// Requisite header files.
#include <avr/io.h>
#include <util/delay.h>

// Frequency of the IR carrier signal (Hertz).
#define F_IR_CARRIER (37000)

// Timing of the data bits (microseconds).
#define T_DX_MARK   (440)
#define T_D0_SPACE  (440)
#define T_D1_SPACE (1310)

// Timing of the lead-in and lead-out bits (microseconds).
#define T_LEAD_IN_MARK    (3500)
#define T_LEAD_IN_SPACE   (1750)
#define T_LEAD_OUT_MARK    (440)
#define T_LEAD_OUT_SPACE (74000)

// Commands definitions.
#define OEM_DEVICE_1_CODE         (2)
#define OEM_DEVICE_2_CODE        (32)
#define CAMCORDER_DEVICE_ID     (112)
#define CAMCORDER_SUB_DEVICE_ID  (40)
#define CAMCORDER_COMMAND_EJECT   (1)

// Transmits a single unformatted byte.
void panasonic_send_byte(uint8_t value) {
    // Send eight data bits.
    for (uint8_t bit = 0; bit < 8; ++bit, value >>= 1) {
        // Send the mark/burst.
        DDRB |= _BV(1);
        _delay_us(T_DX_MARK);
        // Send the space.
        DDRB &= (uint8_t)~_BV(1);
        _delay_us(T_D0_SPACE);
        // Extend the space if it's a "1" data bit.
        if (value & (uint8_t)1) {
            _delay_us(T_D1_SPACE - T_D0_SPACE);
        }
    }
}

// Transmits a formatted command packet to the IR device.
void panasonic_send_command(uint8_t oem_device_code_1, uint8_t oem_device_code_2, uint8_t device_code, uint8_t sub_device_code, uint8_t command) {
    // Send the lead in.
    DDRB |= _BV(1);
    _delay_us(T_LEAD_IN_MARK);
    DDRB &= (uint8_t)~_BV(1);
    _delay_us(T_LEAD_IN_SPACE);

    // Send the five command bytes.
    panasonic_send_byte(oem_device_code_1);
    panasonic_send_byte(oem_device_code_2);
    panasonic_send_byte(device_code);
    panasonic_send_byte(sub_device_code);
    panasonic_send_byte(command);

    // Send the checksum.
    panasonic_send_byte(device_code ^ sub_device_code ^ command);

    // Send the lead out.
    DDRB |= _BV(1);
    _delay_us(T_LEAD_OUT_MARK);
    DDRB &= (uint8_t)~_BV(1);
    _delay_us(T_LEAD_OUT_SPACE);
}

// Main program entry point.
int main(void) {

    TCCR0A |= _BV(COM0B0) | _BV(WGM01);     // Toggle OC0B when on CTC reload. Use CTC mode.
    TCCR0B |= _BV(CS00);                    // Set clock source to CPU clock/1.
    OCR0A = (F_CPU / F_IR_CARRIER / 2) - 1; // Set the CTC reload value to generate an IR signal at the correct carrier frequency.

    // Send the "eject" command ad infinitum.
    for(;;) {
        panasonic_send_command(OEM_DEVICE_1_CODE, OEM_DEVICE_2_CODE, CAMCORDER_DEVICE_ID, CAMCORDER_SUB_DEVICE_ID, CAMCORDER_COMMAND_EJECT);
    }
}