// Arduino SPWM Sine Inverter
// https://electronoobs.com/eng_arduino_tut88.php

#include <avr/io.h>
#include <avr/interrupt.h>

// Look up tables with 200 entries each, normalised to have max value of 1600 which is the period of the PWM loaded into register ICR1.
uint16_t sine_table[] = {
     0,   50,  100,  150,  200,  250,  300,  349,  398,  446,
   494,  542,  589,  635,  681,  726,  770,  814,  857,  899,
   940,  980, 1019, 1057, 1095, 1131, 1166, 1199, 1232, 1263, 
  1294, 1323, 1350, 1376, 1401, 1425, 1447, 1467, 1487, 1504, 
  1521, 1536, 1549, 1560, 1571, 1579, 1586, 1592, 1596, 1598, 
  1599
};


#include <avr/io.h>
#include <avr/interrupt.h>
#include <math.h>


void setup() {
  // pinMode(LED_BUILTIN, OUTPUT);
  DDRB |= (1 << PB1) | (1 << PB2) | (1 << PB5); // Set D9 (PB1), D10 (PB2) and D13 (PB5) as outputs

  // Configure Timer1
  TCCR1A = (1 << COM1A1) | (1 << COM1B1) | (1 << WGM11); // Non-inverting mode for both channels
  TCCR1B = (1 << WGM12) | (1 << WGM13) | (1 << CS10); // No prescaler
  ICR1 = 1599; // TOP value for 10 kHz sample rate
  TIMSK1 = (1 << TOIE1); // Enable overflow interrupt
  sei(); // Enable global interrupts
}

ISR(TIMER1_OVF_vect) {
  static uint8_t index = 0;
  static uint16_t nextOCR1A = 0;
  static uint16_t nextOCR1B = 0;

  // Always output positive part on OCR1A (D9)
  OCR1A = nextOCR1A;

  // For OCR1B (D10), output inverted sine only if negative, else 0
  OCR1B = nextOCR1B;

  asm volatile ("sbi %0, %1" :: "I" (_SFR_IO_ADDR(PORTB)), "I" (PB5)); // Set LED_BUILTIN
  index = (index == 199) ? 0 : index + 1; // Move to next sample
  if (index < 100) {
    nextOCR1B = 0;
    if (index < 50) {
      nextOCR1A = sine_table[index];        // index < 50
    } else {
      nextOCR1A = sine_table[100 - index];  // 50 <= index < 100 -> 0 < (100 - index) <= 50
    }
  } else {
    nextOCR1A = 0;
    if (index < 150) {
      nextOCR1B = sine_table[index - 100];  // 100 <= index < 150 -> 0 <= (index - 100) < 50
    } else {
      nextOCR1B = sine_table[200 - index];  // 150 <= index < 200 -> 0 < (200 - index) <= 50
    }
  }
  asm volatile ("cbi %0, %1" :: "I" (_SFR_IO_ADDR(PORTB)), "I" (PB5)); // Clear LED_BUILTIN
}

void loop() {
  // Nothing here; everything is handled in the ISR
}