SAM9G10_14 Datasheet, PDF (612/750 Pages) ATMEL Corporation – Additional Embedded Memories

37.5.3
Controlling Device States
A USB device has several possible states. Refer to Chapter 9 of the Universal Serial Bus Speci-
fication, Rev 2.0.
Figure 37-14. USB Device State Diagram
Attached
Hub Reset
or
Deconfigured
Hub
Configured
Power
Interruption
Powered
Bus Inactive
Bus Activity
Reset
Reset
Bus Inactive
Default
Bus Activity
Address
Assigned
Bus Inactive
Address
Bus Activity
Device
Deconfigured
Device
Configured
Bus Inactive
Configured
Bus Activity
Suspended
Suspended
Suspended
Suspended
Movement from one state to another depends on the USB bus state or on standard requests
sent through control transactions via the default endpoint (endpoint 0).
After a period of bus inactivity, the USB device enters Suspend Mode. Accepting Sus-
pend/Resume requests from the USB host is mandatory. Constraints in Suspend Mode are very
strict for bus-powered applications; devices may not consume more than 500 µA on the USB
bus.
While in Suspend Mode, the host may wake up a device by sending a resume signal (bus activ-
ity) or a USB device may send a wake up request to the host, e.g., waking up a PC by moving a
USB mouse.
The wake up feature is not mandatory for all devices and must be negotiated with the host.
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