Xilinx UG773 LogiCORE IP 10-Gigabit Ethernet MAC v11.1, User ...

Chapter 6: Interfacing to the Core: Data Interfaces
X-Ref Target - Figure 6-2
Transmission with In-Band FCS Passing
tx_clk0
tx_axis_tvalid
tx_axis_tready
tx_axis_tdata[7:0]
tx_axis_tdata[15:8]
tx_axis_tdata[23:16]
tx_axis_tdata[31:24]
tx_axis_tdata[39:32]
tx_axis_tdata[47:40]
tx_axis_tdata[55:48]
tx_axis_tdata[63:56]
tx_axis_tstrb[7:0]
tx_axis_tlast
If the MAC core is configured to have the FCS field passed in by the client on the AXI4-
Stream Transmit interface, the transmission timing is as shown in Figure 6-2. In this case, it
is the responsibility of the client to ensure that the frame meets the Ethernet minimum
frame length requirements; the MAC core will not perform any padding of the payload If
the client transmits a frame less than the Ethernet minimum length requirements, then the
frame will not be counted in the statistics.
Aborting a Transmission
DA SA D D D DA SA D D
DA SA D D D DA SA D D
DA SA D D D DA SA D D
DA SA D D D DA SA D FCS
DA L/T D D FCS DA L/T D FCS
DA L/T D D FCS DA L/T D FCS
SA D D D FCS SA D D FCS
SA D D D FCS SA D D
0x00 0xFF 0xFF 0xFF 0xFF 0X7F
Figure 6-2: Transmission with In-Band FCS Passing
The aborted transfer of a packet on the client interface is called an underrun. This can
happen, for instance, if a FIFO in the AXI Transmit client interface empties before a frame
is completed. This is indicated to the core in one of two ways:
1. An explicit underrun, in which a Frame Transfer is aborted by asserting
tx_axis_tuser HIGH while tx_axis_tvalid is HIGH and data transfer is
continuing. (See Figure 6-3)
An underrun packet must have the DA, SA, L/T fields in it. This is true even if Custom
Preamble is enabled for transmission.
2. An implicit underrun, in which a Frame Transfer is aborted by deasserting
tx_axis_tvalid without asserting tx_axis_tlast. (See Figure 6-4)
46 www.xilinx.com 10-Gigabit Ethernet MAC User Guide
UG773 March 1, 2011