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 <px4_config.h>
#include <px4_tasks.h>
#include <px4_posix.h>
#include <unistd.h>
#include <stdio.h>
#include <poll.h>
#include <string.h>
#include <uORB/uORB.h>
#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/rw_uart.h>

static bool thread_should_exit = false;
static
4000
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
c197
<mail@example.com>
*/

#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/rw_uart.h>

__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 <stdio.h>
#include <wiringPi.h>
#include <wiringSerial.h>
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