lightctrl: 1 second system tick

1 files changed, 37 insertions, 0 deletions

diff --git a/tick.c b/tick.c
new file mode 100644
index 0000000..87dcbc6
--- /dev/null
+++ b/tick.c
@@ -0,0 +1,37 @@
+#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);
+}
+