Re: [gentoo-embedded] displaying serial port status

[Bob Dunlop]

Hi again,

On Wed, Apr 21 at 01:14, Relson, David wrote:
> Gretings,
>
> In the old days when we used direct port I/O to perform serial port actions, code like the following would display the port's status:
>
> #define BASE    0x03F8     /* COM1 port base address */
> #define LS_REG (BASE+5)    /* Line Status Register   */
>
> void ShowLineStatus(void)
> {
>     int status = inportb(LS_REG);
>     if (status & 0x02) printf("Overrun Error\n");
>     if (status & 0x04) printf("Parity Error\n");
>     if (status & 0x08) printf("Framing Error\n");
>     if (status & 0x10) printf("Break Interrupt\n");
>     if (status & 0x80) printf("Timeout Error\n");
> }
>
> How does one perform the same thing for /dev/ttyS0 (or any other serial port)?

  #include <termios.h>			/* or ioctl.h (can't remember) */

  int fd = open("/dev/ttyS0", O_RDWR);
  int status;

  ioctl (fd, TIOCSERGETLSR, &status);
  /* Print as above */

You might want to add error checking.  Also remember the live LSR may not be
syncronised with the characters your are currently reading if there is a
queue anywhere.  To get an inline marker of an error use PARMRK in your
termios structure.


Alternativly you might want to look at the TIOCGICOUNT ioctl.  This fills out
a serial_icounter_struct (see /usr/include/linux/serial.h) with counts of the
number of overrun errors etc.


-- 
        Bob Dunlop