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Copy file name to clipboardExpand all lines: controller_manager/doc/userdoc.rst
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@@ -11,10 +11,9 @@ Determinism
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For best performance when controlling hardware you want the controller manager to have as little jitter as possible in the main control loop.
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The normal linux kernel is optimized for computational throughput and therefore is not well suited for hardware control.
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The two easiest kernel options are the `Real-time Ubuntu 22.04 LTS Beta <https://ubuntu.com/blog/real-time-ubuntu-released>`_ or `linux-image-rt-amd64 <https://packages.debian.org/bullseye/linux-image-rt-amd64>`_ on Debian Bullseye.
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If you have a realtime kernel installed, the main thread of Controller Manager attempts to configure ``SCHED_FIFO`` with a priority of ``50``.
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Independent of the kernel installed, the main thread of Controller Manager attempts to
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configure ``SCHED_FIFO`` with a priority of ``50``.
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By default, the user does not have permission to set such a high priority.
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To give the user such permissions, add a group named realtime and add the user controlling your robot to this group:
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@@ -36,6 +35,16 @@ Afterwards, add the following limits to the realtime group in ``/etc/security/li
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The limits will be applied after you log out and in again.
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The normal linux kernel is optimized for computational throughput and therefore is not well suited for hardware control.
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Alternatives to the standard kernel include
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- `Real-time Ubuntu 22.04 LTS Beta <https://ubuntu.com/blog/real-time-ubuntu-released>`_ on Ubuntu 22.04
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- `linux-image-rt-amd64 <https://packages.debian.org/bullseye/linux-image-rt-amd64>`_ on Debian Bullseye
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- lowlatency kernel (``sudo apt install linux-lowlatency``) on any ubuntu
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Though installing a realtime-kernel will definitely get the best results when it comes to low
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jitter, using a lowlatency kernel can improve things a lot with being really easy to install.
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