Below I mocked up a basic C serial program for linux. My requirement is to toggle the RTS port to high on a rs-232 serial port, wait 5 milliseconds, send a hart frame (which consists of 11 bytes), wait 5 milliseconds, and then toggle the RTS port to low. Now the requirement seems simple. But I am wondering if the sleep function is exactly the same thing as "waiting". The sleep function suspends the current thread for n seconds. If the thread is suspended, does that also suspend the influence on the RTS port? If it won't have any affect on the RTS signal, I still would like to know if there is a better way to wait a few milliseconds when communicating across an rs-232 serial port. Thanks.
Code:#include <stdio.h> /* Standard input/output definitions */ #include <string.h> /* String function definitions */ #include <unistd.h> /* UNIX standard function definitions */ #include <fcntl.h> /* File control definitions */ #include <errno.h> /* Error number definitions */ #include <termios.h> /* POSIX terminal control definitions */ #include <unistd.h> /* Sleep Function */ #define BUFFER_SIZE 1000 unsigned char Buffer[BUFFER_SIZE]; struct termios options; int open_port() { int fd; /* File descriptor for the port */ fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY); if (fd == -1) { perror("open_port: Unable to open /dev/ttyS0 - "); } else { fcntl(fd, F_SETFL, 0); return (fd); } } void configure_port(int fd) { tcgetattr(fd, &options); cfsetispeed(&options, B1200); cfsetospeed(&options, B1200); options.c_cflag |= (CLOCAL | CREAD); options.c_cflag &= ~PARENB options.c_cflag |= PARODD options.c_cflag &= ~CSTOPB options.c_cflag &= ~CSIZE; options.c_cflag |= CS8; options.c_cflag &= ~CNEW_RTSCTS; options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG); options.c_oflag &= ~OPOST; options.c_cc[VMIN] = 0; options.c_cc[VTIME] = 10; tcsetattr(fd, TCSANOW, &options); } void raise_rts_signal(int fd) { int status; ioctl(fd, TIOCMGET, &status); status &= TIOCM_RTS; ioctl(fd, TIOCMSET, status); } void drop_rts_signal(int fd) { int status; ioctl(fd, TIOCMGET, &status); status &= ~TIOCM_RTS; ioctl(fd, TIOCMSET, status); } int send_hart_frame(int fd) { int bytes; unsigned char hart_buff[11] = {0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x2, 0x0, 0x0, 0x0, 0x2 }; bytes = write(fd, hart_buff, 11); if (bytes != 11) return -1; else return 0; } int get_bytes_available(int fd, unsigned char *Buf) { int bytes; ioctl(fd, FIONREAD, &bytes); if (bytes >= 1) { bytes = read(fd, Buf, BUFFER_SIZE); if (bytes < 0) return -1; printf("Received Bytes from Hart: %s", Buf); return 0; } else printf("No data available."); return -1; } int main(void) { int fd = open_port(); configure_port(fd); while(1) { raise_rts_signal(fd); // sleep 5 milliseconds sleep(0.005); send_hart_frame(fd); // sleep 5 milliseconds sleep(0.005); drop_rts_signal(fd); // now poll for bytes available in serial buffer get_bytes_available(fd, Buffer); // try again in 30 seconds sleep(30); } close(fd); return 0; }
