/******************************************************************
 * Compile: gcc -o fade1 -Wall -I/usr/local/include -L/usr/local/lib 
 *          fade2.c -lwiringPi
 * 
 * Execute: sudo ./fade2
 *
 * All pin numbers are wiringPi numbers unless otherwise specified.
 ******************************************************************/

#include <wiringPi.h>

int main()
{
  wiringPiSetup();              // Setup required by wiringPi

  pinMode (1, PWM_OUTPUT);      // 
  pwmSetMode(PWM_MODE_MS);      // Mark/Space mode

  while(1) 
  {
    int i;
    int x = 1;
    for (i = 0; i > -1; i = i + x)
    {
      int d = (16-i/16)^2;     // calc inverse square of index
      pwmWrite(1, i);
      delay(d);
      if (i == 255) x = -1;   // switch direction at peak
    }
  } 
}