AVR und Piezo Buzzer

#include <avr/io.h>

int main(void)

{

  uint8_t i = 0;                  // timer (0, 50ms, 100ms, 150ms...)

  uint8_t j = 0;                  // counter (0...6: signal, 6...18: pause)

  uint8_t k = 0;                  // signal counter

  const uint16_t p1 = 253;        // TCD value 1 (tone 1)

  const uint16_t p2 = 235;        // TCD value 2 (tone 2)

  uint16_t s1 = p1 - 10;          // pulse start value (tone 1)

  uint16_t s2 = p2 - 10;          // pulse start value (tone 2)

  _PROTECTED_WRITE(CLKCTRL.MCLKCTRLB, CLKCTRL_PDIV_10X_gc | CLKCTRL_PEN_bm); // 2 MHz main clock

  _PROTECTED_WRITE(TCD0.FAULTCTRL, TCD_CMPAEN_bm | TCD_CMPBEN_bm);

  TCD0.CTRLB = TCD_WGMODE_TWORAMP_gc;                     // two ramp mode

  TCD0.CTRLC = TCD_FIFTY_bm | TCD_AUPDATE_bm;             // symmetrical, automatically update

  TCD0.CMPBSET = s1;                                      // pulse start value (tone 1)

  TCD0.CMPBCLR = p1;                                      // tone 1

  while(!(TCD0.STATUS & TCD_ENRDY_bm)){}                  // ensure ENRDY bit is set

  TCD0.CTRLA = TCD_CLKSEL_SYSCLK_gc | TCD_ENABLE_bm;      // select clock, enable TCD

  TCB0.CCMP = 0xC34F;                                     // timeout value (50ms @ 1MHz TCB clock)

  TCB0.CTRLA = TCB_CLKSEL_CLKDIV2_gc | TCB_ENABLE_bm;     // 1MHz TCB clock, enable TCB

  while(1)

  {

    if(TCB0.INTFLAGS)

    {

      TCB0.INTFLAGS = TCB_CAPT_bm;              // clear the interrupt flag

      i++;

      if(i == 2)                                // 100ms

      {

        TCD0.CMPBSET = s2;                      // pulse start 2

        TCD0.CMPBCLR = p2;                      // tone 2

      }

      else if(i == 4)                           // 200ms

      {

        TCD0.CMPBSET = s1;                      // pulse start 1

        TCD0.CMPBCLR = p1;                      // tone 1

        i = 0;

        j++;

        if(j == 6)                              // after 6*(100ms tone 1 + 100ms tone 2)

        {

          TCD0.CTRLE = TCD_DISEOC_bm;           // pause

          k++;

          if(k == 4)                            // after 4 times "quiet"

          {

            s1 = 0;                             // switch to "loud"

            s2 = 0;                             // switch to "loud"

          }

          else if(k == 10)                      // after 6 times "loud"

          {

            TCB0.CTRLA = 0;                     // stop

          }

        }

        else if(j == 18)                                       // end of pause

        {

          while(!(TCD0.STATUS & TCD_ENRDY_bm)){}               // ensure ENRDY bit is set

          TCD0.CTRLA = TCD_CLKSEL_SYSCLK_gc | TCD_ENABLE_bm;   // enable again

          j = 0;

        }

      }

    }

  }

}