AR# 35835: LogiCORE IP 10-Gigabit Ethernet MAC v10.x and earlier - tx_underrun must be assert with tx_data_valid
LogiCORE IP 10-Gigabit Ethernet MAC v10.x and earlier - tx_underrun must be assert with tx_data_valid
The users guide shows tx_underrun being asserted in the clock cycle after tx_data_valid has gone to 0x00. This can result in incorrect operation. If tx_underrun is asserted after tx_data_valid is no longer 0xFF, this could result in the error insertion (0xFE) and terminate (0xFD) occurring after the current frame has already been terminated without any error. Thus, errors would not be correctly inserted into the frame and there could be duplicate terminates.
To avoid incorrect behavior, tx_underrun should always be asserted while tx_data_valid is 0xFF.