The rate match FIFO in the transceiver compensates for the frequency difference between the recovered clock and the receive clock by inserting or removing inter-packet gaps between packets. You may observe corrupted packets in variations of the MegaCore function operating at 10/100 Mbps with GXB transceiver for certain combinations of ppm difference and packet size. For 200 ppm difference, the largest supported ppm difference, you get corrupted packets if the packet size is greater than 160 bytes in 10-Mbps designs or 1600 bytes in 100-Mbps designs.
This issue affects all designs that contain SGMII PCS variations with GXB transceiver operating at 10/100 Mbps.
Set the GXB transceiver to operate in basic mode. To do so, you must instantiate the MegaCore function with an external transceiver. The Instantiate TSE with External ALTGX / ALTLVDS page includes a design example that demonstrates this configuration and lists the required parameter settings.
This issue is fixed in version 10.1 of the Triple-Speed Ethernet MegaCore function.