The block level of the core contains the QSGMII Adaptation Module (this is illustrated in This Figure ). This QSGMII adaptation module is described in the remainder of this section.
Because the GMII of the core always operates at 125 MHz, the core makes no differentiation between the three QSGMII speeds of operation. It always effectively operates at 1 Gbps. However, as described previously in Using the Encrypted Core Level Client-Side GMII/MII , at 100 Mbps, every data byte run through the core is repeated ten times to achieve the required bit rate; at 10 Mbps, each data byte run through the core is repeated 100 times to achieve the required bit rate. Dealing with this repetition of bytes is the function of the QSGMII adaptation module. In addition in PHY mode and operating in MII, the QSGMII adaptation module is also responsible for conversion of the 4-bit MII interface to an 8-bit GMII core interface.
The provided QSGMII adaptation module ( This Figure ) creates a GMII interface that drives/samples the GMII data and control signals at the following frequencies:
• 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).
Therefore, the result of the QSGMII adaptation module is to create a proprietary interface that is based on GMII (true GMII only operates at a clock frequency of 125 MHz). This interface 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 QSGMII adaptation module can be used to interface to the QSGMII core, operating in MAC, to four instances of the Xilinx Tri-Mode Ethernet MAC core directly. The GMII interface of the QSGMII adaptation module can brought out to the pads and connected to an external PHY module that converts GMII to PMD signals when the QSGMII core is operating in PHY mode.