example.c

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

#include <linux/joystick.h>

int main (int argc, char **argv)
{
	int fd;

	if (argc < 2) {
		printf("Usage: %s <device>\n\n", argv[0]);
		exit(1);
	}

	if ((fd = open(argv[argc - 1], O_RDONLY)) < 0) {
		perror("failed to open device");
		exit(1);
	}
	else {
		unsigned char axes = 2;
		unsigned char buttons = 2;
		int *axis;
		int *button;
		int i;
		struct js_event js;
		float clutch;
		float steering;
		float throttle;
		float brake;
		float throttle_cruise;
		float throttle_cur = 0.0f;
		int cruise = 0;
		int cruise_inc = 0;
		int cruise_dec = 0;
		int shifter;

		ioctl(fd, JSIOCGAXES, &axes);
		ioctl(fd, JSIOCGBUTTONS, &buttons);
		fcntl(fd, F_SETFL, O_NONBLOCK);

		axis = calloc(axes, sizeof(int));
		button = calloc(buttons, sizeof(char));

		while (1) {
			while (read(fd, &js, sizeof(struct js_event)) == sizeof(struct js_event)) {
				switch(js.type & ~JS_EVENT_INIT) {
				case JS_EVENT_BUTTON:
					button[js.number] = js.value;
					break;
				case JS_EVENT_AXIS:
					axis[js.number] = js.value;
					break;
				}
			}

			if (errno != EAGAIN) {
				perror("\nerror reading");
				exit (1);
			}

			printf("\r");

			steering = axis[0] / 32767.0f;
			clutch = (axis[1] + 32767) / 65534.0f;
			throttle = (32767 - axis[2]) / 65534.0f;
			brake = (32767 - axis[3]) / 65534.0f;

			if (cruise) {
				if (button[18] || !(button[12] || button[13]) || brake > 0.25f) {
					cruise = 0;
				}
				else {
					if (button[7] && !cruise_inc) {
						throttle_cruise += 0.05f;
					}
					if (button[20] && !cruise_dec) {
						throttle_cruise -= 0.05f;
					}
					if (throttle_cruise < 0.0f) {
						throttle_cruise = 0.0f;
					}
					else if (throttle_cruise > 1.0f) {
						throttle_cruise = 1.0f;
					}
					if (throttle < throttle_cruise) {
						throttle = throttle_cruise;
					}
					throttle_cur += 0.05f * (throttle - throttle_cur);

					cruise_inc = button[7];
					cruise_dec = button[20];
				}
			}
			else {
				if ((button[12] || button[13]) && button[6]) {
					throttle_cruise = throttle_cur;
					cruise = 1;
				}
				else {
					brake *= brake;
					brake *= brake;

					if ((button[12] || button[13] || button[22]) && throttle <= 0.1f) {
						throttle = 0.1f; // idle
					}
					throttle *= clutch;
					throttle *= button[22] ? -1.0f : 1.0f; // reverse
					throttle_cur += 0.01f * (throttle - throttle_cur);
					throttle_cur *= 1.0f - brake;
				}
			}

			if (button[12]) { // first gear
				shifter = 1;
			}
			else if (button[13]) { // second gear
				shifter = 2;
			}
			else if (button[22]) { // reverse gear
				shifter = 1;
			}
			else { // neutral
				shifter = 0;
			}

			printf("Throttle: %f ", throttle_cur);
			printf("Steering: %f ", steering);
			printf("Shifter: %d ", shifter);
			printf("Clutch: %f ", clutch);
			printf("Cruise: %s ", cruise ? "on" : "off");

			fflush(stdout);

			usleep(10000);
		}
	}
}



int
set_interface_attribs (int fd, int speed, int parity)
	{
	        struct termios tty;
	        memset (&tty, 0, sizeof tty);
	        if (tcgetattr (fd, &tty) != 0)
		        {
		                error_message ("error %d from tcgetattr", errno);
		                return -1;
		        }

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

	        tty.c_cflag = (tty.c_cflag & ~CSIZE) | CS8;     // 8-bit chars
	        // disable IGNBRK for mismatched speed tests; otherwise receive break
	        // as \000 chars
	        tty.c_iflag &= ~IGNBRK;         // disable break processing
	        tty.c_lflag = 0;                // no signaling chars, no echo,
	                                        // no canonical processing
	        tty.c_oflag = 0;                // no remapping, no delays
	        tty.c_cc[VMIN]  = 0;            // read doesn't block
	        tty.c_cc[VTIME] = 5;            // 0.5 seconds read timeout

	        tty.c_iflag &= ~(IXON | IXOFF | IXANY); // shut off xon/xoff ctrl

	        tty.c_cflag |= (CLOCAL | CREAD);// ignore modem controls,
	                                        // enable reading
	        tty.c_cflag &= ~(PARENB | PARODD);      // shut off parity
	        tty.c_cflag |= parity;
	        tty.c_cflag &= ~CSTOPB;
	        tty.c_cflag &= ~CRTSCTS;

	        if (tcsetattr (fd, TCSANOW, &tty) != 0)
		        {
		                error_message ("error %d from tcsetattr", errno);
		                return -1;
		        }
	        return 0;
	}

void
set_blocking (int fd, int should_block)
	{
	        struct termios tty;
	        memset (&tty, 0, sizeof tty);
	        if (tcgetattr (fd, &tty) != 0)
	        {
	                error_message ("error %d from tggetattr", errno);
	                return;
	        }

	        tty.c_cc[VMIN]  = should_block ? 1 : 0;
	        tty.c_cc[VTIME] = 5;            // 0.5 seconds read timeout

	        if (tcsetattr (fd, TCSANOW, &tty) != 0)
	                error_message ("error %d setting term attributes", errno);
	}


...
char *portname = "/dev/ttyACM0"
 ...
int fd = open (portname, O_RDWR | O_NOCTTY | O_SYNC);
if (fd < 0)
{
        error_message ("error %d opening %s: %s", errno, portname, strerror (errno));
        return;
}

set_interface_attribs (fd, B115200, 0);  // set speed to 115,200 bps, 8n1 (no parity)
set_blocking (fd, 0);                // set no blocking

write (fd, "hello!\n", 7);           // send 7 character greeting

usleep ((7 + 25) * 100);             // sleep enough to transmit the 7 plus
                                     // receive 25:  approx 100 uS per char transmit
char buf [100];
int n = read (fd, buf, sizeof buf);  // read up to 100 characters if ready to read