Assertion of tx_axis_mac_tuser
The assertion of tx_axis_mac_tuser indicates that there is an error in
the data streaming transmission. Upon the assertion of
tx_axis_mac_tuser and tx_axis_mac_tvalid, the
Triple Speed Ethernet MAC core terminates the frame with an error indication
and discards the remaining portion of the frame.
When tx_axis_mac_tuser is asserted at the first cycle, the frame is
dropped silently, and there is no indicator of the dropped frame. No statistic counter
is incremented in this case.
However, if tx_axis_mac_tuser is asserted while
tx_axis_mac_tlast remains low from the 2nd cycle onwards
but still within the Ethernet header, the header is considered incomplete. In this
condition, the Triple Speed Ethernet MAC core terminates the frame, discards the
remaining portion, and asserts the corresponding PHY error signal (e.g.,
gm_tx_err for SGMII or GMII interface).
When tx_axis_mac_tvalid is low, all tx_axis_mac signals
(tdata, tstrb, tlast, tuser) interface are considered invalid, as described in TX AXI ST Interface. Therefore, an assertion of
tx_axis_mac_tuser during a cycle where
tx_axis_mac_tvalid is deasserted does not indicate an error
condition.
However, in Cut Through mode, if
tx_axis_mac_tvalid is deasserted prematurely (before the end of
frame), the Triple Speed Ethernet MAC core terminates the transmission as a bad
frame, as described in Dropped tx_axis_mac_tvalid Before End of Frame.