Serial port : Read data problem, not reading complete data
- by Anuj Mehta
Hi
I have an application where I am sending data via serial port from PC1 (Java App) and reading that data in PC2 (C++ App). The problem that I am facing is that my PC2 (C++ App) is not able to read complete data sent by PC1 i.e. from my PC1 I am sending 190 bytes but PC2 is able to read close to 140 bytes though I am trying to read in a loop.
Below is code snippet of my C++ App
Open the connection to serial port
serialfd = open( serialPortName.c_str(), O_RDWR | O_NOCTTY | O_NDELAY);
if (serialfd == -1)
{
/*
* Could not open the port.
*/
TRACE << "Unable to open port: " << serialPortName << endl;
}
else
{
TRACE << "Connected to serial port: " << serialPortName << endl;
fcntl(serialfd, F_SETFL, 0);
}
Configure the Serial Port parameters
struct termios options;
/*
* Get the current options for the port...
*/
tcgetattr(serialfd, &options);
/*
* Set the baud rates to 9600...
*/
cfsetispeed(&options, B38400);
cfsetospeed(&options, B38400);
/*
* 8N1
* Data bits - 8
* Parity - None
* Stop bits - 1
*/
options.c_cflag &= ~PARENB;
options.c_cflag &= ~CSTOPB;
options.c_cflag &= ~CSIZE;
options.c_cflag |= CS8;
/*
* Enable hardware flow control
*/
options.c_cflag |= CRTSCTS;
/*
* Enable the receiver and set local mode...
*/
options.c_cflag |= (CLOCAL | CREAD);
// Flush the earlier data
tcflush(serialfd, TCIFLUSH);
/*
* Set the new options for the port...
*/
tcsetattr(serialfd, TCSANOW, &options);
Now I am reading data
const int MAXDATASIZE = 512;
std::vector<char> m_vRequestBuf;
char buffer[MAXDATASIZE];
int totalBytes = 0;
fcntl(serialfd, F_SETFL, FNDELAY);
while(1) {
bytesRead = read(serialfd, &buffer, MAXDATASIZE);
if(bytesRead == -1)
{
//Sleep for some time and read again
usleep(900000);
}
else
{
totalBytes += bytesRead;
//Add data read to vector
for(int i =0; i < bytesRead; i++)
{
m_vRequestBuf.push_back(buffer[i]);
}
int newBytesRead = 0;
//Now keep trying to read more data
while(newBytesRead != -1)
{
//clear contents of buffer
memset((void*)&buffer, 0, sizeof(char) * MAXDATASIZE);
newBytesRead = read(serialfd, &buffer, MAXDATASIZE);
totalBytes += newBytesRead;
for(int j = 0; j < newBytesRead; j++)
{
m_vRequestBuf.push_back(buffer[j]);
}
}//inner while
break;
} //while
