Triple-Speed Ethernet Intel® FPGA IP User Guide

ID 683402
Date 10/04/2021
Public

A newer version of this document is available. Customers should click here to go to the newest version.

Document Table of Contents

4.1.4.6. CRC Checking

The following equation shows the CRC polynomial, as specified in the IEEE 802.3 standard:

FCS(X) = X 32 +X 26 +X 23 +X 22 +X 16 +X 12 +X 11 +X 10 +X 8 +X 7 +X 5 +X 4 +X 2 +X 1 +1

The 32-bit CRC value occupies the FCS field with X31 in the least significant bit of the first byte. The CRC bits are thus received in the following order: X31, X30,..., X1, X0.

If the MAC function detects CRC-32 error, it marks the frame invalid by asserting the following signals:

  • rx_err[2] in MAC variations with internal FIFO buffers.
  • data_rx_error[1] in MAC variations without internal FIFO buffers.

The MAC function discards frames with CRC-32 error if the RX_ERR_DISC bit in the command_config register is set to 1.

For frames less than the required minimum length, the MAC function forwards the CRC-32 field to the user application if the CRC_FWD and PAD_EN bits in the command_config register are 1 and 0 respectively. Otherwise, the CRC-32 field is removed from the frame.