a500kbd: src/timer.c annotate

a500kbd

first working version

author	John Tsiombikas <nuclear@member.fsf.org>
date	Tue, 17 Oct 2017 15:25:33 +0300
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rev	line source
nuclear@2	1 #include <avr/io.h>
nuclear@2	2 #include <avr/interrupt.h>
nuclear@2	3 #include <avr/power.h>
nuclear@2	4 #include "timer.h"
nuclear@2	5
nuclear@2	6 #define PRESCL_256 4
nuclear@2	7 /* 256 ticks per interrupt, 256 clock divisor */
nuclear@2	8 #define TICKS_PER_SEC (F_CPU / 256 / 256)
nuclear@2	9
nuclear@2	10 static volatile unsigned long ticks;
nuclear@2	11
nuclear@2	12 void init_timer(void)
nuclear@2	13 {
nuclear@2	14 power_timer0_enable();
nuclear@2	15
nuclear@2	16 TCCR0A = 0;
nuclear@2	17 TCCR0B = PRESCL_256;
nuclear@2	18
nuclear@2	19 TIMSK0 \|= (1 << TOIE0); /* enable ovf intr. */
nuclear@2	20 }
nuclear@2	21
nuclear@2	22 void reset_timer(void)
nuclear@2	23 {
nuclear@2	24 ticks = 0;
nuclear@2	25 }
nuclear@2	26
nuclear@2	27 unsigned long get_msec(void)
nuclear@2	28 {
nuclear@2	29 return 1000 * ticks / TICKS_PER_SEC;
nuclear@2	30 }
nuclear@2	31
nuclear@2	32 ISR(TIMER0_OVF_vect)
nuclear@2	33 {
nuclear@2	34 ++ticks;
nuclear@2	35 }