Xilinx LOGICORE UG144 - Manual (Page 40)

40 www.xilinx.com 1-Gigabit Ethernet MAC v8.5 User Guide
UG144 April 24, 2009
Chapter 5: Using the Client Side Data Path R
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Frame parameters (destination address, source address, length/type and optionally FCS)
are supplied on the data bus according to the timing diagram.
If the length/type field in the frame has a length interpretation, indicating that the
inbound frame has been padded to meet the Ethernet minimum frame size, the padding is
not passed to the client in the data payload. The exception to this is where FCS passing is
enabled. See
“Client-Supplied FCS Passing.”
When Client-Supplied FCS passing is disabled, rx_data_valid is equal to zero between
frames for the duration of the padding field (if present), the FCS field, carrier extension (if
present), the interframe gap following the frame, and the preamble field of the next frame.
When Client-Supplied FCS passing is enabled, rx_data_valid is equal to zero between
frames for the duration of carrier extension (if present), the interframe gap, and the
preamble field of the following frame.
rx_good_frame, rx_bad_frame timing
Although the timing diagram ( Figure 5-1 ) shows the rx_good_frame signal asserted
shortly after the last valid data on rx_data, this is not always the case. The
rx_good_frame
or rx_bad_frame signals are asserted only after all frame checks are
completed. This is after the FCS field has been received (and after reception of carrier
extension, if present).
Therefore, either rx_good_frame or rx_bad_frame is asserted following frame
reception at the beginning of the interframe gap.
Figure 5-1: Normal Frame Reception
gmii_rx_clk
rx_data[7:0]
rx_data_valid
rx_good_frame
rx_bad_frame
DA SA DATA L/T