[gentoo-embedded] displaying serial port status

[gentoo-embedded] displaying serial port status

[Relson, David]

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)?

I've been looking at various ioctl's, but haven't yet spotted one that provides information on overrun errors, parity errors, etc.

Thanks in advance!
 
David

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

RE: [gentoo-embedded] displaying serial port status

[Relson, David]

Hi Bob,

Great tip!  It lead to serial_core.c (for processing TIOCSERGETLSR) and
to serial_reg.h (for defining UART_LSR_BI/FE/PE/etc).  I'm pleasantly
surprised to see that the UART_LSR_xx symbols have values that
numerically match the register bits. 

Thanks for the tip!

Regards,
 
David

-----Original Message-----
From: Bob Dunlop [mailto:bob.dunlop@xyzzy.org.uk] 
Sent: Wednesday, April 21, 2010 2:51 PM
To: gentoo-embedded@lists.gentoo.org
Subject: Re: [gentoo-embedded] displaying serial port status

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