We’ve talked quite a lot about the new USB specifications in recent articles (see here, here, and here). One feature we haven’t covered in depth is Fast Role Swap (FRS), defined in the latest USB Power Delivery specification (USB PD) version 3.0.
Why do we need it? Picture this common scenario: You're hanging out in your Wagga Wagga apartment watching reruns of “Skippy The Bush Kangaroo.” Then the unthinkable happens. Your pet wombat (or puppy if you’re not Down Under) accidentally disconnects the power cord to the USB hub that’s supplying your laptop, screen, and wireless router (Fig. 1).
Disaster looms. An end to your viewing pleasure is just milliseconds away.
FRS was designed to prevent such an event. It’s intended to keep the devices in a USB ecosystem powered when the hub they’re attached to loses power. This supports the vision of USB as a flexible and robust power-delivery system for low-voltage devices, with power coming from a variety of sources as appropriate.