tick.c


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37

#define HAVE_TICK

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

ISR(TIMER1_COMPA_vect)
{
	systick.u32++;
}

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('.');
	uart_puthex16(frac);
	_uart_putch(' ');
}

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