QNX RTOS v4 Knowledge Base
QNX RTOS v4 Knowledge Base
| Title |
Detecting any parity and framing errors on a RS-232 serial line |
| Ref. No. |
QNX.000009289 |
| Category(ies) |
Development, Character I/O |
| Issue |
We have a simple application that collects data from a robot across an RS-232C connection. In the application, we'd like to detect any parity and framing errors that may occur on the serial line. How do we do this?
|
| Solution |
Parity and framing errors can be detected by using the POSIX terminal I/O settings. Here's an example of how to setup the termios structure on the serial port so that an application will catch these errors:
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <termios.h>
#include <sys/dev.h>
#include <sys/uio.h>
#define SERDEV1 "/dev/ser1"
#define BAUD 9600
int open_device (char *device);
void serial_device_init(int file_des);
void read_device (int file_des);
main()
{
x09int file_des;
x09file_des = open_device (SERDEV1);
x09serial_device_init (file_des);
x09for(;;)
x09x09read_device (file_des);
}
int open_device (char *device)
{
x09int file_des;
x09struct _dev_info_entry info;
x09if ((file_des = open(device, O_RDWR)) = -1{
x09x09printf("error opening %s: %sn",
x09x09x09device, strerror(errno));
x09x09exit(1);
x09}
x09if(dev_info(file_des, &info) != -1)
x09x09printf("NODE %d, TTY %dn", info.nid, info.tty);
x09else
x09x09printf("dev_info failedn",strerror(errno));
x09return(file_des);
}
void serial_device_init(int file_des)
{
x09int i;
x09struct termios termios_p;
x09speed_t speed = BAUD;
// get the control structure for /dev/ser1
x09tcgetattr(file_des, &termios_p);
x09/* get control structure for /dev/ser1 */
// Set the baud (will he set with tcsetattr())
x09cfsetispeed(&termios_p, speed); // input
x09cfsetospeed(&termios_p, speed); // output
// Control modes:
//
// CS8----> 8 bits-per-byte
// CREAD--> Enable receiver. If this bit is not set,
//x09no characters are received.
// PARENB-> Parity generation and detection is enabled and
//x09parity bit is added to each character.
x09termios_p.c_cflag &= ~CSIZE;
x09termios_p.c_cflag |= CS8|CREAD|PARENB;
// Input modes:
//
// INPCK --> Enables parity checking
// IGNPAR -> Parity and framing errors are ignored
// PARMRK -> If PARMARK is set, and IGNPAR is not set,
//x09a byte with a framing or parity error will
//x09be read by the application as the following
//x09three-byte sequence:
//
//x09x09Byte 1 ' |
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