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IDT Power Management
Notes
PES48H12G2 User Manual
• This requires transitioning the link to the L0 state when the completion needs to be transmitted
on the link by the bridge Function and the link is not in L0.
– All request TLPs received on the secondary interface are treated as unsupported requests (UR).
PME Messages
PES48H12G2 does not support generation of PME messages from the D3
generation is only supported by downstream ports (i.e., the PCI-to-PCI bridge Function associated with an
upstream port does not support PME message generation).
Downstream ports (i.e., PCI-to-PCI bridges associated with downstream ports) support the generation
of hot-plug PME events (i.e., a PM_PME power management message) from the D3
both the case when the downstream port is in the D3
state.
PCI Express Power Management Fence Protocol
The root complex takes the following steps to turn off power to a system.
– The root places all devices in the D3 state
– Upon entry to D3, all devices transition their links to the L1 state
– The root broadcasts a PME_Turn_Off message.
• The links temporarily transition to L0 in order to transfer the message.
– Devices acknowledge the PME_Turn_Off message by returning a PME_TO_ACK message
• After transmitting a PME_TO_ACK, a device places its link in L2/L3-Ready state.
The PME_Turn_Off / PME_TO_Ack protocol may be initiated by the root when the switch Function's are
in any power management state. The port's handling of the power management fence protocol depends on
its operating mode as described below.
Upstream Switch Port or Downstream Switch Port Mode
– When a port configured in 'Upstream Switch Port' mode receives a PME_Turn_Off message, it
broadcasts the PME_Turn_Off message on all active downstream ports of the associated parti-
tion. The upstream port transmits a PME_TO_Ack message and transitions its link state to L2/L3
Ready after it has received a PME_TO_Ack message on each of its active downstream ports of
the partition. This process is called PME_TO_Ack aggregation.
– The aggregation of PME_TO_Ack messages on downstream ports is abandoned by the upstream
switch port when this port receives a TLP after having previously received a PME_Turn_Off
message but before having responded with a PME_TO_Ack message. Once a PME_TO_Ack
message has been scheduled for transmission on the upstream switch port and the PME_TO_Ack
aggregation process has completed, received TLPs at that point are discarded.
– If the TLP that causes PME_TO_Ack aggregation to be abandoned targets a PES48H12G2 Func-
tion, then the targeted Function responds to the TLP normally. If the TLP that causes aggregation
to be abandoned is routed to a downstream port's link and the link is in L0, then the TLP is trans-
mitted on the downstream port. If the downstream port's link is not in L0 (i.e., it is in L2/L3 Ready),
then the port transitions the link to Detect and then to L0. Once the link is reaches L0, the TLP is
transmitted on the downstream port.
– When PME_TO_Ack aggregation is abandoned, the PES48H12G2 makes no attempt to abandon
the PME_Turn_Off and PME_TO_Ack protocol on downstream ports. Devices downstream of
PES48H12G2 are allowed to respond with a PME_TO_Ack and transition to L2/L3 Ready. When
a TLP is received that needs to be routed to the downstream port's link, then the switch transitions
the link to Detect and then to L0. Once the link reaches L0, the TLP is transmitted on the down-
stream port.
state or the entire switch partition is in the D3
hot
11 - 3
state. PME message
cold
state. This includes
hot
hot
April 5, 2013
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