Xenomai brief introduction

What is Xenomai?

Xenomai is a RTOS-to-Linux Portability Framework.

It comes in two flavors.

  • As a dual-kernel / co-kernel extension for (patched) Linux.

    • Allows more stringent real-time requirements.

    • More complex installation.

  • As libraries for native Linux (including PREEMPT-RT)

    • Less predictable.

    • Can be used on standard Linux.

For what is it used?

Many areas:

  • Machine control systems, PLCs.

  • Printing machines (manroland).

  • Printers / copying machines.

  • Network switches (e.g. Ruggedcom).

  • Magnetic resonance tomographs (Siemens Healthcare).

  • OROCOS (OSS robotics framework).

  • Many robotic research projects.

  • And many others ...

Architecture

Co-kernel: Cobalt

Supplements Linux with a real-time co-kernel running side-by-side with it.

Cobalt extension built into the Linux kernel and deals with all time-critical activities (e.g. interrupts, scheduling).

The Cobalt core has higher priority than native kernel activities.

Best real-time performance, but requires kernel patch (Adeos) and compilation.

What is a co-kernel architecture

Based on Adeos: nanokernel hardware abstraction layer (HAL), or hypervisor, that operates between computer hardware and the operating system.

Single (Linux) kernel: Mercure

Uses only the native real-time capabilities of the native Linux kernel.

PREEMPT-RT enhances the real-time behavior.

  • Not mandatory.

  • Depends on app requirements with respect to latency/jitter.

All the non-POSIX RTOS APIs that Xenomai provides are emulated over the native Linux threading.

  • “Skins” are also supported

Task migration: Cobalt only

Every cobalt thread is also a Linux task.

Thread states are shared/synchronized among domains.

Only one can run at a time.

  • Migration to RT:

    • On syscall xnshadow_harden().

    • Linux task suspended; Cobalt thread resumed.

  • Migration to Linux.

    • On syscall xnshadow_relax(), or fault/trap, signal.

    • Cobalt thread suspended; Linux task resumed.

Real-Time Driver Model

Goals and principles.

  • Provide environment for co-kernel real-time drivers.

  • Service interface towards applications and other drivers.

  • Low-level primitives from implementing drivers.

  • Linux for non-RT purposes: setup / shutdown, resource discovery and claiming, etc.

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