
IDT Multicast
PES32NT24xG2 User Manual
17 - 11
January 30, 2013
Notes
When the OVRSIZE field value is six or greater, NT multicast address overlay processing is performed
on all NT multicast TLPs transmitted by the port as described below.
–
Address bits in the NT multicast TLP with bit positions greater than or equal to OVRSIZE are
replaced by the corresponding address bits in the multicast overlay base address. The multicast
overlay base address is contained in the Multicast Overlay BAR Low (MCBARL) field in the
NTMCOVRxBARL register and the Multicast Overlay BAR High (MCBARH) field in the MCOVR-
BARH register.
–
Address bits less than OVRSIZE are not modified. As a result of multicast overlay processing, a
multicast TLP with an original address above 4 GB may be translated into a multicast TLP with
address below 4 GB, and vice-versa. Thus, address translation may change the size of a multicast
TLP header (e.g., from 4 DWords to 3 DWords).
–
Unlike transparent multicast, for NT multicast the OVRSIZE field in the NTMCOVRxBARL register
must not be set to less than six. Otherwise the operation of NT multicast egress processing is
undefined. As noted earlier, NT multicast address overlay can be explicitly disabled via the
NTMCAOE bit in the NT Multicast Control (NTMCC) register.
A side-effect of modifying the TLP’s address and requester ID due to NT multicast overlay processing is
that the ECRC associated with the original TLP may not be correct for the new modified TLP. Therefore,
egress ports perform the following ECRC processing.
1
–
If NT multicast overlay processing is disabled, then no ECRC processing is performed as part of
NT multicast egress processing.
–
If an NT multicast TLP does not contain an ECRC, then no ECRC processing is performed as part
of NT multicast egress processing.
–
If an NT multicast TLP contains an ECRC and NT multicast overlay processing is enabled (i.e.,
either requester ID overlay or address overlay), then the following actions are performed.
The ECRC of the original multicast TLP is checked while simultaneously the ECRC for the new
modified TLP is computed or “regenerated.” This is implemented in the same pipeline stage
such that there is virtually no possibility of silent data corruption (e.g., a TLP bit flip that does not
result in a computed ECRC error in the original or regenerated ECRC).
If no error is detected in the ECRC associated with the original TLP, then the modified TLP is
forwarded with the regenerated ECRC.
If an error is detected in the ECRC associated with the original TLP, then the modified TLP is
forwarded with inverted regenerated ECRC (i.e., the computed ECRC of the modified TLP is
inverted).
After performing egress processing of an NT multicast TLP, the port transmits the TLP on the link. No
routing checks are performed and no errors are reported due to NT multicast egress processing.
–
The NT multicast TLP transmitted by a port must never be claimed by a function in that port. Other-
wise operation is undefined.
–
Egress port control registers that normally enable the capability of a port to transmit TLPs (e.g.,
Bus Master Enable it in the PCICMD register) do not have any effect on NT Multicast TLPs emitted
by the port.
Usage Restrictions
The following is a usage restriction associated with NT multicast operation:
–
Modifying the port operating mode of a switch port configured to transmit NT multicast TLPs
requires that the Operating Mode Change Action (OMA) field in the SWPORTxCTL register be set
to reset. Note that this results in the NT Multicast Transmit Enable (NTMCTEN) bit in the port’s
NTMCC register to be cleared, thus causing the port to stop transmission of NT multicast TLPs.
Software must explicitly set the NTMCTEN bit in order to re-enable NT multicast transmission by
the port.
1.
Note that NT Multicast ECRC processing is not dependent on the setting of the ECRC Checking Enable
(ECRCCE) or ECRC Generation Enable (ECRCGE) bits in the AERCTL register of any of the port functions.
Содержание PCI Express 89HPES32NT24xG2
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