Visualize data from NuttX NxScope with PlotJuggler

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PlotJuggler is a cool tool for visualizing time series data, supporting live data streaming. Since version 0.5.1, my nxscli tool has included support for data streaming over UDP port, which can be easily captured by PlotJuggler.

Let's see how to set up both tools and plot data from the NuttX NxScope library.

Nxslib with a dummy device

The simplest way to test this new feature is by using built-in nxslib dummy device. It allows you to simulate the NxScope protocol without the need to run the NuttX application. This simplifies the development process with nxslib and nxscli tools.

Step by step instructions:

  1. Start the nxscli with the dummy device enabled:

    nxscli dummy --streamsleep 0.1 chan 2,9 pudp 0

    In this case, select dummy channels 2 and 9 and limit the samples frequency with the --streamsleep 0.1 option. The last argument ... 0 means that the stream will be generated until the Enter key is hit.

    /images/posts/2024/1/plotjuggler-with-nxscope/1.thumbnail.png

  2. Configure the PlotJuggler data source: select "UDP stream" and hit the "Start" button:

    /images/posts/2024/1/plotjuggler-with-nxscope/2.thumbnail.png

    The default port of the UDP server is 9870, and the supported message protocol is json.

    timestamp must be enabled and set to "timestamp".

    /images/posts/2024/1/plotjuggler-with-nxscope/3.thumbnail.png

  3. Start the stream on PlotJuggler; some values should appear in the "Timeseries List":

    /images/posts/2024/1/plotjuggler-with-nxscope/4.thumbnail.png

  4. Finally, split the plot tab horizontally and add the captured data:

    /images/posts/2024/1/plotjuggler-with-nxscope/5.thumbnail.png

NxScope on a NuttX sim device

Now, let's communicate with the real NuttX instance. We'll stream data from the NuttX application running in Linux simulator, so no special hardware is required, only a machine with Linux or a compatible system.

Step by step instructions:

  1. First, build the NuttX sim:nxscope configuration (link). Use the following command for CMake:

    cmake -B build_sim -DBOARD_CONFIG=sim:nxscope -GNinja
cmake --build build_sim

    Verify that the build was successful:

    /images/posts/2024/1/plotjuggler-with-nxscope/6.thumbnail.png

  2. Next, establish a communication channel between the NuttX application and nxscli. Create a simualted UART device (blocking operation) with

    sudo socat PTY,link=/dev/ttySIM0 PTY,link=/dev/ttyNX0

    Then, configure the created PTY to RAW mode in another terminal (we use /dev/* path so privileged access is required):

    sudo chmod a+rw /dev/ttySIM0
sudo chmod a+rw /dev/ttyNX0
stty -F /dev/ttySIM0 raw
stty -F /dev/ttyNX0 raw

  3. Run the NuttX binary and start the nxscope example application:

    ./build_sim/nuttx
nsh> nxscope
nxscope_samples_thr
nxscope_charlog_thr
nxscope_crichan_thr

  4. Start nxscli:

    nxscli serial /dev/ttyNX0 chan 0 pudp 0

    This connects to the previously created serial device /dev/ttyNX0.

  5. Connect to the UDP stream and plot chan0 from the Timeseries List:

    /images/posts/2024/1/plotjuggler-with-nxscope/7.thumbnail.png

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