IDT PCI Express 89HPES32NT24xG2, User Manual, Page: 332 / 744

IDT Multicast
PES32NT24xG2 User Manual 17 - 2 January 30, 2013
Notes
The following multicast register fields must be configured to the same value in all functions associated
with a switch partition. Violating this requirement results in undefined behavior on receipt of a multicast TLP.
Non-multicast TLPs are not affected.
– MCCTL Register
NUMGROUP
MEN
– MCBARL Register
INDEXPOS
MCBARL
– MCBARH Register
MCBARH
Unless otherwise noted, TLP processing associated with a multicast TLP is the same as that for any
other TLP. For example, malformed checks are the same, poison bit processing is the same, ECRC
checking and error reporting is the same, and so on. When the Multicast Enable (MEN) bit is cleared in the
Multicast Control (MCCTL) register, multicast is disabled and no TLP received on the link associated with
that port is a multicast TLP.
A TLP determined not to be a multicast TLP is routed using traditional unicast PCI Express routing rules.
Thus, unroutable “multicast TLPs” are handled in the same manner as any other unroutable TLP.
Only posted memory write TLPs and address routed message TLPs can be multicast TLPs. The primary
determinant of whether or not a memory write or address routed message TLP is a multicast TLP is its
address and the address associated with multicast address regions. A multicast address region may
overlap a non-multicast address region.
Multicast TLPs that target a multicast address region are routed to all multicast group members while
other TLPs, such as non-posted reads, may be routed to only one, possibly different, destination. Multicast
TLPs are posted TLPs and have the same ordering requirements as other posted TLPs. There are no new
multicast TLP ordering rules.
The maximum number of multicast groups supported in an implementation is contained in the Max Multi-
cast Groups (MAXGROUP) field in the Multicast Capability (MCCAP) register. The number of multicast
groups that are actually enabled is determined by the value in the Number of Multicast Groups
(NUMGROUP) field in the Multicast Control (MCCTL) register.
As illustrated in Figure 17.1, multicast TLP group membership is determined by address. Associated
with each multicast group is an address region. Posted memory write and address routed message TLPs
whose address is equal to that associated with a multicast group when the Multicast Enable (MEN) bit is
set, are defined to be multicast TLPs associated with that group.