Normal Frame Transmission
Normal outbound frame transfer timing is
illustrated 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 does not
recognize the different fields within a frame and treats any value placed on gmii_txd_chx[7:0] within the gmii_tx_en_chx assertion window as data.
Error Propagation
A corrupted frame transfer is illustrated in the
following figure. An error can be injected into the frame by asserting
gmii_tx_er_chx at any point during the
gmii_tx_en_chx assertion window. The core ensures that all
errors are propagated through both transmit and receive paths so that the error is
eventually detected by the link partner.
