Datasheet 119
Functional Description
5.2.2 Power Management
5.2.2.1 S3/S4/S5 Support
Software initiates the transition to S3/S4/S5 by performing an I/O write to the Power
Management Control register in the PCH. After the I/O write completion has been
returned to the processor, each root port will send a PME_Turn_Off TLP (Transaction
Layer Packet) message on its downstream link. The device attached to the link will
eventually respond with a PME_TO_Ack TLP message followed by sending a
PM_Enter_L23 DLLP (Data Link Layer Packet) request to enter the L2/L3 Ready state.
When all of the PCH root ports links are in the L2/L3 Ready state, the PCH power
management control logic will proceed with the entry into S3/S4/S5.
Prior to entering S3, software is required to put each device into D3
HOT
. When a device
is put into D3
HOT
, it will initiate entry into a L1 link state by sending a PM_Enter_L1
DLLP. Thus, under normal operating conditions when the root ports sends the
PME_Turn_Off message, the link will be in state L1. However, when the root port is
instructed to send the PME_Turn_Off message, it will send it whether or not the link
was in L1. Endpoints attached to PCH can make no assumptions about the state of the
link prior to receiving a PME_Turn_Off message.
5.2.2.2 Resuming from Suspended State
The root port contains enough circuitry in the suspend well to detect a wake event
through the WAKE# signal and to wake the system. When WAKE# is detected asserted,
an internal signal is sent to the power management controller of the PCH to cause the
system to wake up. This internal message is not logged in any register, nor is an
interrupt/GPE generated due to it.
5.2.2.3 Device Initiated PM_PME Message
When the system has returned to a working state from a previous low power state, a
device requesting service will send a PM_PME message continuously, until
acknowledged by the root port. The root port will take different actions depending upon
whether this is the first PM_PME that has been received, or whether a previous
message has been received but not yet serviced by the operating system.
If this is the first message received (RSTS.PS - D28:F0/F1/F2/F3/F4/F5/F6/F7:Offset
60h:bit 16 is cleared), the root port will set RSTS.PS, and log the PME Requester ID
into RSTS.RID (D28:F0/F1/F2/F3/F4/F5/F6/F7:Offset 60h:bits 15:0). If an interrupt is
enabled using RCTL.PIE (D28:F0/F1/F2/F3/F4/F5/F6/F7:Offset 5Ch:bit 3), an interrupt
will be generated. This interrupt can be either a pin or an MSI if MSI is enabled using
MC.MSIE (D28:F0/F1/F2/F3/F4/F5/F6/F7:Offset 82h:Bit 0). See Section 5.2.2.4 for
SMI/SCI generation.
If this is a subsequent message received (RSTS.PS is already set), the root port will set
RSTS.PP (D28:F0/F1/F2/F3/F4/F5/F6/F7:Offset 60h:Bit 17) and log the PME Requester
ID from the message in a hidden register. No other action will be taken.
When the first PME event is cleared by software clearing RSTS.PS, the root port will set
RSTS.PS, clear RSTS.PP, and move the requester ID from the hidden register into
RSTS.RID.
If RCTL.PIE is set, an interrupt will be generated. If RCTL.PIE is not set, a message will
be sent to the power management controller so that a GPE can be set. If messages
have been logged (RSTS.PS is set), and RCTL.PIE is later written from a 0 to a 1, an
interrupt will be generated. This last condition handles the case where the message
was received prior to the operating system re-enabling interrupts after resuming from
a low power state.
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