Design and realization of experiments for an embedded Linux Laboratory class

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Design and realization of experiments for an
embedded Linux Laboratory class

• Ciaran mc Girl
• 4th Electronic and Computer
• Engineering
• Project Presentation
• April 2008

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Topics

• Brief Project Overview
• Real Time Systems
• RTAI
• Experiments Documented
• Problems Encountered
• Future development
• Questions

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Brief Project Overview

• -Set up a working set of real-time laboratory
• exercises, together with proper documentation,
• a supporting software infrastructure and some
• Guidelines for laboratory supervisors.
• -Experiments vary from running a single task
• program to a task with a variable period.

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Real-time Systems

• A real time system is where its application is
  considered to be mission critical, with a set
  deadline in which to be completed, if the
  application misses its deadline then its said
  to have failed
• Hard Real-time Systems
• Soft Real-time Systems

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RTAI Real Time Application Interface

• RTAI is not a real time operating system but
• instead takes priority over Linux at low level
  and in doing so leaves Linux as a low priority
  task so it cannot interrupt the RTAI.

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RTAI - How It works

• Consists basically of an interrupt dispatcher,
• mainly traps the peripherals interrupts and if
• necessary re-routes them to Linux using the
• concept of HAL (Hardware Abstraction Layer)

kernel
kernel
RTAI
Hardware
Hardware
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RTAI Installation

• Download a new kernel and the RTAI
• Patching this kernel with the RTAI
• Compile and install the kernel
• Documented for student installation

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Experiments Documented

• Single Periodic Task
• Periodic scheduling of two tasks
• Variable Period Task

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Single Periodic Task

• Single Task using a set period
• Toggles the PC speaker, emits a tone using Pulse
  width modulation

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Single Periodic Task Contd.

• Laboratory Session Developed
• Initialise a task
• Name a task
• Remove a module

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Periodic Scheduling of Two Tasks

• Two tasks that run at two different periods
• One task toggles the PC speaker every 100ms like
  the first experiment with the addition of having
  to decrement a variable before each toggle.
• The other task runs every second and increments
  the variable used by the first task.
• This increases the time between toggles and
  causes the tone to lower.

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Periodic Scheduling of Two Tasks Contd.

• Laboratory Session Developed
• Working with the original experiment, develop
  another task to increase the delay between the
  toggles (using a shared variable)

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Variable period Task

• Uses One-Shot mode
• Task runs until completion
• A delay is incremented and decremented and so the
  tone from the PC speaker is increased and
  decreased repeatedly.

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Variable period Task contd.

• Laboratory session developed
• Introduce the students to one shot mode and how
  the task operates.
• The students must then incorporate the delay for
  the task to sleep.

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RTAI-Lab

• XRTAILAB - GUI Included with the installation of
  RTAI
• Scilab (open source MATLAB Equivalent) with a
  Scicos extension.
• Then RTAI-Lib extension is added to Scicos
• Various other Installations including Mesa

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RTAI-Lab contd.

• Sine Wave example

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Problems Encountered

• 64 bit Architecture
• AMD Processor
• Ubuntu Distribution of Linux
• Mesa library problems

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Future Development

• More Documented Experiments
• Remove any teething problems with current
  documented ones.
• The RTAI-Lab could be used to help students with
  the understanding of real-time programming with
  the visual aid of the blocks in the system.

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Questions?