strange timing with setTimeout

Ok, I'm pretty sure I've figured this out now. It's definitely a firmware issue that's been around for a while I think.

In fact if you:

• Paste in var dt = new Date();setTimeout(function(){console.log­(new Date() - dt);},100);
  
• Wait X seconds then press Enter
  
• Timeout happens X seconds after this
  
  

It's to do with the device sleeping - you probably don't notice it in STM32 boards because they don't sleep when you're connected via USB