Перший додаток (Hello Sky)

У цій темі пояснюється, як створити та запустити свій перший бортовий додаток. Він охоплює всі основні концепції та API, необхідні для розробки додатків на PX4.

INFO

For simplicity, more advanced features like start/stop functionality and command-line arguments are omitted. These are covered in Application/Module Template.

Вимоги

Вам знадобиться наступне:

• PX4 SITL Simulator or a PX4-compatible flight controller.
• PX4 Development Toolchain for the desired target.
• Download the PX4 Source Code from Github

The source code PX4-Autopilot/src/examples/px4_simple_app directory contains a completed version of this tutorial that you can review if you get stuck.

• Rename (or delete) the px4_simple_app directory.

Мінімальна програма

In this section we create a minimal application that just prints out Hello Sky!. This consists of a single C file and a cmake definition (which tells the toolchain how to build the application).

1. Create a new directory PX4-Autopilot/src/examples/px4_simple_app.

2. Create a new C file in that directory named px4_simple_app.c:

   • Скопіюйте заголовок за замовчуванням у верхній частині сторінки. Це повинно бути присутнім у всіх розміщених файлах!

     /****************************************************************************
      *
      *   Copyright (c) 2012-2022 PX4 Development Team. All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
      *
      * 1. Redistributions of source code must retain the above copyright
      *    notice, this list of conditions and the following disclaimer.
      * 2. Redistributions in binary form must reproduce the above copyright
      *    notice, this list of conditions and the following disclaimer in
      *    the documentation and/or other materials provided with the
      *    distribution.
      * 3. Neither the name PX4 nor the names of its contributors may be
      *    used to endorse or promote products derived from this software
      *    without specific prior written permission.
      *
      * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
      * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
      * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
      * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
      * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
      * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
      * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
      * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
      * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
      * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
      * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
      * POSSIBILITY OF SUCH DAMAGE.
      *
      ****************************************************************************/

   • Скопіюйте наступний код під заголовком за замовчуванням. Це повинно бути присутнім у всіх розміщених файлах!

     /**
      * @file px4_simple_app.c
      * Minimal application example for PX4 autopilot
      *
      * @author Example User <mail@example.com>
      */
     
     #include <px4_platform_common/log.h>
     
     __EXPORT int px4_simple_app_main(int argc, char *argv[]);
     
     int px4_simple_app_main(int argc, char *argv[])
     {
     	PX4_INFO("Hello Sky!");
     	return OK;
     }

     TIP

     The main function must be named <module_name>_main and exported from the module as shown.

:::

 :::tip
 `PX4_INFO` is the equivalent of `printf` for the PX4 shell (included from **px4_platform_common/log.h**).
 There are different log levels: `PX4_INFO`, `PX4_WARN`, `PX4_ERR`, `PX4_DEBUG`.
 Warnings and errors are additionally added to the [ULog](../dev_log/ulog_file_format.md) and shown on [Flight Review](https://logs.px4.io/).

:::

3. Create and open a new cmake definition file named CMakeLists.txt. Скопіюйте текст нижче:

   ############################################################################
   #
   #   Copyright (c) 2015 PX4 Development Team. All rights reserved.
   #
   # Redistribution and use in source and binary forms, with or without
   # modification, are permitted provided that the following conditions
   # are met:
   #
   # 1. Redistributions of source code must retain the above copyright
   #    notice, this list of conditions and the following disclaimer.
   # 2. Redistributions in binary form must reproduce the above copyright
   #    notice, this list of conditions and the following disclaimer in
   #    the documentation and/or other materials provided with the
   #    distribution.
   # 3. Neither the name PX4 nor the names of its contributors may be
   #    used to endorse or promote products derived from this software
   #    without specific prior written permission.
   #
   # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   # "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   # LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   # FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   # COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   # INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   # BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
   # OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
   # AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   # LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   # ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   # POSSIBILITY OF SUCH DAMAGE.
   #
   ############################################################################
   px4_add_module(
   	MODULE examples__px4_simple_app
   	MAIN px4_simple_app
   	STACK_MAIN 2000
   	SRCS
   		px4_simple_app.c
   	DEPENDS
   	)

   The px4_add_module() method builds a static library from a module description.

   • The MODULE block is the Firmware-unique name of the module (by convention the module name is prefixed by parent directories back to src).
   • The MAIN block lists the entry point of the module, which registers the command with NuttX so that it can be called from the PX4 shell or SITL console.

   TIP

   The px4_add_module() format is documented in PX4-Autopilot/cmake/px4_add_module.cmake.

:::

INFO

If you specify DYNAMIC as an option to px4_add_module, a shared library is created instead of a static library on POSIX platforms (these can be loaded without having to recompile PX4, and shared to others as binaries rather than source code). Your app will not become a builtin command, but ends up in a separate file called examples__px4_simple_app.px4mod. You can then run your command by loading the file at runtime using the dyn command: dyn ./examples__px4_simple_app.px4mod

4. Create and open a new Kconfig definition file named Kconfig and define your symbol for naming (see Kconfig naming convention). Скопіюйте текст нижче:

   menuconfig EXAMPLES_PX4_SIMPLE_APP
   	bool "px4_simple_app"
   	default n
   	---help---
   		Enable support for px4_simple_app

Побудуйте Програму/прошивку

Додаток завершено. Для запуску його спершу потрібно переконатись, що він побудований як частина PX4. Applications are added to the build/firmware in the appropriate board-level px4board file for your target:

• PX4 SITL (Simulator): PX4-Autopilot/boards/px4/sitl/default.px4board
• Pixhawk v1/2: PX4-Autopilot/boards/px4/fmu-v2/default.px4board
• Pixracer (px4/fmu-v4): PX4-Autopilot/boards/px4/fmu-v4/default.px4board
• px4board files for other boards can be found in PX4-Autopilot/boards/

To enable the compilation of the application into the firmware add the corresponding Kconfig key CONFIG_EXAMPLES_PX4_SIMPLE_APP=y in the px4board file or run boardconfig make px4_fmu-v4_default boardconfig:

examples  --->
    [x] PX4 Simple app  ----

INFO

The line will already be present for most files, because the examples are included in firmware by default.

Побудуйте приклад, використовуючи команду для конкретної плати:

• jMAVSim Simulator: make px4_sitl_default jmavsim
• Pixhawk v1/2: make px4_fmu-v2_default (or just make px4_fmu-v2)
• Pixhawk v3: make px4_fmu-v4_default
• Other boards: Building the Code

Тестовий додаток (апаратне забезпечення)

Завантажте прошивку на вашу плату

Увімкніть завантажувач, а потім скиньте плату:

• Pixhawk v1/2: make px4_fmu-v2_default upload
• Pixhawk v3: make px4_fmu-v4_default upload

Перед скиданням дошки повинно бути надруковано певну кількість компілювальних повідомлень та в кінці:

Завантажена прошивка для X, X, очікування на загрузчик...

Після того, як плату скинуто і завантажено, вона починає друкувати:

Erase  : [====================] 100.0%
Program: [====================] 100.0%
Verify : [====================] 100.0%
Rebooting.

[100%] Built target upload

Підключіть консоль

Now connect to the system console either via serial or USB. Hitting ENTER will bring up the shell prompt:

nsh>

Введіть ''help'' та натисніть ENTER

nsh> help
  help usage:  help [-v] [<cmd>]

  [           df          kill        mkfifo      ps          sleep
  ?           echo        losetup     mkrd        pwd         test
  cat         exec        ls          mh          rm          umount
  cd          exit        mb          mount       rmdir       unset
  cp          free        mkdir       mv          set         usleep
  dd          help        mkfatfs     mw          sh          xd

Builtin Apps:
  reboot
  perf
  top
  ..
  px4_simple_app
  ..
  sercon
  serdis

Note that px4_simple_app is now part of the available commands. Start it by typing px4_simple_app and ENTER:

nsh> px4_simple_app
Hello Sky!

Заява зараз правильно зареєстрована в системі і може бути розширена для фактичного виконання корисних завдань.

Тестовий додаток (SITL)

If you're using SITL the PX4 console is automatically started (see Building the Code > First Build (Using a Simulator)). As with the nsh console (see previous section) you can type help to see the list of built-in apps.

Enter px4_simple_app to run the minimal app.

pxh> px4_simple_app
INFO  [px4_simple_app] Hello Sky!

Додаток тепер може бути розширений для фактичного виконання корисних завдань.

Підписка на дані сенсорів

Для того щоб зробити щось корисне, додаток повинен підписати входи та опублікувати виходи (наприклад, команди для мотору або серводвигуна).

TIP

The benefits of the PX4 hardware abstraction comes into play here! Немає потреби взаємодіяти з драйверами сенсорів та оновлювати додаток, якщо плата або сенсори оновлені.

Individual message channels between applications are called topics. For this tutorial, we are interested in the SensorCombined topic, which holds the synchronized sensor data of the complete system.

Підписка на тему проста:

#include <uORB/topics/sensor_combined.h>
..
int sensor_sub_fd = orb_subscribe(ORB_ID(sensor_combined));

The sensor_sub_fd is a topic handle and can be used to very efficiently perform a blocking wait for new data. Поточний потік переходить у режим сну і автоматично буде розбуджений планувальником, як тільки буде доступні нові дані, не використовуючи жодних циклів ЦП під час очікування. To do this, we use the poll() POSIX system call.

Adding poll() to the subscription looks like (pseudocode, look for the full implementation below):

#include <poll.h>
#include <uORB/topics/sensor_combined.h>
..
int sensor_sub_fd = orb_subscribe(ORB_ID(sensor_combined));

/* one could wait for multiple topics with this technique, just using one here */
px4_pollfd_struct_t fds[] = {
    { .fd = sensor_sub_fd,   .events = POLLIN },
};

while (true) {
	/* wait for sensor update of 1 file descriptor for 1000 ms (1 second) */
	int poll_ret = px4_poll(fds, 1, 1000);
	..
	if (fds[0].revents & POLLIN) {
		/* obtained data for the first file descriptor */
		struct sensor_combined_s raw;
		/* copy sensors raw data into local buffer */
		orb_copy(ORB_ID(sensor_combined), sensor_sub_fd, &raw);
		PX4_INFO("Accelerometer:\t%8.4f\t%8.4f\t%8.4f",
					(double)raw.accelerometer_m_s2[0],
					(double)raw.accelerometer_m_s2[1],
					(double)raw.accelerometer_m_s2[2]);
	}
}

Знову скомпілюйте додаток, введіть:

make

Тестування підписки на uORB

Останнім кроком є запуск вашої програми як фонового процесу / завдання, набираючи наступне у оболонці nsh:

px4_simple_app &

Ваш застосунок відображатиме 5 значень датчиків у консолі, а потім завершить виконання:

[px4_simple_app] Accelerometer:   0.0483          0.0821          0.0332
[px4_simple_app] Accelerometer:   0.0486          0.0820          0.0336
[px4_simple_app] Accelerometer:   0.0487          0.0819          0.0327
[px4_simple_app] Accelerometer:   0.0482          0.0818          0.0323
[px4_simple_app] Accelerometer:   0.0482          0.0827          0.0331
[px4_simple_app] Accelerometer:   0.0489          0.0804          0.0328

TIP

The Module Template for Full Applications can be used to write background process that can be controlled from the command line.

Публікація Даних

To use the calculated outputs, the next step is to publish the results. Нижче ми покажемо, як опублікувати тему ставлення.

INFO

We've chosen attitude because we know that the mavlink app forwards it to the ground control station - providing an easy way to look at the results.

The interface is pretty simple: initialize the struct of the topic to be published and advertise the topic:

#include <uORB/topics/vehicle_attitude.h>
..
/* advertise attitude topic */
struct vehicle_attitude_s att;
memset(&att, 0, sizeof(att));
orb_advert_t att_pub_fd = orb_advertise(ORB_ID(vehicle_attitude), &att);

У головному циклі опублікуйте інформацію, коли вона буде готова:

orb_publish(ORB_ID(vehicle_attitude), att_pub_fd, &att);

Наприклад: Код Повного Прикладу

The complete example code is now:

/****************************************************************************
 *
 *   Copyright (c) 2012-2019 PX4 Development Team. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name PX4 nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/**
 * @file px4_simple_app.c
 * Minimal application example for PX4 autopilot
 *
 * @author Example User <mail@example.com>
 */

#include <px4_platform_common/px4_config.h>
#include <px4_platform_common/tasks.h>
#include <px4_platform_common/posix.h>
#include <unistd.h>
#include <stdio.h>
#include <poll.h>
#include <string.h>
#include <math.h>

#include <uORB/uORB.h>
#include <uORB/topics/sensor_combined.h>
#include <uORB/topics/vehicle_attitude.h>

__EXPORT int px4_simple_app_main(int argc, char *argv[]);

int px4_simple_app_main(int argc, char *argv[])
{
	PX4_INFO("Hello Sky!");

	/* subscribe to sensor_combined topic */
	int sensor_sub_fd = orb_subscribe(ORB_ID(sensor_combined));
	/* limit the update rate to 5 Hz */
	orb_set_interval(sensor_sub_fd, 200);

	/* advertise attitude topic */
	struct vehicle_attitude_s att;
	memset(&att, 0, sizeof(att));
	orb_advert_t att_pub = orb_advertise(ORB_ID(vehicle_attitude), &att);

	/* one could wait for multiple topics with this technique, just using one here */
	px4_pollfd_struct_t fds[] = {
		{ .fd = sensor_sub_fd,   .events = POLLIN },
		/* there could be more file descriptors here, in the form like:
		 * { .fd = other_sub_fd,   .events = POLLIN },
		 */
	};

	int error_counter = 0;

	for (int i = 0; i < 5; i++) {
		/* wait for sensor update of 1 file descriptor for 1000 ms (1 second) */
		int poll_ret = px4_poll(fds, 1, 1000);

		/* handle the poll result */
		if (poll_ret == 0) {
			/* this means none of our providers is giving us data */
			PX4_ERR("Got no data within a second");

		} else if (poll_ret < 0) {
			/* this is seriously bad - should be an emergency */
			if (error_counter < 10 || error_counter % 50 == 0) {
				/* use a counter to prevent flooding (and slowing us down) */
				PX4_ERR("ERROR return value from poll(): %d", poll_ret);
			}

			error_counter++;

		} else {

			if (fds[0].revents & POLLIN) {
				/* obtained data for the first file descriptor */
				struct sensor_combined_s raw;
				/* copy sensors raw data into local buffer */
				orb_copy(ORB_ID(sensor_combined), sensor_sub_fd, &raw);
				PX4_INFO("Accelerometer:\t%8.4f\t%8.4f\t%8.4f",
					 (double)raw.accelerometer_m_s2[0],
					 (double)raw.accelerometer_m_s2[1],
					 (double)raw.accelerometer_m_s2[2]);

				/* set att and publish this information for other apps
				 the following does not have any meaning, it's just an example
				*/
				att.q[0] = raw.accelerometer_m_s2[0];
				att.q[1] = raw.accelerometer_m_s2[1];
				att.q[2] = raw.accelerometer_m_s2[2];

				orb_publish(ORB_ID(vehicle_attitude), att_pub, &att);
			}

			/* there could be more file descriptors here, in the form like:
			 * if (fds[1..n].revents & POLLIN) {}
			 */
		}
	}

	PX4_INFO("exiting");

	return 0;
}

Виконання повного прикладу

І, нарешті, запустіть свою програму:

px4_simple_app

If you start QGroundControl, you can check the sensor values in the real time plot (Analyze > MAVLink Inspector).

Підсумок

Цей посібник охоплює все необхідне для розробки базової програми автопілота PX4. Keep in mind that the full list of uORB messages/topics is available here and that the headers are well documented and serve as reference.

Further information and troubleshooting/common pitfalls can be found here: uORB.

Наступна сторінка презентує шаблон для написання повної програми з можливістю запуску та зупинки.