PM3350-SW datasheet(49/224 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

other channel that is destined for an end-station on the flow-controlled channel), the

MAC channel will cease transmitting the backpressure pattern, wait for a normal

interframe gap, and then transmit the desired frame(s). After all the pending frames

have been transmitted, the MAC logic will resume backpressuring the channel.

The backpressure mechanism described above is an optional feature that may be

enabled on a per-port basis by means of configuration parameters in the boot image. It

should be noted that the backpressure method will result in the complete shutdown of

the MAC channel (i.e., even local segment traffic will not be allowed to proceed), and so

it is recommended that backpressure be enabled only on ports that are connected to a

small number of end-stations.

The ELAN 8x10 MAC channels also provide a frame type filtering feature that extracts

the 16-bit EtherType fields of incoming frames (occupying the portion of the Ethernet

frame header immediately after the destination and source MAC addresses), compares

it to a programmable 16-bit value, and signals the Switch Processor firmware if a match

is found. This facility may be used, for example, to quickly identify MAC Control frames

(defined in IEEE 802.3x) or Address Resolution Protocol frames belonging to the

TCP/IP protocol. The Switch Processor firmware may then handle such marked frames

in a special manner.

Each MAC channel maintains a pair of control and status registers that allow the Switch

Processor to monitor and manage the state of the MAC channels. The MAC interfaces

are configurable (as a group) by a set of configuration registers that are loaded at

initialization time. The following parameters are configurable:

Parameter

Min

Max

Units

Interframe spacing, Part 1

255

bit times

Interframe spacing, Part 2

255

bit times

Transmitted preamble length (not

including SFD byte)

255

bits

Jam length (after collision)

255

bit times

Maximum frame size

4095

bytes

Minimum frame size

255

bytes

Late collision threshold

1024

bit times

Receiver blind time

255

bit times

EtherType comparison value

65535

N/A

It should be noted that the Part 1 interframe spacing may be set to zero, in which case

the interframe behavior of the ELAN 8x10 MAC defaults to that specified by the

Ethernet V2.0 standard. If the Part 1 interframe spacing is non-zero, then the minimum

interframe gap that can be tolerated by the MAC port during back-to-back frame receive

will be the greater of the Part 1 interframe spacing and the receiver blind time.

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