Updated TB to use access ports. Added missing invalidate of residue when modulus is updated. Minor cleanup.

2 files changed, 361 insertions, 217 deletions

diff --git a/src/rtl/modexp.v b/src/rtl/modexp.v
index afd7a84..30b703e 100644
--- a/src/rtl/modexp.v
+++ b/src/rtl/modexp.v
@@ -24,33 +24,34 @@
 //
 //
 // Author: Joachim Strombergson, Peter Magnusson
-// Copyright (c) 2015, NORDUnet A/S All rights reserved.
+// Copyright (c) 2015, Assured AB
+// All rights reserved.
 //
-// Redistribution and use in source and binary forms, with or without
-// modification, are permitted provided that the following conditions are
-// met:
-// - Redistributions of source code must retain the above copyright notice,
-//   this list of conditions and the following disclaimer.
+// Redistribution and use in source and binary forms, with or
+// without modification, are permitted provided that the following
+// conditions are met:
 //
-// - Redistributions in binary form must reproduce the above copyright
-//   notice, this list of conditions and the following disclaimer in the
-//   documentation and/or other materials provided with the distribution.
+// 1. Redistributions of source code must retain the above copyright
+//    notice, this list of conditions and the following disclaimer.
 //
-// - Neither the name of the NORDUnet nor the names of its contributors may
-//   be used to endorse or promote products derived from this software
-//   without specific prior written permission.
+// 2. Redistributions in binary form must reproduce the above copyright
+//    notice, this list of conditions and the following disclaimer in
+//    the documentation and/or other materials provided with the
+//    distribution.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+// FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+// COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+// BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+// ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 //
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
-// IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
-// TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
-// PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
-// HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
-// TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
-// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
-// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
-// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
-// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 //
 //======================================================================
 
@@ -86,27 +87,19 @@ module modexp(
   localparam ADDR_EXPONENT_LENGTH = 8'h21;
   localparam ADDR_LENGTH          = 8'h22; // Should be deprecated.
 
+  localparam ADDR_MODULUS_PTR_RST  = 8'h30;
+  localparam ADDR_MODULUS_DATA     = 8'h31;
 
-  localparam MODULUS_PREFIX      = 4'h1;
-  localparam ADDR_MODULUS_START  = 8'h00;
-  localparam ADDR_MODULUS_END    = 8'hff;
-
-
-  localparam EXPONENT_PREFIX     = 4'h2;
-  localparam ADDR_EXPONENT_START = 8'h00;
-  localparam ADDR_EXPONENT_END   = 8'hff;
+  localparam ADDR_EXPONENT_PTR_RST = 8'h40;
+  localparam ADDR_EXPONENT_DATA    = 8'h41;
 
+  localparam ADDR_MESSAGE_PTR_RST  = 8'h50;
+  localparam ADDR_MESSAGE_DATA     = 8'h51;
 
-  localparam MESSAGE_PREFIX      = 4'h3;
-  localparam MESSAGE_START       = 8'h00;
-  localparam MESSAGE_END         = 8'hff;
+  localparam ADDR_RESULT_PTR_RST   = 8'h60;
+  localparam ADDR_RESULT_DATA      = 8'h61;
 
-
-  localparam RESULT_PREFIX       = 4'h4;
-  localparam RESULT_START        = 8'h00;
-  localparam RESULT_END          = 8'hff;
-
-  localparam DEFAULT_MODLENGTH   = 8'h80;
+  localparam DEFAULT_MODLENGTH   = 8'h80; // 2048 bits.
   localparam DEFAULT_EXPLENGTH   = 8'h80;
 
   localparam MONTPROD_SELECT_ONE_NR = 3'h0;
@@ -136,7 +129,7 @@ module modexp(
 
   localparam CORE_NAME0          = 32'h6d6f6465; // "mode"
   localparam CORE_NAME1          = 32'h78702020; // "xp  "
-  localparam CORE_VERSION        = 32'h302e3530; // "0.50"
+  localparam CORE_VERSION        = 32'h302e3531; // "0.51"
 
 
   //----------------------------------------------------------------
@@ -204,17 +197,14 @@ module modexp(
   reg [07 : 0]  modulus_mem_int_rd_addr;
   wire [31 : 0] modulus_mem_int_rd_data;
   wire [31 : 0] modulus_mem_api_rd_data;
-  reg           modulus_mem_api_we;
 
   reg [07 : 0]  message_mem_int_rd_addr;
   wire [31 : 0] message_mem_int_rd_data;
   wire [31 : 0] message_mem_api_rd_data;
-  reg           message_mem_api_we;
 
   reg [07 : 0]  exponent_mem_int_rd_addr;
   wire [31 : 0] exponent_mem_int_rd_data;
   wire [31 : 0] exponent_mem_api_rd_data;
-  reg           exponent_mem_api_we;
 
   wire [31 : 0] result_mem_api_rd_data;
   reg  [07 : 0] result_mem_int_rd_addr;
@@ -271,6 +261,22 @@ module modexp(
   reg           invalidate_residue;
   reg           residue_valid_int_validated;
 
+  reg           modulus_mem_api_rst;
+  reg           modulus_mem_api_cs;
+  reg           modulus_mem_api_wr;
+
+  reg           exponent_mem_api_rst;
+  reg           exponent_mem_api_cs;
+  reg           exponent_mem_api_wr;
+
+  reg           message_mem_api_rst;
+  reg           message_mem_api_cs;
+  reg           message_mem_api_wr;
+
+  reg           result_mem_api_rst;
+  reg           result_mem_api_cs;
+
+
   //----------------------------------------------------------------
   // Concurrent connectivity for ports etc.
   //----------------------------------------------------------------
@@ -331,52 +337,57 @@ module modexp(
                            .write_data(residue_opa_wr_data)
                           );
 
-  blockmem2r1w modulus_mem(
-                           .clk(clk),
-                           .read_addr0(modulus_mem_int_rd_addr),
-                           .read_data0(modulus_mem_int_rd_data),
-                           .read_addr1(address[7 : 0]),
-                           .read_data1(modulus_mem_api_rd_data),
-                           .wr(modulus_mem_api_we),
-                           .write_addr(address[7 : 0]),
-                           .write_data(write_data)
-                          );
-
-
-  blockmem2r1w message_mem(
-                           .clk(clk),
-                           .read_addr0(message_mem_int_rd_addr),
-                           .read_data0(message_mem_int_rd_data),
-                           .read_addr1(address[7 : 0]),
-                           .read_data1(message_mem_api_rd_data),
-                           .wr(message_mem_api_we),
-                           .write_addr(address[7 : 0]),
-                           .write_data(write_data)
-                          );
-
-
-  blockmem2r1w exponent_mem(
-                           .clk(clk),
-                           .read_addr0(exponent_mem_int_rd_addr),
-                           .read_data0(exponent_mem_int_rd_data),
-                           .read_addr1(address[7 : 0]),
-                           .read_data1(exponent_mem_api_rd_data),
-                           .wr(exponent_mem_api_we),
-                           .write_addr(address[7 : 0]),
-                           .write_data(write_data)
-                           );
-
-
-  blockmem2r1w result_mem(
-                          .clk(clk),
-                          .read_addr0(result_mem_int_rd_addr[7 : 0]),
-                          .read_data0(result_mem_int_rd_data),
-                          .read_addr1(address[7 : 0]),
-                          .read_data1(result_mem_api_rd_data),
-                          .wr(result_mem_int_we),
-                          .write_addr(result_mem_int_wr_addr),
-                          .write_data(result_mem_int_wr_data)
-                         );
+  blockmem2r1wptr modulus_mem(
+                              .clk(clk),
+                              .reset_n(reset_n),
+                              .read_addr0(modulus_mem_int_rd_addr),
+                              .read_data0(modulus_mem_int_rd_data),
+                              .read_data1(modulus_mem_api_rd_data),
+                              .rst(modulus_mem_api_rst),
+                              .cs(modulus_mem_api_cs),
+                              .wr(modulus_mem_api_wr),
+                              .write_data(write_data)
+                             );
+
+
+  blockmem2r1wptr message_mem(
+                              .clk(clk),
+                              .reset_n(reset_n),
+                              .read_addr0(message_mem_int_rd_addr),
+                              .read_data0(message_mem_int_rd_data),
+                              .read_data1(message_mem_api_rd_data),
+                              .rst(message_mem_api_rst),
+                              .cs(message_mem_api_cs),
+                              .wr(message_mem_api_wr),
+                              .write_data(write_data)
+                             );
+
+
+  blockmem2r1wptr exponent_mem(
+                               .clk(clk),
+                               .reset_n(reset_n),
+                               .read_addr0(exponent_mem_int_rd_addr),
+                               .read_data0(exponent_mem_int_rd_data),
+                               .read_data1(exponent_mem_api_rd_data),
+                               .rst(exponent_mem_api_rst),
+                               .cs(exponent_mem_api_cs),
+                               .wr(exponent_mem_api_wr),
+                               .write_data(write_data)
+                              );
+
+
+  blockmem2rptr1w result_mem(
+                             .clk(clk),
+                             .reset_n(reset_n),
+                             .read_addr0(result_mem_int_rd_addr[7 : 0]),
+                             .read_data0(result_mem_int_rd_data),
+                             .read_data1(result_mem_api_rd_data),
+                             .rst(result_mem_api_rst),
+                             .cs(result_mem_api_cs),
+                             .wr(result_mem_int_we),
+                             .write_addr(result_mem_int_wr_addr),
+                             .write_data(result_mem_int_wr_data)
+                            );
 
   blockmem2r1w p_mem(
                      .clk(clk),
@@ -410,7 +421,7 @@ module modexp(
           modexp_ctrl_reg     <= CTRL_IDLE;
           one_reg             <= 32'h0;
           b_one_reg           <= 32'h0;
-          length_reg          <= 8'h0;
+          length_reg          <= DEFAULT_MODLENGTH;
           length_m1_reg       <= 8'h0;
           loop_counter_reg    <= 13'b0;
           ei_reg              <= 1'b0;
@@ -419,9 +430,9 @@ module modexp(
         end
       else
         begin
-          one_reg <= one_new;
-          b_one_reg <= b_one_new;
-          residue_valid_reg <= residue_valid_new;
+          one_reg             <= one_new;
+          b_one_reg           <= b_one_new;
+          residue_valid_reg   <= residue_valid_new;
 
           if (exponent_length_we)
             exponent_length_reg <= exponent_length_new;
@@ -473,12 +484,25 @@ module modexp(
       exponent_length_we  = 1'b0;
       start_new           = 1'b0;
       start_we            = 1'b0;
-      modulus_mem_api_we  = 1'b0;
-      exponent_mem_api_we = 1'b0;
-      message_mem_api_we  = 1'b0;
       length_we           = 1'b0;
       invalidate_residue  = 1'b0;
 
+      modulus_mem_api_rst  = 1'b0;
+      modulus_mem_api_cs   = 1'b0;
+      modulus_mem_api_wr   = 1'b0;
+
+      exponent_mem_api_rst = 1'b0;
+      exponent_mem_api_cs  = 1'b0;
+      exponent_mem_api_wr  = 1'b0;
+
+      message_mem_api_rst  = 1'b0;
+      message_mem_api_cs   = 1'b0;
+      message_mem_api_wr   = 1'b0;
+
+      result_mem_api_rst   = 1'b0;
+      result_mem_api_cs    = 1'b0;
+
+
       //TODO: Add API code to enable fast exponation for working with public exponents.
       exponation_mode_we  = 1'b0;
 
@@ -512,19 +536,58 @@ module modexp(
                           start_we  = 1'b1;
                         end
 
+                      ADDR_MODULUS_LENGTH:
+                        begin
+                          modulus_length_we = 1'b1;
+                        end
+
+                      ADDR_EXPONENT_LENGTH:
+                        begin
+                          exponent_length_we = 1'b1;
+                        end
+
                       ADDR_LENGTH:
                         begin
                           length_we = 1'b1;
                         end
 
-                      ADDR_MODULUS_LENGTH:
+                      ADDR_MODULUS_PTR_RST:
                         begin
-                          modulus_length_we = 1'b1;
+                          modulus_mem_api_rst = 1'b1;
                         end
 
-                      ADDR_EXPONENT_LENGTH:
+                      ADDR_MODULUS_DATA:
                         begin
-                          exponent_length_we = 1'b1;
+                          modulus_mem_api_cs = 1'b1;
+                          modulus_mem_api_wr = 1'b1;
+                          invalidate_residue = 1'b1;
+                        end
+
+                      ADDR_EXPONENT_PTR_RST:
+                        begin
+                          exponent_mem_api_rst = 1'b1;
+                        end
+
+                      ADDR_EXPONENT_DATA:
+                        begin
+                          exponent_mem_api_cs = 1'b1;
+                          exponent_mem_api_wr = 1'b1;
+                        end
+
+                      ADDR_MESSAGE_PTR_RST:
+                        begin
+                          message_mem_api_rst = 1'b1;
+                        end
+
+                      ADDR_MESSAGE_DATA:
+                        begin
+                          message_mem_api_cs = 1'b1;
+                          message_mem_api_wr = 1'b1;
+                        end
+
+                      ADDR_RESULT_PTR_RST:
+                        begin
+                          result_mem_api_rst = 1'b1;
                         end
 
                       default:
@@ -559,53 +622,35 @@ module modexp(
                       ADDR_LENGTH:
                         tmp_read_data = {24'h000000, length_reg};
 
-                      default:
+                      ADDR_MODULUS_DATA:
                         begin
+                          modulus_mem_api_cs = 1'b1;
+                          tmp_read_data      = modulus_mem_api_rd_data;
                         end
-                    endcase // case (address[7 : 0])
-                  end
-              end
 
-            MODULUS_PREFIX:
-              begin
-                if (we)
-                  begin
-                    modulus_mem_api_we = 1'b1;
-                    invalidate_residue = 1'b1;
-                  end
-                else
-                  begin
-                    tmp_read_data = modulus_mem_api_rd_data;
-                  end
-              end
+                      ADDR_EXPONENT_DATA:
+                        begin
+                          exponent_mem_api_cs = 1'b1;
+                          tmp_read_data       = exponent_mem_api_rd_data;
+                        end
 
-            EXPONENT_PREFIX:
-              begin
-                if (we)
-                  begin
-                    exponent_mem_api_we = 1'b1;
-                  end
-                else
-                  begin
-                    tmp_read_data = exponent_mem_api_rd_data;
-                  end
-              end
+                      ADDR_MESSAGE_DATA:
+                        begin
+                          message_mem_api_cs = 1'b1;
+                          tmp_read_data      = message_mem_api_rd_data;
+                        end
 
-            MESSAGE_PREFIX:
-              begin
-                if (we)
-                  begin
-                    message_mem_api_we = 1'b1;
-                  end
-                else
-                  begin
-                    tmp_read_data = message_mem_api_rd_data;
-                  end
-              end
+                      ADDR_RESULT_DATA:
+                        begin
+                          result_mem_api_cs = 1'b1;
+                          tmp_read_data     = result_mem_api_rd_data;
+                        end
 
-            RESULT_PREFIX:
-              begin
-                tmp_read_data = result_mem_api_rd_data;
+                      default:
+                        begin
+                        end
+                    endcase // case (address[7 : 0])
+                  end
               end
 
             default:
diff --git a/src/tb/tb_modexp.v b/src/tb/tb_modexp.v
index a7159b7..0bb81e8 100644
--- a/src/tb/tb_modexp.v
+++ b/src/tb/tb_modexp.v
@@ -6,33 +6,33 @@
 //
 //
 // Author: Joachim Strombergson, Peter Magnusson
-// Copyright (c) 2015, NORDUnet A/S All rights reserved.
+// Copyright (c) 2015, Assured AB
+// All rights reserved.
 //
-// Redistribution and use in source and binary forms, with or without
-// modification, are permitted provided that the following conditions are
-// met:
-// - Redistributions of source code must retain the above copyright notice,
-//   this list of conditions and the following disclaimer.
+// Redistribution and use in source and binary forms, with or
+// without modification, are permitted provided that the following
+// conditions are met:
 //
-// - Redistributions in binary form must reproduce the above copyright
-//   notice, this list of conditions and the following disclaimer in the
-//   documentation and/or other materials provided with the distribution.
+// 1. Redistributions of source code must retain the above copyright
+//    notice, this list of conditions and the following disclaimer.
 //
-// - Neither the name of the NORDUnet nor the names of its contributors may
-//   be used to endorse or promote products derived from this software
-//   without specific prior written permission.
+// 2. Redistributions in binary form must reproduce the above copyright
+//    notice, this list of conditions and the following disclaimer in
+//    the documentation and/or other materials provided with the
+//    distribution.
 //
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
-// IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
-// TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
-// PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
-// HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
-// TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
-// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
-// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
-// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
-// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+// FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+// COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+// BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+// ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 //
 //======================================================================
 
@@ -50,48 +50,53 @@ module tb_modexp();
   //----------------------------------------------------------------
   // Internal constant and parameter definitions.
   //----------------------------------------------------------------
-  parameter DEBUG = 0;
-  parameter DEBUG_EI = 1;
+  // Debug output control.
+  parameter DEBUG               = 0;
+  parameter DEBUG_EI            = 0;
+  parameter DISPLAY_TEST_CYCLES = 1;
 
+
+  // Clock defines.
   localparam CLK_HALF_PERIOD = 1;
   localparam CLK_PERIOD      = 2 * CLK_HALF_PERIOD;
 
+
   // The DUT address map.
-  localparam GENERAL_PREFIX      = 4'h0;
-  localparam ADDR_NAME0          = 8'h00;
-  localparam ADDR_NAME1          = 8'h01;
-  localparam ADDR_VERSION        = 8'h02;
+  localparam GENERAL_PREFIX        = 4'h0;
+  localparam ADDR_NAME0            = 8'h00;
+  localparam ADDR_NAME1            = 8'h01;
+  localparam ADDR_VERSION          = 8'h02;
 
-  localparam ADDR_CTRL           = 8'h08;
-  localparam CTRL_START_BIT      = 0;
+  localparam ADDR_CTRL             = 8'h08;
+  localparam CTRL_START_BIT        = 0;
 
-  localparam ADDR_STATUS         = 8'h09;
-  localparam STATUS_READY_BIT    = 0;
+  localparam ADDR_STATUS           = 8'h09;
+  localparam STATUS_READY_BIT      = 0;
 
-  localparam ADDR_MODULUS_LENGTH  = 8'h20;
-  localparam ADDR_MESSAGE_LENGTH  = 8'h21;
-  localparam ADDR_EXPONENT_LENGTH = 8'h22;
+  localparam ADDR_MODULUS_LENGTH   = 8'h20;
+  localparam ADDR_EXPONENT_LENGTH  = 8'h21;
+  localparam ADDR_LENGTH           = 8'h22;
 
-  localparam MODULUS_PREFIX      = 4'h1;
-  localparam ADDR_MODULUS_START  = 8'h00;
-  localparam ADDR_MODULUS_END    = 8'hff;
+  localparam ADDR_MODULUS_PTR_RST  = 8'h30;
+  localparam ADDR_MODULUS_DATA     = 8'h31;
 
-  localparam EXPONENT_PREFIX     = 4'h2;
-  localparam ADDR_EXPONENT_START = 8'h00;
-  localparam ADDR_EXPONENT_END   = 8'hff;
+  localparam ADDR_EXPONENT_PTR_RST = 8'h40;
+  localparam ADDR_EXPONENT_DATA    = 8'h41;
 
-  localparam MESSAGE_PREFIX      = 4'h3;
-  localparam MESSAGE_START       = 8'h00;
-  localparam MESSAGE_END         = 8'hff;
+  localparam ADDR_MESSAGE_PTR_RST  = 8'h50;
+  localparam ADDR_MESSAGE_DATA     = 8'h51;
 
-  localparam RESULT_PREFIX       = 4'h4;
-  localparam RESULT_START        = 8'h00;
-  localparam RESULT_END          = 8'hff;
+  localparam ADDR_RESULT_PTR_RST   = 8'h60;
+  localparam ADDR_RESULT_DATA      = 8'h61;
 
 
   //----------------------------------------------------------------
   // Register and Wire declarations.
   //----------------------------------------------------------------
+  reg [31 : 0]  test_cycle_ctr;
+  reg           test_cycle_ctr_rst;
+  reg           test_cycle_ctr_inc;
+
   reg [31 : 0]  cycle_ctr;
   reg [31 : 0]  error_ctr;
   reg [31 : 0]  tc_ctr;
@@ -153,12 +158,62 @@ module tb_modexp();
         end
     end
 
+
+  //----------------------------------------------------------------
+  // test_cycle_counter
+  //
+  // Used to measure the number of cycles it takes to perform
+  // a given test case.
+  //----------------------------------------------------------------
+  always @ (posedge tb_clk)
+    begin
+      if (test_cycle_ctr_rst)
+        test_cycle_ctr = 64'h0000000000000000;
+
+      if (test_cycle_ctr_inc)
+        test_cycle_ctr = test_cycle_ctr + 1;
+    end
+
+
+  //----------------------------------------------------------------
+  // start_test_cycle_ctr
+  //
+  // Reset and start the test cycle counter.
+  //----------------------------------------------------------------
+  task start_test_cycle_ctr();
+    begin
+      test_cycle_ctr_rst = 1;
+      #(CLK_PERIOD);
+      test_cycle_ctr_rst = 0;
+
+      test_cycle_ctr_inc = 1;
+    end
+  endtask // start_test_cycle_ctr()
+
+
+  //----------------------------------------------------------------
+  // stop_test_cycle_ctr()
+  //
+  // Stop the test cycle counter and optionally display the
+  // result.
+  //----------------------------------------------------------------
+  task stop_test_cycle_ctr();
+    begin
+      test_cycle_ctr_inc = 0;
+      #(CLK_PERIOD);
+
+      if (DISPLAY_TEST_CYCLES)
+        $display("*** Number of cycles performed during test: 0x%016x", test_cycle_ctr);
+    end
+  endtask // stop_test_cycle_ctr()
+
+
   //----------------------------------------------------------------
   // ei_monitor()
   //
   // Displays ei_new, the most important variable for determining
-  // what modexp will do (i.e. should Z=MONTPROD( Z, P, M) be 
-  // performed 
+  // what modexp will do (i.e. should Z=MONTPROD( Z, P, M) be
+  // performed
   //----------------------------------------------------------------
   always @*
     begin : ei_monitor
@@ -307,7 +362,7 @@ module tb_modexp();
       tb_write_data = word;
       tb_cs = 1;
       tb_we = 1;
-      #(2 * CLK_PERIOD);
+      #(CLK_PERIOD);
       tb_cs = 0;
       tb_we = 0;
     end
@@ -484,22 +539,31 @@ module tb_modexp();
       $display("TC1: Trying to calculate 3**7 mod 11 = 9");
 
       // Write 3 to message memory.
-      write_word({MESSAGE_PREFIX, 8'h00}, 32'h00000003);
+      write_word({GENERAL_PREFIX, ADDR_MESSAGE_PTR_RST}, 32'h00000000);
+      write_word({GENERAL_PREFIX, ADDR_MESSAGE_DATA}, 32'h00000003);
+      write_word({GENERAL_PREFIX, ADDR_LENGTH}, 32'h00000001);
 
       // Write 7 to exponent memory and set length to one word.
-      write_word({EXPONENT_PREFIX, 8'h00}, 32'h00000007);
+      write_word({GENERAL_PREFIX, ADDR_EXPONENT_PTR_RST}, 32'h00000000);
+      write_word({GENERAL_PREFIX, ADDR_EXPONENT_DATA}, 32'h00000007);
       write_word({GENERAL_PREFIX, ADDR_EXPONENT_LENGTH}, 32'h00000001);
 
       // Write 11 to modulus memory and set length to one word.
-      write_word({MODULUS_PREFIX, 8'h00}, 32'h0000000b);
+      write_word({GENERAL_PREFIX, ADDR_MODULUS_PTR_RST}, 32'h00000000);
+      write_word({GENERAL_PREFIX, ADDR_MODULUS_DATA}, 32'h0000000b);
       write_word({GENERAL_PREFIX, ADDR_MODULUS_LENGTH}, 32'h00000001);
 
+      start_test_cycle_ctr();
+
       // Start processing and wait for ready.
       write_word({GENERAL_PREFIX, ADDR_CTRL}, 32'h00000001);
       wait_ready();
 
+      stop_test_cycle_ctr();
+
       // Read out result word and check result.
-      read_word({RESULT_PREFIX, 8'h00});
+      write_word({GENERAL_PREFIX, ADDR_RESULT_PTR_RST}, 32'h00000000);
+      read_word({GENERAL_PREFIX, ADDR_RESULT_DATA});
       read_data = tb_read_data;
 
       if (read_data == 32'h00000009)
@@ -534,23 +598,32 @@ module tb_modexp();
       tc_ctr = tc_ctr + 1;
       $display("TC2: Trying to calculate 251**251 mod 257 = 183");
 
-      // Write 13 to (m)esaage memory.
-      write_word({MESSAGE_PREFIX, 8'h00}, 32'h000000fb);
+      // Write 13 to message memory.
+      write_word({GENERAL_PREFIX, ADDR_MESSAGE_PTR_RST}, 32'h00000000);
+      write_word({GENERAL_PREFIX, ADDR_MESSAGE_DATA}, 32'h000000fb);
+      write_word({GENERAL_PREFIX, ADDR_LENGTH}, 32'h00000001);
 
       // Write 11 to exponent memory and set length to one word.
-      write_word({EXPONENT_PREFIX, 8'h00}, 32'h000000fb);
+      write_word({GENERAL_PREFIX, ADDR_EXPONENT_PTR_RST}, 32'h00000000);
+      write_word({GENERAL_PREFIX, ADDR_EXPONENT_DATA}, 32'h000000fb);
       write_word({GENERAL_PREFIX, ADDR_EXPONENT_LENGTH}, 32'h00000001);
 
       // Write 7 to modulus memory and set length to one word.
-      write_word({MODULUS_PREFIX, 8'h00}, 32'h00000101);
+      write_word({GENERAL_PREFIX, ADDR_MODULUS_PTR_RST}, 32'h00000000);
+      write_word({GENERAL_PREFIX, ADDR_MODULUS_DATA}, 32'h00000101);
       write_word({GENERAL_PREFIX, ADDR_MODULUS_LENGTH}, 32'h00000001);
 
+      start_test_cycle_ctr();
+
       // Start processing and wait for ready.
       write_word({GENERAL_PREFIX, ADDR_CTRL}, 32'h00000001);
       wait_ready();
 
+      stop_test_cycle_ctr();
+
       // Read out result word and check result.
-      read_word({RESULT_PREFIX, 8'h00});
+      write_word({GENERAL_PREFIX, ADDR_RESULT_PTR_RST}, 32'h00000000);
+      read_word({GENERAL_PREFIX, ADDR_RESULT_DATA});
       read_data = tb_read_data;
 
       if (read_data == 32'h000000b7)
@@ -561,7 +634,7 @@ module tb_modexp();
       else
         begin
           $display("*** ERROR: TC2 NOT successful.");
-          $display("Expected: 0x06, got 0x%08x", read_data);
+          $display("Expected: 0x000000b7, got 0x%08x", read_data);
           error_ctr = error_ctr + 1;
         end
     end
@@ -584,22 +657,31 @@ module tb_modexp();
       tc_ctr = tc_ctr + 1;
       $display("TC3: Trying to calculate 0x81 ** 0x41 mod 0x87 = 0x36");
 
-      write_word({MESSAGE_PREFIX, 8'h00}, 32'h00000081);
+      write_word({GENERAL_PREFIX, ADDR_MESSAGE_PTR_RST}, 32'h00000000);
+      write_word({GENERAL_PREFIX, ADDR_MESSAGE_DATA}, 32'h00000081);
+      write_word({GENERAL_PREFIX, ADDR_LENGTH}, 32'h00000001);
 
       // Write 11 to exponent memory and set length to one word.
-      write_word({EXPONENT_PREFIX, 8'h00}, 32'h00000041);
+      write_word({GENERAL_PREFIX, ADDR_EXPONENT_PTR_RST}, 32'h00000000);
+      write_word({GENERAL_PREFIX, ADDR_EXPONENT_DATA}, 32'h00000041);
       write_word({GENERAL_PREFIX, ADDR_EXPONENT_LENGTH}, 32'h00000001);
 
       // Write 7 to modulus memory and set length to one word.
-      write_word({MODULUS_PREFIX, 8'h00}, 32'h00000087);
+      write_word({GENERAL_PREFIX, ADDR_MODULUS_PTR_RST}, 32'h00000000);
+      write_word({GENERAL_PREFIX, ADDR_MODULUS_DATA}, 32'h00000087);
       write_word({GENERAL_PREFIX, ADDR_MODULUS_LENGTH}, 32'h00000001);
 
+      start_test_cycle_ctr();
+
       // Start processing and wait for ready.
       write_word({GENERAL_PREFIX, ADDR_CTRL}, 32'h00000001);
       wait_ready();
 
+      stop_test_cycle_ctr();
+
       // Read out result word and check result.
-      read_word({RESULT_PREFIX, 8'h00});
+      write_word({GENERAL_PREFIX, ADDR_RESULT_PTR_RST}, 32'h00000000);
+      read_word({GENERAL_PREFIX, ADDR_RESULT_DATA});
       read_data = tb_read_data;
 
       if (read_data == 32'h00000036)
@@ -616,6 +698,9 @@ module tb_modexp();
     end
   endtask // tc3
 
+
+  //----------------------------------------------------------------
+  //----------------------------------------------------------------
   function assertEquals(
       input [31:0] expected,
       input [31:0] actual
@@ -635,6 +720,9 @@ module tb_modexp();
 
   integer success;
 
+
+  //----------------------------------------------------------------
+  //----------------------------------------------------------------
   task autogenerated_BASIC_M4962768465676381896();
     reg [31 : 0] read_data;
     begin
@@ -642,25 +730,36 @@ module tb_modexp();
       tc_ctr = tc_ctr + 1;
       $display("autogenerated_BASIC_M4962768465676381896: 00000001946473e1 ** h000000010e85e74f mod 0000000170754797 ");
 
-      write_word({MESSAGE_PREFIX, 8'h00}, 32'h00000001); //TEMPLATE_MESSAGE_VALES
-      write_word({MESSAGE_PREFIX, 8'h01}, 32'h946473e1); //TEMPLATE_MESSAGE_VALES
-      write_word({EXPONENT_PREFIX, 8'h00}, 32'h00000001); //TEMPLATE_EXPONENT_VALES
-      write_word({EXPONENT_PREFIX, 8'h01}, 32'h0e85e74f); //TEMPLATE_EXPONENT_VALES
-      write_word({MODULUS_PREFIX, 8'h00}, 32'h00000001); //TEMPLATE_MODULUS_VALUES
-      write_word({MODULUS_PREFIX, 8'h01}, 32'h70754797); //TEMPLATE_MODULUS_VALUES
+      write_word({GENERAL_PREFIX, ADDR_MESSAGE_PTR_RST}, 32'h00000000);
+      write_word({GENERAL_PREFIX, ADDR_MESSAGE_DATA}, 32'h00000001); //TEMPLATE_MESSAGE_VALUES
+      write_word({GENERAL_PREFIX, ADDR_MESSAGE_DATA}, 32'h946473e1); //TEMPLATE_MESSAGE_VALUES
+
+      write_word({GENERAL_PREFIX, ADDR_EXPONENT_PTR_RST}, 32'h00000000);
+      write_word({GENERAL_PREFIX, ADDR_EXPONENT_DATA}, 32'h00000001); //TEMPLATE_EXPONENT_VALUES
+      write_word({GENERAL_PREFIX, ADDR_EXPONENT_DATA}, 32'h0e85e74f); //TEMPLATE_EXPONENT_VALUES
+
+      write_word({GENERAL_PREFIX, ADDR_MODULUS_PTR_RST}, 32'h00000000);
+      write_word({GENERAL_PREFIX, ADDR_MODULUS_DATA}, 32'h00000001); //TEMPLATE_MODULUS_VALUES
+      write_word({GENERAL_PREFIX, ADDR_MODULUS_DATA}, 32'h70754797); //TEMPLATE_MODULUS_VALUES
 
       write_word({GENERAL_PREFIX, ADDR_EXPONENT_LENGTH}, 32'h00000002); //TEMPLATE_MESSAGE_LENGTH
       write_word({GENERAL_PREFIX, ADDR_MODULUS_LENGTH}, 32'h00000002); //TEMPLATE_MODULUS_LENGTH
+      write_word({GENERAL_PREFIX, ADDR_LENGTH}, 32'h00000002); //TEMPLATE_LENGTH
+
+      start_test_cycle_ctr();
 
       // Start processing and wait for ready.
       write_word({GENERAL_PREFIX, ADDR_CTRL}, 32'h00000001);
       wait_ready();
 
-      read_word({RESULT_PREFIX, 8'h00}); read_data = tb_read_data; success = success & assertEquals(32'h00000000, read_data); //TEMPLATE_EXPECTED_VALUES 
-      read_word({RESULT_PREFIX, 8'h01}); read_data = tb_read_data; success = success & assertEquals(32'h7761ed4f, read_data); //TEMPLATE_EXPECTED_VALUES 
-     
+      stop_test_cycle_ctr();
+
+      write_word({GENERAL_PREFIX, ADDR_RESULT_PTR_RST}, 32'h00000000);
+      read_word({GENERAL_PREFIX, ADDR_RESULT_DATA}); read_data = tb_read_data; success = success & assertEquals(32'h00000000, read_data); //TEMPLATE_EXPECTED_VALUES
+      read_word({GENERAL_PREFIX, ADDR_RESULT_DATA}); read_data = tb_read_data; success = success & assertEquals(32'h7761ed4f, read_data); //TEMPLATE_EXPECTED_VALUES
+
       if (success !== 1)
-        begin  
+        begin
           $display("*** ERROR: autogenerated_BASIC_M4962768465676381896 was NOT successful.");
           error_ctr = error_ctr + 1;
         end