IDT 89HPES48T12G2, User Manual

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Notes
PES48T12G2 User Manual 13 - 1 April 5, 2013
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Chapter 13
Multicast
Introduction
This IDT PCIe Switch implements multicast as defined by the PCI-SIG Multicast ECN. The multicast
capability enables a single TLP to be forwarded to multiple destinations. The destinations to which a multi-
cast TLP is forwarded are referred to as a multicast group.
– A multicast group may contain zero or more destinations.
The PES48T12G2 supports up to 64 multicast groups -- this is the maximum allowed by the PCIe stan-
dard.
– The number of supported groups is advertised via the MAXGROUP field in the MCCAP register.
The default value of this field corresponds to 32 groups. This field may be re-programmed during
initial switch configuration (e.g., EEPROM) to advertise up to 64 groups.
A function need not be a member of a multicast group in order generate a multicast TLP that is
forwarded to a multicast group. For example, any endpoint or root may generate a multicast TLP by trans-
mitting a posted TLP with an address that maps to a multicast group.
Multicast is compatible with legacy PCIe roots and endpoints.
Addressing and Routing
Multicast addressing and routing may be partitioned into the task of determining that a TLP is a multicast
TLP, routing a multicast TLP to functions (e.g., PCI-to-PCI bridges associated with egress ports), and multi-
cast egress processing performed at each function. These tasks are described in the following sections.
Multicast TLP Determination
The determination of whether or not a TLP is a multicast TLP is made by functions that receive the TLP.
All functions associated with the switch are expected to have identical multicast routing configuration. Thus,
multicast TLP determination may be made using register values associated with the capability structure of
any function in the switch.
– Modification of multicast routing fields requires that multicast traffic be quiesed.
The following multicast register fields must be configured to the same value in all functions in the switch.
Violating this requirement results in undefined behavior on receipt of a multicast TLP. Non-multicast TLPs
are not affected.
Register: MCCTL, field: NUMGROUP
Register: MCBARL, fields: INDEXPOS, MCBARL
Register: MCBARH, field: 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, etc. When the Multicast Enable (MEN) bit is cleared in the Multi-
cast Control (MCCTL) register, multicast is disabled and no TLP received on the link is a multicast TLP. A
TLP determined not to be a multicast TLP is routed using traditional unicast PCIe routing rules. Thus,
unroutable “multicast TLPs” are handled in the same manner as any other unroutable TLP.