58 lines
913 B
C
58 lines
913 B
C
/*
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clock.c
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a system clock with 1ms ticks
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*/
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#include "clock.h"
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#include <avr/io.h>
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#include <avr/interrupt.h>
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#include "arduino.h"
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// global clock
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volatile uint32_t clock = 0;
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// 1/4 second tick
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uint8_t clock_counter_250ms = 0;
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volatile uint8_t clock_flag_250ms = 0;
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void clock_setup() {
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// use system clock
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ASSR = 0;
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// no compare match, CTC mode
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TCCR2A = MASK(WGM21);
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// 128 prescaler (16MHz / 128 = 125KHz)
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TCCR2B = MASK(CS22) | MASK(CS20);
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// 125KHz / 125 = 1KHz for a 1ms tick rate
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OCR2A = 125;
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// interrupt on overflow, when counter reaches OCR2A
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TIMSK2 |= MASK(OCIE2A);
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}
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ISR(TIMER2_COMPA_vect) {
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// global clock
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clock++;
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// 1/4 second tick
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if (++clock_counter_250ms == 250) {
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clock_flag_250ms = 255;
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clock_counter_250ms = 0;
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}
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}
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uint32_t clock_read() {
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uint32_t c;
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cli(); // set atomic
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c = clock; // copy clock value
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sei(); // release atomic
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return c;
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}
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