PM3350-SW datasheet(102/224 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

100

data with the master device and transmit packets on its behalf, but do not maintain the

spanning tree data structures.) Two different data structures are used by the spanning

tree algorithm: a per-bridge data structure, only one of which is present in a system,

and a per-port data structure, which is replicated for each port in the system.

Further description of the spanning tree data structures is TBD.

Broadcast Restriction Mask

A special data structure, referred to as the

broadcast restriction mask, is used by the

ELAN 8x10 to limit packet broadcasts in response to the results of the spanning tree

algorithm. This mask consists of sixteen bits: eight bits correspond to the physical MAC

ports implemented within the ELAN 8x10 itself, and the remaining eight bits are

assigned to the external ELAN 8x10 devices connected to the PCI expansion bus, as

shown below:

9876543210

The eight port-related bits are indicated as P0 through P7, corresponding to physical

ports 0 through 7 respectively, while the eight device-related bits are denoted as D0

through D7. Note that the device-related bit corresponding to the given ELAN 8x10

device itself must always be zero, as it is not permissible for an ELAN 8x10 device to

send broadcasts to itself across the PCI bus. In addition, further device-related bits will

be set to zero if there are less than eight devices in the system.

When a broadcast or multicast frame, or one directed to an unknown MAC address

(which must be flooded) is received, the ELAN 8x10 inspects the broadcast restriction

mask to determine the permissible destinations to which the packet may be sent. The

mask is initialized as required upon power-on, and subsequently modified by the

spanning tree algorithm or system manager to remove specific ports and devices from

the broadcast topology. Note that hash buckets for multicast MAC addresses contain

their own restriction masks, which are logically ANDed with the global broadcast

restriction mask to further limit the broadcast topology; this feature may be used to

implement multicast groups. In addition, broadcast restriction on a per-source-port basis

is made possible by a similar multicast restriction mask in each of the local port

descriptors, which is also ANDed into the global broadcast restriction mask.

RTOS Requirements

This section details the general requirements and specific data structures of interest

that are implemented by the optional Real-Time Operating System.

This section is TBD.

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