Xilinx LOGICORE UG144 - Manual (Page 41)

1-Gigabit Ethernet MAC v8.5 User Guide www.xilinx.com 41
UG144 April 24, 2009
Receiving Inbound Frames R
-- DISCONTINUED PRODUCT --
Frame Reception with Errors
Figure 5-2 illustrates an unsuccessful frame reception (for example, a fragment frame or a
frame with an incorrect FCS). In this case, the rx_bad_frame signal is asserted to the
client at the end of the frame. It is then the responsibility of the client to drop the data
already transferred for this frame.
The following conditions cause the assertion of rx_bad_frame:
•
FCS errors occur.
•
Packets are shorter than 64 bytes (undersize or fragment frames).
•
Jumbo frames are received when jumbo frames are not enabled.
•
VLAN frames of length 1519-1522 are received when VLAN frames are not enabled.
• A value of 0x0000 to 0x002D is in the type/length field. In this situation, the frame
should be padded to minimum length. If it is not padded to exactly minimum frame
length, the frame is marked as bad (when length/type checking is enabled).
• A value of 0x002E to 0x0600 is in the type/length field, but the real length of the
received frame does not match this value (when length/type checking is enabled).
•
Any control frame that is received is not exactly the minimum frame length (unless
control frame length checks are disabled).
•
gmii_rx_er is asserted at any point during frame reception.
• An error code is received in the 1-Gigabit frame extension field.
• A valid pause frame, addressed to the MAC, is received when flow control is enabled.
Please see
“Overview of Flow Control,” on page 53 .
Figure 5-2: Frame Reception with Error
gmii_rx_clk
rx_data[7:0]
rx_data_valid
rx_good_frame
rx_bad_frame
DA SA DATA L/T