Communication with ROS through USART Serial Port

We always need to communicate with ROS through serial port as we have many devices like sensors, touch-screen, actuators to be controlled through USART serial protocol.

After some investigation, I found several ways that can make ROS work with the serial-port-devices:

• Use the package: rosserial. It seems like only the "connected rosserial-enabled device" can work upon that, including Aduino, Windows, XBee, etc.(ROS community said: rosserial is used with mcus that have rosserial code running on them.)
  
• Use the driver package: serial. It seems like a serial port driver for ROS programming. This should be the most free way but I didn't find out how to use it.
• Use the package: cereal_port, a serial port library for ROS, you can find it in theserial_communication stack, it's easy to use.
• The package: rosbridgemay also suit your needs (full disclosure, author of rosbridge here). Check outthis video of using rosbridge with an Arduino (though the principles apply to any uController).
  
• A simple approach is to write a ROS node that can read/write text messages exchanged with the microcontroller over a serial port and convert these serial messages to ROS style std_msgs/String messages.Here we are going to share this way first.
  
• Kevin: a service given by Kevin. It seems to work pretty good. This works well cuz a lot of our serial stuff is sending a message and receiving a response back, instead of separate publish/subscribes.reference web
  
• 
  

A simple approach is to write a ROS node that can read/write text messages exchanged with the microcontroller over a serial port and convert these serial messages to ROS style std_msgs/String messages. Here we are going to share this way first. ref:reference web 

In that page, Bart says:
"A simple approach is to write a ROS node that can read/write text messages exchanged with the microcontroller over a serial port and convert these serial messages to ROS style std_msgs/String messages. A separate ROS node can then be written to convert the simple text messages to specific ROS message formats (cmd_vel, odom, etc) based on whatever message protocol was defined for the exchange with the microcontroller.

Attached below is the source for code that I used for this purpose. There is nothing original in the code, but it may be helpful to someone new to ROS and Unix/Linux serial communication. Posting this type of a listing may be a bit unconventional for this site as short answers are generally preferred. Hopefully no one is offended. I would be interested in hearing if there are other successful approaches to the problem."

Let's implement this approach:

Enter the catkin workspace, build the package: (tutorial page)

$ cd ~/catkin_ws/src
$ catkin_create_pkg r2serial_driver std_msgs rospy roscpp
$ cd ~/catkin_ws
$ catkin_make

To add the workspace to your ROS environment you need to source the generated setup file:

$ . ~/catkin_ws/devel/setup.bash
$ cd ~/catkin_ws/src/r2serial_driver/src

Add a file: "r2serial.cpp", Source code:

/*                                                                                                                       
 * Copyright (c) 2010, Willow Garage, Inc.                                                                               
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 *       this software without specific prior written permission.                                                        
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 */
//r2serial.cpp
// communicate via RS232 serial with a remote uController.
// communicate with ROS using String type messages.
// subscribe to command messages from ROS
// publish command responses to ROS
// program parameters - ucontroller# (0,1), serial port, baud rate
//Thread main
//  Subscribe to ROS String messages and send as commands to uController
//Thread receive
//  Wait for responses from uController and publish as a ROS messages
#include "ros/ros.h"
#include "std_msgs/String.h"
#include <sstream>
#include <pthread.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <fcntl.h>
#include <termios.h>
#include <stdio.h>
#include <stdlib.h>
#define DEFAULT_BAUDRATE 19200
#define DEFAULT_SERIALPORT "/dev/ttyUSB0"
//Global data
FILE *fpSerial = NULL;   //serial port file pointer
ros::Publisher ucResponseMsg;
ros::Subscriber ucCommandMsg;
int ucIndex;          //ucontroller index number
//Initialize serial port, return file descriptor
FILE *serialInit(char * port, int baud)
{
int BAUD = 0;
int fd = -1;
struct termios newtio;
FILE *fp = NULL;
//Open the serial port as a file descriptor for low level configuration
// read/write, not controlling terminal for process,
fd = open(port, O_RDWR | O_NOCTTY | O_NDELAY );
if ( fd<0 )
{
ROS_ERROR("serialInit: Could not open serial device %s",port);
return fp;
}
// set up new settings
memset(&newtio, 0,sizeof(newtio));
newtio.c_cflag =  CS8 | CLOCAL | CREAD;  //no parity, 1 stop bit
newtio.c_iflag = IGNCR;    //ignore CR, other options off
newtio.c_iflag |= IGNBRK;  //ignore break condition
newtio.c_oflag = 0;        //all options off
newtio.c_lflag = ICANON;     //process input as lines
// activate new settings
tcflush(fd, TCIFLUSH);
//Look up appropriate baud rate constant
switch (baud)
{
case 38400:
default:
BAUD = B38400;
break;
case 19200:
BAUD  = B19200;
break;
case 9600:
BAUD  = B9600;
break;
case 4800:
BAUD  = B4800;
break;
case 2400:
BAUD  = B2400;
break;
case 1800:
BAUD  = B1800;
break;
case 1200:
BAUD  = B1200;
break;
}  //end of switch baud_rate
if (cfsetispeed(&newtio, BAUD) < 0 || cfsetospeed(&newtio, BAUD) < 0)
{
ROS_ERROR("serialInit: Failed to set serial baud rate: %d", baud);
close(fd);
return NULL;
}
tcsetattr(fd, TCSANOW, &newtio);
tcflush(fd, TCIOFLUSH);
//Open file as a standard I/O stream
fp = fdopen(fd, "r+");
if (!fp) {
ROS_ERROR("serialInit: Failed to open serial stream %s", port);
fp = NULL;
}
return fp;
} //serialInit
//Process ROS command message, send to uController
void ucCommandCallback(const std_msgs::String::ConstPtr& msg)
{
ROS_DEBUG("uc%dCommand: %s", ucIndex, msg->data.c_str());
fprintf(fpSerial, "%s", msg->data.c_str()); //appends newline
} //ucCommandCallback
//Receive command responses from robot uController
//and publish as a ROS message
void *rcvThread(void *arg)
{
int rcvBufSize = 200;
char ucResponse[rcvBufSize];   //response string from uController
char *bufPos;
std_msgs::String msg;
std::stringstream ss;
ROS_INFO("rcvThread: receive thread running");
while (ros::ok()) {
bufPos = fgets(ucResponse, rcvBufSize, fpSerial);
if (bufPos != NULL) {
ROS_DEBUG("uc%dResponse: %s", ucIndex, ucResponse);
msg.data = ucResponse;
ucResponseMsg.publish(msg);
}
}
return NULL;
} //rcvThread
int main(int argc, char **argv)
{
char port[20];    //port name
int baud;     //baud rate
char topicSubscribe[20];
char topicPublish[20];
pthread_t rcvThrID;   //receive thread ID
int err;
//Initialize ROS
ros::init(argc, argv, "r2serial_driver");
ros::NodeHandle rosNode;
ROS_INFO("r2serial_driver starting");
//Open and initialize the serial port to the uController
if (argc > 1) {
if(sscanf(argv[1],"%d", &ucIndex)==1) {
sprintf(topicSubscribe, "uc%dCommand",ucIndex);
sprintf(topicPublish, "uc%dResponse",ucIndex);
}
else {
ROS_ERROR("ucontroller index parameter invalid");
return 1;
}
}
else {
strcpy(topicSubscribe, "uc0Command");
strcpy(topicPublish, "uc0Response");
}
strcpy(port, DEFAULT_SERIALPORT);
if (argc > 2)
strcpy(port, argv[2]);
baud = DEFAULT_BAUDRATE;
if (argc > 3) {
if(sscanf(argv[3],"%d", &baud)!=1) {
ROS_ERROR("ucontroller baud rate parameter invalid");
return 1;
}
}
ROS_INFO("connection initializing (%s) at %d baud", port, baud);
fpSerial = serialInit(port, baud);
if (!fpSerial )
{
ROS_ERROR("unable to create a new serial port");
return 1;
}
ROS_INFO("serial connection successful");
//Subscribe to ROS messages
ucCommandMsg = rosNode.subscribe(topicSubscribe, 100, ucCommandCallback);
//Setup to publish ROS messages
ucResponseMsg = rosNode.advertise<std_msgs::String>(topicPublish, 100);
//Create receive thread
err = pthread_create(&rcvThrID, NULL, rcvThread, NULL);
if (err != 0) {
ROS_ERROR("unable to create receive thread");
return 1;
}
//Process ROS messages and send serial commands to uController
ros::spin();
fclose(fpSerial);
ROS_INFO("r2Serial stopping");
return 0;
}

Modify the CMakeList.txt file:

$ cd ~/catkin_ws/src/r2serial_driver
$ gedit CMakeList.txt

add/modify these lines as below:

find_package(catkin REQUIRED COMPONENTS
  roscpp
  rospy
  std_msgs
)
include_directories(
${catkin_INCLUDE_DIRS}
)
add_executable(r2serial_driver src/r2serial.cpp)
add_dependencies(r2serial_driver ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
target_link_libraries(r2serial_driver
${catkin_LIBRARIES}
)

$ cd ~/catkin_ws
$ catkin_make -DCMAKE_BUILD_TYPE=Release 

He also offered a simple launch file that interfaces to two microcontrollers using two serial connections, put the code into
  "~/catkin_ws/src/r2serial_driver/launch/r2serial_driver.launch" file:

<launch>
  <node pkg="r2serial_driver" type="r2serial_driver" name="r2serial0" args="0 /dev/ttyUSB0 9600" output="screen" >
  <remap from="ucCommand" to="uc0Command" />
  <remap from="ucResponse" to="uc0Response" />
  </node>
<node pkg="r2serial_driver" type="r2serial_driver" name="r2serial1" args="1 /dev/ttyUSB1 9600" output="screen" >
<remap from="ucCommand" to="uc1Command" />
<remap from="ucResponse" to="uc1Response" />
</node>
</launch>

Usage:

$ rosrun r2serial_driver r2serial_driver 0 /dev/ttyUSB0 9600

or

$ roslaunch r2serial_driver r2serial_driver.launch

try:

$ rostopic pub -r 1 /uc0Command std_msgs/String hello_my_serial
$ rostopic echo /uc0Response

But Kevin mentioned a question: "Interesting, but a lot of my serial stuff is send a message and receive a response back. Instead of separate publish/subscribes have you tried a service? That seems like it would work nicely for this."

I also noticed a problem: The Linux's System RAM and CPU will be much costed by r2serial_driver when it is running.

Next time, we'll see how to use Kevin's service to play ROS serial communication.

2. Use Service to play ROS-Serial communication

see this blog brother below...

http://blog.csdn.net/sonictl/article/details/51372534