Figure 4-8: Sgmii Adaptation Module - Xilinx LogiCORE Getting Started Manual

Ethernet 1000base-x pcs/pma or sgmii v7.0

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Table Of Contents

Table of Contents

SGMII Adaptation Module

The GMII of the core always operates at 125 MHz. The core makes no differentiation

between the three speeds of operation; it always effectively operates at 1 Gbps. However,

at 100 Mbps, every data byte run through the core should be repeated 10 times to achieve

the required bit rate; at 10 Mbps, each data byte run through the core should be repeated

100 times to achieve the required bit rate. Dealing with this repetition of bytes is the

function of the SGMII adaptation module.

The provided SGMII adaptation module

clocks at a frequency of 125 MHz when operating at a speed of 1 Gbps (with no repetition

of data bytes); 12.5 MHz at a speed of 100 Mbps (each data byte is repeated and run

through the core 10 times); 1.25 MHz at a speed of 10 Mbps (each data byte is repeated and

run through the core 100 times).

This GMII-style interface is not a standard interface (true GMII only operates at a clock

frequency of 125 MHz), but it does allow a straightforward internal connection to an

Ethernet MAC core. For example, the SGMII adaptation module can be used to interface

the Ethernet 1000BASE-X PCS/PMA or SGMII LogiCORE, operating in SGMII mode, to

the Xilinx Tri-Mode Ethernet MAC LogiCORE (see the Xilinx LogiCORE Ethernet

1000BASE-X PCS/PMA or SGMII User Guide for more information).

The top-level HDL for the SGMII adaptation module is described in the following files:

VHDL

From Client MAC

GMII

Signals to form

SGMII reference

clock

Speed Control

To Client MAC

GMII

userclk2

(125 MHz

reference clock)