ustimer.h File Reference

micro-second(us) timer More...

#include <inttypes.h>
#include <avr/io.h>
#include <avr/signal.h>
#include <avr/interrupt.h>

Functions
void	us_timer_init (void)
	initiates the timer
uint32_t	us_time_get (void)
	get current time
uint32_t	us_time_get_difference (uint32_t time1)
	calculates the difference between a saved and the current time
double	us_time_get_difference_d (uint32_t time1)
	calculates the difference between a saved and the current time in micro-seconds

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Detailed Description

micro-second(us) timer

Functions for precise time measurements. Tested with

• Timer3, ATMega128, 16bit
• Timer1, ATMega16, 16bit

No tests with 8bit-Timers so far, but it should work with minor changes.

Todo:

ustimer could become a project on its own.

29 March 2006
Sven Kreiss

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Function Documentation

uint32_t us_time_get (  void   )

get current time Calculates the current time from an incremented variable and the counter register of the timer. { uint16_t timer; /* It is really, really important to stop global interrupts before * reading 16bit registers. See the avr-libc FAQ! */ cli(); timer = TCNT3; sei(); return ((us_time << 16) + timer); }

uint32_t us_time_get_difference (  uint32_t  time1  )

calculates the difference between a saved and the current time Uses us_time_get() to get the current time. The if-condition at the end checks whether the later time is smaller. If so, then an timer overflow is assumed and the appropriate action is taken that the correct time can still be calculated. Therefore, the maximum time one can measure is 2^32 micro-seconds. { uint32_t time2; time2 = us_time_get(); if(time2 >= time1) return (time2-time1); else return (0xFFFFFFFF - time1+time2); //2^32 }

double us_time_get_difference_d (  uint32_t  time1  )

calculates the difference between a saved and the current time in micro-seconds Same as us_time_get_difference(), but returns the value in micro seconds. { return ((double)(us_time_get_difference(time1) * US_TIMER_PRESCALER) / (double)XTAL); }

void us_timer_init (  void   )

initiates the timer Initiates 16bit-Timer3 for the precise measurement. Enables Timer overflow interrupt. < for XTAL > 8 MHz: 8, else: 1 < cpu-freq in MHz { #define US_TIMER_PRESCALER 8 ///< for XTAL > 8 MHz: 8, else: 1 #define XTAL 11.0562 ///< cpu-freq in MHz TCCR3A = 0; //normal mode TCCR3B = (1<<CS31); //CS31: Prescaler 8, CS00: Prescaler 1 ETIMSK = (1<<TOIE3); //enable Timer3 overflow interrupt //TIMSK = (1<<TOIE1); //enable Timer1 overflow interrupt TCNT3 = 0; }

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