What happens to the existing packet whent the TX Etherne Fleximac underruns?
When it detects TX fifo_underrun, the FLXMC sends a column of 1FBh (SOP) and
then continuously sends a column of 107h (IDLE) until more data is available.
It then treats the subsequent data as a new packet.
The FLXMC cannot terminate the packet based on underflow.
If you send an EOP, either after all the bytes of the corrupted packet have been sent, or as soon as the corruption is detected, the FLXMC will terminate the bad packet correctly (by sending bad CRC), and be ready to send the next good packet.