PM3350-SW datasheet(98/224 Pages) PMC

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ELAN 8X10

PM3350 ELAN 8 X10

DATA SHEET

PMC-970109

ISSUE 3

8 PORT ETHERNET SWITCH

PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND PMC-SIERRA, INC. CUSTOMERS ONLY

The 16-bit MulticastMask field is used to restrict broadcasts, multicasts and floods of

packets directed to a given multicast MAC address (i.e., when the contents of the

MACAddr field is an IEEE group/functional address). The lower 8 bits of this mask are

unused, and set to zeros during the forwarding tag creation process. The upper 8 bits of

the mask correspond to the eight possible devices in the system. The MulticastMask

field is logically ANDed with the upper 8 bits of the global restriction mask managed by

the spanning tree protocol entity to implement multicasts on a per-MAC-address basis.

It is ignored for unicast frames.

The SrcHashBkt field contains the 24-bit memory address of the actual hash bucket

that holds the necessary physical port routing information and the per-MAC statistics

associated with this MAC address. This address is valid only in the memory address

space of the remote device, and has no significance to the ELAN 8x10 containing the

forwarding tag.

The remote device supplies the information placed in the SrcHashBkt field when it

requests that a forwarding tag be created during the learning process. If the destination

MAC address of a received Ethernet frame resolves to a forwarding tag, then the ELAN

8x10 device will transfer the frame to the remote device indicated by the ChipNum field

in the forwarding tag, and will also place the SrcHashBkt value in the HashBkt field of

the data descriptor associated with the frame. The remote device is expected to use the

hash bucket address passed by this ELAN 8x10 to avoid having to perform yet another

hash lookup in its own version of the address table; instead, it will locate the hash

bucket indicated by the HashBkt field of the data descriptor, verify that it is indeed valid,

and use the information within the hash bucket to switch the frame.

FTFlags supplies control bits that are used to determine the operation of the switching

firmware when handling Ethernet frames that are directed to this MAC address. This

field is formatted as:

3210

reserved

Special

Type

reserved

Special:

If set, indicates that the frame data must not be processed by the normal

switching firmware, but must be handled specially by external code. Normally

zero.

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