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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 .... 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/README.rst

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Latency Monitoring with Latmon and Latmus
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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 GPIO events using:
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- **Latmon**: Runs on a Zephyr-based board to generate and monitor GPIO events while collecting metrics
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- **Latmus**: Runs on the SUT to respond to the falling edge of input GPIO event and display metrics.
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This project is part of the open-source initiative `EVL Project - Latmus GPIO Response Time <https://evlproject.org/core/benchmarks/#latmus-gpio-response-time>`_.
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Why Not Just Use a Timer?
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-------------------------
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A timer-based test only measures internal response times and often neglects external factors such as GPIO signal propagation, hardware interaction, and interrupt handling.
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By using Latmon and Latmus, you can simulate real-world hardware-driven scenarios, capturing comprehensive end-to-end latency metrics, including hardware, drivers, and user-space threads.
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This provides a more accurate assessment of the system's real-time responsiveness.
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- **Real-Time Thread Testing**: Evaluates how a user-space thread processes external interrupts.
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- **End-to-End Latency Measurement**: Captures delays from hardware, drivers, and user-space threads.
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- **Versatile Platform Support**: Works on EVL, PREEMPT_RT, and other platforms.
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Overview
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--------
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The main program is designed to monitor latency using GPIO pins on a Zephyr-based system.
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It generates a pulse signal on a GPIO pin and measures the time it takes for the SUT (executing Latmus) to respond to the signal.
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The SUT must be running Latmus to capture the latency metrics and historgram information reported over the network .
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The program uses LEDS to indicate the different states, such as DHCP binding(red), waiting for the Latmus connection (blue) and sampling (green).
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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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1. **Application Logic (`samples/net/latmon/main.c`)**:
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This file contains the main application logic for Latmon. It initializes the hardware, the networking interface, configures the GPIO pins, and manages the state machine for the latency monitoring process.
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It also handles LED indicators for different states (e.g., DHCP binding, waiting for connection, sampling).
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2. **Library (`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**: A board with external GPIO support (e.g., FRDM-K64F).
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- **SUT**: A system with external GPIO pins running Latmus.
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- **Network Connection**: A DHCP server for IP assignment.
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- **Physical Connection**: GPIO wires connecting the Zephyr board to the SUT.
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Setup and Usage
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---------------
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1. Flash Latmon onto the Zephyr board.
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2. Connect GPIO pins for TX (Zephyr to SUT) and RX (SUT to Zephyr).
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3. Run Latmus on the SUT with appropriate options (e.g., ``-p`` for period, ``-g`` for histogram generation).
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4. Monitor results such as min, max, and average latencies.
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Example
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-------
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Run Latmon and Latmus as follows:
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On the host and to flash the Zephyr board::
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$ west flash
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On the SUT, latmus **MUST** track the falling edge of the signal::
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$ latmus -I gpiochip2,23,falling-edge -O gpiochip2,21 -z <ip_address> -g "histogram"
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On completion, generate a latency histogram on the host (a PNG file) using gnuplot::
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$ gnuplot plot_data.gp
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The `plot_data.gp` script should look like this:
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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"
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Contributions
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-------------
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Contributions are welcome. Please submit a pull request or open an issue.

‎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) 2024 Jorge Ramirez-Ortiz <[email protected]>
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*/
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/ {
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latmon: latency-monitor {
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compatible = "latency-monitor";
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latmon_pulse: latmon_pulse {
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gpios = <&gpioe 24 GPIO_ACTIVE_HIGH>;
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pinctrl-0 = <&pinmux_pulse>;
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pinctrl-names = "default";
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};
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latmon_ack: latmon_ack {
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gpios = <&gpioe 25 GPIO_ACTIVE_HIGH>;
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pinctrl-0 = <&pinmux_ack>;
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pinctrl-names = "default";
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};
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};
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};
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&pinctrl {
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pinmux_pulse:pinmux_pulse {
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group0 {
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pinmux = <PTE24>;
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drive-strength = "high";
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slew-rate = "slow";
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};
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};
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pinmux_ack:pinmux_ack {
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group0 {
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pinmux = <PTE25>;
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drive-strength = "high";
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slew-rate = "slow";
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};
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};
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};
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&i2c0 {
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status = "disabled";
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};

‎samples/net/latmon/dts/bindings/latency-monitor.yaml

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# Copyright (c) 2024 Jorge Ramirez-Ortiz <[email protected]>
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# SPDX-License-Identifier: Apache-2.0
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description: GPIO latency monitor
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compatible: "latency-monitor"
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child-binding:
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properties:
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gpios:
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type: phandle-array
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required: true
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pinctrl-0:
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type: phandle
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required: false
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pinctrl-names:
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type: string
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required: false

‎samples/net/latmon/prj.conf

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# General config
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CONFIG_LOG=y
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CONFIG_GPIO=y
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CONFIG_REBOOT=y
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CONFIG_TICKLESS_KERNEL=y
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CONFIG_CONSOLE_SUBSYS=y
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CONFIG_CONSOLE_GETLINE=y
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CONFIG_NEWLIB_LIBC=y
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CONFIG_INIT_STACKS=y
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# Networking config
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CONFIG_NETWORKING=y
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CONFIG_NET_LATMON=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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name: Latency Benchmarking Tool
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tests:
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sample.basic.latmon
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tags:
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- gpio
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- devicetree
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integration_platforms:
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- frdm_k64f
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depends_on: gpio
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harness: console

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