PM3350-SW datasheet(133/224 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

131

The NextDD field is set up properly when the message descriptor is queued. The Flags

field is formatted as shown below:

76543210

01000100

The encoding of the Flags field indicates that this is a message descriptor that is

notifying the recipient of the need to delete the forwarding tag corresponding to an

aged-out hash bucket.

The HashIndex and HashBktAddr fields are expected to be used by the recipient in

locating the forwarding tag that must be removed. The HashIndex field is simply the

index of the hash pointer array at which the hash bucket itself is located, which will be

identical to the index at which the forwarding tag will be located in the remote device.

The HashBktAddr value is the 24-bit address of the hash bucket being deleted, and will

be compared to the corresponding field in the forwarding tag to ensure that the correct

forwarding tag will be removed.

The notification messages described above are treated as standard data descriptors

and transferred to the remote device by the owner of the hash bucket using the normal

PCI expansion port transfer protocol (with the exception that no packet buffers are

transferred, as the FirstPB pointers in the message descriptors are NULL). Upon receipt

of a notification message, a remote device (ELAN 8x10 or other) must access its own

address table, locate the proper forwarding tag using the data specified in the message,

and remove and de-allocate the forwarding tag.

Buffer and Queue Management

The Switch Processor implements all of the buffer and queue management in an ELAN

8x10 device, using mechanisms implemented as firmware routines. Buffer management

is carried out by means of a collection of per-port buffer allocation limits, plus the global

broadcast frame limit that prevents excessive use of system resources by high levels of

broadcasts. Queue management (on the transmit queues) is performed via a

background task that periodically monitors the different transmit queues and handles

housekeeping tasks as required. In addition, broadcast rate limiting is implemented to

avoid system overload during broadcast storms or other malfunctions.

All of the parameters associated with the buffer and queue management functions

implemented by the ELAN 8x10 device are configurable by means of system variables.

These variables may be set statically to default values at boot time, or altered during

normal system operation as required.

PM3350-SW Datasheet(PDF) 133 Page - PMC-Sierra, Inc

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