============================
PREEMPT_RT Kernel for Jetson
============================

We provide a PREEMPT_RT kernel for ``Jetpack 6.0``. This kernel is recommended only for use with robot manipulators, as many manipulator manufacturers recommend a low-latency kernel for interfacing with their robots.

Install PREEMPT_RT kernel from apt server
-------------------------------------------

1. Follow instructions from `Developer guide <https://docs.nvidia.com/jetson/archives/r36.3/DeveloperGuide/SD/SoftwarePackagesAndTheUpdateMechanism.html#installing-the-real-time-kernel-packages-on-a-jetson-device>`__
   to install PREEMPT_RT kernel on Jetson.
2. Check if PREEMPT_RT kernel is active by running the below command which should return text that
   contains ``PREEMPT RT``.

    .. code:: bash

        uname -a

Reduce Ethernet Latency
------------------------

When connecting your robot through Ethernet, it's helpful to reduce the latency by running the
following commands.

1. Install Ethernet tools.

    .. code:: bash

        sudo apt-get install ethtool net-tools


2. Bring down the Ethernet interface.

    .. code:: bash

        ifconfig eth1 down

3. Tune the ``rx-usecs`` parameter using ``ethtool``.

    .. code:: bash

        sudo ethtool -C eth1 rx-usecs 64

4. Bring up the interface.

    .. code:: bash

        ifconfig eth1 up

5. Check if the new value is reflected as ``rx-usecs: 64`` in the output of ``ethtool``.

    .. code:: bash

        ethtool -c eth1 | grep rx-usecs

6. Now ping your robot's IP address (``<ROBOT_IP_ADDRESS>``) to check the latency.

    .. code:: bash

        sudo ping <ROBOT_IP_ADDRESS> -i 0.001 -D -c 10000 -s 1200


Uninstall PREEMPT_RT kernel
----------------------------

1. Remove kernel headers and modules

    .. code:: bash

        sudo apt remove nvidia-l4t-rt-kernel nvidia-l4t-rt-kernel-headers nvidia-l4t-rt-kernel-oot-modules nvidia-l4t-display-rt-kernel

2. Reboot your machine

    .. code:: bash

        sudo reboot

3. Verify the kernel version does not include ``PREEMPT RT``.

    .. code:: bash

        uname -a