Altera 10-Gbps Ethernet MAC MegaCore Function - Manual (Page 81)

7–14 Chapter 7: Functional Description
Receive Datapath
10-Gbps Ethernet MAC MegaCore Function User Guide February 2014 Altera Corporation
7.5.7. CRC-32 and Pad Removal
By default, the MAC RX forwards receive frames to the client without removing pad
bytes from the frames. You can, however, configure the MAC RX to remove pad bytes
by setting the bit rx_padcrc_control[1] to 1. When the bit is set to 1, the MAC RX
removes the pad bytes as well as the CRC-32 field from receive frames before
forwarding the frames to the client.
The MAC RX removes pad bytes from receive frames whose payload length is less
than the following values for the different frame types:
■ 46 bytes for basic frames
■ 42 bytes for VLAN tagged frames
■ 38 bytes for stacked VLAN tagged frames
To retain the CRC-32 field, set the rx_padcrc_control register to 0.
Figure 7–9 on page 7–14 shows the timing for the Avalon-ST transmit and receive
interface where the MAC TX receives a frame with pad bytes and CRC-32 field
inserted. The MAC RX removes the pad bytes and CRC-32 field from the receive
frame when the rx_padcrc_control[1] bit is set to 1.
Figure 7–9. Avalon-ST Transmit and Receive Interface with Pad Bytes and CRC-32 Field Removed
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
0000000000000000
1A1B1C1D1E1F2021
0
00000000AB704587
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]
1A1B1C1D1E1F2021
FD07070707070707
0