Pixhawk固件PX4之串口通讯

本文主要是介绍Pixhawk固件PX4之串口通讯，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

1、目的

为进一步扩展pixhawk的接口及功能，通过pixhawk现有接口（串口、I2C等）连接外部设备来实现，本节内容主要介绍串口通讯方式。

2、测试平台

硬件：pixhawk 2.4.8

px4固件版本：1.9.0

pixhawk串口采用SERIAL4: /dev/ttyS6，连接图如下：

3、功能实现

主要实现pixhawk从STM32串口端读取数据，并将数据发给PC，通过串口调试助手查看。

pixhawk端代码参考网上pixhawk串口通讯代码，具体如下：

/*** @file px4_uorb_subs.c*/#include <stdio.h>
#include <termios.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <errno.h>
#include <drivers/drv_hrt.h>
#include <systemlib/err.h>
#include <fcntl.h>
#include <systemlib/mavlink_log.h>#include <px4_defines.h>
#include <px4_config.h>
#include <px4_posix.h>
#include <px4_shutdown.h>
#include <px4_tasks.h>
#include <px4_time.h>static bool thread_should_exit = false;		/**< px4_uorb_subs exit flag */
static bool thread_running = false;		/**< px4_uorb_subs status flag */
static int rw_uart_task;				/**< Handle of px4_uorb_subs task / thread */static int uart_init(char * uart_name);
static int set_uart_baudrate(const int fd, unsigned int baud);/*** daemon management function.*/
__EXPORT int rw_uart_main(int argc, char *argv[]);/*** Mainloop of daemon.*/
int rw_uart_thread_main(int argc, char *argv[]);/*** Print the correct usage.*/
static void usage(const char *reason);static void
usage(const char *reason)
{if (reason) {warnx("%s\n", reason);}warnx("usage: px4_uorb_adver {start|stop|status} [-p <additional params>]\n\n");
}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;/* 以新的配置填充结构体 *//* 设置某个选项，那么就使用"|="运算，* 如果关闭某个选项就使用"&="和"~"运算* */tcgetattr(fd, &uart_config); // 获取终端参数/* clear ONLCR flag (which appends a CR for every LF) */uart_config.c_oflag &= ~ONLCR;// 将NL转换成CR(回车)-NL后输出。/* 无偶校验，一个停止位 */uart_config.c_cflag &= ~(CSTOPB | PARENB);// CSTOPB 使用两个停止位，PARENB 表示偶校验/* 设置波特率 */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;}// 设置与终端相关的参数，TCSANOW 立即改变参数if ((termios_state = tcsetattr(fd, TCSANOW, &uart_config)) < 0) {warnx("ERR: %d (tcsetattr)\n", termios_state);return false;}return true;
}int uart_init(char * uart_name)
{int serial_fd = open(uart_name, O_RDWR | O_NOCTTY);/*Linux中，万物皆文件，打开串口设备和打开普通文件一样，使用的是open（）系统调用*/// 选项 O_NOCTTY 表示不能把本串口当成控制终端，否则用户的键盘输入信息将影响程序的执行if (serial_fd < 0) {err(1, "failed to open port: %s", uart_name);printf("failed to open port: %s\n", uart_name);return false;}printf("Open the %s\n",serial_fd);return serial_fd;
}/**
消息发布进程，会不断的接收自定义消息*/
int rw_uart_main(int argc, char *argv[])
{if (argc < 2) {usage("missing command");return 1;}if (!strcmp(argv[1], "start")) {if (thread_running) {warnx("px4_uorb_subs already running\n");/* this is not an error */return 0;}thread_should_exit = false;//定义一个守护进程rw_uart_task = px4_task_spawn_cmd("rw_uart",SCHED_DEFAULT,SCHED_PRIORITY_DEFAULT,//调度优先级2000,//堆栈分配大小rw_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("\trunning\n");}else {warnx("\tnot started\n");}return 0;}usage("unrecognized command");return 1;
}int rw_uart_thread_main(int argc, char *argv[])
{char data = '0';//char out_buf[5]="endl";char buffer[5] = "";	/** 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("/dev/ttyS6");if (false == uart_read)return -1;if (false == set_uart_baudrate(uart_read, 9600)) {printf("[JXF]set_uart_baudrate is failed\n");return -1;}printf("[JXF]uart init is successful\n");//warnx("[rw_uart] starting\n");thread_running = true;//write(uart_read, &out_buf[0],4);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;write(uart_read, &buffer[i], sizeof(buffer[i]));data = '0';usleep(5000);//5ms pause}printf("%s\n", buffer);}printf("rw_uart TX-test:running!\n");usleep(1000000);}//write(uart_read, &out_buf[0],4);warnx("[rw_uart] exiting.\n");thread_running = false;int fd=close(uart_read);printf("close stauts: %d\n",fd);return 0;
}

4、实验结果

QGC端的Mavlink Console端输出结果：