[SOLVED] CRC for SENT Protocol

// Fast way for any µC with low memory and compute capabilities
char Data[8] = {…}; // contains the input data (status nibble , 6 data nibble , CRC)
// required variables and LUT
char CheckSum, i;
char CrcLookup[16] = {0, 13, 7, 10, 14, 3, 9, 4, 1, 12, 6, 11, 15, 2, 8, 5};
CheckSum= 5; // initialize checksum with seed "0101"
for (i=0; i<7; i++) {
CheckSum = CheckSum ^ Data;
CheckSum = CrcLookup[CheckSum];
}
; // finally check if Data [7] is equal to CheckSum

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// CRC module for data[27:0] , crc[3:0]=1+x^2+x^3+x^4;
//-----------------------------------------------------------------------------
module crcj(
input [27:0] data_in,//The computation is performed with data including data (6 nibble) and sync (1 nibble which is alawys 0 for valid transmission) in total 7 nibble=28 bit
input crc_en,
output reg [3:0] crc_out,
input rst,
input clk);

reg [3:0] lfsr_c;


always @(*) begin
//The first values represent the seed which is 4'b0101 (5)
lfsr_c[0] = 1'b1 ^ data_in[0] ^ data_in[1] ^ data_in[3] ^ data_in[7] ^ data_in[8] ^ data_in[10] ^ data_in[14] ^ data_in[15] ^ data_in[17] ^ data_in[21] ^ data_in[22] ^ data_in[24];
lfsr_c[1] = 1'b0 ^ data_in[1] ^ data_in[2] ^ data_in[4] ^ data_in[8] ^ data_in[9] ^ data_in[11] ^ data_in[15] ^ data_in[16] ^ data_in[18] ^ data_in[22] ^ data_in[23] ^ data_in[25];
lfsr_c[2] = 1'b1 ^ data_in[0] ^ data_in[1] ^ data_in[2] ^ data_in[5] ^ data_in[7] ^ data_in[8] ^ data_in[9] ^ data_in[12] ^ data_in[14] ^ data_in[15] ^ data_in[16] ^ data_in[19] ^ data_in[21] ^ data_in[22] ^ data_in[23] ^ data_in[26];
lfsr_c[3] = 1'b0 ^ data_in[0] ^ data_in[2] ^ data_in[6] ^ data_in[7] ^ data_in[9] ^ data_in[13] ^ data_in[14] ^ data_in[16] ^ data_in[20] ^ data_in[21] ^ data_in[23] ^ data_in[27];

end // always

always @(posedge clk, posedge rst) begin
if(rst) begin
crc_out <= {4'h0};
end
else begin
crc_out <= crc_en ? lfsr_c : 4'hZ;
end
end // always
endmodule // crc

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dpaul said:

Just one point: crc_out <= crc_en ? lfsr_c : 4'hZ;

If you want to use this crc block as part of a larger design, it is not a good idea to propagate 'Z' to crc_out if crc_en is LOW. Avoid Z's in ckt design wherever possible.

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