A Platform for Digital Real-Time Control.
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Xenomai Lab

A Platform for Digital Real-Time Control.

This is an early alpha release.


Users wanting to bypass the rather complicated Xenomai installation process may want to try out the VirtualBox VM (1.5GB) instead. See guide here.


Xenomai Lab needs Xenomai installed on the target system. Xenomai and 2.5.6 are known to be supported. To install Xenomai please refer to the how-to-page or to the official Xenomai wiki page.

In addition to this, Xenomai Lab needs non-root real-time access. Instructions for this are available here, but an abridged tutorial for Ubuntu or other Debian based systems is available in the Appendix section.


$ sudo apt-get install build-essential libqt4-dev libboost-graph-dev

Compile Xenomai Lab:

$ qmake

$ make


$ sudo make install


$ sudo make uninstall

Working with Blocks

Create a new block

Xenomai Lab comes bundled with several useful blocks, but adding new ones is easy. All blocks are stored in ~/.xenomailab/blocks. To add a new one, simply run the newblock.sh script in that folder.

Here's an example

$ cd ~/.xenomailab/blocks/
$ ./newblock.sh example_block

If you start Xenomai Lab, you'll see your new block listed on the left-hand side under "Real-Time".

If your block is not supposed to run in real-time, you can change it in the blocks.conf text-file in the blocks directory.

$ gedit ~/.xenomailab/blocks/blocks.conf

There, you can see your block listed.


Add some block settings

One of the most powerfull features of Xenomai Lab's blocks is the ability to change some operational settings in runtime. The procedure to edit or add new settings to your own block is not complex per say, but it is somewhat extensive.

There are four types of settings:

  • Strings (char[])
  • Integer (int)
  • Doubles (double)
  • Matrices (Matrix)

A block setting lives in 4 distinct places inside the block folder.

Lets illustrate these four places using our example_block from the previous section.


The .conf carries the default value of all settings. When you drag a new block to the canvas in Xenomai Lab, its settings will be initialized with the values specified in this file. Here's an example .conf exemplifying the four type of settings

aMatrix=[1 0; 0 1]


Notice that these variables must be a single word, with no spaces.


This file contains both the declaration of the struct which holds the settings, and the declaration of the gs variable used to access these settings from your code.

struct global_settings{
    char aString[40];
    int anInt;
    double aDouble;
    Matrix aMatrix;

    int task_prio;//Real time task priority (0-99, higher is greater)
extern struct global_settings* gs;

Accessing these variables is as straightforward as it seems. To print the aString variable, the code would be



This file contains some unavoidable boilerplate code. Functions load_gs and unload_gs load and store the settings from the .conf, respectively. In effect, these are the functions that map the text written in the .conf with the variables declared in the struct. The variable name in the .conf does not need to be the same as the variable name in the struct, but it is a good practice to use the same name.

Continuing our example

void load_gs(void){

void unload_gs(void){
    store_string("Operation", "aString", gs->aString);
    store_int("Operation", "anInt", gs->anInt);
    store_double("Operation", "aDouble", gs->aDouble);



Finally, we need a GUI to edit them. The setSettings member of the MainWindow class contains all the different settings.

The only detail that may not work as expected is the string. A string setting is presented in the GUI as a combo box, not as a text entry. You don't write a string with the keyboard, you select it from a list.

The signal_generator block uses this setting to allow a user to choose between different types of waves. A block that outputs to a serial port might use a string to allow the user to choose between /dev/ttyUSB0 or /dev/ttyUSB1.

Continuing with our example

void MainWindow::setSettings()
    newComboBox("aString:",QStringList("Str1") << "Str2" << "Str3",gs->aString);

Using libraries

Using a library involves creating two files and editing a makefile. If the block you're programming is very simple, then using a library is overkill. As a general rule of thumb though, decoupling the block code from its functionality is considered a good practice because

  • If the block API changes, your interface may need to change, but your functionality code remains unaltered.
  • The block code follows a strict standard and messing with it can generate unexpected bugs. Decoupling assures that the block is almost always innocent and bugs can be localized to your own library.
  • A group of blocks can and sometimes should use the same library. This avoids duplication of common code and centralization can greatly increase legibility in some cases, e.g. hardware I/O blocks, control alghorithms,etc.

Here's an example. If you intend to program a block that adds a DC offset to incoming signals, creating a library is overkill. If you intend to program high-pass, low-pass and band-pass block filters, then you should create a library with 3 functions and have each individual block call one of them.

To make your custom block use a .h/.c couple is a matter of altering its makefile. The recommended way is to leave your .h/.c library in ~/.xenomailab/include and add it to the DEP variable in the Makefile.

Using the example_block introduced in the last section, we should edit ~/.xenomailab/blocks/example\_block/Makefile to use an example_library

DEP=template.c template_settings.c $(INCLUDE)rt_block_io.c $(INCLUDE)settings.c $(INCLUDE)strmap.c $(INCLUDE)mtrx.c $(INCLUDE)example_library.c

Using the Oscilloscope

As of yet, the oscilloscope is not deployment ready. However, due to its usefullness I have packaged it in data/oscilloscope.tar.gz.

Installing the oscilloscope is a two-step process.

Install Qwt

The Oscilloscope requires Qwt 6.0 or greater installed on the system.

To install Qwt, download it from the official site and extract the tarball to a folder. In that folder, run

$ qmake
$ make
$ sudo make install

Afterwards, add the library to ldconfig. To do this, find out Qwt's installation path

cd /usr/local/qwt*/lib/

This returns something like /usr/local/qwt-6.0.1/lib. Add this string to

sudo vim /etc/ld.so.conf.d/qwt.conf

Afterwards, call ldconfig to refresh all available libraries

sudo ldconfig

To confirm this worked

ldconfig -p | grep qwt

Which should return something akin to

libqwtmathml.so.6 (libc6) => /usr/local/qwt-6.0.1/lib/libqwtmathml.so.6
libqwtmathml.so (libc6) => /usr/local/qwt-6.0.1/lib/libqwtmathml.so
libqwt.so.6 (libc6) => /usr/local/qwt-6.0.1/lib/libqwt.so.6
libqwt.so (libc6) => /usr/local/qwt-6.0.1/lib/libqwt.so

Install the block

Extract data/oscilloscope.tar.gz to ~/.xenomailab/blocks/ and add the oscilloscope to the non real-time list of blocks

sudo gedit ~/.xenomailab/blocks.conf

So that

[Non Real-Time]


Enable non-root user access to real-time in Ubuntu

Enabling non-root real-time access in Ubuntu (or other similiar Debian based distros) consists in merely two steps. One must add the intended user to the xenomai group, and then pass the xenomai group id to xenomai nucleus during boot.

Adding a user to the xenomai group can be doing via usermod

$ sudo usermod -a -G xenomai USERNAME

To confirm, we can check /etc/groups with

$ cat /etc/group | grep xenomai

which would yield


This means the xenomai group id is 123, and has for members only USERNAME.

To pass this argument to the nucleus is a question of adding the parameter to grub. For example

$ sudo gedit /etc/default/grub

And edit the line


so that it has the argument at the end

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash xeno_nucleus.xenomai_gid=125"

Finally, updating grub will load the new configuration

$ sudo update-grub

Copyright and license

Copyright (C) 2012 Jorge Azevedo

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.