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--- en:robotics:computing:linux_asynchronous_serial_programming_how_to [2011/10/10 17:38]
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-====== Introduction ======
-This article describes asynchrous serial programming using signal handler.
-== References ==
-  * Serial Programming HOWTO : [[http://tldp.org/HOWTO/Serial-Programming-HOWTO/]]
-== Hardware used : ==
-  * A desktop PC.
-  * An internet connection.
-== Softwares : ==
-  * Ubuntu 10.10 installed : [[http://www.ubuntu.com/]]
-  * Package **build-essential** and **socat** already installed on your Ubuntu operating system.
-====== Asynchronous serial I/O library ======
-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.
-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 function
-  * At the end of the handler, application go back to its previous work.
-This signal handler is given as a parameter of the **serialConfiguration** function. Then you can develop your own handler and just pass it to **serialConfiguration**.
-Here is the header file **serialCom.h** :
-<code>#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)
-#define NO_PARITY_CHECK 0
-#define PARITY_CHECK    1
-  /* 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</code>
-And the source file **serialCom.c** with more explanations in code comments :
-<code>#ifdef __cplusplus
-extern "C"
-{
-#endif
-#include <fcntl.h>
-#include <sys/signal.h>
-#include <sys/types.h>
-#include <unistd.h>
-#include <stdio.h>
-#include <termios.h>
-#include <serialCom.h>
-  int
-  serialConfiguration(serial_handler handler, const char *device,
-      tcflag_t baudrate, char parity)
-  {
-    /* Definition of new serial port configuration */
-    struct termios newtio;
-    /* Definition of signal action */
-    struct sigaction saio;
-    /* Open the device
-     * O_RDWR     : open in read/write mode
-     * O_NONBLOCK : open in not blocked mode. Read will return immediatly */
-    int fdesc = open(device, O_RDWR | O_NONBLOCK);
-    if (fdesc < 0)
-      {
-        perror(device);
-        return fdesc;
-      }
-    /* Install the signal handler before making the device asynchronous */
-    saio.sa_handler = handler;
-    saio.sa_flags = 0;
-    saio.sa_restorer = NULL;
-    sigaction(SIGIO, &saio, NULL);
-    /* Allow the process to receive SIGIO */
-    fcntl(fdesc, F_SETOWN, getpid());
-    /* Make the file descriptor asynchronous.
-     * It is not possible to enable SIGIO receiving by specifying
-     * O_ASYNC when calling open (see open man page)  */
-    fcntl(fdesc, F_SETFL, O_ASYNC);
-    /* Set new port settings */
-    newtio.c_cflag = baudrate | SERIAL_CONTROL;
-    /* Input settings */
-    if (parity == NO_PARITY_CHECK)
-      {
-        newtio.c_iflag = IGNPAR | SERIAL_INPUT;
-      }
-    else
-      {
-        newtio.c_iflag = SERIAL_INPUT;
-      }
-    tcflush(fdesc, TCIFLUSH);
-    tcflush(fdesc, TCOFLUSH);
-    tcsetattr(fdesc, TCSANOW, &newtio);
-    return fdesc;
-  }
-#ifdef __cplusplus
-}
-#endif</code>
-To generate the library :
-<code>$ gcc -o libSerialCom.so --shared serialCom.c -I.</code>
-====== Test program ======
-Here is a little test program **testSerialCom.cpp** which just print the byte it received, reading bytes one by one.
-We use C++ there just to show the lib is usable with C/C++ project.
-Explanations are in code comments :
-<code>using namespace std;
-#include <iostream>
-#include <serialCom.h>
-/* Flag indicating datas are ready to be read */
-static bool flag = false;
-/* SIGIO handler */
-void
-my_handler(int status)
-{
-  /* Data ready to be read */
-  flag = true;
-}
-/* MAIN */
-int
-main(int argc, char **argv)
-{
-  /* Initialize the serial communication */
-  int fdesc = serialConfiguration(my_handler, "/dev/ttyS0", B115200,
-      NO_PARITY_CHECK);
-  /* Data buffer */
-  char buf;
-  /* Reading result */
-  int res = 0;
-  /* Initialize data flag */
-  flag = false;
-  while (buf != '\t')
-    {
-      /* If there is a data to be read */
-      if (flag == true)
-        {
-          /* Read one byte */
-          do
-            {
-              res = read(fdesc, &buf, 1);
-              cout << buf << endl;
-            }
-          while (res > 0);
-          flag = false;
-        }
-    }
-  return 0;
-}</code>
-To generate the binary :
-<code>$ g++ -o testSerialCom testserialcom.cpp -I../../SerialCom/ -L../../SerialCom/ -lSerialCom</code>
-====== Performing the test ======
-If you have no serial port to test your code, just create two virtual ports with **socat** in a terminal. :
-<code>$ socat -d -d PTY: PTY:
-/02/17 23:58:36 socat[12866] N PTY is /dev/pts/3
-/02/17 23:58:36 socat[12866] N PTY is /dev/pts/4
-/02/17 23:58:36 socat[12866] N starting data transfer loop with FDs [3,3] and [5,5]</code>
-Before launching test program, do not forget to change the port asked in the main function of the **testSerialCom.c**. And rebuild your program.
-Then in an other terminal just launch the test program :
-<code>$ sudo LD_LIBRARY_PATH=../SerialCom/ ./testSerialCom</code>
-And finally run **cutecom** with following parameters :
-{{:robotics:computing:linux_asynchronous_serial_programming:cutecom.png|}}
-To test just type some characters on **cutecom** input, you must see them appear on the test program terminal. :)

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