ROS学习篇第（六）篇：通信

2023-05-16

串口通信　ros-serial 包的使用

下载

	sudo apt-get install ros-melodic-serial  #ros为melodic版本

下载完查看以下重启终端，输入以下命令可以检测到serial包的路径说明已经安装好：(路径为 opt/ros/indigo/share/serial)

	roscd serial

程序

#include "ros/ros.h"  
#include <serial/serial.h>  
#include <std_msgs/String.h>  
#include "ros2stm32/data.h"           //自定义的数据类型头文件
#include <sstream>  

unsigned char speed_data[22]={0};   //要发给串口的数据
serial::Serial ros_ser;　　　　　　//声明串口对象
// 接收到订阅的消息后，会进入消息回调函数
void chatterCallback(const ros2stm32::data::ConstPtr& msg)
{
   
   speed_data[0] = 0x55;
   ……
   speed_data[21]=0x55;
   
 	// 通过usb口写入
   ros_ser.flush ();
   ros_ser.write(speed_data,22);
   ROS_INFO_STREAM("\nSend date finished!\n");

　  //通过usb口收到消息
   if(ros_ser.available()){ 
   	ROS_INFO_STREAM("Reading from serial port: "); 
   	std_msgs::String result; 
   	result.data = ros_ser.read(ros_ser.available()); 
   	ROS_INFO_STREAM("Read: " << result.data); 		
   }
}


int main (int argc, char** argv){

    ros::init(argc, argv, "data_listener");

    ros::NodeHandle n;

    try
    {
        ros_ser.setPort("/dev/ttyUSB0");//串口号可以修改
        ros_ser.setBaudrate(9600);
        serial::Timeout to = serial::Timeout::simpleTimeout(1000);
        ros_ser.setTimeout(to);
        ros_ser.open();
    }
    catch (serial::IOException& e)
    {
        ROS_ERROR_STREAM("Unable to open port ");
        return -1;
    }
    if(ros_ser.isOpen()){
        ROS_INFO_STREAM("Serial Port opened");
    }else{
        return -1;
    }
    ROS_INFO_STREAM("Init Finished!");

    // 创建一个Subscriber，订阅名为data_chatter的topic，注册回调函数chatterCallback 
    ros::Subscriber sub = n.subscribe("data_chatter", 1000, chatterCallback); 

    ros::spin();
}

权限
如果提示Unable to open port，是由于权限不够引起的，进行如下操作

  	sudo chmod 666 /dev/ttyUSB0

ROS分布式多机通信　ssh的使用

１、目的

实现一个：笔记本发送topic，树莓派（树莓派３Ｂ＋）订阅topic，接收数据，控制机械臂，达成笔记本远程控制机械臂运动的效果。

2、关于SSR

SSH为Secure Shell的缩写，由 IETF 的网络工作小组（Network Working Group）所制定；SSH 为建立在应用层和传输层基础上的安全协议。
SSH是目前可靠的，专为远程登录会话和其他网络服务提供安全性的协议。常用于远程登录，以及用户之间进行资料拷贝。利用SSH协议可以有效防止远程管理过程中的信息泄露问题
使用SSH服务，则两个机器都需要安装SSR

3、实现

前提
二者处于同一个局域网
安装
两台机子都需要安装openssh，直接

	sudo apt-get install openssh

设置 ip 和 ~/.bashrc 文件
　１、先找两台机子的IP地址：

zyf@zyf-TM1707:~/chuankou$ ifconfig
lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (本地环回)
        RX packets 7252  bytes 789872 (789.8 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 7252  bytes 789872 (789.8 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
wlp3s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.104  netmask 255.255.255.0  broadcast 192.168.1.255
        inet6 fe80::def0:b93b:962f:9b9c  prefixlen 64  scopeid 0x20<link>
        ether c0:b6:f9:8a:64:d9  txqueuelen 1000  (以太网)
        RX packets 32666  bytes 29085588 (29.0 MB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 23644  bytes 4418820 (4.4 MB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

无线网下的ip就是在wlp3s0下的inet
　２、分别了解了之后，需要在两台机子上的/etc/hosts文件加入对方的IP地址和对应的计算机名字
举例如下：

zyf@zyf-TM1707:~$ sudo gedit /etc/hosts

格式：　工控机的局域网地址　工控机的用户名
笔记本这里放工控机的地址和用户名192.168.1.105 ahong-desktop
工控机那边放笔记本的地址和用户名192.168.1.104 zyf.TM1707　
示例如下：（笔记本里）

127.0.0.1	localhost
127.0.1.1	zyf-TM1707
192.168.1.105   ahong-desktop

# The following lines are desirable for IPv6 capable hosts
::1     ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

这时候可以　ping　一下看通信是否正常

zyf@zyf-TM1707:~$ ping 192.168.1.105
PING 192.168.1.105 (192.168.1.105) 56(84) bytes of data.
64 bytes from 192.168.1.105: icmp_seq=1 ttl=64 time=19.1 ms
64 bytes from 192.168.1.105: icmp_seq=2 ttl=64 time=7.32 ms
64 bytes from 192.168.1.105: icmp_seq=3 ttl=64 time=4.81 ms
64 bytes from 192.168.1.105: icmp_seq=4 ttl=64 time=4.28 ms
64 bytes from 192.168.1.105: icmp_seq=5 ttl=64 time=4.38 ms
64 bytes from 192.168.1.105: icmp_seq=6 ttl=64 time=4.23 ms
^C
--- 192.168.1.105 ping statistics ---
6 packets transmitted, 6 received, 0% packet loss, time 5009ms
rtt min/avg/max/mdev = 4.237/7.357/19.103/5.362 ms

３、设置~/.bashrc 文件
从　机——笔记本

export ROS_HOSTNAME=zyf-TM1707					　　#笔记本
export ROS_MASTER_URI=http://ahong-desktop:11311　　#工控机

工控机——树莓派

export ROS_HOSTNAME=ahong-desktop　　　　　　　　　　#工控机
export ROS_MASTER_URI=http://ahong-desktop:11311　　#工控机

这里就是把ROS_MASTER_URI设置为工控机那边，如果笔记本要使用roscore需要将那两句话注释掉，否则运行会出现以下问题：

NODES
WARNING: ROS_MASTER_URI [http://ahong-desktop:11311] host is not set to this machine

设置好IP后，最好 source ~/.bashrc 刷新一下，就可以通信了。

通信

zyf@zyf-TM1707:~$ ssh ahong@192.168.1.105
The authenticity of host '192.168.1.105 (192.168.1.105)' cant be established.
ECDSA key fingerprint is SHA256:l5GPEMvAgqONnXRdXRk5fBCMefOlyc0+PQRANqkiGo0.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.1.105' (ECDSA) to the list of known hosts.
ahong@192.168.1.105's password: 
Welcome to Ubuntu 16.04.2 LTS (GNU/Linux 4.9.80-v7+ armv7l)

 * Documentation:  https://help.ubuntu.com
 * Management:     https://landscape.canonical.com
 * Support:        https://ubuntu.com/advantage

583 packages can be updated.
0 updates are security updates.

The programs included with the Ubuntu system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Ubuntu comes with ABSOLUTELY NO WARRANTY, to the extent permitted by applicable law.

4、问题

（１）openssh没装好

zyf@zyf-TM1707:~$ ssh ahong@192.168.1.105
ssh: connect to host 192.168.1.105 port 22: Connection refused

安装ssh服务：sudo apt-get install openssh
启动ssh服务：service sshd start
重新运行：ssh 用户名@ip 即可
（２）启动失败

sudo service ssh start
报错
Failed to start ssh.service: Unit ssh.service not found.

解决

sudo systemctl enable ssh.service       #添加ssh.service
sudo systemctl start ssh.service
sudo systemctl status ssh.service

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