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samples: net: latmon: latency monitor tool
Supports the EVL/Xenomai4 benchmarking tool as described in the documentation. The benchmarking tool is accessed via the latmon service. This code uses the J2 socket on FRDMk64-F: PIN_20: tx pulse to SUT PIN_18: rx ack from SUT The client code running on the SUT shall monitor the falling edge of PIN_20. Example usage from the latmus client running Xenomai4: $ latmus -I gpiochip2,23,falling-edge \ -O gpiochip2,21 -g"histogram" \ -z broadcast Signed-off-by: Jorge Ramirez-Ortiz <[email protected]>
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‎samples/net/latmon/CMakeLists.txt

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# SPDX-License-Identifier: Apache-2.0
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cmake_minimum_required(VERSION 3.20.0)
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find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
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project(latmon)
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target_sources(app PRIVATE src/main.c)

‎samples/net/latmon/Kconfig

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# Private config options for Latmon Sample app
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# SPDX-License-Identifier: Apache-2.0
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# Copyright (c) 2025 Jorge Ramirez-Ortiz <[email protected]>
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mainmenu "Latmon Sample application"
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config LATMON_LOOPBACK_CALIBRATION
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bool "Run the sample code in calibration mode"
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default n
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help
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Run Latmon in calibration mode.
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source "Kconfig.zephyr"

‎samples/net/latmon/README.rst

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.. zephyr:code-sample:: latmon-client
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:name: Latmon Client
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:relevant-api: latmon
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Measures delta time between GPIO events and reports the latency metrics via latmon to the latmus
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service executing on the SUT.
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Overview
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********
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This project provides tools to measure the worst-case response time of a system under test (SUT) to
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GPIO events using:
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- **Latmon**:
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Runs on a Zephyr-based board to generate and monitor GPIO events while collecting metrics
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- **Latmus**:
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Runs on the SUT to respond to the falling edge of input GPIO event, displaying the latency metrics
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and generate histogram data.
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This project is part of the open-source initiative
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`EVL Project - Latmus GPIO Response Time <https://evlproject.org/core/benchmarks/#latmus-gpio-response-time>`_.
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The main program is designed to monitor latency using GPIO pins on a Zephyr-based system. It generates a
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pulse signal on a GPIO pin and measures the time it takes for the SUT (executing Latmus) to respond to
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it.
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The SUT must be running Latmus to capture the latency metrics and histogram information reported over the
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network. The program uses LEDs to indicate the different states, such as DHCP binding(red), waiting for the
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Latmus connection (blue) and sampling (green).
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Why Not Just Use a Timer?
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=========================
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Timer tests miss external factors like GPIO signals, hardware, and interrupt handling.
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Latmon and Latmus simulate real-world scenarios, capturing end-to-end latency metrics.
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This ensures accurate assessment of real-time responsiveness across the entire system.
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- **Real-Time Thread Testing**:
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Evaluates how a user-space thread processes external interrupts.
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- **End-to-End Latency Measurement**:
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Captures delays from hardware, drivers, and user-space threads.
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- **Versatile Platform Support**:
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Works on EVL, PREEMPT_RT, and other platforms.
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Code Structure
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==============
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The Latmon sample application is divided into two main components:
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- **Application Logic** (:zephyr_file:`samples/net/latmon/main.c`):
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This file contains the application logic for Latmon.
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It initializes networking, provides the instrumentation mechanism and handles LED indicators for the
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different states.
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- **Library** (:zephyr_file:`subsys/net/lib/latmon/latmon.c`):
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This file provides reusable functions and abstractions for latency monitoring via Latmus.
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It includes the core logic for reporting latency metrics and histogram data.
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Requirements
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************
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- **Zephyr-Compatible Board**:
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A board with external GPIO support and an IPv4 network interface (e.g., FRDM-K64F).
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- **System under Test**:
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A system with external GPIO pins running the Latmus service and an IPv4 network interface.
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- **Network Connection**:
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A DHCP server for IP assignment.
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- **Physical Connection**:
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GPIO wires connecting the Zephyr board to the SUT and both systems connected to the network.
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Setup and Usage
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***************
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- **Flash Latmon onto the Zephyr board**:
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The application will connect to the network and wait for a connection from the SUT. The application
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will use DHCP to obtain an IPv4 address.
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- **Connect GPIO pins for transmit (Zephyr to SUT) and receive (SUT to Zephyr)**
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On **FRDM-K64F**, the sample code uses the **Arduino header J2**, ``pin 20`` for transmit the pulse to
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the SUT and ``pin 18`` to receive the acknowledgment from the SUT.
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- **Run Latmus on the SUT**
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Request the appropriate options with `Latmus <https://evlproject.org/core/testing/#latmus-program>`_. Users
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can for example modify the sampling period with the ``-p`` option or generate historgram data for
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postprocessing with the ``-g`` option,
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- **Monitor results from the SUT**
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Latmus will report latency figures and, if requested, generate the histogram data file.
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- **Calibrating the Latmus latencies: CONFIG_LATMON_LOOPBACK_CALIBRATION**:
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Users can connect the GPIO pins in loopback mode (transmit to ack) and build the Latmon sample application with
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CONFIG_LATMON_LOOPBACK_CALIBRATION enabled. When connecting to Latmus in this configuration, Latmus is providing
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a calibration value that can be used to adjust the final latencies.
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Example
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=======
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On the host and to build and flash the Zephyr FRDM-K64F board with the Latmon sample:
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.. code-block:: console
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user@host:~$ west build -b frdm_k64f samples/net/latmon
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user@host:~$ west flash
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On the SUT running on Linux, latmus **MUST** track the falling edge of the signal:
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.. code-block:: console
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root@target:~$ latmus -I gpiochip2,23,falling-edge -O gpiochip2,21 -z -g"histogram" "broadcast"
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Monitoring both consoles, you should see the following:
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.. code-block:: console
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[00:00:03.311,000] <inf> phy_mc_ksz8081: PHY 0 is up
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[00:00:03.311,000] <inf> phy_mc_ksz8081: PHY (0) Link speed 100 Mb, full duplex
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[00:00:03.312,000] <inf> eth_nxp_enet_mac: Link is up
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*** Booting Zephyr OS build v4.1.0-3337-g886443a190b1 ***
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[00:00:03.313,000] <inf> sample_latmon: DHCPv4: binding...
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[00:00:03.313,000] <inf> latmon: Latmon server thread priority: 14
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[00:00:10.964,000] <inf> net_dhcpv4: Received: 192.168.1.58
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[00:00:10.964,000] <inf> sample_latmon: Listening on 192.168.1.58
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[00:00:30.966,000] <inf> latmon: Waiting for Latmus ...
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[00:00:31.356,000] <inf> latmon: Monitor thread priority: -16
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[00:00:31.356,000] <inf> latmon: monitoring started:
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[00:00:31.356,000] <inf> latmon: - samples per period: 1000
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[00:00:31.356,000] <inf> latmon: - period: 1000 usecs
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[00:00:31.356,000] <inf> latmon: - histogram cells: 200
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[00:00:31.393,000] <inf> latmon: Transfer thread priority: 14
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.. code-block:: console
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root@target:~$ latmus -I gpiochip2,23,falling-edge -O gpiochip2,21 -Z -g"histogram" broadcast
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Received broadcast message: 192.168.1.58
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warming up on CPU0 (not isolated)...
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connecting to latmon at 192.168.1.58:2306...
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RTT| 00:00:16 (oob-gpio, 1000 us period, priority 98, CPU0-noisol)
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RTH|----lat min|----lat avg|----lat max|-overrun|---msw|---lat best|--lat worst
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RTD| 26.375| 30.839| 33.508| 0| 0| 26.375| 33.508
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RTD| 26.333| 30.801| 37.633| 0| 0| 26.333| 37.633
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RTD| 26.375| 30.801| 31.966| 0| 0| 26.333| 37.633
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RTD| 26.375| 30.911| 49.675| 0| 0| 26.333| 49.675
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RTD| 26.333| 30.830| 41.658| 0| 0| 26.333| 49.675
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RTD| 26.375| 31.107| 59.216| 0| 0| 26.333| 59.216
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RTD| 26.333| 30.767| 30.925| 0| 0| 26.333| 59.216
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RTD| 26.333| 30.781| 41.616| 0| 0| 26.333| 59.216
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RTD| 26.375| 30.768| 32.925| 0| 0| 26.333| 59.216
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RTD| 26.375| 30.768| 37.633| 0| 0| 26.333| 59.216
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On completion and from your host, retrieve the histogram file from the SUT, and generate a plot (a PNG file) using
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gnuplot:
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.. code-block:: console
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user@host:~$ gnuplot plot_data.gp
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The ``plot_data.gp`` script should look like this for a file named ``histogram``:
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.. code-block:: gnuplot
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set terminal pngcairo size 800,600
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set output 'plot.png'
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set title "Data Plot"
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set xlabel "Latency (usec)"
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set ylabel "Sample Count"
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set grid
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set style data linespoints
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plot 'histogram' using 1:2 with linespoints title "Data Points"

‎samples/net/latmon/boards/frdm_k64f.overlay

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/*
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* SPDX-License-Identifier: Apache-2.0
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*
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* Copyright (c) 2025 Jorge Ramirez-Ortiz <[email protected]>
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*/
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/ {
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zephyr,user {
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pulse_gpios = <&gpioe 24 GPIO_ACTIVE_HIGH>;
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ack_gpios = <&gpioe 25 GPIO_ACTIVE_HIGH>;
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};
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};

‎samples/net/latmon/prj.conf

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# SPDX-License-Identifier: Apache-2.0
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# Copyright (c) 2025 Jorge Ramirez-Ortiz <[email protected]>
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CONFIG_POSIX_API=y
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# General config
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CONFIG_LOG=y
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CONFIG_GPIO=y
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# Networking config
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CONFIG_NETWORKING=y
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CONFIG_NET_DHCPV4=y
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CONFIG_NET_IPV4=y
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CONFIG_NET_LOG=y
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CONFIG_NET_TCP=y
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# Latmon config
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CONFIG_NET_LATMON=y
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CONFIG_LATMON_LOG_LEVEL_DBG=y
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# Heap for Latmon
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CONFIG_HEAP_MEM_POOL_SIZE=8192

‎samples/net/latmon/sample.yaml

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sample:
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description: Latency Benchmarking Tool
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name: Latmon sample app
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common:
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harness: net
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tags:
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- net
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- latmon
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tests:
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sample.net.latmon:
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build_only: true
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platform_allow:
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- frdm_k64f
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depends_on: eth

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