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April 28, 2012. 3. Agenda. Platform Power for USBMobile platforms and USBPower states for USB devicesSummary. April 28, 2012. 4. Instantly Available PC. PC that acts like an applianceAppears off, but can respond to external eventsVery low power consumption (less than 5 Watts)Huge cost savings
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2. April 29, 2012 2 USB Power Management Brad Hosler
USB Engineering ManagerIntel Corporation
3. April 29, 2012 3 Agenda Platform Power for USB
Mobile platforms and USB
Power states for USB devices
Summary
4. April 29, 2012 4 Instantly Available PC PC that acts like an appliance
Appears off, but can respond to external events
Very low power consumption (less than 5 Watts)
Huge cost savings in corporate environments
Greater impact in consumer applications
5. April 29, 2012 5 System Power States
6. April 29, 2012 6 S3 Characteristics Much of system HW is not powered
Enough alive to detect wake up events
Limited power available
Aux power supply typically provides 720ma at 5V
shared between platform, PCI, and USB
7. April 29, 2012 7 S3 Power Consumers
8. April 29, 2012 8 USB Dynamic Power Suspend to Remote Wakeup transition
Device can go to full power immediately
Could be as high as 500ma
Insertion of new device into empty port
Device can draw up to 100ma
Remote wakeup does NOT wake all USB devices
Selective suspend is done at all ports
9. April 29, 2012 9 Platform Dynamics Switch from Vaux to Main supply takes ~250msec
HW controlled starting with any power event
USB remote wakeup, PCI PME#, USB device insertion
Power supply Vaux has dynamic characteristics
Testing shows >3A for 500msec
10. April 29, 2012 10 USB S3 Power Use 10ma/port rule for static power calculation
Assume only one power event from USB
Multiples within 1/4 second are unlikely
Max for that one event is 500ma
Dynamics of Vaux supply easily handle 500ma
11. April 29, 2012 11 Mobile Platforms and USB
12. April 29, 2012 12 C3 Processor State Low power state for processors
Extends battery life by ~10%
Entered when system is idle (including IO traffic)
Can be entered in milliseconds (10 to 50)
Any bus master activities keep processor alive
USB host controllers poll memory every millisecond
13. April 29, 2012 13 Use Selective Suspend New feature in Windows XP will stop HC polling if all ports are suspended
This will allow process to go to C3 state
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. April 29, 2012 14 Power States for USB Devices
15. April 29, 2012 15 USB Feature Specification Interface Power Management Specification defines some additional PM states for devices
D0 - Fully on
D1, D2, D3 - Less than fully on
Relationship between Dx states and USB PM states (active/suspended) is orthogonal
Device required to suspend/resume no matterwhat Dx state
Suspend/resume doesnt effect device Dx state
16. April 29, 2012 16 New Power Values If device is in D1, D2, or D3 and enabled for remote wakeup, then 100ma is current limit for suspend
If device is in D1, D2, or D3 and signaling a remote wakeup, then device is limited to 100ma
17. April 29, 2012 17 Budgeting USB Power New 100ma suspend current can exceedVaux capacity
If OS does power budgeting, OS will manageUSB Dx states to stay within Vaux capacity
OS has to know Vaux capacity
If OS doesnt power budget, OS will make sure devices are in D0 before suspending
Devices cant count on more power while suspended
18. April 29, 2012 18 USB Driver Behavior OS will ask USB driver if system sleep is OK
IRP_MN_QUERY_POWER
Driver can fail the request in certain cases
When doing critical IO (like modem connection)
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
19. April 29, 2012 19 Summary USB is an important feature of IAPCs
USB power characteristics are easilyhandled by IAPCs
Mobile platforms have power savings when USB device drivers suspend their device
New USB power states dont guaranteehigher suspend power
Drivers need to be PM aware
20. April 29, 2012 20 Call to Action OEMs: Use power budgeting to fully enable USB devices while in S3 state
IHVs: Suspend your device when not in use
Make your device mobile friendly
IHVs: See if your peripheral can benefit from the USB PM feature specification
Limit device power on remote wakeup
More power to detect events