PX4模块设计之三：自定义uORB消息

Posted 2022-07-12 lida2003

PX4模块设计之三：自定义uORB消息

• 1. 新增自定义uORB消息步骤
• 2. 应用ext_hello_world消息示例
• 3. 编译执行结果
• 4. 参考资料

基于PX4开源软件框架简明简介和PX4模块设计之二：uORB消息代理, 了解了更多关于中间件uORB消息代理作为PX4系统内部消息传递的重要性。

关于新增消息或者消息主题，可以分为PX4代码库内部新增（通常是PX4开源组织在进行维护）和外部新增两种方式。

这里自定义uORB消息主要侧重的是外部新增主题消息，后续将会结合一个示例进行相关应用的Demo。

1. 新增自定义uORB消息步骤

1. 新增与PX4-Autopilot平行目录PX4-ExternalModule；
2. 建立PX4-ExternalModule下相应的msg、src目录；
3. 在PX4-ExternalModule的msg目录下新建.msg文件，参考PX4-Autopilot下msg目录下的相关文件；

1 uint64 timestamp	# time since system start (microseconds)
2 int8 hello          # index of hello variable
3 
4 # TOPICS ext_hello_world

4. 在PX4-ExternalModule的msg目录下新建CMakeLists.txt文件;
5. 在CMakeList.txt文件中添加.msg文件；

34 set(config_msg_list_external
35    ext_hello_world.msg
36    PARENT_SCOPE
37    )

6. 在make的时候，框架代码会自动根据上述源文件生成对应的两个C/C++文件；

PX4-Autopilot\\build\\px4_sitl_default\\uORB\\topics\\ext_hello_world.h
PX4-Autopilot\\build\\px4_sitl_default\\msg\\topics_sources\\ext_hello_world.cpp

注：自此已经完成新增自定义uORB消息ext_hello_world。

2. 应用ext_hello_world消息示例

定义消息的目的主要是为了不同的任务之间进行通信，这里写了一个Demo：两个任务，一个任务publish消息，一个任务subscribe消息；

1. 在Demo代码里面包含头文件；

#include <uORB/topics/ext_hello_world.h>

2. 使用ORB_ID(ext_hello_world)唯一定位消息主题；
3. 使用px4_task_spawn_cmd函数建立两个任务；
4. 使用uORB消息处理接口函数Demo应用；

/****************************************************************************
 *
 *   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_custom_uorb.c
 * extern custom uorb example for PX4 autopilot
 *
 * @author Example User <[e-mail]>
 */

#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 <sys/types.h>
#include <stdlib.h>
#include <sched.h>
#include <errno.h>


#include <uORB/uORB.h>
#include <uORB/topics/ext_hello_world.h>

#define TASK_NAME_CUSTOM_UORB_SUBSCRIBE  "orb subscribe"
#define TASK_NAME_CUSTOM_UORB_PUBLISH    "orb publish"

#define TASK_SUBSCRIBE_NUM                8
#define TASK_PUBLISH_NUM                  5

__EXPORT int px4_custom_uorb_main(int argc, char *argv[]);

int px4_custom_uorb_subscribe(int argc, char *argv[])

	/* listen */
	int hello_fd = orb_subscribe(ORB_ID(ext_hello_world));
	/* limit the update rate to 5 Hz */
	orb_set_interval(hello_fd, 200);
	/* one could wait for multiple topics with this technique, just using one here */
	px4_pollfd_struct_t fds[] = 
		 .fd = hello_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 < TASK_SUBSCRIBE_NUM; i++) 
		/* wait for sensor update of 1 file descriptor for 1000 ms (1 second) */
		int poll_ret = px4_poll(fds, 1, 5000);

		/* 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 ext_hello_world_s tmp;
				/* copy sensors raw data into local buffer */
				orb_copy(ORB_ID(ext_hello_world), hello_fd, &tmp);
				PX4_INFO("Hello world(subscribe):\\t%d", tmp.hello);
			
			
			/* there could be more file descriptors here, in the form like:
			 * if (fds[1..n].revents & POLLIN) 
			 */
		
	
	
	PX4_INFO("px4_custom_uorb_subscribe exiting");
	
	return 0;


int px4_custom_uorb_publish(int argc, char *argv[])

	/* advertise */
	struct ext_hello_world_s hello_world;
	memset(&hello_world, 0, sizeof(hello_world));
	orb_advert_t hello_world_pub = orb_advertise(ORB_ID(ext_hello_world), &hello_world);
	
	for (int i = 0; i < TASK_PUBLISH_NUM; i++) 
		
		/* Wait for subscriber */
		sleep(5);

		/* set att and publish this information for other apps
		 the following does not have any meaning, it's just an example
		*/
		hello_world.hello = i + 1;

		PX4_INFO("Hello world(puslish):\\t%d", hello_world.hello);
		orb_publish(ORB_ID(ext_hello_world), hello_world_pub, &hello_world);
	
	
	PX4_INFO("px4_custom_uorb_publish exiting");
	
	return 0;


int px4_custom_uorb_main(int argc, char *argv[])

	int task_subscribe, task_publish;

	task_publish = px4_task_spawn_cmd(TASK_NAME_CUSTOM_UORB_PUBLISH, SCHED_DEFAULT, SCHED_PRIORITY_DEFAULT, 2000, px4_custom_uorb_publish, argv);
	PX4_INFO("creating %s task_publish = %d", TASK_NAME_CUSTOM_UORB_PUBLISH, task_publish);
	
	sleep(1);
		
	task_subscribe = px4_task_spawn_cmd(TASK_NAME_CUSTOM_UORB_SUBSCRIBE, SCHED_DEFAULT, SCHED_PRIORITY_DEFAULT, 2000, px4_custom_uorb_subscribe, argv);
	PX4_INFO("creating %s task_subscribe = %d", TASK_NAME_CUSTOM_UORB_SUBSCRIBE, task_subscribe);
	
	while(px4_task_is_running(TASK_NAME_CUSTOM_UORB_SUBSCRIBE) || px4_task_is_running(TASK_NAME_CUSTOM_UORB_PUBLISH))
		sleep(1);
	

	PX4_INFO("px4_custom_uorb_main exiting");

	return 0;

整个DEMO结构如下所示：

目录结构
 ├── PX4-Autopilot
 │      └── build/px4_sitl_default
 │          ├── external_modules
 │          │    └── examples
 │          │         └── px4_custom_uorb/libexamples__px4_custom_uorb.a
 │          ├── uORB
 │          │    └── topics/ext_hello_world.h
 │          └── msg
 │               └── ttopics_sources/ext_hello_world.cpp
 └── PX4-ExternalModule
        ├── msg
        │   ├── CMakeLists.txt
        │   └── ext_hello_world.msg
        └── src
            ├── CMakeLists.txt
            └── examples
                └── px4_custom_uorb
                    ├── CMakeLists.txt
                    ├── Kconfig
                    └── px4_custom_uorb.c

完整的PX4-ExternalModule代码，请链接下载。

3. 编译执行结果

基于SITL仿真环境，在PX4-Autopilot目录下，进行编译；

$ make px4_sitl EXTERNAL_MODULES_LOCATION=../PX4-ExternalModule/

然后，执行仿真环境；

$ make px4_sitl jmavsim

最后，测试下效果。

pxh> px4_custom_uorb 
INFO  [px4_custom_uorb] creating orb publish task_publish = 13
INFO  [px4_custom_uorb] creating orb subscribe task_subscribe = 14
INFO  [px4_custom_uorb] Hello world(subscribe):	0
INFO  [px4_custom_uorb] Hello world(puslish):	1
INFO  [px4_custom_uorb] Hello world(subscribe):	1
INFO  [px4_custom_uorb] Hello world(puslish):	2
INFO  [px4_custom_uorb] Hello world(subscribe):	2
INFO  [px4_custom_uorb] Hello world(puslish):	3
INFO  [px4_custom_uorb] Hello world(subscribe):	3
INFO  [px4_custom_uorb] Hello world(puslish):	4
INFO  [px4_custom_uorb] Hello world(subscribe):	4
INFO  [px4_custom_uorb] Hello world(puslish):	5
INFO  [px4_custom_uorb] px4_custom_uorb_publish exiting
INFO  [px4_custom_uorb] Hello world(subscribe):	5
ERROR [px4_custom_uorb] Got no data within a second
ERROR [px4_custom_uorb] Got no data within a second
INFO  [px4_custom_uorb] px4_custom_uorb_subscribe exiting
INFO  [px4_custom_uorb] px4_custom_uorb_main exiting

4. 参考资料

【1】uorb messaging
【2】out of tree uorb message definitions