github4manu / atmega-timers

Arduino/Avr compatible libraries to control timers

atmega-timers

atmega-timers is an Arduino/Avr compatible library to control timers 0, 1 and 2.

Description

This library contains several functions to use the timers in different ways.

• One way is using the timers to execute a function on a defined period, indefinitely.

    void timer0(uint8_t prescaler, uint8_t ticks, void (*f)())
    void timer1(uint8_t prescaler, uint16_t ticks, void (*f)())
    void timer2(uint8_t prescaler, uint8_t ticks, void (*f)())
  
    void timer0_stop()
    void timer1_stop()
    void timer2_stop()
  

  • prescaler are predefined constants in the header file. For example:

      TIMER0_PRESCALER_8
      TIMER0_PRESCALER_64
      ...
    

  • ticks are the number of steps the timer will count. Current limits are:

      timer0: 0 - 255
      timer1: 0 - 65535
      timer2: 0 - 255
    

  • f is the function to execute after all ticks are consumed. Must be declared void with no parameters:

      void sample() {
      	...
      }
    

  • timerX_stop() disables that timer by setting prescaler to "none". Energy saving feature.

  • You can disable interrupt definition if you want to use that timer for your own purposes. Just comment or delete one of those lines inside atmega-timers.h file:

      #define ENABLE_TIMER0
      #define ENABLE_TIMER1
      #define ENABLE_TIMER2
    

• Other way is implementing the traditional delay routine. The function will block-wait until the count is done.

    void wait0(uint8_t prescaler, uint8_t ticks)
    void wait1(uint8_t prescaler, uint16_t ticks)
    void wait2(uint8_t prescaler, uint8_t ticks)
  

  • prescaler are predefined constants in the header file. For example:

      TIMER0_PRESCALER_8
      TIMER0_PRESCALER_64
      ...
    

  • ticks are the number of steps the timer will count. Current limits are:

      timer0: 0 - 255
      timer1: 0 - 65535
      timer2: 0 - 255
    

Usage

You need to know your CPU clock frequency before setting the timers.

1. Divide CPU clock by selected prescaler:

    16000000 / 64 = 250000 Hz
   

2. Get timer period:

    1 / 250000 = 4 us
   

3. Divide your desired period by timer period, for example 20 milliseconds:

    20000 us / 4 us = 5000 ticks
   

4. Use timer1, as timer0 and timer2 can't support more than 256 ticks:

    timer1(TIMER1_PRESCALER_64, 5000U, do_something);
   

5. Enable global interrupts:

    sei();
   

Sample Code

• Using wait* functions:

    #include <avr/io.h>
    #include "atmega-timers.h"
  
    // toggle PORTB status
    void toggle() {
    	static uint8_t output = 0xff;
  
    	PORTB = output;
    	output = !output;
    }
  
    void main() {
    	// set all pins of PORTB as output
    	DDRB = 0xff;
    	
    	// toggle PORTB every 500ms (using 16Mhz clock)
    	while(1) {
    		toggle();
    		wait1(TIMER1_PRESCALER_1024, 7812U);
    	}
    }
  

• Using timer* functions:

    #include <avr/io.h>
    #include "atmega-timers.h"
  
    // toggle PORTB status
    void toggle() {
    	static uint8_t output = 0xff;
  
    	PORTB = output;
    	output = !output;
    }
  
    void main() {
    	// set all pins of PORTB as output
    	DDRB = 0xff;
    	
    	// toggle PORTB every 500ms (using 16Mhz clock)
    	timer1(TIMER1_PRESCALER_1024, 7812U, toggle);
    	
    	// enable global interrupts
    	sei();
  
    	while(1) {
    		// your code goes here
    	}
    }
  

Both examples have the same result.

Running it in Arduino

1. Download the source code by using the Download Button on this page
2. Rename and install the library as: {arduino_path}/libraries/AtmegaTimers
3. Open Arduino and go to "Import Library" option. Choose AtmegaTimers from menu.

Atmel Model Support

It should work with a long range of devices, for example:

• atmega48, 88, 168, 328
• atmega164, 324, 644, 1284
• atmega640, 1280, 1281, 2560, 2561
• atmega325, 645
• ...