PLX PEX 8112 Fwd Riser, Справочный проект

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PEX 8112 Fwd Riser Reference Design for Board Revision 1.0 – Version 1.1
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Copyright © 2010 by PLX Technology, Inc. All rights reserved
3.7 Power Management Signaling
PCI devices assert the PME# pin (connected to the PEX 8112 PMEIN# ball) to signal a Power Management
event. The PEX 8112 converts the PME# signal to PCI Express Power Management Event (PME) messages.
There are no internal events that cause a PME message to be sent upstream.
Power Management messages are used to support PMEs signaled by devices downstream of the PEX 8112.
System software needs to identify the source of a PCI PME reported by a PM_PME message. When the PME
comes from an agent on a PCI Bus, then the PM_PME Message Requester ID reports the Bus Number from
which the PME was collected, and the Device Number and Function Number reported must both be zero (0).
When the PME message is sent to the host, the PWRMNGCSR register PME Status bit is set and a 100-ms timer
is started. If the status bit is not cleared within 100 ms, another PME message is sent.
When the upstream device is powering down the downstream devices, it first places all devices into the D3
hot
state. It then sends a PCI Express PME_Turn_Off message. After the PEX 8112 receives this message, it stops
sending PME messages upstream. The PEX 8112 then sends a PME_TO_Ack message to the upstream device
and places its link into the L2/L3 Ready state. The downstream device is now ready to be powered down. If the
upstream device changes the PEX 8112 power state back to D0, PME messages are re-enabled. The PCI
Express PME_Turn_Off message terminates at the PEX 8112, and is not communicated to the PCI devices. The
PEX 8112 does not issue a PM_PME message on behalf of a downstream PCI device while its upstream link is in
the L2/L3 non-communicating state.
To avoid loss of PME# assertions in the conversion of the level-sensitive PME# signal to the edge- triggered PCI
Express PM_PME message, the PCI PME# signal is polled every 256 ms by the PEX 8112 and a PCI Express
PM_PME message is generated if PME# is asserted.
The PMEIN# ball is used only when the PEX 8112 is in Forward Bridge Mode.
3.7.1 Wakeup
The PEX 8112 asserts the WAKEOUT# signal or sends a PCI Express beacon for the following:
ƒ
PCI PME# pin is asserted while link is in L2 state
ƒ
PCI Express beacon is received while link is in L2 state
ƒ
PCI Express PM_PME Message is received
A beacon is transmitted if the following are true:
ƒ
PCI PME# pin is asserted while link is in L2 state
ƒ
DEVSPECCTL register Beacon Generate Enable bit is set
ƒ
PWRMNGCSR register PME Enable bit is set
The WAKEOUT# signal is used only when the PEX 8112 is in Forward Bridge mode.