RTT freezes inside the interrupt handler, the board ARDUINO DUE

void setup() {
  int prescaler = 0x8000; 
  RTT->RTT_MR = (prescaler | RTT_MR_RTTRST | RTT_MR_ALMIEN);
 
  RTT->RTT_AR = 0x2; // alarm the third second
  //  NVIC_DisableIRQ(RTT_IRQn);
  //  NVIC_ClearPendingIRQ(RTT_IRQn);
  //  NVIC_SetPriority(RTT_IRQn, 0);
  NVIC_EnableIRQ(RTT_IRQn); 
  Serial.begin(115200);
}
 
void RTT_Handler() {

//////////// <<<<<<<<<<< FREEZES HERE

  //тут будет обработчик если этот сраный таймер заработает
}
 
void loop() {
  int a = RTT->RTT_VR;
  Serial.println(a);
  delay(100);
}

I see that the timer is running and then executed in the interrupt and freezes.
somebody know why?

add

int vvv = RTT->RTT_SR;

in to loop() and RTT_Handler()
all works.