Enhanced Host Controller Interface Specification: Addendum

The document defines energy-efficiency extensions for the USB 2.0 host controller based on the enhanced host controller interface (EHCI) specification.

● Hardware prefetching: The ability for host controller hardware to safely prefetch information from the asynchronous and periodic schedules beyond what was defined in previous EHCI implementations to improve system memory access behavior.
● Link power management: Defines the mechanisms by which software can discover and use link power management support offered in EHCI host controllers and USB devices.
● Per-port change events: Addresses an issue where system software is required to read and parse the port status registers for all enabled root ports upon every port change event (interrupt).
● Shorter periodic frame list: The ability for system software to convey and use a much shorter periodic frame list (32 frames) to better facilitate hardware prefetching.