#define HAVE_TICK

static union {
	uint32_t u32;
	uint8_t u8[4];
} systick = { .u32 = 0 };

#ifndef SYSTICK_USER_1HZ
#define systick_user_1hz()
#endif

static uint8_t tick_sub;

ISR(TIMER1_COMPA_vect)
{
#ifdef SYSTICK_USER_100HZ
	systick_user_100hz();
	if (++tick_sub < 100)
		return;

	tick_sub = 0;
#endif
	systick.u32++;
	systick_user_1hz();
}

static void uart_puttick(void)
{
	uint16_t frac = TCNT1;

	_uart_putch('@');
	uart_puthex(systick.u8[3]);
	uart_puthex(systick.u8[2]);
	uart_puthex(systick.u8[1]);
	uart_puthex(systick.u8[0]);
	_uart_putch('.');
#ifdef SYSTICK_USER_100HZ
	uart_puthex(tick_sub);
#else
	uart_puthex16(frac);
#endif
#if DEBUG_SP
	_uart_putch('~');
	uint8_t spl, sph;
	asm ("\n\
		in %[spl], 0x3d\n\
		in %[sph], 0x3e\n\
	" : [spl] "=r" (spl), [sph] "=r" (sph));
	uart_puthex(sph);
	uart_puthex(spl);
#endif
	_uart_putch(' ');
}

static void tick_init(void)
{
	TCCR1A = 0;
#ifdef SYSTICK_USER_100HZ
	TCCR1B = (1 << WGM12) | (0 << CS12) | (1 << CS11) | (0 << CS10); // 8 MHz / 8 = 1 MHz
	asm volatile ("" ::: "memory");
	TCNT1 = 0;
	OCR1A = 9999; // 100 Hz
#else
	TCCR1B = (1 << WGM12) | (1 << CS12) | (0 << CS11) | (0 << CS10); // 8 MHz / 256 = 31250 Hz
	asm volatile ("" ::: "memory");
	TCNT1 = 0;
	OCR1A = 31249; // 1 Hz
#endif
	asm volatile ("" ::: "memory");
	TIFR1 = (1 << OCF1A);
	TIMSK1 = (1 << OCIE1A);
}