Altera Low Latency Ethernet 10G MAC - Manual (Page 27)

CRC-32 Insertion
By default, the MAC TX computes and inserts CRC-32 checksum into TX frames. The MAC TX
computes the CRC-32 checksum over frame bytes that include the source address, destination address,
length, data, and padding bytes. The computation excludes the preamble and SFD bytes. The MAC TX
then inserts the CRC-32 checksum into the TX frame. Bit 31 st of the checksum occupies the least signifi‐
cant bit of the first byte in the CRC field.
You can disable this function by setting the
tx_crc_control[1]
register bit to 0.
The following figure shows the timing diagram on the Avalon-ST data interfaces where CRC insertion is
enabled on transmit and CRC removal is disabled on receive. The frame from the client is without
CRC-32 checksum. The MAC TX inserts the CRC-32 checksum (4EB00AF4) into the frame. The frame is
then looped back to the RX datapath with the CRC-32 checksum.
Figure 3-4: Avalon-ST TX and RX Interfaces with CRC Insertion Enabled
tx_312_5_clk
avalon_st_tx_ready
avalon_st_tx_valid
avalon_st_tx_startofpacket
avalon_st_tx_endofpacket
avalon_st_tx_data[31:0]
avalon_st_tx_empty[1:0]
avalon_st_tx_error
...00000000
0
rx_312_5_clk
avalon_st_rx_ready
avalon_st_rx_valid
avalon_st_rx_startofpacket
avalon_st_rx_endofpacket
avalon_st_rx_data[31:0]
avalon_st_rx_empty[1:0]
avalon_st_rx_error[5:0]
...4EB30AF4
0
UG-01144
2014.12.15
CRC-32 Insertion 3-5
Functional Description of LL Ethernet 10G MAC Altera Corporation
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