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.