Normal outbound frame transfer timing is shown in the following figure. This figure shows that
an Ethernet frame is proceeded by an 8-byte preamble field (inclusive of the Start of
Frame Delimiter (SFD)), and completed with a 4-byte Frame Check Sequence (FCS) field.
This frame is created by the MAC connected to the other end of the GMII. The PCS logic
itself does not recognize the different fields within a frame and treats any value
placed on gmii_txd[7:0] within the gmii_tx_en
assertion window as data.
Figure 1. GMII Normal Frame Transmission
