serial_jsd.c

#include <errno.h>
#include <fcntl.h> 
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <termios.h>
#include <unistd.h>
#include <sys/ioctl.h>

#define MSG_SIZE 36

int set_interface_attribs(int fd, int speed)
{
    struct termios tty;

    if (tcgetattr(fd, &tty) < 0) {
        printf("Error from tcgetattr: %s\n", strerror(errno));
        return -1;
    }

    cfmakeraw(&tty);

    cfsetospeed(&tty, (speed_t)speed);
    cfsetispeed(&tty, (speed_t)speed);

    tty.c_cc[VMIN] = 0;
    tty.c_cc[VTIME] = 1;

    if (tcsetattr(fd, TCSANOW, &tty) != 0) {
        printf("Error from tcsetattr: %s\n", strerror(errno));
        return -1;
    }
    return 0;
}

void sendBuffer(const unsigned char *buffer)
{
    static int outFDs[] = {-1, -1, -1, -1};
    char device[16];
    int index = buffer[0] & 0x0F;

    if (index < 0 || index > 3)
    {
	    printf("Invalid message\n");
	    return;
    }

    if (outFDs[index] == -1)
    {
	sprintf(device, "/dev/serial_js%d", index);
        outFDs[index] = open(device, O_RDWR);
    }

    write(outFDs[index], buffer + 1, MSG_SIZE - 1);
}

int connect(const char *portname)
{
    int fd = -1;
    while (fd < 0)
    {
	fd = open(portname, O_RDONLY | O_NOCTTY);
	if (fd < 0) {
	    printf("Error opening %s: %s\n", portname, strerror(errno));
	    sleep(5);
	}
    }

    /*baudrate 115200, 8 bits, no parity, 1 stop bit */
    set_interface_attribs(fd, B115200);

    return fd;
}

int main(int argc, char *argv[])
{
    int fd;
    unsigned char buf[2 * MSG_SIZE];
    unsigned char *pBuf = buf;

    bool starting = true;
    unsigned int emptyCount = 0;

    if (argc != 2)
    {
	    printf("Error on number of program arguments %d\n", argc);
	    return -1;
    }

    fd = connect(argv[1]);

    /* simple noncanonical input */
    do {
        int rdlen;

        rdlen = read(fd, pBuf, sizeof(buf) - (pBuf - buf) - 1);
        if (rdlen > 0) {
	    unsigned char *firstBreak = strchr(buf, '\n');

	    starting = false;
	    emptyCount = 0;

            pBuf[rdlen] = 0;
	    pBuf += rdlen;

	    if (firstBreak == NULL)
	    {
		    continue;
	    }

	    if (firstBreak - buf == MSG_SIZE)
	    {
		    sendBuffer(buf);
	    }

	    memmove(buf, firstBreak + 1, (pBuf - firstBreak));
	    pBuf = strchr(buf, '\0');
	    memset(pBuf, 0, sizeof(buf) - (pBuf - buf));
        }
	else if (rdlen < 0 || emptyCount > 2)
	{
	    int flags;
            printf("Error from read: %d: %s\n", rdlen, strerror(errno));
	    
	    close(fd);

	    starting = true;
	    emptyCount = 0;

	    // Try to reconnect
	    fd = connect(argv[1]);
	    
	    flags = TIOCM_DTR;
            ioctl(fd, TIOCMBIC, &flags);
            flags = TIOCM_DTR;
            ioctl(fd, TIOCMBIS, &flags);
        }
	else // rdlen == 0
	{
            if (starting)
	    {
            	sleep(1);
	    }

	    emptyCount++;
	}
        /* repeat read to get full message */
    } while (1);
}