Pixhawk原生固件PX4之串口添加读取传感器实现

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

__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_sensor
        MAIN read_uart_sensor
    COMPILE_FLAGS
        -Os
    SRCS
                read_uart_sensor.c
    DEPENDS
        platforms__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 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#include 
#include 

__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。

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