May 17, 2000 2

USB Power Management

USB Power Management

Brad HoslerBrad Hosler

USB Engineering ManagerUSB Engineering ManagerIntel CorporationIntel Corporation

May 17, 2000 3

AgendaAgenda

PC Power Management OverviewPC Power Management Overview USB PM CharacteristicsUSB PM Characteristics Power states for USB devicesPower states for USB devices SummarySummary

May 17, 2000 4

Instantly Available PCInstantly Available PC

PC that acts like an appliancePC that acts like an appliance– Appears off, but can respond to external eventsAppears off, but can respond to external events– Very low power consumption (less than 5 Watts)Very low power consumption (less than 5 Watts)

Huge cost savings in corporate environmentsHuge cost savings in corporate environments Greater impact in consumer applicationsGreater impact in consumer applications

USB Is Very Important in These PCs,USB Is Very Important in These PCs,Especially As PCs Become ‘Legacy Free’Especially As PCs Become ‘Legacy Free’

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System Power StatesSystem Power States

S0 - Fully ONS0 - Fully ON USB operationalUSB operational

S1 - SleepingS1 - Sleeping USB suspendedUSB suspended

S3 - Suspend to RamS3 - Suspend to Ram USB suspendedUSB suspended

S4 - Suspend to DiskS4 - Suspend to Disk USB suspendedUSB suspended

S5 - OffS5 - Off USB offUSB off

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S3 CharacteristicsS3 Characteristics

Much of system HW is not poweredMuch of system HW is not powered– Enough alive to detect wake up eventsEnough alive to detect wake up events

Limited power availableLimited power available– Aux power supply typically provides 720ma at 5VAux power supply typically provides 720ma at 5V– shared between platform, PCI, and USBshared between platform, PCI, and USB

S3 Is the ‘OFF’ State for IAPCsS3 Is the ‘OFF’ State for IAPCs

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S3 Power ConsumersS3 Power Consumers

Base BoardBase Board

Memory SubsystemMemory Subsystem

PCIPCIRemote Wakeup SlotsRemote Wakeup SlotsOther SlotsOther Slots

USBUSB

~100ma~100ma

~100ma~100ma

375ma 375ma

20ma20ma

10ma/port10ma/port

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USB Dynamic PowerUSB Dynamic Power

Suspend to Remote Wakeup transitionSuspend to Remote Wakeup transition– Device can go to full power immediatelyDevice can go to full power immediately– Could be as high as 500maCould be as high as 500ma

Insertion of new device into empty portInsertion of new device into empty port– Device can draw up to 100maDevice can draw up to 100ma

Remote wakeup does NOT wake all USB devicesRemote wakeup does NOT wake all USB devices– Selective suspend is done at all portsSelective suspend is done at all ports

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Platform DynamicsPlatform Dynamics

Switch from Vaux to Main supply takes ~250msecSwitch from Vaux to Main supply takes ~250msec– HW controlled starting with any power eventHW controlled starting with any power event

USB remote wakeup, PCI PME#, USB device insertionUSB remote wakeup, PCI PME#, USB device insertion

Power supply Vaux has dynamic characteristicsPower supply Vaux has dynamic characteristics– Testing shows >3A for 500msecTesting shows >3A for 500msec

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USB S3 Power USB S3 Power

Use 10ma/port rule for static power calculationUse 10ma/port rule for static power calculation Assume only one power event from USBAssume only one power event from USB

– Multiples within 1/4 second are unlikelyMultiples within 1/4 second are unlikely– Max for that one event is 500maMax for that one event is 500ma

Dynamics of Vaux supply easily handle 500maDynamics of Vaux supply easily handle 500ma

Use USB Static Power for Vaux SizingUse USB Static Power for Vaux SizingVaux Supply’s Easily Handle USB Dynamic PowerVaux Supply’s Easily Handle USB Dynamic Power

May 17, 2000 11

Power States for USB Devices

Power States for USB Devices

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USB Feature SpecificationUSB Feature Specification

Interface Power Management Specification Interface Power Management Specification defines some additional PM states for devicesdefines some additional PM states for devices– D0 - Fully onD0 - Fully on– D1, D2, D3 - Less than fully onD1, D2, D3 - Less than fully on

Relationship between Dx states and USB PM Relationship between Dx states and USB PM states (active/suspended) is orthogonalstates (active/suspended) is orthogonal– Device required to suspend/resume no matterDevice required to suspend/resume no matter

what Dx statewhat Dx state– Suspend/resume doesn’t effect device Dx state Suspend/resume doesn’t effect device Dx state

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New Power ValuesNew Power Values

If device is in D1, D2, or D3 and enabled for If device is in D1, D2, or D3 and enabled for remote wakeup, then 100ma is current limit for remote wakeup, then 100ma is current limit for suspendsuspend

If device is in D1, D2, or D3 and signaling a remote If device is in D1, D2, or D3 and signaling a remote wakeup, then device is limited to 100mawakeup, then device is limited to 100ma

May 17, 2000 14

Budgeting USB PowerBudgeting USB Power

New 100ma ‘suspend’ current can exceedNew 100ma ‘suspend’ current can exceedVaux capacityVaux capacity

If OS does power budgeting, OS will manageIf OS does power budgeting, OS will manageUSB Dx states to stay within Vaux capacityUSB Dx states to stay within Vaux capacity– OS has to know Vaux capacityOS has to know Vaux capacity

If OS doesn’t power budget, OS will make sure If OS doesn’t power budget, OS will make sure devices are in D0 before suspendingdevices are in D0 before suspending– Devices can’t count on more power while suspendedDevices can’t count on more power while suspended

May 17, 2000 15

USB Driver BehaviorUSB Driver Behavior

OS will ask USB driver if system ‘sleep’ is OKOS will ask USB driver if system ‘sleep’ is OK– IRP_MN_QUERY_POWERIRP_MN_QUERY_POWER

Driver can ‘fail’ the request in certain casesDriver can ‘fail’ the request in certain cases– When doing ‘critical’ IO (like modem connection)When doing ‘critical’ IO (like modem connection)

If able to suspend, driver should finish pending If able to suspend, driver should finish pending IOs and pass IRP down the stackIOs and pass IRP down the stack– Passing IRP without completing IOs can result in Passing IRP without completing IOs can result in

system hangsystem hang

Device Drivers Must Be PM AwareDevice Drivers Must Be PM Aware

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SummarySummary

USB is an important feature of IAPCsUSB is an important feature of IAPCs USB power characteristics are easilyUSB power characteristics are easily

handled by IAPCshandled by IAPCs New USB power states don’t guaranteeNew USB power states don’t guarantee

higher suspend powerhigher suspend power Make your device driver PM awareMake your device driver PM aware

May 17, 2000 17

Call to ActionCall to Action

OEMs: Use power budgeting to fully enable USB OEMs: Use power budgeting to fully enable USB devices while in S3 state devices while in S3 state

IHVs: See if your peripheral can benefit from the IHVs: See if your peripheral can benefit from the USB PM feature specificationUSB PM feature specification– Limit device power on remote wakeupLimit device power on remote wakeup– More power to detect eventsMore power to detect events

Make Sure Your Device Driver Is PM AwareMake Sure Your Device Driver Is PM Aware