[otp_ctrl] Fix UNKNOWN error due to array indexing

Under error conditions, the ECC register array may be indexed with an invalid index, thus producing Xes in RTL. This patch ensures that we always output defined data from the ECC register, no matter the index value. Signed-off-by: Michael Schaffner <[email protected]>
lowRISC · Jan 23, 2024 · 914dee7 · 914dee7
1 parent 2ba74d6
commit 914dee7
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Showing 3 changed files with 27 additions and 17 deletions.
diff --git a/hw/ip/otp_ctrl/rtl/otp_ctrl_ecc_reg.sv b/hw/ip/otp_ctrl/rtl/otp_ctrl_ecc_reg.sv
@@ -18,6 +18,7 @@ module otp_ctrl_ecc_reg #(
   input  logic                        wren_i,
   input  logic [Aw-1:0]               addr_i,
   input  logic [Width-1:0]            wdata_i,
+  output logic [Width-1:0]            rdata_o,
 
   // Concurrent output of the register state.
   output logic [Depth-1:0][Width-1:0] data_o,
@@ -46,8 +47,12 @@ module otp_ctrl_ecc_reg #(
       data_d = data_q;
       ecc_d  = ecc_q;
 
-      if (wren_i && 32'(addr_i) < Depth) begin
-        {ecc_d[0], data_d[0]} = ecc_enc;
+      rdata_o = '0;
+      if (32'(addr_i) < Depth) begin
+        rdata_o = data_q[0];
+        if (wren_i) begin
+          {ecc_d[0], data_d[0]} = ecc_enc;
+        end
       end
     end
   end else begin : gen_multiple_words
@@ -56,8 +61,12 @@ module otp_ctrl_ecc_reg #(
       data_d = data_q;
       ecc_d  = ecc_q;
 
-      if (wren_i && 32'(addr_i) < Depth) begin
-        {ecc_d[addr_i], data_d[addr_i]} = ecc_enc;
+      rdata_o = '0;
+      if (32'(addr_i) < Depth) begin
+        rdata_o = data_q[addr_i];
+        if (wren_i) begin
+          {ecc_d[addr_i], data_d[addr_i]} = ecc_enc;
+        end
       end
     end
   end
@@ -87,9 +96,10 @@ module otp_ctrl_ecc_reg #(
     end
   end
 
-  `ASSERT_KNOWN(EccKnown_A,     ecc_q)
-  `ASSERT_KNOWN(DataKnown_A,    data_q)
-  `ASSERT_KNOWN(DataOutKnown_A, data_o)
-  `ASSERT_KNOWN(EccErrKnown_A,  ecc_err_o)
+  `ASSERT_KNOWN(EccKnown_A,      ecc_q)
+  `ASSERT_KNOWN(DataKnown_A,     data_q)
+  `ASSERT_KNOWN(RDataOutKnown_A, rdata_o)
+  `ASSERT_KNOWN(DataOutKnown_A,  data_o)
+  `ASSERT_KNOWN(EccErrKnown_A,   ecc_err_o)
 
 endmodule : otp_ctrl_ecc_reg
diff --git a/hw/ip/otp_ctrl/rtl/otp_ctrl_part_buf.sv b/hw/ip/otp_ctrl/rtl/otp_ctrl_part_buf.sv
@@ -637,25 +637,24 @@ module otp_ctrl_part_buf
   // Always transfer 64bit blocks.
   assign otp_size_o = OtpSizeWidth'(unsigned'(ScrmblBlockWidth / OtpWidth) - 1);
 
-  logic [Info.size*8-1:0] data;
-  assign scrmbl_data_o = data[{cnt, {$clog2(ScrmblBlockWidth){1'b0}}} +: ScrmblBlockWidth];
-
   assign data_mux = (data_sel == ScrmblData) ? scrmbl_data_i : otp_rdata_i;
 
   /////////////////
   // Buffer Regs //
   /////////////////
 
   // SEC_CM: PART.DATA_REG.INTEGRITY
+  logic [Info.size*8-1:0] data;
   otp_ctrl_ecc_reg #(
     .Width ( ScrmblBlockWidth ),
     .Depth ( NumScrmblBlocks  )
   ) u_otp_ctrl_ecc_reg (
     .clk_i,
     .rst_ni,
     .wren_i    ( buffer_reg_en ),
-    .addr_i    ( cnt         ),
+    .addr_i    ( cnt           ),
     .wdata_i   ( data_mux      ),
+    .rdata_o   ( scrmbl_data_o ),
     .data_o    ( data          ),
     .ecc_err_o ( ecc_err       )
   );

diff --git a/hw/ip/otp_ctrl/rtl/otp_ctrl_part_unbuf.sv b/hw/ip/otp_ctrl/rtl/otp_ctrl_part_unbuf.sv
@@ -353,11 +353,12 @@ module otp_ctrl_part_unbuf
     ) u_otp_ctrl_ecc_reg (
       .clk_i,
       .rst_ni,
-      .wren_i     ( digest_reg_en ),
-      .addr_i     ( '0            ),
-      .wdata_i    ( otp_rdata_i   ),
-      .data_o     ( digest_o      ),
-      .ecc_err_o  ( ecc_err       )
+      .wren_i    ( digest_reg_en ),
+      .addr_i    ( '0            ),
+      .wdata_i   ( otp_rdata_i   ),
+      .rdata_o   (               ),
+      .data_o    ( digest_o      ),
+      .ecc_err_o ( ecc_err       )
     );
   end else begin : gen_no_ecc_reg
     logic unused_digest_reg_en;