How is cyclic redundancy check calculated

[elizajona]

ssign CrcNext[0] = Enable & (Data[0] ^ Crc[28]);
assign CrcNext[1] = Enable & (Data[1] ^ Data[0] ^ Crc[28] ^ Crc[29]);
assign CrcNext[2] = Enable & (Data[2] ^ Data[1] ^ Data[0] ^ Crc[28] ^ Crc[29] ^ Crc[30]);
assign CrcNext[3] = Enable & (Data[3] ^ Data[2] ^ Data[1] ^ Crc[29] ^ Crc[30] ^ Crc[31]);
assign CrcNext[4] = (Enable & (Data[3] ^ Data[2] ^ Data[0] ^ Crc[28] ^ Crc[30] ^ Crc[31])) ^ Crc[0];
assign CrcNext[5] = (Enable & (Data[3] ^ Data[1] ^ Data[0] ^ Crc[28] ^ Crc[29] ^ Crc[31])) ^ Crc[1];
assign CrcNext[6] = (Enable & (Data[2] ^ Data[1] ^ Crc[29] ^ Crc[30])) ^ Crc[ 2];
assign CrcNext[7] = (Enable & (Data[3] ^ Data[2] ^ Data[0] ^ Crc[28] ^ Crc[30] ^ Crc[31])) ^ Crc[3];
assign CrcNext[8] = (Enable & (Data[3] ^ Data[1] ^ Data[0] ^ Crc[28] ^ Crc[29] ^ Crc[31])) ^ Crc[4];
assign CrcNext[9] = (Enable & (Data[2] ^ Data[1] ^ Crc[29] ^ Crc[30])) ^ Crc[5];
assign CrcNext[10] = (Enable & (Data[3] ^ Data[2] ^ Data[0] ^ Crc[28] ^ Crc[30] ^ Crc[31])) ^ Crc[6];
assign CrcNext[11] = (Enable & (Data[3] ^ Data[1] ^ Data[0] ^ Crc[28] ^ Crc[29] ^ Crc[31])) ^ Crc[7];
assign CrcNext[12] = (Enable & (Data[2] ^ Data[1] ^ Data[0] ^ Crc[28] ^ Crc[29] ^ Crc[30])) ^ Crc[8];
assign CrcNext[13] = (Enable & (Data[3] ^ Data[2] ^ Data[1] ^ Crc[29] ^ Crc[30] ^ Crc[31])) ^ Crc[9];
assign CrcNext[14] = (Enable & (Data[3] ^ Data[2] ^ Crc[30] ^ Crc[31])) ^ Crc[10];
assign CrcNext[15] = (Enable & (Data[3] ^ Crc[31])) ^ Crc[11];
assign CrcNext[16] = (Enable & (Data[0] ^ Crc[28])) ^ Crc[12];
assign CrcNext[17] = (Enable & (Data[1] ^ Crc[29])) ^ Crc[13];
assign CrcNext[18] = (Enable & (Data[2] ^ Crc[30])) ^ Crc[14];
assign CrcNext[19] = (Enable & (Data[3] ^ Crc[31])) ^ Crc[15];
assign CrcNext[20] = Crc[16];
assign CrcNext[21] = Crc[17];
assign CrcNext[22] = (Enable & (Data[0] ^ Crc[28])) ^ Crc[18];
assign CrcNext[23] = (Enable & (Data[1] ^ Data[0] ^ Crc[29] ^ Crc[28])) ^ Crc[19];
assign CrcNext[24] = (Enable & (Data[2] ^ Data[1] ^ Crc[30] ^ Crc[29])) ^ Crc[20];
assign CrcNext[25] = (Enable & (Data[3] ^ Data[2] ^ Crc[31] ^ Crc[30])) ^ Crc[21];
assign CrcNext[26] = (Enable & (Data[3] ^ Data[0] ^ Crc[31] ^ Crc[28])) ^ Crc[22];
assign CrcNext[27] = (Enable & (Data[1] ^ Crc[29])) ^ Crc[23];
assign CrcNext[28] = (Enable & (Data[2] ^ Crc[30])) ^ Crc[24];
assign CrcNext[29] = (Enable & (Data[3] ^ Crc[31])) ^ Crc[25];
assign CrcNext[30] = Crc[26];
assign CrcNext[31] = Crc[27];


can any one tell under what logic this code works ,what is data sequence and how crc is calculated

 

[buffallo]

Hi,

there is a neat example given here :

https://en.wikipedia.org/wiki/Cyclic_redundancy_check

 

[p.0774023179]

can any one tell under what logic this code works ,what is data sequence and how crc is calculated[/QUOTE]

The code you listed is one of the many ways of expressing CRC computations in an iterative manner.
(there is a register CrcNext that is updated with the current CRC plus some new data... and it goes on like that)

There is nothing very complicated about these codes. In general they are based on polynomials over Galois Fields GF(2). Check the wiki link provided above. If you like the math you can also check this https://www.math.msu.edu/~jhall/classes/codenotes/Cyclic.pdf