Difference between revisions of "Xenomai"

Revision as of 21:25, 19 April 2013

What is Xenomai ?

Xenomai is a real time co-kernel which cooperates with Linux via Adeos. With its help, hard real time applications can be developed and run on the Armadeus boards.

Thanks to Adeos, Xenomai will receive the interrupts first and decide to handle them or not. If not, they will then be transfered to the regular Linux kernel. Also, Xenomai provides a framework to develop applications which can be easily moved between the Real Time Xenomai environment and the regular Linux system.

Moreover, Xenomai provides a set of APIs (called "skins") that emulate traditional RTOSes such as VxWorks and pSOS and implement other APIs such as POSIX. Thus, porting third party real time applications to Xenomai is a fairly simple process.

Explanation of the process used to install Xenomai

Note: Xenomai has only be really tested on APF9328 and APF27 with 2.6.29 kernel.

The main steps are:

• selection of Xenomai package on the Buildroot menuconfig,
• selection of Xenomai features in Kernel menuconfig,
• compilation of the new version,
• validation of the Xenomai behaviour.

Note: These steps must be done with a fresh compiled view or, at least, after having suppressed buildroot/output/built/linux-x.y.z directory.

Selecting Xenomai package

• First of all, you need to select Xenomai package and Adeos patch in Buildroot menuconfig:

 $ make menuconfig

Package Selection for the target --->
    Real-Time --->
        [*] Xenomai Userspace

Kernel --->
    Linux Kernel Extensions
        [*] Adeos/Xenomai Real-time patch

Note: It's possible to enable (or not) some skins in a first menu.

• Exit and save your configuration
• If you plan to use xeno-test (Xenomai performance tool) then CONFIG_ASH_GETOPTS should be activated in Busybox:

 $ make busybox-menuconfig

Shells  --->
        Choose your default shell (ash)  --->
    --- ash
    ---   Ash Shell Options
          ...
          [*]   Builtin getopt to parse positional parameters 

• Exit and save your configuration
• rebuild Busybox & Buildroot:

$ make busybox-clean && make

Kernel greater than 2.6.29

For kernels greater than 2.6.29, it's needed to suppress all patches in buildroot/packages/xenomai/ and then modify URL and Adeos patch name:

2.6.38

Kernel --->
    Linux Kernel Extensions  --->
        [*] Adeos/Xenomai Real-time patch
        (http://download.gna.org/adeos/patches/v2.6/$(BR2_ARCH)) Adeos patch URL
        (adeos-ipipe-2.6.38.8-arm-1.18-09.patch) Path for Adeos patch file

Xenomai kernel space support

• At first time, to have Linux kernel patched with Xenomai and Adeos patches, you must type:

 $ make

• Then you can configure the Xenomai kernel options from Linux menuconfig:

 $ make linux-menuconfig

You should see the new entry :

 Real-time sub-system  --->

Enter in it and check the following to compile Xenomai as a part of the Linux kernel :

 [*] Xenomai
   <*> Nucleus 
   [*]   Pervasive real-time support in user-space
   [ ]     Interrupt shield support
   [*]     Priority coupling support
   [*]   Optimize as pipeline head
   (32)  Number of pipe devices
   (512) Number of registry slots
   (128) Size of the system heap (Kb)
   (32)  Size of the private stack pool (Kb)
   [*]   Statistics collection
   [ ]   Debug support
   [ ]   Shared interrupts
      Timing  --->
      Scalability  --->
      Machine  --->
      Interfaces  --->
      Drivers  --->

Additionaly, to enable / disable the different available skins, go into Interfaces ---> :

 <*> Native API  --->
 <*> POSIX API  --->
 < > pSOS+ emulator  --->
 < > uITRON API  --->
 < > VRTX emulator  --->
 < > VxWorks emulator  --->
 < > RTAI emulator  --->
 <*> Real-Time Driver Model  --->

Finally, compile everything:

 $ make linux && make

Deploy

You can now transfer the rootfs and the kernel on the APF.

Validate the installation

• Boot the APF and logon as root.
• You can double check Xenomai is installed correctly:

 $ dmesg | grep Xenomai
  I-pipe: Domain Xenomai registered.
  Xenomai: hal/arm started.
  Xenomai: real-time nucleus v2.4.3 (Back to Shalla-Bal) loaded.
  Xenomai: starting native API services.
  Xenomai: starting POSIX services.
  Xenomai: starting RTDM services.

• Now we can run the performance test provided by Xenomai:

 $ xeno-test

Deinstalling or disabling Xenomai

There are two parts needed for disabling Xenomai features

Kernel

For disabling kernel part, two solutions are available

• The first solution is to unselect kernel's features :

 $ make linux-menuconfig

And disable following options:

Real-time sub-system --->
    [ ] Xenomai

and

Kernel Features ---> 
    [ ] Interrupt pipeline

• The second solution is to destroy the kernel tree :

 $ make linux-dirclean

Userspace / package

For disabling userspace/package part :

 $ make menuconfig

and disable Xenomai

Package Selection for the target ---> 
    [ ] Xenomai

then use the dirclean command:

 $ make xenomai-dirclean

Going further

• Using Armadeus Xenomai custom examples
• Xenomai tutorial (blinking LED)

Links

• Adeos website
• Xenomai website
• Adeos installation
• Xenomai manual installation (for reference)
• Mise en œuvre de Xenomai pour créer un noyau Temps Réel dur - Fedora (french)
• Latencies measurements on ARM platforms