IDT PCI Express 89HPES32NT24xG2, User Manual, Page: 165 / 744

Notes
PES32NT24xG2 User Manual 9 - 1 January 30, 2013
®
Chapter 9
Power Management
Overview
This chapter describes the PES32NT24xG2 device power management support. This chapter does not
describe link active state power management (ASPM). For a description of this topic, refer to section Link
Active State Power Management (ASPM) on page 7-12.
Located in the configuration space of each function in the PES32NT24xG2 (i.e., PCI-to-PCI Bridge, NT,
and DMA functions) is a power management capability structure. The switch’s functions support the
following device power management states:
– D0 (D0
uninitialized
and D0
active
)
– D3
Hot
– D3
Cold
.
A power management state transition diagram for the states supported by the switch is provided in
Figure 9.1 and described in Table 9.1. Transitioning a function’s power management state from D3
hot
to
D0
uninitialized
does not result in any logic being reset or re-initialization of register values. Thus, the default
value of the No Soft Reset (NOSOFTRST) bit in the function’s PCI Power Management Control and Status
(PMCSR) register corresponds to the functional context being maintained in the D3
hot
state.
The power management capability structure associated with each function affects the power state of
that function only. The link’s power state is derived from the power state of the function(s) in the port. When
a function enters the D0 state (i.e., D0
uninitialized
or D0
active
), the function transitions the port’s link to the L0
state. When a function enters the D3
Hot
state, the function transitions the port’s link to the L1 state.
– When the upstream port operates in a multi-function mode, the port’s link enters the L1 power
state only when all functions in the port are placed in a non-D0 state. For example, a port operating
in upstream switch port with NT function mode places its link in the L1 state when both functions
of the port are placed in the D3
Hot
state. A port operating in upstream switch port with NT and DMA
functions places its link in the L1 state when all three functions of the port are placed in the D3
Hot
state.
– A port configured in ‘Downstream Switch Port’ mode always accepts entry into L1 when requested
by the link partner.
1
1.
This applies when entry into L1 is a result of the link partner being placed in D3hot. This does not apply for entry
into L1-ASPM, where the L1 entry request may be rejected by the downstream switch port. Refer to section Link
Active State Power Management (ASPM) on page 7-12 for further details on L1 ASPM.