It is due to the reason that the 100Mbps operation causes the MAC internal signal to remain high even after speed change to 1000Mbps operation where this signal is expected to be low initially. This signal will cause the MAC to sample a false EOP condition.
The following patch provides a solution to mask a signal being generated by the tx_rden signal when the MAC is operating in 1000Mbps mode to determine the valid or invalid EOP signal. When the mask signal is high and EOP is detected, the logic will filter out the EOP as an invalid EOP condition.
Please download the appropriate Quartus® II software version 10.0SP1 patch 1.210 from the following links:
You must either have previously installed the Quartus II 10.0 SP1 software or must install the Quartus II 10.0 SP1 software before installing this patch. Otherwise, the patch will not be installed correctly and the Quartus II software will not run properly.
After you install the patch please regenerate your Triple Speed Ethernet MegaCore® before you compile your design.