The maximum legal length of a
frame specified in IEEE 802.3-2008 is 1,518 bytes for non-VLAN
tagged frames. VLAN tagged frames can be extended to 1,522 bytes.
When jumbo frame handling is disabled and the core receives a frame
that exceeds the maximum legal length, rx_axis_mac_tuser is asserted. When jumbo
frame handling is enabled, frames that are longer than the legal
maximum are received in the same way as shorter frames.
It is also possible to specify a
different maximum frame size. If this is enabled and the frame
exceeds the configured value, the frame is rejected, that is, rx_axis_mac_tuser is asserted at the end of
the frame. In this case, VLAN frames are not treated separately. If
jumbo frame handling is enabled, that takes precedence and the
configured value is ignored.