irblaster.c

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

#define IR_FREQ 38000uL
#define IR_ADDRESS   0x00u
#define IR_DATA_ON   0x80u
#define IR_DATA_OFF  0x90u

static void delay_time_unit(void)
{
    static const int time_unit = 562u;
    _delay_us(time_unit);
}

static void enable_wave_output(void)
{
    DDRD |= (1u << PD6);
    PORTB |= (1u << PB5);
}

static void disable_wave_output(void)
{
    DDRD &= ~(1u << PD6);
    PORTB &= ~(1u << PB5);
}

static void init_square_wave(void)
{
    static const int half_period = (F_CPU/IR_FREQ)/2u;
    OCR0A = half_period;

    // COM0A = toggle on match
    // COM0B = disabled
    // WGM = Clear Timer on Compare match (CTC)
    // FOCx = disabled
    // CS = timer activated, no prescaler
    TCCR0A = ((0u << COM0A1) |
              (1u << COM0A0) |
              (0u << COM0B1) |
              (0u << COM0B0) |
              (0u << COM0B1) |
              (1u << WGM01) |
              (0u << WGM00));
    TCCR0B = ((0u << FOC0A) |
              (0u << FOC0B) |
              (0u << WGM02) |
              (0u << CS02) |
              (0u << CS01) |
              (1u << CS00));

    enable_wave_output();
}

static void set_wave_output_for_time(bool enabled, uint8_t units)
{
    if (enabled)
    {
        enable_wave_output();
    }
    else
    {
        disable_wave_output();
    }

    for (uint8_t i = 0u; i < units; i++)
    {
        delay_time_unit();
    }
}

static void send_begin_sequence(void)
{
        set_wave_output_for_time(true, 16u);
        set_wave_output_for_time(false, 8u);
}

static void send_end_sequence(void)
{
        set_wave_output_for_time(true, 1u);
        set_wave_output_for_time(false, 87u);
}

static void send_bit_value(bool value)
{
    set_wave_output_for_time(true, 1u);
    set_wave_output_for_time(false, (value ? 3u : 1u));
}

static void send_byte_value(uint8_t value)
{
    uint8_t bits = value;

    for (int i = 0; i < 8; i++)
    {
        send_bit_value(bits & 0x80);
        bits <<= 1u;
    }
}

static void send_encoded_byte_value(uint8_t value)
{
    send_byte_value(value);
    send_byte_value(~value);
}

static void send_command_to_address(uint8_t address, uint8_t command)
{
    send_begin_sequence();
    send_encoded_byte_value(address);
    send_encoded_byte_value(command);
    send_end_sequence();
}

static void send_command_to_address_several_times(uint8_t address, uint8_t command, uint8_t times)
{
    for (int i = 0; i < times; i++)
    {
        send_command_to_address(address, command);
    }
}

int main(int argc, char **argv)
{
    init_square_wave();

    while(true) {
        send_command_to_address_several_times(IR_ADDRESS, IR_DATA_ON, 5u);
        _delay_ms(1000u);

        send_command_to_address_several_times(IR_ADDRESS, IR_DATA_OFF, 5u);
        _delay_ms(1000u);
    }

    return 42;
}