//
// hello.speaker.45.c
//
// speaker PWM hello-world
//    square wave, pseudo-random frequency
//
// Neil Gershenfeld
// 11/14/10
//
// (c) Massachusetts Institute of Technology 2010
// This work may be reproduced, modified, distributed,
// performed, and displayed for any purpose. Copyright is
// retained and must be preserved. The work is provided
// as is; no warranty is provided, and users accept all 
// liability.
//

#include <avr/io.h>
#include <util/delay.h>

#define output(directions,pin) (directions |= pin) // set port direction for output
#define set(port,pin) (port |= pin) // set port pin
#define clear(port,pin) (port &= (~pin)) // clear port pin
#define pin_test(pins,pin) (pins & pin) // test for port pin
#define bit_test(byte,bit) (byte & (1 << bit)) // test for bit set

#define cycle_delay() _delay_us(20000) // cycle delay
#define current 150 // PWM current
#define off 255 // PWM off
#define PWM_delay() _delay_us(25) // PWM delay

#define MOSFET_pin (1 << PB1)
#define MOSFET_port PORTB
#define MOSFET_direction DDRB

int main(void) {
   //
   // main
   //
   //
	unsigned char count, pwm;
   // set clock divider to /1
   //
   CLKPR = (1 << CLKPCE);
   CLKPR = (0 << CLKPS3) | (0 << CLKPS2) | (0 << CLKPS1) | (0 << CLKPS0);
   //
   //
   //
   TCCR0A = ((1 << COM0B0) | (1 << COM0B1) | (1 << WGM01) | (1 << WGM00)); // set OC0B on compare match and set fast PWM mode, 0xFF TOP
   TCCR0B = (1 << CS00); // set timer 0 prescalar to 1
   //
   // initialize MOSFET pin
   //
   clear(MOSFET_pin);
   output(MOSFET_direction, MOSFET_pin);

   //
   // main loop
   //
   while (1) {
 	for (count = 0; count < 25; ++count) {
         OCR0B = current;
         for (pwm = count; pwm < 25; ++pwm)
            PWM_delay();
         OCR0B = off;
         for (pwm = 0; pwm < count; ++pwm)
            PWM_delay();
         }
      }
   }