307013-003 Datasheet, PDF (210/848 Pages) Intel Corporation – Intel I/O Controller Hub 7

Functional Description
5.20.7
5.20.7.1
5.20.7.2
5.20.7.3
USB 2.0 Power Management
Pause Feature
This feature allows platforms (especially mobile systems) to dynamically enter low-
power states during brief periods when the system is idle (i.e., between keystrokes).
This is useful for enabling power management features like Intel SpeedStep technology
in the ICH7 mobile/ultra mobile only. The policies for entering these states typically are
based on the recent history of system bus activity to incrementally enter deeper power
management states. Normally, when the EHC is enabled, it regularly accesses main
memory while traversing the DMA schedules looking for work to do; this activity is
viewed by the power management software as a non-idle system, thus preventing the
power managed states to be entered. Suspending all of the enabled ports can prevent
the memory accesses from occurring, but there is an inherent latency overhead with
entering and exiting the suspended state on the USB ports that makes this
unacceptable for the purpose of dynamic power management. As a result, the EHCI
software drivers are allowed to pause the EHC’s DMA engines when it knows that the
traffic patterns of the attached devices can afford the delay. The pause only prevents
the EHC from generating memory accesses; the SOF packets continue to be generated
on the USB ports (unlike the suspended state).
Suspend Feature
The Enhanced Host Controller Interface (EHCI) For Universal Serial Bus Specification,
Section 4.3 describes the details of Port Suspend and Resume.
ACPI Device States
The USB 2.0 function only supports the D0 and D3 PCI Power Management states.
Notes regarding the ICH7 implementation of the Device States:
1. The EHC hardware does not inherently consume any more power when it is in the
D0 state than it does in the D3 state. However, software is required to suspend or
disable all ports prior to entering the D3 state such that the maximum power
consumption is reduced.
2. In the D0 state, all implemented EHC features are enabled.
3. In the D3 state, accesses to the EHC memory-mapped I/O range will master abort.
Note that, since the Debug Port uses the same memory range, the Debug Port is
only operational when the EHC is in the D0 state.
4. In the D3 state, the EHC interrupt must not assert for any reason. The internal
PME# signal is used to signal wake events, etc.
5. When the Device Power State field is written to D0 from D3, an internal reset is
generated. See section EHC Resets for general rules on the effects of this reset.
6. Attempts to write any other value into the Device Power State field other than 00b
(D0 state) and 11b (D3 state) will complete normally without changing the current
value in this field.
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Intel ^® ICH7 Family Datasheet