Notes
PES16NT2 User Manual
3 - 1
April 15, 2008
®
Chapter 3
Link Operation
Introduction
The PES16NT2 contains two ports. The default link width of each port is x8 and the SerDes lanes are
statically assigned to a port.
Polarity Inversion
Each port of the PES16NT2 supports automatic polarity inversion as required by the PCIe® specifica-
tion. Polarity inversion is a function of the receiver and not the transmitter. The transmitter never inverts its
data. During link training, the receiver examines symbols six through 16 of the TS1 and TS2 ordered sets
for inversion of the PExAP[n] and PExAN[n] signals. If an inversion is detected, then logic for the receiving
lane automatically inverts received data.
Polarity inversion is a lane and not a link function. Therefore, it is possible for some lanes of link to be
inverted and for others to not be inverted.
Link Width Negotiation
The PES16NT2 supports the option link variable width negotiation feature outlined in the PCIe specifica-
tion. During link training, each of the x8 ports is capable of negotiating to a x8, x4, x2 or x1 link width. The
negotiated width of each link may be determined from the Link Width (LW) field in the corresponding port’s
PCI Express® Link Status (PCIELSTS) register.
The Maximum Link Width (MAXLNKWDTH) field in a port’s PCI Express Link Capabilities (PCIELCAP)
register contains the maximum link width of the port. This field is of RWL type and may be modified when
the REGUNLOCK bit is set in the PA_SWCTL register. Modification of this field allows the maximum link
width of the port to be configured. The new link width takes effect the next time link training occurs.
To force a link width to x4 despite a link partner’s ability to negotiate to x8, the MAXLNKWDTH field
could be configured through Serial EEPROM initialization and link retraining forced. Assuming the link
partner has a link width greater than or equal to x4 and the capability to negotiate to a width of x4, the link
width will negotiate to x4.
Lanes associated with a x8 link are partitioned into two groups of four lanes.When a link negotiates to a
width less than x8, then the unused group of four lanes are powered down to save power. In addition,
unused SerDes in a four lane group are put in a low power state (i.e. L1 state).
Lane Reversal
The PCIe specification describes an optional lane reversal feature. The PES16NT2 does not support the
automatic lane reversal feature outlined in the PCIe specification. However, it does support static lane
reversal on a per port basis.
Associated with each PES16NT2 switch port is a lane reversal signal. The lane reversal signal for port A
is PEALREV and for port C is PECLREV. The status of the lane reversal signals sampled during a funda-
mental reset may be determined from the PALREV and PCLREV fields in the PA_SWSTS register.
The port lane reversal signals are sampled during a fundamental reset and used as the initial value of
the PALREV and PCLREV fields in the PA_SWCTL register. When these bits are set, then the lanes of the
corresponding port(s) are reversed during link training. Lane reversal mapping for the various non-trivial
maximum link width configurations is illustrated in Figures 3.1 through 3.3.
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Страница 14: ...DT List of Figures PES16NT2 User Manual viii April 15 2008 Notes...
Страница 20: ...IDT Register List PES16NT2 User Manual xiv April 15 2008 Notes...
Страница 32: ...IDT PES16NT2 Device Overview PES16NT2 User Manual 1 12 April 15 2008 Notes...
Страница 44: ...IDT Clocking Reset and Initialization Clock Operation PES16NT2 User Manual 2 12 April 15 2008 Notes...
Страница 50: ...IDT Link Operation PES16NT2 User Manual 3 6 April 15 2008 Notes...
Страница 62: ...IDT Power Management PES16NT2 User Manual 5 4 April 15 2008 Notes...
Страница 78: ...IDT SMBus Interfaces PES16NT2 User Manual 6 16 April 15 2008 Notes...
Страница 83: ...IDT NTB Upstream Port Failover PES16NT2 User Manual 7 5 April 15 2008 Notes...
Страница 84: ...IDT NTB Upstream Port Failover PES16NT2 User Manual 7 6 April 15 2008 Notes...
Страница 130: ...IDT Transparent Mode Operation PES16NT2 User Manual 9 44 April 15 2008 Notes...
Страница 284: ...IDT Non Transparent Mode Operation PES16NT2 User Manual 10 154 April 15 2008 Notes...