MDS213 Datasheet, PDF (62/120 Pages) Zarlink Semiconductor Inc – 12-Port 10/100Mbps + 1Gbps Ethernet Switch

MDS213
Data Sheet
TG provided by
Search Eng
TG Hash Key
(2 bits) (3 bits)
Hash Keys
Dev ID
(1 bit)
Port ID
(4 bit)
..
.
.
.
.
Port Mapping Table for MDS213
Figure 23 - Port Mapping Table
In Figure 23, the Trunk Port Mapping Table is 32 entries deep (4 groups * 8 hash entries), and each entry is 5 bits
wide (1-bit device ID, 4-bit port ID), as show in the following format.
17.2 Multicast Packet Forwarding
For multicast packet forwarding, the destination device must determine the proper set of ports to transmit the
packet based on the VLAN Index and Hash Key, generated by the source Search Engine. Two functions are
needed to distribute multicast packets to the appropriate destination ports in a Trunk Group.
1. Selecting a Forwarding Port per Trunk Group:
Only one port per Trunk Group will be used to forward multicast packets. This can be done with a VLAN INDEX
Table and a Forwarding Port MASK Table set up by CPU.
2. Blocking Multicast Packet Back to the Source Trunk:
For multicast forwarding that includes ports in Trunk Groups in the same device as source port, all ports in the same
Trunk Group at the receiving port must be excluded. Otherwise, this multicast packet will be looped back to the
same source Trunk Group. This is achieved through a Trunk Group ID Register that contains 36 bits (36=12x3).
17.2.1 Select One Forwarding Port per Trunk Group
To forward multicast frames, the Frame Engine retrieves the VLAN member ports from one of the 256 entries in the
VLAN Port Mapping Table (VMAP) as described in the VLAN section. By using the Hash Key and the Forwarding
Port Mask table, the Frame Engine can obtain the corresponding FP Mask. The final forwarding ports can then be
determined by the logical AND of the FP Mask and the VLAN Member Port bit map. The Forwarding Port- Mask
Table must be set by the CPU to THKM[0:7] registers beforehand. The format of this table and the method of setting
it up are shown below.
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