PM3350-SW datasheet(96/224 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

Type:

This 2-bit field denotes the type of MAC address (and hence the disposition

of the Ethernet frame directed towards the MAC address). It is interpreted as

follows:

Type

Interpretation

Invalid for hash buckets, reserved for forwarding tags

Unicast MAC address reachable via a local MAC channel

Invalid for hash buckets, reserved for forwarding tags

Broadcast MAC address reachable via a local MAC channel

The Type field is only valid if the Special bit is clear, indicating that the frame

can be treated as a normal Ethernet frame. The Type field of the hash bucket

corresponding to the destination MAC address is generally used to set up the

Type subfield of the Flags field of the data descriptor (and thus to switch the

frame).

The AgeControl field holds a 32-bit timestamp which records the absolute time a frame

was last received from the source host with a MAC address corresponding to this hash

bucket. The timestamp has a resolution of 1 microsecond and a range of approximately

1.12 hours. It is used during the aging process to locate hash buckets that have not

been refreshed for some time, and are thus candidates for removal. The Switch

Processor updates the AgeControl field with the contents of its built-in CLOCK real-time

clock register whenever it receives a valid Ethernet frame, and the hash lookup engine

resolves the source MAC address in the frame to the given hash bucket.

The CreateTime field is similar to the AgeControl field, but holds the time of creation for

this hash bucket for RMON and SNMP counter purposes.

The remainder of the local port descriptor holds per-MAC counters that are maintained

and updated by the switching firmware in order to support the RMON MIB statistics. A

total of seven 32-bit counters are implemented. Note that the RXErrorFrames counter is

only updated if sufficient bytes of the frame are received to permit the hash lookup

engine to successfully resolve the source hash bucket.

The Switch Processor does not cache any hash bucket at any time in its internal data

cache. It is therefore possible to read the contents of any hash bucket via the PCI bus

interface without data consistency issues.

Forwarding Tags

A 16-byte forwarding tag (occupying the first 16 bytes of a 64-byte memory block, with

the remaining 48 bytes being unused) is created whenever it is necessary to record that

a particular MAC address is reachable by an external device (such as another ELAN

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