PX4固件通过UART连接串口读取超声波，和树莓派3通信

添加串口读取程序

首先在Firmware/msg文件夹下添加rw_uart.msg

char[5] datastr
int16 data
#TOPICS rw_uart

记住在这一文件夹下的CMakeLists.txt下注册这个msg，添加rw_uart.msg即可。

上面的文件make之后会自动产生rw_uart.h头文件，里面会有结构体rw_uart_s,存取了我们刚才定义的data和datastr。然后在Firmware/src/module文件夹下新建文件夹rw_uart，在里面添加CMakeLists.txt和rw_uart.c。
CMakeLists.txt内容如下：

set(MODULE_CFLAGS)
px4_add_module(
        MODULE modules__rw_uart
        MAIN rw_uart
    COMPILE_FLAGS
        -Os
    SRCS
                rw_uart.c
    DEPENDS
        platforms__common
    )

读取程序rw_uart.c如下：

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

static bool thread_should_exit = false;
static bool thread_running = false;
static int daemon_task;


__EXPORT int rw_uart_main(int argc, char *argv[]);
int rw_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)//自动选取波特率
{
    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;
    /**
/*termios 函数族提供了一个常规的终端接口，用于控制非同步通信端口。 这个结构包含了至少下列成员：
/*tcflag_t c_iflag;      /* 输入模式 */
/*tcflag_t c_oflag;      /* 输出模式 */
/*tcflag_t c_cflag;      /* 控制模式 */
/*tcflag_t c_lflag;      /* 本地模式 */
/*cc_t c_cc[NCCS];       /* 控制字符 */
*/
    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: position_estimator_inav {start|stop|status} [param]\n\n");
    exit(1);
}

int rw_uart_main(int argc, char *argv[])
{
    if (argc < 2) {
        usage("[FC]missing command");
    }

    if (!strcmp(argv[1], "start")) {
        if (thread_running) {
            warnx("[FC]already running\n");
            exit(0);
        }

        thread_should_exit = false;
        daemon_task = px4_task_spawn_cmd("rw_uart",//任务接口句柄
                         SCHED_DEFAULT,
                         SCHED_PRIORITY_MAX - 5,
                         2000,
                         rw_uart_thread_main,
                         (argv) ? (char * const *)&argv[2] : (char * const *)NULL);
        exit(0);
    }

    if (!strcmp(argv[1], "stop")) {
        thread_should_exit = true;
        exit(0);
    }

    if (!strcmp(argv[1], "status")) {
        if (thread_running) {
            warnx("[FC]running");

        } else {
            warnx("[FC]stopped");
        }

        exit(0);
    }

    usage("unrecognized command");
    exit(1);
}

int rw_uart_thread_main(int argc, char *argv[])
{

    if (argc < 2) {
        errx(1, "[FC]need a serial port name as argument");
        usage("eg:");
    }

    const char *uart_name = argv[1];

    warnx("[FC]opening port %s", uart_name);
    char data = '0';
    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(uart_name);
    if(false == uart_read)return -1;
    if(false == set_uart_baudrate(uart_read,9600)){
        printf("[FC]set_uart_baudrate is failed\n");
        return -1;
    }
    printf("[FC]uart init is successful\n");

    thread_running = true;

    /*初始化数据结构体 */
    struct rw_uart_s sonardata;
    memset(&sonardata, 0, sizeof(sonardata));
    /* 公告主题 */
    orb_advert_t rw_uart_pub = orb_advertise(ORB_ID(rw_uart), &sonardata);


    while(!thread_should_exit){
        read(uart_read,&data,1);
        if(data == 'R'){//这个地方是模拟树莓派发送的R1100数据，在超声波处注释掉这个if条件语句，直接读取
            for(int i = 0;i <4;++i){

                read(uart_read,&data,1);

                buffer[i] = data;

                //data = '0';
            }
           // printf("%s\n",buffer);
            strncpy(sonardata.datastr,buffer,4);
            sonardata.data = atoi(sonardata.datastr);
           // printf("[YCM]sonar.data=%s\n",sonardata.datastr);
            orb_publish(ORB_ID(rw_uart), rw_uart_pub, &sonardata);
        }
    }

    warnx("[FC]exiting");
    thread_running = false;
    close(uart_read);

    fflush(stdout);
    return 0;
}

超声波和px4的硬件连接

首先说一下，这里用的是pixhawk的TELEM2口，TELEM1接口给的是数传。TELEM1和TELEM2接口是一样的，分布如下：

对于UART主要是TX,RX,VCC,GND这四个接口，这里面我用的是HC-SRO4超声波传感器，这个传感器给的是触发信号，并没有直接给出距离，需要自己通过计时器来获得距离，这个找度娘就可以了，这里验证的是能读到数据。TELEM2和超声波的连接方式：VCC-VCC，TX-RX，RX-TX，GND-GND，这里我的超声波的连接是：TX-Trigger，RX-Echo。最后的结果如下：

这里我使用的是数据订阅的方式——uORB通信机制
在Firmware/src/examples/px4_simple_app文件夹下，修改px4_simple_app.c如下：

/****************************************************************************
 *
 *   Copyright (c) 2012-2015 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.
 *
 ****************************************************************************/

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

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#include 
#include 



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

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

    /* subscribe to rw_uart_sonar topic */
    int sonar_sub_fd = orb_subscribe(ORB_ID(rw_uart));
    /*设置以一秒钟接收一次，并打印出数据*/
    orb_set_interval(sonar_sub_fd, 1000);
   // bool updated;
    struct rw_uart_s sonar;

    /*接收数据方式一：start*/
    /*
    while(true){
        orb_check(sonar_sub_fd, &updated);

        if (updated) {
            orb_copy(ORB_ID(rw_uart_sonar), sonar_sub_fd, &sonar);
            printf("[YCM]sonar.data=%d\n",sonar.data);
        }
        //else printf("[YCM]No soanar data update\n");
    }
    */
    /*接收数据方式一：end*/

    /*接收数据方式二：start*/
    /* one could wait for multiple topics with this technique, just using one here */
    struct pollfd fds[] = {
        { .fd = sonar_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++) {
        /* 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_simple_app] 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_simple_app] 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 rw_uart_s sonar;
                /* copy sensors raw data into local buffer */
                orb_copy(ORB_ID(rw_uart), sonar_sub_fd, &sonar);
                printf("[px4_simple_app] Sonar data:\t%s\t%d\n",
                       sonar.datastr,
                       sonar.data);
            }

            /* there could be more file descriptors here, in the form like:
             * if (fds[1..n].revents & POLLIN) {}
             */
        }
    }
    /*接收数据方式二：end*/

    return 0;
}

树莓派3和pixhawk通信

树莓派和pixhawk的连接如下:

这里切记不要把VCC和GND的GPIO口接反了，很容易把树莓派的CPU 烧了（我就烧了一次），如果都供电了，建议就不要连接两者之间的VCC。树莓派的发送程序如下：

#include  
#include 
#include  
int main() 
{ 
int fd; 
char data[5]=“R1100”; 
int flag=1;
if(wiringPiSetup()<0)return 1; 
if((fd=serialOpen("/dev/ttyAMA0",9600))<0) return 1;
printf("serial test start ...\n");
serialPrintf(fd,"Hello world!\n"); 
while(flag) 
    { 
      serialPrintf(fd,data);//向串口设备发送data数据 
      delay(300);
        while(serialDataAvail(fd)) 
          { 
          printf("->%3d\n",serialGetchar(fd));
          flag=0; fflush(stdout); 
          } 
     } 
serialFlush(fd); 
serialClose(fd); 
return 0;
 } 

首先需要说一下，这个串口发送程序需要安装wiringPi库，编译运行命令如下：

gcc –Wall uart.c –o uart –lwiringPi
sudo ./uart

这几天坑埋完了，上各种博客链接：
树莓派和pixhawk连接
struct termios结构体详解
树莓派串口发送数据
PX4原生固件添加串口读取传感器