hello.c

/*
 * Userspace program that communicates with the led_vga device driver
 * primarily through ioctls
 *
 * Stephen A. Edwards
 * Columbia University
 */

#include <stdio.h>
#include "vga_led.h"
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>

void write_position(int, int);

int vga_led_fd;

int main()
{
    vga_led_arg_t vla;
    int i;
    static const char filename[] = "/dev/vga_led";
    
    int x_pos, x_vel, y_pos, y_vel;
    
    /* Initial Position and Velocity Vectors */
    x_pos = 666;
    y_pos = 269;
    x_vel = 1;
    y_vel = 1;
    
    printf("VGA LED Userspace program started\n");
    
    if ((vga_led_fd = open(filename, O_RDWR)) == -1) 
    {
	fprintf(stderr, "could not open %s\n", filename);
	return -1;
    }
    
    while (1)
    {
	x_pos = x_pos + x_vel;
	y_pos = y_pos + y_vel;
	
	if (x_pos > X_MAX)
	{
	    x_pos = X_MAX;
	    x_vel = -x_vel;
	}
	else if (x_pos < X_MIN)
	{
	    x_pos = X_MIN;
	    x_vel = -x_vel;
	}
	
	if (y_pos > Y_MAX)
	{
	    y_pos = Y_MAX;
	    y_vel = -y_vel;
	}
	else if (y_pos < Y_MIN)
	{
	    y_pos = Y_MIN;
	    y_vel = -y_vel;
	}
	
	write_position(x_pos, y_pos);
	usleep(10000);    
    }  
    
    printf("VGA LED Userspace program terminating\n");
    return 0;
}

void write_position(int x, int y)
{
    vga_led_arg_t vla;  
    printf("BALL POSITION (%d, %d)\n", x, y);
    vla.x = (unsigned int) x;
    vla.y = (unsigned int) y;
    
    if (ioctl(vga_led_fd, VGA_LED_DRAW_BALL, &vla))
    {
	perror("ioctl(VGA_LED_DRAW_BALL) failed");
	return;
    }
}