18.104.22.168. Frame Check Sequence (CRC-32) Insertion
As long as the i_skip_crc signal on the TX client interface is not asserted, the TX MAC computes and inserts a frame check sequence (FCS) in the transmitted MAC frame. The FCS field contains a 32-bit Cyclic Redundancy Check (CRC32) value. The MAC computes the CRC32 over the frame bytes that include the source address, destination address, length/type field, data, and pad (if applicable). The FCS computation excludes the preamble and SFD. The encoding is defined by the following generating polynomial:
FCS(X) = X32 +X26 +X23 +X22 +X16 +X12 +X11 +X10 +X8 +X7 +X5 +X4 +X2 +X1 +1
CRC bits are transmitted with MSB (X32) first.
If i_skip_crc is asserted while writing frame data, the TX MAC will not append an FCS to the end of the frame. This will cause the resulting packet to be invalid unless the last 4 bytes of frame data are a correctly computed FCS value.
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