c #include <stdio.h> #include <sys/io.h> #define LED_PIN 4 int main() { if (iopl(3) < 0) { perror("iopl"); return 1; } outb(0x00, LED_PIN); usleep(1000000); outb(0x01, LED_PIN); return 0; } gcc -o led_control_app led_control_app.c