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/*
mh-timer.c -- Advanced functions using Timer/Counter
Author : Ajith Kumar, Inter-University Accelerator Centre, New Delhi.
License : GNU GPL version 3 or later
Date : 23-Oct-2013
*/
#include <avr/io.h>
#include <avr/interrupt.h>
//------------------- Frequency measurement ----------------------------
#define MTIME 250 // We count 100 on TC0
uint32_t measure_freq(void)
{
DDRB &= ~(1 << PB1); // Timer/Counter1 clock in T1 (PB1) as input
TCCR0 = (1 << CS02) |(1 << CS00); // Normal mode , CPU Clock / 1024
TIFR |= (1 << OCF0); // Clear OCF flag for T0
TCCR1B = (1 << CS12) | (1 << CS11) | (1 << CS10); // External clock on T1 pin
TCNT0 = 0; // Clear TCNT0
TCNT1 = 0; // Clear TCNT1
while(TCNT0 < MTIME) ;
TCCR1B = 0;
return TCNT1;
}
//----------------------- Time interval measurement--------------------------
volatile uint16_t HIWORD;
ISR(TIMER1_COMPA_vect) // TIMER1 Compare Match A Interrupt
{
TCNT1 = 0;
++HIWORD;
PORTB = 1;
}
void start_timer()
{
/*
When TCNT1 reaches OCR1A, the ISR will run. It will clear TCNT1 and increment HIWORD.
The total time elapsed between start_timer and get_timer = HIWORD * 50000 + TCNT1
*/
TCCR1B = (1 << CS11); // Normal mode, with 1MHz clock
HIWORD = 0;
OCR1A = 50000;
OCR1B = 0xffff;
TIMSK = (1 << OCIE1A); // Enable compare match interrupt
TIFR = (1 << OCF1A);
TCNT1 = 0;
sei();
}
uint32_t read_timer()
{
uint32_t x;
TCCR1B = 0; // stop TC1 clock
x = HIWORD * 50000 + TCNT1;
cli();
return x;
}
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