Additional Client-Side SGMII Logic - 16.2 English

1G/2.5G Ethernet PCS/PMA or SGMII LogiCORE IP Product Guide (PG047)

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16.2 English

When the core is generated in SGMII or Dynamic Switching mode, the block level of the core contains the SGMII Adaptation Module (this is shown in the following figure for a core using a device specific transceiver as the physical interface). This SGMII adaptation module is described in the remainder of this section.

Figure 1. Block Level Diagram of an SGMII Example Design

Because the GMII of the core always operates at 125 MHz (312.5 MHz for the 2.5G data rate), the core does not differentiate between the three SGMII speeds of operation (for the 1 Gbps maximum data rate); it always effectively operates at 1/2.5 Gbps. However, as described in Using the Client-Side GMII for the 1000BASE-X Standard, at 100 Mbps, every data byte run through the core is repeated ten times to achieve the required bit rate; similarly, at 10 Mbps, each data byte run though the core is repeated 100 times to achieve the required bit rate. Dealing with this repetition of bytes is the function of the SGMII adaptation module.

The SGMII adaptation module (as shown in the following figure) creates a GMII-style interface that drives/samples the GMII data and control signals at the following frequencies:
  • 125/312.5 MHz when operating at a speed of 1/2.5 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)

When the core is connected to Ethernet MAC peripherals of the processing subsystem present in Zynq and Versal devices, the SGMII adaptation module performs the additional function of converting the 8 bits from the core to a 4-bit MII interface and vice versa. The function of the SGMII adaptation module is therefore to create a proprietary interface that is based on GMII (true GMII only operates at a clock frequency of 125 MHz for an Ethernet line rate of 1.25 Gbps). This interface then allows a straightforward internal connection to an Ethernet MAC core when operating in MAC mode or the GMII can be brought out on pads to connect to an external PHY when the core operates in PHY mode. For example, the SGMII adaptation module can be used to interface the core, operating in SGMII configuration with MAC mode, to the AMD Tri-Mode Ethernet MAC core directly (see Interfacing to Other Cores). The GMII interface of the SGMII adaptation module can brought out to the pads and connected to an external PHY module that converts GMII to a Physical Medium Dependent (PMD) signal when the core is operating in SGMII configuration and PHY mode.