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robotics:computing:linux_asynchronous_serial_programming_how_to [2011/02/09 19:18] gdo |
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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. | ||
| - | * 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. | ||
| - | |||
| - | == Softwares : == | ||
| - | * Ubuntu 10.10 installed on both Roboard and desktop PC : [[http://www.ubuntu.com/]] | ||
| - | * Package **build-essential** 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) | ||
| - | |||
| - | /* 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 == 0) | ||
| - | { | ||
| - | 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> | ||
robotics/computing/linux_asynchronous_serial_programming_how_to.1297275539.txt.gz · Dernière modification: 2012/09/20 10:52 (modification externe)
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