Altera 10-Gbps Ethernet MAC MegaCore Function - Manual (Page 75)

7–8 Chapter 7: Functional Description
Transmit Datapath
10-Gbps Ethernet MAC MegaCore Function User Guide February 2014 Altera Corporation
Figure 7–6 shows the timing diagram of the Avalon-ST transmit and receive interface
where the FCS insertion function is off. The MAC TX receives the frame which
contains a CRC-32 checksum (4EB00AF4) and forwards the frame without performing
CRC computation. The frame with the same CRC-32 field is then loopback to the
receive datapath.
7.4.4. XGMII Encapsulation
The 10GbE MAC TX inserts 7-byte preamble, 1-byte SFD and 1-byte EFD (0xFD) into
frames received from the client. When you enable the preamble passthrough mode,
the 10GbE MAC TX accepts 8-byte client-defined preamble in the frames received
from the client and inserts a 1-byte EFD into the frames. For XGMII encapsulation, the
first byte of the preamble data is converted to a 1-byte START (0xFB).
An underflow could occur on the Avalon-ST transmit interface. An underflow occurs
when the avalon_st_tx_valid signal is deasserted in the middle of frame
transmission. When this happens, the 10GbE MAC TX inserts an error character |E|
into the frame and forwards the frame to the XGMII.
Figure 7–6. Avalon-ST Transmit and Receive Interface with CRC-32 Computation Disabled
tx_clk_clk
avalon_st_tx_ready
avalon_st_tx_valid
avalon_st_tx_startofpacket
avalon_st_tx_endofpacket
avalon_st_tx_data[63:0]
avalon_st_tx_empty[2:0]
avalon_st_tx_error
0
rx_clk_clk
avalon_st_rx_ready
avalon_st_rx_valid
avalon_st_rx_startofpacket
avalon_st_rx_endofpacket
avalon_st_rx_data[63:0]
avalon_st_rx_empty[2:0]
avalon_st_rx_error[5:0]
...4EB30AF4
...4EB30AF4
0