Pixhawk原生固件PX4之串口添加读取传感器实现

本博客承接前一篇，对FreeApe的串口添加超声波传感器博文后半部分进行学习。

为什么叫前奏呢，因为用了伪传感器，把单片机用串口发送的有规律的数据当作了传感器读取到的数据。但是无碍的。

开发环境：Ubuntu Firmware 1.4.1

在无人机运行时，首先是要将应用随系统启动时就启动起来的，且将获得的超声波数据不断的发布出去，从而让其他应用得以订阅使用。这里也使用Pixhawk里面的通用模式，即主线程，检测app命令输入，创建一个线程来不断的发布数据。

定义主题和发布主题

在Firmware/msg目录下新建read_uart_sensor.msg文件。传送门

char[4] datastr
int16 data#TOPICS read_uart_sensor

并添加到CMakeLists.txt中，编译后自动生成uORB/topics/read_uart_sensor.h头文件

串口读取例程

在Firmware/src/modules目录下新建文件夹read_uart_sensor

添加文件read_uart_sensor.c。传送门

/** read_uart_sensor.c* * read sensor through uart*/#include <stdio.h>
#include <termios.h>
#include <unistd.h>
#include <stdbool.h>
#include <errno.h>
#include <drivers/drv_hrt.h>
#include <string.h>
#include <systemlib/err.h>
#include <systemlib/systemlib.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <uORB/topics/read_uart_sensor.h>__EXPORT int read_uart_sensor_main(int argc, char *argv[]);static bool thread_should_exit = false; /*Ddemon exit flag*/
static bool thread_running = false;  /*Daemon status flag*/
static int daemon_task;/*** Main loop*/
int read_uart_thread_main(int argc, char *argv[]);static int uart_init(const char * uart_name);
static int set_uart_baudrate(const int fd, unsigned int baud);
static void usage(const char *reason);int set_uart_baudrate(const int fd, unsigned int baud)
{int speed;switch (baud) {case 9600:   speed = B9600;   break;case 19200:  speed = B19200;  break;case 38400:  speed = B38400;  break;case 57600:  speed = B57600;  break;case 115200: speed = B115200; break;default:warnx("ERR: baudrate: %d\n", baud);return -EINVAL;}struct termios uart_config;int termios_state;/* fill the struct for the new configuration */tcgetattr(fd, &uart_config);/* clear ONLCR flag (which appends a CR for every LF) */uart_config.c_oflag &= ~ONLCR;/* no parity, one stop bit */uart_config.c_cflag &= ~(CSTOPB | PARENB);/* set baud rate */if ((termios_state = cfsetispeed(&uart_config, speed)) < 0) {warnx("ERR: %d (cfsetispeed)\n", termios_state);return false;}if ((termios_state = cfsetospeed(&uart_config, speed)) < 0) {warnx("ERR: %d (cfsetospeed)\n", termios_state);return false;}if ((termios_state = tcsetattr(fd, TCSANOW, &uart_config)) < 0) {warnx("ERR: %d (tcsetattr)\n", termios_state);return false;}return true;
}int uart_init(const char * uart_name)
{int serial_fd = open(uart_name, O_RDWR | O_NOCTTY);if (serial_fd < 0) {err(1, "failed to open port: %s", uart_name);return false;}return serial_fd;
}static void usage(const char *reason)
{if (reason) {fprintf(stderr, "%s\n", reason);}fprintf(stderr, "usage: read_uart_sensor {start|stop|status} [param]\n\n");exit(1);
}int read_uart_sensor_main(int argc, char *argv[])
{if (argc < 2) {usage("[Fantasy]missing command");}if (!strcmp(argv[1], "start")) {if (thread_running) {warnx("[Fantasy]already running\n");return 0;}thread_should_exit = false;daemon_task = px4_task_spawn_cmd("read_uart_sensor",SCHED_DEFAULT,SCHED_PRIORITY_MAX - 5,2000,read_uart_thread_main,(argv) ? (char * const *)&argv[2] : (char * const *)NULL);return 0;}if (!strcmp(argv[1], "stop")) {thread_should_exit = true;return 0;}if (!strcmp(argv[1], "status")) {if (thread_running) {warnx("[Fantasy]running");return 0;} else {warnx("[Fantasy]stopped");return 1;}return 0;}usage("unrecognized command");return 1;
}int read_uart_thread_main(int argc, char *argv[])
{if (argc < 2) {errx(1, "[Fantasy]need a serial port name as argument");usage("eg:");}const char *uart_name = argv[1];warnx("[Fantasy]opening port %s", uart_name);char data = '0';char buffer[4] = "";/** TELEM1 : /dev/ttyS1* TELEM2 : /dev/ttyS2* GPS    : /dev/ttyS3* NSH    : /dev/ttyS5* SERIAL4: /dev/ttyS6* N/A    : /dev/ttyS4* IO DEBUG (RX only):/dev/ttyS0*/int uart_read = uart_init(uart_name);if(false == uart_read)return -1;if(false == set_uart_baudrate(uart_read,9600)){printf("[Fantasy]set_uart_baudrate is failed\n");return -1;}printf("[Fantasy]uart init is successful\n");thread_running = true;/*初始化数据结构体 */struct read_uart_sensor_s sensordata;memset(&sensordata, 0, sizeof(sensordata));/* 公告主题 */orb_advert_t read_uart_sensor_pub = orb_advertise(ORB_ID(read_uart_sensor), &sensordata);while(!thread_should_exit){read(uart_read,&data,1);if(data == 'R'){for(int i = 0;i <4;++i){read(uart_read,&data,1);buffer[i] = data;data = '0';}strncpy(sensordata.datastr,buffer,4);// 复制字符串Buffer中前４个数字到Datastr中sensordata.data = atoi(sensordata.datastr);//将字符串转换成整形数据//printf("[Fantasy]sensor.data=%d\n",sensordata.data);orb_publish(ORB_ID(read_uart_sensor), read_uart_sensor_pub, &sensordata);}}warnx("[Fantasy]exiting");thread_running = false;close(uart_read);fflush(stdout);return 0;
}

添加CMakeLists.txt文件

set(MODULE_CFLAGS)
px4_add_module(MODULE modules__read_uart_sensorMAIN read_uart_sensorCOMPILE_FLAGS-OsSRCSread_uart_sensor.cDEPENDSplatforms__common)
# vim: set noet ft=cmake fenc=utf-8 ff=unix :

在Firmware/cmake/configs/nuttx/nuttx_px4fmu-v2_default.cmake中注册该模块

测试发布的主题

测试可以随便一个启动的app中进行主题订阅，然后将订阅的数据打印出来，看是否是超声波的数据。这里新建一个应用px4_test进行测试。

px4_test.c

/** px4_test.c*  * test the uart sensor app*/
#include <px4_config.h>
#include <px4_tasks.h>
#include <px4_posix.h>
#include <unistd.h>
#include <stdio.h>
#include <poll.h>
#include <string.h>
#include <math.h>#include <uORB/uORB.h>
#include <uORB/topics/read_uart_sensor.h>__EXPORT int px4_test_main(int argc, char *argv[]);int px4_test_main(int argc, char *argv[])
{PX4_INFO("Hello Sky!\n");/* subscribe to rw_uart_sensor topic */int sensor_sub_fd = orb_subscribe(ORB_ID(read_uart_sensor));/*limit the update rate to 20 Hz */orb_set_interval(sensor_sub_fd, 50);/* 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++) { // infinite loop/* wait for sensor update of 1 file descriptor for 1000 ms (1 second) */int poll_ret = poll(fds, 1, 1000);/* handle the poll result */if (poll_ret == 0) {/* this means none of our providers is giving us data */printf("[px4_test] Got no data within a second\n");} 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) */printf("[px4_test] ERROR return value from poll(): %d\n", poll_ret);}error_counter++;} else {if (fds[0].revents & POLLIN) {/* obtained data for the first file descriptor */struct read_uart_sensor_s raw;/* copy sensors raw data into local buffer */orb_copy(ORB_ID(read_uart_sensor), sensor_sub_fd, &raw);PX4_INFO("[px4_test] sensor data:\t%s\t%d\n",raw.datastr,raw.data);}/* there could be more file descriptors here, in the form like:* if (fds[1..n].revents & POLLIN) {}*/}}PX4_INFO("exiting");return 0;
}

编译并上传固件
- make px4fmu-v2_default upload
在NSH中测试
- read_uart_sensor start /dev/ttyS2
- px4_test

这个大有搞头！

添加到脚本文件

在rcS中仿照mavlink的启动方式添加了上面的应用，使得与ttyS2连接的外设默认为启动状态

现在如果ttyS2上连接了设备，就是自动启动的，在nsh中可以直接调用px4_test应用就可以读取数据了，与使用px4_simple_app读取内部传感器的方式无异。

大致模型就是这样了，接下来就是具体的代码优化以及应用了。

By Fantasy