core API.
    • Inproc and outproc non-blocking communication framework.
    • Thread-safe data types, with object-bound mutexes.

Levels of Real-time

The following is a common classification of levels of real-time:

  1. Soft real-time: Delayed process completion may degrade a system’s quality of service, but is tolerable.
  2. Firm real-time: Delayed process completion may degrade a system’s quality of service, but is tolerable if infrequent.
  3. Hard real-time: Delayed process completion results in system failure.

At least for the initial stages, Lodestar will try to get to the level where one could reliably call it a firm real-time framework. With sufficient testing and profiling in a hardware emulator, it is possible to extend a firm real-time system to a hard real-time system, but it could be the case that additional safety features and fallbacks are expected. This is, for now, beyond the scope of the library.

  1. ROS: Robot Operating System. ↩︎

  2. API: Application Programming Interface. ↩︎

  3. POSIX: Portable Operating System Interface, a family of standards described in IEEE 1003 and ISO/IEC 9945. ↩︎

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