rvecc_decode.sv

// SPDX-License-Identifier: Apache-2.0
// Copyright 2019 Western Digital Corporation or its affiliates.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

module rvecc_decode  (
		      input         en,
		      input [31:0]  din,
		      input [6:0]   ecc_in,
                      input         sed_ded,    // only do detection and no correction. Used for the I$
		      output [31:0] dout,
                      output [6:0]  ecc_out,
		      output        single_ecc_error,
		      output        double_ecc_error

		      );

   logic [6:0] 			    ecc_check;
   logic [38:0] 		    error_mask;
   logic [38:0] 		    din_plus_parity, dout_plus_parity;

   // Generate the ecc bits
   assign ecc_check[0] = ecc_in[0]^din[0]^din[1]^din[3]^din[4]^din[6]^din[8]^din[10]^din[11]^din[13]^din[15]^din[17]^din[19]^din[21]^din[23]^din[25]^din[26]^din[28]^din[30];
   assign ecc_check[1] = ecc_in[1]^din[0]^din[2]^din[3]^din[5]^din[6]^din[9]^din[10]^din[12]^din[13]^din[16]^din[17]^din[20]^din[21]^din[24]^din[25]^din[27]^din[28]^din[31];
   assign ecc_check[2] = ecc_in[2]^din[1]^din[2]^din[3]^din[7]^din[8]^din[9]^din[10]^din[14]^din[15]^din[16]^din[17]^din[22]^din[23]^din[24]^din[25]^din[29]^din[30]^din[31];
   assign ecc_check[3] = ecc_in[3]^din[4]^din[5]^din[6]^din[7]^din[8]^din[9]^din[10]^din[18]^din[19]^din[20]^din[21]^din[22]^din[23]^din[24]^din[25];
   assign ecc_check[4] = ecc_in[4]^din[11]^din[12]^din[13]^din[14]^din[15]^din[16]^din[17]^din[18]^din[19]^din[20]^din[21]^din[22]^din[23]^din[24]^din[25];
   assign ecc_check[5] = ecc_in[5]^din[26]^din[27]^din[28]^din[29]^din[30]^din[31];

   // This is the parity bit
   assign ecc_check[6] = ((^din[31:0])^(^ecc_in[6:0])) & ~sed_ded;

   assign single_ecc_error = en & (ecc_check[6:0] != 0) & ecc_check[6];   // this will never be on for sed_ded
   assign double_ecc_error = en & (ecc_check[6:0] != 0) & ~ecc_check[6];  // all errors in the sed_ded case will be recorded as DE

   // Generate the mask for error correctiong
   genvar i;
   generate
   for (i=1; i<40; i = i + 1) begin
      assign error_mask[i-1] = (ecc_check[5:0] == i);
   end
   endgenerate
   // Generate the corrected data
   assign din_plus_parity[38:0] = {ecc_in[6], din[31:26], ecc_in[5], din[25:11], ecc_in[4], din[10:4], ecc_in[3], din[3:1], ecc_in[2], din[0], ecc_in[1:0]};

   assign dout_plus_parity[38:0] = single_ecc_error ? (error_mask[38:0] ^ din_plus_parity[38:0]) : din_plus_parity[38:0];
   assign dout[31:0]             = {dout_plus_parity[37:32], dout_plus_parity[30:16], dout_plus_parity[14:8], dout_plus_parity[6:4], dout_plus_parity[2]};
   assign ecc_out[6:0]           = {(dout_plus_parity[38] ^ (ecc_check[6:0] == 7'b1000000)), dout_plus_parity[31], dout_plus_parity[15], dout_plus_parity[7], dout_plus_parity[3], dout_plus_parity[1:0]};

endmodule // rvecc_decode