64 lines
1.7 KiB
C
64 lines
1.7 KiB
C
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/*
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* Low resolution implementation of timer using a 8 bit clock with prescaler,
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* etc. Clicks approximately every millisecond. Microseconds are not available,
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* and any queries to the function will just return milliseconds * 1000.
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* You can use this file when you don't need high resolution timing, and don't care
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* about slight clock drift, inaccuracy, etc. For timing most human-related activities,
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* though, it should be more than sufficient.
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*/
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#include "timer.h"
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static volatile uint64_t _timer_millis;
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/*
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* Initializes the timer, and resets the timer count to 0. Sets up the ISRs
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* linked with timer0.
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*/
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void timer_init(){
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//Set up the timer to run at F_CPU / 256, in normal mode (we reset TCNT0 in the ISR)
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TCCR0A = 0x0;
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TCCR0B |= _BV(CS02);
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//Set compare value to be F_CPU / 1000 -- fire interrupt every millisecond
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OCR0A = F_CPU / 256 / 1000;
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//Enable compare interrupt
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TIMSK0 = _BV(OCIE0A);
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//Reset count variables
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_timer_millis = 0;
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//Enable interrupts if the NO_INTERRUPT_ENABLE define is not set. If it is, you need to call sei() elsewhere.
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#ifndef NO_INTERRUPT_ENABLE
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sei();
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#endif
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DDRB = 0xFF;
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}
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/*
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* Returns the number of milliseconds which have elapsed since the
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* last time timer_init() was called. Overflows after about 49 days.
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*/
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uint64_t timer_millis(){
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return _timer_millis;
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}
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/*
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* Returns the number of microseconds which have elapsed since the
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* last time timer_init() was called. Overflows after about 71 minutes.
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*/
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uint64_t timer_micros(){
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return (_timer_millis * 1000);
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}
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/*
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* The ISR for timer0 overflow. Increment the _timer_count here, and do the calculcations
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* to increment _timer_millis as needed.
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*/
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ISR(TIMER0_COMPA_vect){
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TCNT0 = 0;
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_timer_millis++;
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}
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