1. October 10, 20001

2. 2 USB Power Management Brad Hosler USB Engineering Manager Intel Corporation

3. October 10, 20003 Agenda w Platform Power for USB w Mobile platforms and USB w Power states for USB devices w Summary

4. October 10, 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. October 10, 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. October 10, 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. October 10, 20007 S3 Power Consumers Base Board Memory Subsystem PCI Remote Wakeup Slots Other Slots USB~100ma~100ma 375ma 20ma 375ma 20ma10ma/port

8. October 10, 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. October 10, 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. October 10, 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. October 10, 200011 Mobile Platforms and USB

12. October 10, 200012 C3 Processor State w Low power state for processors w Extends battery life by ~10% w Entered when system is idle (including IO traffic) w Can be entered in milliseconds (10 to 50) w Any bus master activities keep processor alive – USB host controllers poll memory every millisecond USB Device Drivers must take special action to allow host controller to stop polling memory

13. October 10, 200013 Use Selective Suspend w New feature in “Whistler” will stop HC polling if all ports are suspended – This will allow process to go to C3 state w Device drivers should ‘suspend’ their device whenever it is idle – Camera not open, disk drive not being accessed – Use defined PM IOCTLs to manipulate device state and let the device do wakeup

14. October 10, 200014 Power States for USB Devices

15. October 10, 200015 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

16. October 10, 200016 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

17. October 10, 200017 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

18. October 10, 200018 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

19. October 10, 200019 Summary w USB is an important feature of IAPCs w USB power characteristics are easily handled by IAPCs w Mobile platforms have power savings when USB device drivers suspend their device w New USB power states don’t guarantee higher suspend power w Drivers need to be PM aware

20. October 10, 200020 Call to Action w OEMs: Use power budgeting to fully enable USB devices while in S3 state w IHVs: Suspend your device when not in use – Make your device ‘mobile friendly’ 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