Arduino Timer1

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Arduino Forum >  Using Arduino >  Programming Questions >  Reading count value from Timer1
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Topic: Reading count value from Timer1 (Read 2938 times) Previous Topic - Next Topic
soulid
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Reading count value from Timer1
Nov 25, 2012, 02:17 pm
Hi,
I need to read the count value from the Timer1. How can I read out the 16bit value from Timer1? I cannot find a starting point...
billroy
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Re: Reading count value from Timer1
#1
Nov 25, 2012, 02:26 pm
See the 328p data sheet here: http://www.atmel.com/Images/doc8161.pdf, page 117, for a C code example.

-br
dhenry
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Re: Reading count value from Timer1
#2
Nov 25, 2012, 02:47 pm
If you can stop the timer, it is very simple.

If you cannot stop the timer, you have to double read it in case the timer advances in between the low/high byte reads. A double read is a fairly typical technique in this kind of solutions.

The fact that those timers don't have a shadow register / read buffer is a shame.
dc42
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Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.
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Re: Reading count value from Timer1
#3
Nov 25, 2012, 07:26 pm
Quote from: dhenry on Nov 25, 2012, 02:47 pm

The fact that those timers don't have a shadow register / read buffer is a shame.


The atmega mcus used in Arduinos do have a shadow register - when the low byte is read, the high byte is latched. See the datasheet.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.
soulid
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Re: Reading count value from Timer1
#4
Nov 25, 2012, 08:53 pm
Hi,
I read the part of the datasheet. The complete 16-bit set can be accessed by reading " TCNT1 " according to 16.11.4 "The two Timer/Counter I/O locations (TCNT1H and TCNT1L, combined TCNT1) give direct access, both for read and for write operations, to the Timer/Counter unit 16-bit counter."

Correct result shown. Thanks for your hint to the right part of the datasheet

Code: [Select]

#include <avr/io.h>
#include <avr/interrupt.h>
#define LEDPIN 13
int timer;
long counter;


void setup()
{
  Serial.begin(9600);
  pinMode(LEDPIN, OUTPUT);
  cli();                    // disable global interrupts
  pinMode(2, INPUT);        // Enable Pin2 as input to interrupt
  EIMSK |= (1 << INT0);     // Enable external interrupt INT0  (see table 13-2-2 in Atmel 328 spec)
  EICRA |= (1 << ISC01);    // Trigger INT0 on rising edge (see table 13-1 in Atmel 328 spec)
  EICRA |= (1 << ISC00);    // Trigger INT0 on riding edge (see table 13-1 in Atmel 328 spec)

  // initialize Timer1
  // ZERO Timer1
  TCCR1A = 0;               // set entire TCCR1A register to 0
  TCCR1B = 0;               // same for TCCR1B

  // set compare match register to desired timer count:
  OCR1A = 7000;            // turn on CTC mode:initial value changed in loop
  OCR1B = 14000;            // turn on CTC mode:initial value changed in loop
//TCCR1B |= (1 << WGM12);   // Set CTC mode. Resets the timer after compA has been reached
  TCCR1B |= (1 << CS10);    // prescaler 1024
  TCCR1B |= (1 << CS12);    // prescaler 1024
  TIMSK1 |= (1 << OCIE1A);  // enable timer compare interrupt:
  TIMSK1 |= (1 << OCIE1B);  // enable timer compare interrupt:
  sei();                    // Enable global interrupts
}

void loop()
{}
ISR(TIMER1_COMPA_vect){
    counter= TCNT1;
  digitalWrite(LEDPIN, HIGH);
  counter= TCNT1;
Serial.print ("counteran:");

  Serial.println(counter);
}

ISR(TIMER1_COMPB_vect){
  digitalWrite(LEDPIN, LOW);
  Serial.print ("counteraus:");
  counter= TCNT1;
  Serial.println(counter);

TCNT1 = 0; // Reset Timer1 Count
}
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