Linux Serial port Programming

[zawii87]

Can any body help me who have experience on handling the serial port using Linux that is

How to open the serial port ?
How to configure serial port like setting Baud rate, how to set parity , stop bit ?
How to write and read from the serial port ?

Any body have used these options regarding serial Communication can guide me please

Thanks in advance

[elija]

Well, that would depend on which language you are using....

[zawii87]

I have written the code , but I am facing problem while reading the data from the port, I just write the simple programe to Initialize, configure , write and reading the same data as I wrote . Some time it reads only 10 bytes and stuck in the read loop and some time only 1 byte and this depends on the sequence or the values of data which I am sending ... it's quite strange . I just want it to read the same as I have sended . I have pasted my code can you please have a look and help me in this regard

#include <stdio.h> /* Standard input/output definitions */
#include <string.h> /* String function definitions */
#include <unistd.h> /* UNIX standard function definitions */
#include <fcntl.h> /* File control definitions */
#include <errno.h> /* Error number definitions */
#include <termios.h> /* POSIX terminal control definitions */

/*
* 'open_port()' - Open serial port 2.
*
* Returns the file descriptor on success or -1 on error.
*/
// opens the serial port
// return code:
// > 0 = fd for the port
// -1 = open failed


// ******** opening port ******************

int open_port(void)
{
int fd; /* File descriptor for the port */


fd = open("/dev/ttyS1", O_RDWR | O_NOCTTY | O_NDELAY);
if (fd == -1)
{
/*
* Could not open the port.
*/

perror("open_port: Unable to open /dev/ttyS1 - ");
}
else
{
fcntl(fd, F_SETFL, 0);
printf("open sucess ttyS1\n");
}

return (fd);
}




// ******** Main Program ********************


int main (void)
{

int fd= open_port();
unsigned char data[20] = { 0x40, 0x28, 0x6b, 0xfe,0x70, 0x08, 0x09, 0x50,0x40, 0x67, 0x81, 0x00,
0x00, 0x00, 0x00, 0x00,0xd9, 0xff, 0xff, 0xff} ;



// Configure Serial port

struct termios options;

/*
* Get the current options for the port...
*/

tcgetattr(fd, &options);

/*
* Set the baud rates to 19200...
*/

cfsetispeed(&options, B115200);
cfsetospeed(&options, B115200);

/*
* Enable the receiver and set local mode...
*/

options.c_cflag |= (CLOCAL | CREAD);

/*
* Set the new options for the port...
*/

// tcsetattr(fd, TCSAFLUSH, &options); // flush i/o buffer and apply the change

tcflush(fd, TCIFLUSH);
tcsetattr(fd, TCSANOW, &options); // Make changes immediately without waiting for output
//data to finish sending or input data to finish receiving



// setting data bits



// setting parity checking


options.c_cflag |= PARENB ; // Enable parity bit
options.c_cflag &= ~PARODD; // use even parity
options.c_cflag &= ~CSTOPB;// 2 stop bits (1 otherwise)
options.c_cflag &= ~CSIZE; // Bit mask for data bits
options.c_cflag |= CS8; // 8 data bits


// setting input parity options

options.c_iflag |= (INPCK | ISTRIP);


// Timeout Settings

options.c_cc[VMIN] = 0; // Minimum number of characters to read
options.c_cc[VTIME] = 10; // Time to wait for data(tenth of seconds)







// writing data to the port

int n=0 ;
n = write(fd, data, 20);
// tcflush(fd, TCOFLUSH);
if (n < 0)
fputs("write() of 20 bytes failed!\n", stderr);
printf("transmitted with n=%d\n", n);



// Reading data
int count = 0;
while(count < 20) {
n = read(fd, data, 1);
count += n;
if( n > 0)
{
printf("Received Byte=%x\n",data[0]);
fflush(stdout);
}

}




// closing serial port


close(fd);


return 0;
}

[elija]

I'm afraid I'm not an advanced enough c programmer to be much help here, but, many years ago when I had to program serial communications in C#, I needed to write a state machine to handle the asynchronous nature of the communication. It may be different in pure c.