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Published byFlorence Nash Modified over 9 years ago
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October 10, 20001
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2 USB Power Management Brad Hosler USB Engineering Manager Intel Corporation
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October 10, 20003 Agenda w Platform Power for USB w Mobile platforms and USB w Power states for USB devices w Summary
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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’
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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
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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
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October 10, 20007 S3 Power Consumers Base Board Memory Subsystem PCI Remote Wakeup Slots Other Slots USB~100ma~100ma 375ma 20ma 375ma 20ma10ma/port
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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
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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
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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
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October 10, 200011 Mobile Platforms and USB
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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
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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
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October 10, 200014 Power States for USB Devices
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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
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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
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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
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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
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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
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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
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