Low Latency 40-Gbps Ethernet IP Core User Guide

ID 683745
Date 3/08/2021
Document Table of Contents LL 40GbE IP Core FCS (CRC-32) Removal

Independent user configuration register bits control FCS CRC removal at runtime. CRC removal supports both narrow and wide bus options. Bit 0 of the MAC_CRC_CONFIG register enables and disables CRC removal; by default, CRC removal is enabled.

In the user interface, the EOP signal (l4_rx_endofpacket or dout_eop ) indicates the end of CRC bytes if CRC is not removed. When CRC is removed, the EOP signal indicates the final byte of payload.

The IP core signals an FCS error by asserting the FCS error output signal l4_rx_fcs_error and the l4_rx_fcs_valid (or rx_fcs_error and the rx_fcs_valid) output signals in the same clock cycle. The l4_rx_error[1] or rx_error[1] also signals an FCS error.

If you turn on Enable alignment EOP on FCS word in the parameter editor, the IP core asserts l4_rx_fcs_error (or rx_fcs_error) and the EOP signal on the same clock cycle if the current frame has an FCS error. However, if you turn off Enable alignment EOP on FCS word , the IP core asserts l4_rx_fcs_error in a later clock cycle than the EOP signal.