volatile uint8_t IntWas;
void SysTick_handler()
{
IntWas=1;
}
int main() {
SysTick_Config(10000);
while (1) {
  if (IntWas) {
    IntWas=0;
}
__WFI();
}
}

void CMU_IRQHandler(void)
{
  /* Clear interrupt flag */
  CMU_IntClear(CMU_IF_LFRCORDY);

  /* Indicate that LFRCO is ready */
  lfrcoReady = true;
}


/***************************************************************************//**
* @brief Main function. Enables LFRCO and waits in EM1 until it is ready
******************************************************************************/
int main(void)
{
  /* Chip revision alignment and errata fixes */
  CHIP_Init();
  
  /* Enable CMU IRQ when LFRCO is ready */
  CMU_IntEnable(CMU_IF_LFRCORDY);
  
  /* Enable CMU interrupt vector in NVIC */
  NVIC_EnableIRQ(CMU_IRQn);
  
  /* Enable LFRCO but do not wait until it is ready */
  CMU_OscillatorEnable(cmuOsc_LFRCO, true, false);
  
  /* Wait in EM1 until LFRCO is ready.
   * Disable interrupts first to avoid interrupt executing between lfrcoReady
   * check and _WFI(); This would have caused the program to get stuck! */
  __disable_irq();
  while(!lfrcoReady)
  {
    __WFI(); /* Pending and enabled IRQs will wake up the CPU, but not go to ISR */
    __enable_irq(); /* ISR for any pending and enabled IRQs will be executed after this */
  }
  
  /* Wait here at the end */
  while(1);    
}

void TIMER0_IRQHandler (void) __irq
{
  // что-то полезное
  T0IR = 0x01;                                // Clear match 0 interrupt
}