title: What happens when an ISR is running and another interrupt happens?
body: <p>What happens if an ISR is running, and another interrupt occurs? Does the first interrupt get interrupted? Will the second interrupt get ignored? Or will it fire when the first ISR is done?</p>
  
  <p><strong>EDIT</strong>
  I forgot to include it in the question (but I included it in the tags) that I meant to ask how this worked on Atmel AVR's.</p>