2. May 17, 20002 USB Power Management Brad Hosler USB Engineering Manager Intel Corporation

3. May 17, 20003 Agenda w PC Power Management Overview w USB PM Characteristics w Power states for USB devices w Summary

4. May 17, 20004 Instantly Available PC w PC that acts like an appliance – Appears off, but can respond to external events – Very low power consumption (less than 5 Watts) w Huge cost savings in corporate environments w Greater impact in consumer applications USB Is Very Important in These PCs, Especially As PCs Become ‘Legacy Free’

5. May 17, 20005 System Power States S0 - Fully ON USB operational S1 - Sleeping USB suspended S3 - Suspend to Ram USB suspended S4 - Suspend to Disk USB suspended S5 - Off USB off

6. May 17, 20006 S3 Characteristics w Much of system HW is not powered – Enough alive to detect wake up events w Limited power available – Aux power supply typically provides 720ma at 5V – shared between platform, PCI, and USB S3 Is the ‘OFF’ State for IAPCs

7. May 17, 20007 S3 Power Consumers Base Board Memory Subsystem PCI Remote Wakeup Slots Other Slots USB~100ma~100ma 375ma 20ma 375ma 20ma10ma/port

8. May 17, 20008 USB Dynamic Power w Suspend to Remote Wakeup transition – Device can go to full power immediately – Could be as high as 500ma w Insertion of new device into empty port – Device can draw up to 100ma w Remote wakeup does NOT wake all USB devices – Selective suspend is done at all ports

9. May 17, 20009 Platform Dynamics w Switch from Vaux to Main supply takes ~250msec – HW controlled starting with any power event u USB remote wakeup, PCI PME#, USB device insertion w Power supply Vaux has dynamic characteristics – Testing shows >3A for 500msec

10. May 17, 200010 USB S3 Power w Use 10ma/port rule for static power calculation w Assume only one power event from USB – Multiples within 1/4 second are unlikely – Max for that one event is 500ma w Dynamics of Vaux supply easily handle 500ma Use USB Static Power for Vaux Sizing Vaux Supply’s Easily Handle USB Dynamic Power

11. May 17, 200011 Power States for USB Devices

12. May 17, 200012 USB Feature Specification w Interface Power Management Specification defines some additional PM states for devices – D0 - Fully on – D1, D2, D3 - Less than fully on w Relationship between Dx states and USB PM states (active/suspended) is orthogonal – Device required to suspend/resume no matter what Dx state – Suspend/resume doesn’t effect device Dx state

13. May 17, 200013 New Power Values w If device is in D1, D2, or D3 and enabled for remote wakeup, then 100ma is current limit for suspend w If device is in D1, D2, or D3 and signaling a remote wakeup, then device is limited to 100ma

14. May 17, 200014 Budgeting USB Power w New 100ma ‘suspend’ current can exceed Vaux capacity w If OS does power budgeting, OS will manage USB Dx states to stay within Vaux capacity – OS has to know Vaux capacity w If OS doesn’t power budget, OS will make sure devices are in D0 before suspending – Devices can’t count on more power while suspended

15. May 17, 200015 USB Driver Behavior w OS will ask USB driver if system ‘sleep’ is OK – IRP_MN_QUERY_POWER w Driver can ‘fail’ the request in certain cases – When doing ‘critical’ IO (like modem connection) w If able to suspend, driver should finish pending IOs and pass IRP down the stack – Passing IRP without completing IOs can result in system hang Device Drivers Must Be PM Aware Device Drivers Must Be PM Aware

16. May 17, 200016 Summary w USB is an important feature of IAPCs w USB power characteristics are easily handled by IAPCs w New USB power states don’t guarantee higher suspend power w Make your device driver PM aware

17. May 17, 200017 Call to Action w OEMs: Use power budgeting to fully enable USB devices while in S3 state w IHVs: See if your peripheral can benefit from the USB PM feature specification – Limit device power on remote wakeup – More power to detect events Make Sure Your Device Driver Is PM Aware