title: USB polling mechanism
body: <p>Why does USB use a polling mechanism instead of an interrupt to detect the device? </p>
  
  <p>I've read here on Stack Overflow that if the event is </p>
  
  <ol>
  <li>Synchronous (i.e. you know when to expect it within a small window)</li>
  <li>Not Urgent (i.e. a slow polling interval has no ill effects), and</li>
  <li>Frequent (i.e. majority of your polling cycles create a 'hit')</li>
  </ol>
  
  <p>then we can use polling. But in case of USB, device detection is not frequent, so an interrupt mechanism would be better.</p>
  
  <p>Thanks for your replies,</p>
  
  <p>Zaheer</p>