PM3350-SW datasheet(147/224 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

145

Let Mdplx represent a per-port multiplier that is 0.5 for half duplex operation and

1.0 for full duplex operation.

Let Mpfsz represent a multiplier that represents the Elan Frame Transfer

Protocol overhead with respect to the time it took for the frame to be sent on the

link media (assuming a standard interframe gap of 96 bit times and nominal

preamble length of 64 bits).

Mpfsz is a function of:

•

the link rate (Mpfsz is directly proportional to the link media rate).

•

the Ethernet framesize

•

the size of the PacketBuffer structure being used on the chip (default size is 80

bytes).

Calculation of Mpfsz for a 64 bytes frame for a 100Mbit link:

link time = 96*10 (ifg) + 64*10 (preamble) + 64*8*10 (data) = 6720 ns

Bits required to have frame read across the PCI bus by one chip:

Data Descriptor = 16 bytes

1 Request counter increment + 1 Acknowledge counter increment = 8 bytes

1 PacketBuffer = 80 bytes

So Mpfsz is (104 bytes * 8 bits/bytes) / 6720 ns = 0.124 bits/ns.

Example 4.2:

Calculation for a 64 bytes frame for a 10Mbit link:

This is simply 1/10 of the Mpfsz for the 100 Mbit example, or 0.0124 bits/ns

A graph of Mpfsz versus framesize is given is shown below. As can be seen from this

figure, the worst case values of Mplfsz is approximately 0.125 bits/ns for 100 Mbit

media (PM3351) and 0.0125 for 10 Mbit media (PM3350).

PM3350-SW Datasheet(PDF) 147 Page - PMC-Sierra, Inc