This article describes asynchrous serial programming using signal handler.

• Serial Programming HOWTO : http://tldp.org/HOWTO/Serial-Programming-HOWTO/

• A desktop PC.
• Roboard RB-100 : http://www.roboard.com/RB-100.htm
• Mini PCI VGA Card : http://www.icop.com.tw/pddetail.aspx?id=93&pid=4
• 4 Go micro SD card plugged in the built-in micro-SD card reader.
• An internet connection.

• Ubuntu 10.10 installed on both Roboard and desktop PC : http://www.ubuntu.com/
• Package build-essential already installed on your Ubuntu operating system.

The following code is very simple. There is just one function to initialize the serial communication. Only serial port device, baudrate and if there is a parity checking can be set.
Everything else is hard coded, supposing we use 8 bits of data, 1 stop bit and a prefix on parity error. Then it results in a very simple header file serialCom.h :

#ifndef _SERIALCOM_H_
#define _SERIALCOM_H_

#ifdef __cplusplus
extern "C"
{
#endif

#include <termios.h>

  /* Controls :  CS8      = 8 bits
   *             CREAD    = Enable reading */
#define SERIAL_CONTROL  (CS8 | CREAD)

  /* Input    :  PARMRK   = If IGNPAR is not set, prefix a character with a parity error  or
   framing  error  with  \377  \0 */
#define SERIAL_INPUT    PARMRK

  /* Handler type definition */
  typedef void
  (*serial_handler)(int status);

  /* Serial port initialization function */
  int
  serialConfiguration(serial_handler, const char* device, tcflag_t baudrate,
      char parity);

#ifdef __cplusplus
}
#endif

#endif

But the most important thing is the definition of a signal handler function type. All signal handlers return nothing and take one integer in parameter. This integer is the signal which throws the interruption. Here is a light description of how signals work :

• Data are available on the serial port
• A signal SIGIO is send to the application waiting for it
• This application stops its actual work
• And it calls the signal handler

As we can see further in the .cpp file, our serialConfiguration function will define the handler to call when a SIGIO signal is incoming.