DCMD_CHR_LINESTATUS

Get line status information for the terminal device

Synopsis:

#include <sys/dcmd_chr.h>

#define DCMD_CHR_LINESTATUS   __DIOF(_CMD_IOCTL_TTY, 106, int) /* TIOCMGET */

Arguments to devctl():

Argument Value
filedes A file descriptor that you obtained by opening the device.
dcmd DCMD_CHR_LINESTATUS
dev_data_ptr A pointer to an int
n_bytes sizeof(int)
dev_info_ptr NULL

Description:

This command gets line status information for the terminal device and is usually associated with the control lines of a serial port. It's also implemented as the TIOCMGET ioctl() command.

The contents of the returned data depend on the device. The stty utility calls this function and displays this information.

Input:

None.

Output:

The line status information, which is a combination of the following bits (depending on the type of device):

Device type Bit Description
Serial _LINESTATUS_SER_DTR (TIOCM_DTR) Data terminal ready
  _LINESTATUS_SER_RTS (TIOCM_RTS) Request to send
  _LINESTATUS_SER_CTS (TIOCM_CTS) Clear to send
  _LINESTATUS_SER_DSR (TIOCM_DSR) Data set ready
  _LINESTATUS_SER_RI (TIOCM_RI or TIOCM_RNG) Ring
  _LINESTATUS_SER_CD (TIOCM_CAR or TIOCM_CD) Carrier detect
Console _LINESTATUS_CON_SCROLL Scroll Lock is on
  _LINESTATUS_CON_NUM Num Lock is on
  _LINESTATUS_CON_CAPS Caps Lock is on
  _LINESTATUS_CON_SHIFT Shift is pressed (not currently used)
  _LINESTATUS_CON_CTRL Ctrl is pressed (not currently used)
  _LINESTATUS_CON_ALT Alt is pressed (not currently used)
Parallel _LINESTATUS_PAR_NOERROR No error detected
  _LINESTATUS_PAR_SELECTED Selected
  _LINESTATUS_PAR_PAPEROUT No paper
  _LINESTATUS_PAR_NOTACK Not acknowledge
  _LINESTATUS_PAR_NOTBUSY Not busy

Example:

Check to see if RTS is set:

int data = 0, error;

if (error = devctl (fd, DCMD_CHR_LINESTATUS, &data, sizeof(data), NULL))
{
   fprintf(stderr, "Error getting RTS: %s\n", strerror ( error ));
   exit(EXIT_FAILURE);
}

if (data & _LINESTATUS_SER_RTS)
{
    printf("RTS is set.\n");
}
else
{
    printf("RTS isn't set.\n");
}

See also:

DCMD_CHR_SERCTL, TIOCMGET

devctl() in the QNX Neutrino C Library Reference

stty in the Utilities Reference