Complete serial port access code is following. Code is released as FOSS under the GPL3 license. The CreateFile call is
CreateFile(serialport, GENERIC_READ|GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
Following is the full coding listing. Firstly, serialport.c, written by me (with contributions from Ming Chin Pua) and based on SerialClass.cpp from Arduino.cc site.
#include <stdio.h> /* Standard input/output definitions */
#include <stdlib.h>
#include <string.h> /* String function definitions */
#include <fcntl.h> /* File control definitions */
#include <errno.h> /* Error number definitions */
#ifdef _WIN32
# include <windows.h>
#else
# include <termios.h> /* POSIX terminal control definitions */
# include <sys/ioctl.h>
#endif
#include "serialport.h"
int serialport_writebyte(SERIALPORT_HANDLE fd, uint8_t b){
#ifdef _WIN32
DWORD errors;
COMSTAT status;
DWORD n;
if(!WriteFile((HANDLE)fd, (void *)(&b), 1, &n, NULL)){
ClearCommError((HANDLE)fd, &errors, &status);
perror("serialport_write: Error writing to COM port");
return -1;
}
#else /* Linux, Mac */
int n = write(fd,&b,1);
if( n!=1)
return -1;
#endif
return 0;
}
int serialport_write(SERIALPORT_HANDLE fd, const char* str){
int len = strlen(str);
#ifdef _WIN32
DWORD n;
DWORD errors;
COMSTAT status;
if(!WriteFile((HANDLE)fd, (void *)str, len, &n, 0)){
ClearCommError((HANDLE)fd, &errors, &status);
perror("serialport_write: Error writing to COM port");
return -1;
}
#else /* Linux, Mac */
int n = write(fd, str, len);
if( n!=len )
return -1;
#endif
return 0;
}
int serialport_read_until(SERIALPORT_HANDLE fd, char* buf, char until){
char b[1] = " ";
int i=0;
do {
#ifdef _WIN32
DWORD n;
if(!ReadFile(fd, b, 1, &n, NULL)){ /* READFILE returns TRUE on success */
return -1;
}
#else /* Linux, Mac */
int n = read(fd, b, 1); // read a char at a time
#endif
if( n==-1){
#if _WIN32
fprintf(stderr,"COULDN'T READ\n");
return -1; // couldn't read
}else if( n==0 ) {
//fprintf(stderr,"READ 0\n");
usleep( 10 ); // wait 10 msec try again
continue;
#else
continue;
#endif
}else{
//fprintf(stderr,"%d=[%c]\n",i,b[0]);
buf[i] = b[0];
i = i + 1;
}
/* TODO add some code to check the length of the buffer is not exceeded */
} while( b[0] != until );
buf[i] = '\0'; // null terminate the string
return 0;
}
int serialport_readbyte(SERIALPORT_HANDLE fd, char *b){
#ifdef _WIN32
DWORD n;
if(ReadFile(fd, b, 1, &n, NULL)){
return -1;
}
#else /* Linux, Mac */
int n = read(fd, b, 1); // read a char at a time
if(n==1)return 0;
return -1;
#endif
}
// takes the string name of the serial port (e.g. "/dev/tty.usbserial","COM1")
// and a baud rate (bps) and connects to that port at that speed and 8N1.
// opens the port in fully raw mode so you can send binary data.
// returns valid fd, or -1 on error
SERIALPORT_HANDLE serialport_init(const char *serialport, int baud, SERIALPORT_TERMIOS *oldsettings){
SERIALPORT_HANDLE fd;
#ifdef _WIN32
{fd = CreateFile(serialport, GENERIC_READ|GENERIC_WRITE, 0, NULL
, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL
);
if(fd==INVALID_HANDLE_VALUE){
DWORD error = GetLastError();
switch(error){
case ERROR_ACCESS_DENIED:
fprintf(stderr,"serislport_init: Unable to open port: Access denied (port in use?)\n");
return SERIALPORT_FILE_ERROR;
case ERROR_FILE_NOT_FOUND:
fprintf(stderr,"serialport_init: Unable to open port '%s'. File not found.\n",serialport);
return SERIALPORT_FILE_ERROR;
default:
perror("serialport_init: Unknown error in CreateFile call.");
return SERIALPORT_FILE_ERROR;
}
}
DCB toptions;
if(!GetCommState(fd, &toptions)){
perror("serialport_init: Couldn't get COM state");
return SERIALPORT_FILE_ERROR;
}
// save old settings if requested
if(oldsettings){
*oldsettings = toptions;
}
DWORD brate;
switch(baud) {
case 4800: brate=CBR_4800; break;
case 9600: brate=CBR_9600; break;
case 14400: brate=CBR_14400; break;
case 19200: brate=CBR_19200; break;
case 38400: brate=CBR_38400; break;
case 57600: brate=CBR_57600; break;
case 115200: brate=CBR_115200; break;
// some other speeds are possible, see DCB structure details (this
// 115200 is the max speed of arduino.
}
toptions.BaudRate = brate;
toptions.ByteSize = 8;
toptions.StopBits = ONESTOPBIT;
toptions.Parity = NOPARITY;
toptions.fOutxCtsFlow = FALSE;
toptions.fOutxDsrFlow = FALSE;
toptions.fOutX = FALSE;
toptions.fInX = FALSE;
toptions.fRtsControl = RTS_CONTROL_DISABLE;
toptions.fTXContinueOnXoff = TRUE;
toptions.fNull = FALSE;
if(!SetCommState(fd, &toptions)) {
perror("serialport_init: Couldn't set COM state");
return SERIALPORT_FILE_ERROR;
}
}
#else /* Linux, Mac */
{struct termios toptions;
//fprintf(stderr,"init_serialport: opening port %s @ %d bps\n",
// serialport,baud);
fd = open(serialport, O_RDWR | O_NOCTTY | O_NDELAY);
if (fd == -1) {
perror("serialport_init: Unable to open port ");
return SERIALPORT_FILE_ERROR;
}
if (tcgetattr(fd, &toptions) < 0) {
perror("serialport_init: Couldn't get term attributes");
return SERIALPORT_FILE_ERROR;
}
// save old settings if requested
if(oldsettings){
*oldsettings = toptions;
}
speed_t brate = baud; // let you override switch below if needed
switch(baud) {
case 4800: brate=B4800; break;
case 9600: brate=B9600; break;
#ifdef B14400
case 14400: brate=B14400; break;
#endif
case 19200: brate=B19200; break;
#ifdef B28800
case 28800: brate=B28800; break;
#endif
case 38400: brate=B38400; break;
case 57600: brate=B57600; break;
case 115200: brate=B115200; break;
}
cfsetispeed(&toptions, brate);
cfsetospeed(&toptions, brate);
// 8N1
toptions.c_cflag &= ~PARENB;
toptions.c_cflag &= ~CSTOPB;
toptions.c_cflag &= ~CSIZE;
toptions.c_cflag |= CS8;
// no flow control
toptions.c_cflag &= ~CRTSCTS;
toptions.c_cflag |= CREAD | CLOCAL; // turn on READ & ignore ctrl lines
toptions.c_iflag &= ~(IXON | IXOFF | IXANY); // turn off s/w flow ctrl
toptions.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG); // make raw
toptions.c_oflag &= ~OPOST; // make raw
// see: http://unixwiz.net/techtips/termios-vmin-vtime.html
toptions.c_cc[VMIN] = 0;
toptions.c_cc[VTIME] = 20;
if( tcsetattr(fd, TCSANOW, &toptions) < 0) {
perror("serialport_init: Couldn't set term attributes");
return SERIALPORT_FILE_ERROR;
}
}
#endif
return fd;
}
int serialport_restoresettings(SERIALPORT_HANDLE fd, SERIALPORT_TERMIOS *oldsettings){
#ifdef _WIN32
if(!SetCommState(fd, oldsettings)) {
perror("serialport_restoresettings: Couldn't set COM state");
return -1;
}
#else
if(tcsetattr(fd, TCSANOW, oldsettings) < 0) {
perror("serialport_restoresettings: Couldn't set term attributes");
return -1;
}
#endif
return 0;
}
int serialport_close(SERIALPORT_HANDLE fd){
if(fd<0){
perror("serialport_close: COM was not open");
return -1;
}
#ifdef _WIN32
CloseHandle(fd);
#else /* Linux, Mac */
close(fd);
#endif
return 0;
}
serialport.h
#ifndef SERIALPORT_H
#define SERIALPORT_H
#include <stdint.h> /* Standard types */
#include <unistd.h> /* UNIX standard function definitions */
#ifdef _WIN32
# include <windows.h>
# define SERIALPORT_TERMIOS DCB
# define SERIALPORT_HANDLE HANDLE
# define SERIALPORT_FILE_ERROR INVALID_HANDLE_VALUE
# define SERIALPORT_SLEEP(N) Sleep(N)
#else
# include <termios.h>
# define SERIALPORT_TERMIOS struct termios
# define SERIALPORT_HANDLE int
# define SERIALPORT_FILE_ERROR -1
# define SERIALPORT_SLEEP(N) usleep(N*1e3)
#endif
/**
Open serial port for communication.
@param serialport name of the port to be opened (eg /dev/tty.usbserial)
@param baud baud rate (integer)
@param oldsettings pointer to a struct in which old comm settings should be
stored, if desired (else NULL if not desired)
@return valid file descriptor, or -1 on error.
*/
SERIALPORT_HANDLE serialport_init(const char* serialport, int baud, SERIALPORT_TERMIOS *oldsettings);
int serialport_writebyte(SERIALPORT_HANDLE fd, uint8_t b);
/*
Read a byte from the serial connection.
@return 0 on success
*/
int serialport_readbyte(SERIALPORT_HANDLE fd, char *byte);
int serialport_write(SERIALPORT_HANDLE fd, const char* str);
int serialport_read_until(SERIALPORT_HANDLE fd, char* buf, char until);
int serialport_restoresettings(SERIALPORT_HANDLE fd, SERIALPORT_TERMIOS *oldsettings);
/**
Close a success-opened connection, return 0 on success.
*/
int serialport_close(SERIALPORT_HANDLE fd);
#endif
