75 lines
1.5 KiB
C
75 lines
1.5 KiB
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 "config.h"
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// global clock
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#ifdef GLOBAL_CLOCK
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volatile uint32_t clock = 0;
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#endif
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// 1/4 second tick
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uint8_t clock_counter_250ms = 0;
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uint8_t clock_counter_1s = 0;
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volatile uint8_t clock_flag = 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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// TODO: Timer 2 has higher priority than Timer 1 used for the stepper
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// interrupts, which is bad. See AVR Reference Manual p. 9:
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// "The interrupts have priority in accordance
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// with their Interrupt Vector position. The
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// lower the Interrupt Vector address, the higher
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// the priority."
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// in conjunction with p. 63 (interrupt vector table).
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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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#ifdef GLOBAL_CLOCK
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clock++;
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#endif
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// 1/4 second tick
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if (++clock_counter_250ms == 250) {
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clock_flag |= CLOCK_FLAG_250MS;
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clock_counter_250ms = 0;
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if (++clock_counter_1s == 4) {
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clock_flag |= CLOCK_FLAG_1S;
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clock_counter_1s = 0;
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}
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}
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}
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#ifdef GLOBAL_CLOCK
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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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#endif
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