/* Name: JJYSimulator_40kHz.c
 * Author: Toshi Nagata
 * Copyright: 2009-2018 (c) Toshi Nagata
 * License: Modified BSD License
 *
 * Clock: External 8MHz
 * Pin 5 (PB0): from ESP8266 (RF on/off)
 * Pin 6 (PB1): antenna out
 */

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

#define F_CPU 8000000.0

inline void pwm_on(void) {
  TCCR0A |= 0b00110000;  // connect OC0B to PWM
}

inline void pwm_off(void) {
  TCCR0A &= 0b11001111;  // disconnect OC0B from PWM
  PORTB  |= 0b00000010;  // output 1 to OC0B(=PB1)
}

/*  Pin change interrupt handler  */
ISR(PCINT0_vect)
{
  if ((PINB & 0b00000001) != 0) {
    pwm_on();
  } else {
    pwm_off();
  }
}

int main(void) {
  cli();                // Disable interrupt
  DDRB = 0b00000010;    // PB1 for output
  PORTB = 0b00000001;   // PB0 enable pull-up
  
  // timer0: Highspeed PWM for 40kHz duty 1/2 Output (to OC0B)
  // external 8MHz, prescale 1/1: 1 timer clock = 0.125 us
  // 40kHz 1 cycle = 25 us = 200 clocks, duty 1/2: 25:25
  TCCR0A = 0b00110011;  // Set OC0B at Compare Match (=OCR0B) and clear at TOP
  TCCR0B = 0b00001001;  // Prescale 1/1, Fast PWM with TOP = OCR0A
  TCNT0 = 0;
  OCR0A = 200;        // PWM interval 25 us
  OCR0B = 100;        // Duty 1/2
  GIMSK  = 0b00100000;  // PCINT enabled
  PCMSK  = 0b00000001;  // PCINT0 (pin 5) enabled 
  set_sleep_mode(SLEEP_MODE_IDLE);  //  Idle mode (PWM will keep running)
  pwm_off();
  sei();                // Enable interrupt

  while (1) {
    sleep_enable();
    sleep_cpu();     //  Sleep until interrupt
    sleep_disable();
    _delay_loop_1(100);  //  Wait for some time and go to sleep again
  }
  return 0;  //  Not reached
}