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

#include <stdbool.h>
#include <stdint.h>


static volatile int8_t kbd_state = 0;

static volatile uint8_t kbd_input = 0;
static volatile uint8_t kbd_output = 0;
static volatile uint8_t kbd_flags = 0;


static volatile uint8_t ts = 10;


#define KBD_FLAG_ERROR  (_BV(0))
#define KBD_FLAG_BREAK  (_BV(1))
#define KBD_FLAG_EXT    (_BV(2))

#define KBD_CODE_UP     0xe075
#define KBD_CODE_LEFT   0xe06b
#define KBD_CODE_DOWN   0xe072
#define KBD_CODE_RIGHT  0xe074



static inline bool kbd_data() {
	return (PINC & (1 << 0));
}

static inline bool kbd_clock() {
	return (PINC & (1 << 1));
}


ISR(PCINT1_vect) {
	if (kbd_clock())
		return;

	if (kbd_state < 0) {
		if (kbd_state >= -8) {
			if (kbd_output & (1 << (-1-kbd_state)))
				PORTC |= 0x01;
			else
				PORTC &= ~0x01;

			kbd_state--;
			return;
		}

		if (kbd_state == -9) {
			if ((__builtin_popcount(kbd_output) & 1) == 0)
				PORTC |= 0x01;
			else
				PORTC &= ~0x01;

			kbd_state--;
			return;
		}

		if (kbd_state == -10) {
			kbd_state--;

			DDRC &= ~0x01;
			PORTC |= 0x01;
			return;
		}

		kbd_state = 0;

		return;
	}

	bool data = kbd_data();

	if (kbd_state == 0) {
		if (!data) { /* start bit */
			kbd_input = 0;
			kbd_state++;
		}

		return;
	}

	if (kbd_state <= 8) {
		kbd_input |= (data << (kbd_state-1));
		kbd_state++;
		return;
	}

	if (kbd_state == 9) {
		if ((__builtin_popcount(kbd_input) & 1) == data)
			kbd_flags |= KBD_FLAG_ERROR;

		kbd_state++;
		return;
	}

	kbd_state = 0;

	if (kbd_flags & KBD_FLAG_ERROR) {
		/* Retry */
		return;
	}

	if (kbd_input == 0xe0) {
		kbd_flags |= KBD_FLAG_EXT;
		return;
	}

	if (kbd_input == 0xf0) {
		kbd_flags |= KBD_FLAG_BREAK;
		return;
	}

	uint16_t code = kbd_input;
	if (kbd_flags & KBD_FLAG_EXT)
		code |= 0xe000;

	if (!(kbd_flags & KBD_FLAG_BREAK)) {
		switch (code) {
		case KBD_CODE_UP:
			if (ts > 0)
				ts--;
			break;

		case KBD_CODE_DOWN:
			if (ts < 31)
				ts++;
			break;
		}
	}

	kbd_flags = 0;
}


void kbd_send(uint8_t command) {
	while (kbd_state) {} /* wait for idle */

	DDRC |= 0x02;
	PORTC &= ~0x02;
	_delay_us(100);

	DDRC |= 0x01;
	PORTC &= ~0x01;
	_delay_us(10);

	DDRC &= ~0x02;
	PORTC |= 0x02;

	kbd_output = command;
	kbd_state = -1;

	/* wait for idle */
	while (kbd_state) {}
	while (!kbd_state) {}
	while (kbd_state) {}
}


int main(void) {
	DDRB  = 0xff;
	PORTB = 0;

	DDRC  = 0x00;
	PORTC = 0x03;

	PCMSK1 = (1 << PCINT9);
	PCICR = (1 << PCIE1);

	sei();

	kbd_send(0xff);

	uint8_t l = 0;

	while(true) {
		uint8_t state = PORTB ^ 0x20;
		PORTB = state;

		if (state & 0x20) {
			l = (l+1)%3;

			kbd_send(0xed);
			kbd_send(1 << l);
		}

		uint32_t i;
		for (i = 0; i < (1 << ts); i++)
			_delay_ms(1);
	}

	return 0;
}