Interrupts and Timers

Official Hardware Mega Due
3

okay so this is the sketch
what it does is , it writes value in t1 whenever interrupt is generated and then stores the previous value in t2. "X" stores the difference value i.e x=t1-t2
By this i can find the time difference between two interrupts.
I have generated the interrupt by using delay function and digitalWrite (as you can see in the sketch) and connected the output to pin2 (int pin of arduino).
by using this i get a resolution of 2^23 bit in arduino due . As arduino due is a 32 BIT uc i could use its resolution to count the same. If i could use the internal timers of arduino due that would help me a lot.
Help is highly appreciated.

volatile unsigned long t1;
volatile unsigned long t2;
volatile unsigned long x;
int flashpin = 10;

void isr()
{
  t1=micros();
}

void setup()
{
  pinMode(flashpin,HIGH);
}

void loop()
{
  attachInterrupt(0,isr,RISING);
  flash(); 
  x=t1-t2;
  t2=t1;
}

void flash()
{
  digitalWrite(flashpin,HIGH);
  delay(1000);
  digitalWrite(flashpin,LOW);
  delay(1000);
}