Pixhawk--uORB深入学习
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注：本文转载自 博主：FreeApe 博客：《PX4/Pixhawk---uORB深入理解和应用》
The Instructions of uORB
『PX4/Pixhawk』 『软件体系结构』 『uORB』 『主题发布』 『主题订阅』
1 简介
1.1 PX4/Pixhawk的软件体系结构
PX4/Pixhawk的软件体系结构主要被分为四个层次，这可以让我们更好的理解PX4/Pixhawk的软件架构和运作：
- 应用程序的API：这个接口提供给应用程序开发人员，此API旨在尽可能的精简、扁平及隐藏其复杂性。
- 应用程序框架: 这是为操作基础飞行控制的默认程序集（节点）。
- 库: 这一层包含了所有的系统库和基本交通控制的函数。
- 操作系统: 最后一层提供硬件驱动程序，网络，UAVCAN和故障安全系统。
uORB(Micro Object Request Broker,微对象请求代理器)是PX4/Pixhawk系统中非常重要且关键的一个模块，它肩负了整个系统的数据传输任务，所有的传感器数据、GPS、PPM信号等都要从芯片获取后通过uORB进行传输到各个模块进行计算处理。实际上uORB是一套跨「进程」 的IPC通讯模块。在Pixhawk中， 所有的功能被独立以进程模块为单位进行实现并工作。而进程间的数据交互就由为重要，必须要能够符合实时、有序的特点。
Pixhawk使用的是NuttX实时ARM系统，uORB实际上是多个进程打开同一个设备文件，进程间通过此文件节点进行数据交互和共享。进程通过命名的「总线」交换的消息称之为「主题」(topic)，在Pixhawk 中，一个主题仅包含一种消息类型，通俗点就是数据类型。每个进程可以「订阅」或者「发布」主题，可以存在多个发布者，或者一个进程可以订阅多个主题，但是一条总线上始终只有一条消息。
1.2 PX4/Pixhawk应用程序框架
应用层中操作基础飞行的应用之间都是隔离的，这样提供了一种安保模式，以确保基础操作独立的高级别系统状态的稳定性。而沟通它们的就是uORB。
2 uORB文件夹说明
2.1 uORB文件夹结构
2.2 文件/目录说明
topics : 系统通用接口定义的标准主题,比如电池电量转态、GPS的位置参数等
module.mk : uORB模块makefile文件
objects_common.cpp: 通用接口标准主题定义集合，如添加新主题在这里定义
ORBMap.hpp : 对象请求器节点链表管理（驱动节点）
ORBSet.hpp : 对象请求器节点管理（非驱动节点）
Publication.cpp : 在不同的发布中遍历使用
Publication.hpp : 在不同的发布中遍历使用
Subscription.cpp : 在不同的订阅中遍历使用
Subscription.hpp : 在不同的订阅中遍历使用
uORB.cpp : uORB的实现
uORB.h : uORB头文件
uORBCommon.hpp : uORB公共部分变量定义实现
uORBCommunicator.hpp : 远程订阅的接口实现，实现了对不同的通信通道管理，如添加/移除订阅者，可以基于TCP/IP或fastRPC;传递给通信链路的实现，以提供在信道上接收消息的回调。
uORBDevices.hpp :
uORBDevices_nuttx.cpp : 节点操作，close,open,read,write
uORBDevices_nuttx.hpp :
uORBDevices_posix.cpp :
uORBDevices_posix.hpp :
uORBMain.cpp : uORB入口
uORBManager.hpp : uORB功能函数实现头文件
uORBManager_nuttx.cpp : uORB功能函数实现(Nuttx)
uORBManager_posix.cpp : uORB功能函数实现(Posix)
uORBTest_UnitTest.cpp : uORB测试
uORBTest_UnitTest.hpp : uORB测试头文件，包括主题定义和声明等
uORBUtiles.cpp :
uORBUtiles.hpp :
3 常用函数功能解析
int poll(struct pollfd fds[], nfds_t nfds, int timeout)
功能：监控文件描述符（多个）；说明：timemout=0,poll()函数立即返回而不阻塞；timeout=INFTIM(-1),poll()会一直阻塞下去，直到检测到return > 0；参数： fds:struct pollfd结构类型的数组； nfds:用于标记数组fds中的结构体元素的总数量； timeout:是poll函数调用阻塞的时间，单位：毫秒；返回值： >0：数组fds中准备好读、写或出错状态的那些socket描述符的总数量； ==0:poll()函数会阻塞timeout所指定的毫秒时间长度之后返回; -1:poll函数调用失败；同时会自动设置全局变量errno；int orb_subscribe(const struct orb_metadata *meta)
功能：订阅主题（topic）;说明：即使订阅的主题没有被公告，但是也能订阅成功；但是在这种情况下，却得不到数据，直到主题被公告；参数： meta:uORB元对象，可以认为是主题id，一般是通过ORB_ID(主题名)来赋值；返回值： 错误则返回ERROR;成功则返回一个可以读取数据、更新话题的句柄；如果待订阅的主题没有定义或声明则会返回-1，然后会将errno赋值为ENOENT;eg: int fd = orb_subscribe(ORB_ID(topicName));int orb_copy(const struct orb_metadata *meta, int handle, void *buffer)
功能：从订阅的主题中获取数据并将数据保存到buffer中；参数： meta:uORB元对象，可以认为是主题id，一般是通过ORB_ID(主题名)来赋值; handle:订阅主题返回的句柄； buffer:从主题中获取的数据；返回值： 返回OK表示获取数据成功，错误返回ERROR;否则则有根据的去设置errno;eg: struct sensor_combined_s raw; orb_copy(ORB_ID(sensor_combined), sensor_sub_fd, &raw);orb_advert_t orb_advertise(const struct orb_metadata *meta, const void *data)
功能：公告发布者的主题；说明：在发布主题之前是必须的；否则订阅者虽然能订阅，但是得不到数据；参数： meta:uORB元对象，可以认为是主题id，一般是通过ORB_ID(主题名)来赋值; data:指向一个已被初始化，发布者要发布的数据存储变量的指针；返回值：错误则返回ERROR;成功则返回一个可以发布主题的句柄；如果待发布的主题没有定义或声明则会返回-1，然后会将errno赋值为ENOENT;eg: struct vehicle_attitude_s att; memset(&att, 0, sizeof(att)); int att_pub_fd = orb_advertise(ORB_ID(vehicle_attitude), &att);int orb_publish(const struct orb_metadata *meta, orb_advert_t handle, const void *data)
功能：发布新数据到主题；参数： meta:uORB元对象，可以认为是主题id，一般是通过ORB_ID(主题名)来赋值; handle:orb_advertise函数返回的句柄； data:指向待发布数据的指针；返回值：OK表示成功；错误返回ERROR；否则则有根据的去设置errno;eg: orb_publish(ORB_ID(vehicle_attitude), att_pub_fd, &att);int orb_set_interval(int handle, unsigned interval)
功能：设置订阅的最小时间间隔；说明：如果设置了，则在这间隔内发布的数据将订阅不到；需要注意的是，设置后，第一次的数据订阅还是由起初设置的频率来获取，参数： handle:orb_subscribe函数返回的句柄； interval:间隔时间，单位ms;返回值：OK表示成功；错误返回ERROR；否则则有根据的去设置errno;eg: orb_set_interval(sensor_sub_fd, 1000);orb_advert_t orb_advertise_multi(const struct orb_metadata *meta, const void *data, int *instance, int priority)
功能：设备/驱动器的多个实例实现公告，利用此函数可以注册多个类似的驱动程序；说明：例如在飞行器中有多个相同的传感器，那他们的数据类型则类似，不必要注册几个不同的话题；参数： meta:uORB元对象，可以认为是主题id，一般是通过ORB_ID(主题名)来赋值; data:指向一个已被初始化，发布者要发布的数据存储变量的指针； instance:整型指针，指向实例的ID（从0开始）； priority:实例的优先级。如果用户订阅多个实例，优先级的设定可以使用户使用优先级高的最优数据源；返回值： 错误则返回ERROR;成功则返回一个可以发布主题的句柄；如果待发布的主题没有定义或声明则会返回-1，然后会将errno赋值为ENOENT;eg: struct orb_test t; t.val = 0; int instance0; orb_advert_t pfd0 = orb_advertise_multi(ORB_ID(orb_multitest), &t, &instance0, ORB_PRIO_MAX);int orb_subscribe_multi(const struct orb_metadata *meta, unsigned instance)
功能：订阅主题（topic）;说明：通过实例的ID索引来确定是主题的哪个实例；参数： meta:uORB元对象，可以认为是主题id，一般是通过ORB_ID(主题名)来赋值; instance:主题实例ID;实例ID=0与orb_subscribe()实现相同；返回值： 错误则返回ERROR;成功则返回一个可以读取数据、更新话题的句柄；如果待订阅的主题没有定义或声明则会返回-1，然后会将errno赋值为ENOENT;eg: int sfd1 = orb_subscribe_multi(ORB_ID(orb_multitest), 1);int orb_unsubscribe(int handle)
功能：取消订阅主题；参数： handle:主题句柄；返回值： OK表示成功；错误返回ERROR;否则则有根据的去设置errno;eg: ret = orb_unsubscribe(handle);int orb_check(int handle, bool *updated)
功能：订阅者可以用来检查一个主题在发布者上一次更新数据后，有没有订阅者调用过ob_copy来接收、处理过；说明：如果主题在在被公告前就有人订阅，那么这个API将返回“not-updated”直到主题被公告。可以不用poll，只用这个函数实现数据的获取。参数： handle:主题句柄； updated:如果当最后一次更新的数据被获取了，检测到并设置updated为ture;返回值： OK表示检测成功；错误返回ERROR;否则则有根据的去设置errno;eg: if (PX4_OK != orb_check(sfd, &updated)) { return printf("check(1) failed"); } if (updated) { return printf("spurious updated flag"); } //or bool updated; struct random_integer_data rd; /* check to see whether the topic has updated since the last time we read it */ orb_check(topic_handle, &updated); if (updated) { /* make a local copy of the updated data structure */ orb_copy(ORB_ID(random_integer), topic_handle, &rd); printf("Random integer is now %d\n", rd.r); }int orb_stat(int handle, uint64_t *time)
功能：订阅者可以用来检查一个主题最后的发布时间；参数： handle:主题句柄； time:存放主题最后发布的时间；0表示该主题没有发布或公告；返回值： OK表示检测成功；错误返回ERROR;否则则有根据的去设置errno;eg: ret = orb_stat(handle,time);int orb_exists(const struct orb_metadata *meta, int instance)
功能：检测一个主题是否存在；参数： meta:uORB元对象，可以认为是主题id，一般是通过ORB_ID(主题名)来赋值; instance:ORB 实例ID;返回值： OK表示检测成功；错误返回ERROR;否则则有根据的去设置errno;eg: ret = orb_exists(ORB_ID(vehicle_attitude),0);int orb_priority(int handle, int *priority)
功能：获取主题优先级别；参数： handle:主题句柄； priority:存放获取的优先级别；返回值： OK表示检测成功；错误返回ERROR;否则则有根据的去设置errno;eg: ret = orb_priority(handle,&priority);4 例程
4.1 例程前准备工作
archives已编译完成(注：2015/10/6号后改为cmake编译系统，不再需要编译archives了)；
添加一个新的模块
- 在Firmware/src/modules中添加一个新的文件夹，命名为px4_simple_app
- 在px4_simple_app文件夹中创建module.mk文件，并输入以下内容：
- MODULE_COMMAND = px4_simple_app
- SRCS = px4_simple_app.c
- 在px4_simple_app文件夹中创建px4_simple_app.c文件
<code class="language-c++ hljs java has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;"><span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/** *<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @file</span> px4_simple_app.c * Minimal application example for PX4 autopilot. */</span>#include <nuttx/config.h>#include <stdio.h>#include <errno.h>__EXPORT <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> px4_simple_app_main(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> argc, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> *argv[]);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> px4_simple_app_main(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> argc, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> *argv[]){ printf(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Hello Sky!\n"</span>); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> OK;}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; opacity: 0.0701001;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul>- 注册新添加的应用到NuttShell中，并编译上传
- Firmware/makefiles/config_px4fmu-v2_default.mk文件中添加如下内容：
- MODULES += modules/px4_simple_app
- 编译
- make clean
- make px4fmu-v2_default
- 上传到板子中
- make upload px4fmu-v2_default
- Firmware/makefiles/config_px4fmu-v2_default.mk文件中添加如下内容：
- 在QGC 中的Terminal(终端)中运行新应用
- nsh > px4_simple_app
接下来的代码修改均是基于此应用。
4.2 订阅主题
sensor_combined主题是官方提供的通用接口标准主题。
<code class="language-c++ hljs cpp has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/** * @file px4_simple_app.c * Minimal application example for PX4 autopilot */</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <nuttx/config.h></span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <unistd.h></span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <stdio.h></span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <poll.h></span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <uORB/uORB.h></span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <uORB/topics/sensor_combined.h></span>__EXPORT <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> px4_simple_app_main(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> argc, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> *argv[]);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> px4_simple_app_main(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> argc, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> *argv[]){ <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Hello Sky!\n"</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*订阅sensor_combined 主题*/</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> sensor_sub_fd = orb_subscribe(ORB_ID(sensor_combined)); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*一个应用可以等待多个主题，在这里只等待一个主题*/</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> pollfd fds[] = { { .fd = sensor_sub_fd, .events = POLLIN }, <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 这里可以添加更多的文件描述符； * { .fd = other_sub_fd, .events = POLLIN }, */</span> }; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> error_counter = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*poll函数调用阻塞的时间为1s*/</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> poll_ret = poll(fds, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1000</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*处理poll返回的结果 */</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (poll_ret == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 这表示时间溢出了，在1s内没有获取到发布者的数据 */</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"[px4_simple_app] Got no data within a second\n"</span>); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (poll_ret < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 出现问题 */</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (error_counter < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span> || error_counter % <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">50</span> == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* use a counter to prevent flooding (and slowing us down) */</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"[px4_simple_app] ERROR return value from poll(): %d\n"</span> , poll_ret); } error_counter++; } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (fds[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>].revents & POLLIN) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*从文件描述符中获取订阅的数据*/</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> sensor_combined_s raw; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* copy sensors raw data into local buffer */</span> orb_copy(ORB_ID(sensor_combined), sensor_sub_fd, &raw); <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"[px4_simple_app] Accelerometer:\t%8.4f\t%8.4f\t%8.4f\n"</span>, (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span>)raw.accelerometer_m_s2[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>], (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span>)raw.accelerometer_m_s2[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>], (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span>)raw.accelerometer_m_s2[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>]); } <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 如果有更多的文件描述符，可以这样： * if (fds[1..n].revents & POLLIN) {} */</span> } } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; opacity: 0.0701001;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li></ul>测试需要在QGC终端启动uORB和初始化该传感器，最后运行应用： nsh > uorb start nsh > sh /etc/init.d/rc.sensors nsh > px4_simple_app &4.3 订阅和发布主题
sensor_combined主题是官方提供的通用接口标准主题。
vehicle_attitude主题是官方提供的通用接口标准主题。
程序流程图如下：
<code class="language-c++ hljs cpp has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/** * @file px4_simple_app.c * Minimal application example for PX4 autopilot */</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <nuttx/config.h></span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <unistd.h></span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <stdio.h></span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <poll.h></span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <uORB/uORB.h></span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <uORB/topics/sensor_combined.h></span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <uORB/topics/vehicle_attitude.h></span>__EXPORT <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> px4_simple_app_main(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> argc, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> *argv[]);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> px4_simple_app_main(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> argc, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> *argv[]){ <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Hello Sky!\n"</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 订阅 sensor_combined 主题 */</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> sensor_sub_fd = orb_subscribe(ORB_ID(sensor_combined)); orb_set_interval(sensor_sub_fd, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1000</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 公告 attitude 主题 */</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> vehicle_attitude_s att; <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">memset</span>(&att, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">sizeof</span>(att)); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> att_pub_fd = orb_advertise(ORB_ID(vehicle_attitude), &att); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*一个应用可以等待多个主题，在这里只等待一个主题*/</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> pollfd fds[] = { { .fd = sensor_sub_fd, .events = POLLIN }, <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* there could be more file descriptors here, in the form like: * { .fd = other_sub_fd, .events = POLLIN }, */</span> }; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> error_counter = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* wait for sensor update of 1 file descriptor for 1000 ms (1 second) */</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> poll_ret = poll(fds, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1000</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* handle the poll result */</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (poll_ret == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* this means none of our providers is giving us data */</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"[px4_simple_app] Got no data within a second\n"</span>); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (poll_ret < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* this is seriously bad - should be an emergency */</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (error_counter < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span> || error_counter % <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">50</span> == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* use a counter to prevent flooding (and slowing us down) */</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"[px4_simple_app] ERROR return value from poll(): %d\n"</span> , poll_ret); } error_counter++; } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (fds[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>].revents & POLLIN) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* obtained data for the first file descriptor */</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> sensor_combined_s raw; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* copy sensors raw data into local buffer */</span> orb_copy(ORB_ID(sensor_combined), sensor_sub_fd, &raw); <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"[px4_simple_app] Accelerometer:\t%8.4f\t%8.4f\t%8.4f\n"</span>, (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span>)raw.accelerometer_m_s2[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>], (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span>)raw.accelerometer_m_s2[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>], (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span>)raw.accelerometer_m_s2[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>]); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 赋值 att 并且发布这些数据给其他的应用 */</span> att.roll = raw.accelerometer_m_s2[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>]; att.pitch = raw.accelerometer_m_s2[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>]; att.yaw = raw.accelerometer_m_s2[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>]; orb_publish(ORB_ID(vehicle_attitude), att_pub_fd, &att); } <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* there could be more file descriptors here, in the form like: * if (fds[1..n].revents & POLLIN) {} */</span> } } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; opacity: 0.0701001;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li></ul>4.4 创建自己的主题
官方提供的通用接口标准主题都放在了topics文件夹下了。如果要定义我们自己的主题，比如我们新添加了超声波传感器，为了将超声波传感器的数据发布出去给其他需要的应用订阅，那么久需要创建我们的主题了。
- 主题头文件（mytopic.h）
- ORB_DECLARE(myTopicName);//声明一个主题
- 定义一个存放发布数据的结构体；
- 主题源文件（mytopic.c）
- ORB_DEFINE(myTopicName);//定义一个主题
- 初始化发布数据
- 公告主题
- 发布主题数据
mytopic.h
<code class="language-c++ hljs cs has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 声明自定义主题，名字可以自定义，不过最好具有一定的意义，如下为随机产生整数数据 */</span>ORB_DECLARE(random_integer);<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 定义要发布的数据结构体 */</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> random_integer_data { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> r;};</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; opacity: 0.0701001;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>mytopic_publish.c
<code class="language-c++ hljs vala has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <topic.h></span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 定义主题 */</span>ORB_DEFINE(random_integer);<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 待发布的主题句柄 */</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> topic_handle;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> init(){ <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 随机产生一个数初始化数据结构体 */</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> random_integer_data rd = { .r = random(), }; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 公告主题 */</span> topic_handle = orb_advertise(ORB_ID(random_integer), &rd);}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> update_topic(){ <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 产生新的数据 */</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> random_integer_data rd = { .r = random(), }; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 发布主题，更新数据 */</span> orb_publish(ORB_ID(random_integer), topic_handle, &rd);}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; opacity: 0.0701001;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li></ul> 对于订阅者来说，就可以参考主题「4.2 订阅例程」了。不过这里还是提供下简单处理例程：
mytopic_subscriber.c
<code class="language-c++ hljs applescript has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">#include <topic.h></span>/* 订阅主题的句柄*/static int topic_handle;int init(){ /* 订阅主题 */ topic_handle = orb_subscribe(ORB_ID(random_integer));}void check_topic(){ bool updated; struct random_integer_data rd; /* check <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> see whether <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> topic has updated <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">since</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">last</span> <span class="hljs-property" style="box-sizing: border-box;">time</span> we <span class="hljs-command" style="box-sizing: border-box;">read</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">it</span> */ orb_check(topic_handle, &updated); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (updated) { /* make a <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">local</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">copy</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">of</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> updated data structure */ orb_copy(ORB_ID(random_integer), topic_handle, &rd); printf(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Random integer is now %d\n"</span>, rd.r); }}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; opacity: 0.0701001;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li></ul>5 参考资料
http://www.pixhawk.com/start?id=zh/dev/px4_simple_app
http://www.pixhawk.com/dev/shared_object_communication
http://blog.arm.so/armteg/pixhawk/183-0503.html
http://pixhawk.org/start?id=dev/software_architecture
http://www.pixhawk.com/dev/add_uorb_topic?s[]=objects&s[]=common
1 0
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