Wednesday, August 7, 2013

atxmega enable internal 32Mhz oscillator (part 2)

The atxmega also supports using the calibrated internal 32kHz clock as auto-calibration reference for the 32Mhz internal oscillator, improving the accuracy.

This code should do the trick. I'm not sure how I could actually verify it. Perhaps I can get the clock signal external and get it on a scope.



#include <avr/io.h>
#include <util/delay.h>

int main( void )
{
  // enable 32Mhz internal oscillator
  OSC.CTRL|=OSC_RC32MEN_bm;
  // wait for it to be stable
  while (!(OSC.STATUS & OSC_RC32MRDY_bm)); 
  // tell the processor we want to change a protected register
  CCP=CCP_IOREG_gc;
  // and start using the 32Mhz oscillator
  CLK.CTRL=CLK_SCLKSEL_RC32M_gc; 
  // disable the default 2Mhz oscillator
  OSC.CTRL&=(~OSC_RC2MEN_bm);
  // enable 32kHz calibrated internal oscillator
  OSC.CTRL|= OSC_RC32KEN_bm;
  while (!(OSC.STATUS & OSC_RC32KRDY_bm)); 
  // set bit to 0 to indicate we use the internal 32kHz
  // callibrated oscillator as auto-calibration source
  // for our 32Mhz oscillator
  OSC.DFLLCTRL &= ~OSC_RC32MCREF_bm;
  // enable auto-calibration for the 32Mhz oscillator
  DFLLRC32M.CTRL |= DFLL_ENABLE_bm;

  // set PA0 as output
  PORTA.DIRSET = 0b00000001;
  
  // blink LED on PA0 with 1 second on, 1 second off
  while (1) {
    PORTA.OUTSET = 0b00000001 ;
    _delay_ms( 1000 );
    PORTA.OUTCLR = 0b00000001 ;
    _delay_ms( 1000 );
  }
}

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