
IDT Link Operation
PES32NT24xG2 User Manual
7 - 16
January 30, 2013
Notes
The L1ASPMRTC register is located in the proprietary port-specific registers located in the PCI-to-PCI
bridge function’s configuration space (see section Proprietary Port-Specific Registers in the PCI-to-PCI
Bridge Function on page 19-11). This timer may be programmed from the nano-second range (i.e., 100 ns)
up to the micro-second range (i.e., 64 µ s). By default, the timer is set to 9.5 µ s (refer to the Implementation
note in Section 5.4.1.2 of the PCI Express Base Specification 2.1).
Normally, this timer starts its count after the switch downstream switch port issues an L1 ASPM rejection
(i.e., PM_Active_State_Nak TLP), without checking activity on the link. The switch also provides an option
to start the timer after the downstream switch port issues an L1 ASPM rejection (i.e., PM_Active_State_Nak
TLP) and no activity is detected on the receive-lanes. The Timer Start Control (TSCTL) field in the
L1ASPMRTC register controls this behavior.
This feature allows the PES32NT24xG2 downstream switch ports to enter L1 ASPM with a variety of
endpoints, even those that don’t meet the 10 µ s gap between subsequent L1 ASPM entry requests.
Link Status
Associated with each switch port is a Port Link Up (PxLINKUPN) status output and a Port Activity
(PxACTIVEN) status output. These outputs are provided on an I/O expander for all ports. In addition, the
port 0, port 4, port 8, and port 16 link up and activity outputs are also provided via GPIO alternate functions
(refer to Chapter 13).
The PxLINKUPN and PxACTIVEN status outputs may be used to provide a visual indication of system
state and activity or for debug. The PxLINKUPN output is asserted when the port’s data link layer is up (i.e.,
when the LTSSM is in the L0, L0s, L1 or recovery states). When the data link layer is down, this output is
negated.
In the L2/L3-Ready state, the PES32NT24xG2 considers the link to be down. The PxLINKUPN signal is
therefore deasserted in this state.
The PxACTIVEN output is asserted whenever any TLP, other than a vendor defined message, is trans-
mitted or received on the corresponding port’s link. Whenever a PxACTIVEN output is asserted, it remains
asserted for at least 200 ms. Since an I/O expander output may change no more frequently than once every
40 ms, this translates into five I/O expander update periods.
De-emphasis Negotiation
The PCI Express Base Specification requires that components support the following levels of de-
emphasis, depending on the link data rate:
–
2.5 GT/s (Gen 1): De-emphasis = -3.5 dB
–
5.0 GT/s (Gen 2): De-emphasis = -3.5 dB or -6.0 dB
When operating at 5.0 GT/s, the de-emphasis is selected by programming the Selectable De-emphasis
(SDE) field in the port’s PCI Express Link Control 2 Register (PCIELCTL2). The chosen de-emphasis for
the link is the result of a negotiation between the two components of the link. Both components must
operate with the same de-emphasis across all lanes of the link.
During normal link operation (i.e, PHY LTSSM not in the polling.compliance state), de-emphasis selec-
tion is done during the Recovery state. The downstream component of the link (e.g., switch upstream port
or endpoint) advertises its desired de-emphasis by transmission of training sets. The upstream component
of the link (e.g., switch downstream switch port or root-complex port) notes its link partner desired de-
emphasis, and makes a decision about the de-emphasis to be used in the link.
The PES32NT24xG2’s upstream port physical layer advertises its desired de-emphasis based on the
setting of the SDE field in the PCIELCTL2 register of function 0 of the port. The upstream port always
accepts the link-partners decision on the de-emphasis to be used in the link. The PES32NT24xG2’s down-
stream switch ports ignore the link partner’s desired de-emphasis and always choose the de-emphasis
setting in the SDE field of the port’s PCIELCTL2 register.
Содержание PCI Express 89HPES32NT24xG2
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