--- /dev/null
+#include <avr/io.h>
+#include "timer.h"
+
+#define BIT(n) (1<<(n))
+
+static void timer_start(uint8_t num, uint32_t period)
+{
+ uint8_t cs;
+
+ if(num==0)
+ {
+ if(period<0x100)
+ {
+ cs = BIT(CS00);
+ }
+ else if(period<0x800)
+ {
+ cs = BIT(CS01);
+ period /= 8;
+ }
+ else if(period<0x4000)
+ {
+ cs = BIT(CS01) | BIT(CS00);
+ period /= 64;
+ }
+ else if(period<0x10000)
+ {
+ cs = BIT(CS02);
+ period /= 256;
+ }
+ else
+ {
+ cs = BIT(CS02) | BIT(CS00);
+ period /= 1024;
+ if(period>0xFF)
+ period = 0xFF;
+ }
+ TCCR0A = BIT(WGM01);
+ TCCR0B = cs;
+ OCR0A = period;
+ TIMSK0 = BIT(OCIE0A);
+ }
+ if(num==1)
+ {
+ if(period<0x10000)
+ {
+ cs = BIT(CS10);
+ }
+ else if(period<0x80000)
+ {
+ cs = BIT(CS11);
+ period /= 8;
+ }
+ else if(period<0x400000)
+ {
+ cs = BIT(CS11) | BIT(CS10);
+ period /= 64;
+ }
+ else if(period<0x1000000)
+ {
+ cs = BIT(CS12);
+ period /= 256;
+ }
+ else
+ {
+ cs = BIT(CS12) | BIT(CS10);
+ period /= 1024;
+ if(period>0xFFFF)
+ period = 0xFFFF;
+ }
+ TCCR1A = 0;
+ TCCR1B = BIT(WGM12) | cs;
+ OCR1AH = period>>8;
+ OCR1AL = period;
+ TIMSK1 = BIT(OCIE1A);
+ }
+}
+
+void timer_start_hz(uint8_t num, uint32_t freq_p, uint8_t freq_q)
+{
+ timer_start(num, F_CPU*freq_q/freq_p);
+}
+
+void timer_start_us(uint8_t num, uint32_t us)
+{
+ timer_start(num, F_CPU/1000000*us);
+}
+
+void timer_stop(uint8_t num)
+{
+ if(num==0)
+ {
+ TCCR0B = 0;
+ TIMSK0 = 0;
+ }
+ else if(num==1)
+ {
+ TCCR1B = 0;
+ TIMSK1 = 0;
+ }
+}