Adding initial versions of rtl for modexp. Montgomery multiplication works for 8192 bit operands. Modexp can build, but lacks proper control and residue generator. Memories has been tested to match block memories in Xilinx and Altera FPGAs.

7 files changed, 1874 insertions, 0 deletions

diff --git a/src/rtl/adder32.v b/src/rtl/adder32.v
new file mode 100644
index 0000000..d9cac45
--- /dev/null
+++ b/src/rtl/adder32.v
@@ -0,0 +1,54 @@
+//======================================================================
+//
+// adder32.v
+// ---------
+// 32bit adder with carry in / carry out
+//
+//
+// Author: Peter Magnusson
+// Copyright (c) 2015, NORDUnet A/S 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.
+//
+// - 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.
+//
+// - 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.
+//
+// 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.
+//
+//======================================================================
+
+
+module adder32(
+   input      [31 : 0] a,
+   input      [31 : 0] b,
+   input               carry_in,
+   output wire [31 : 0] sum,
+   output wire          carry_out);
+
+   reg [32 : 0] adder_result;
+
+   assign sum = adder_result[31:0];
+   assign carry_out = adder_result[32];
+
+   always @(a, b, carry_in)
+     adder_result = {1'b0, a} + {1'b0, b} + {32'b0, carry_in};
+endmodule
diff --git a/src/rtl/blockmem1r1w.v b/src/rtl/blockmem1r1w.v
new file mode 100644
index 0000000..1d84369
--- /dev/null
+++ b/src/rtl/blockmem1r1w.v
@@ -0,0 +1,70 @@
+//======================================================================
+//
+// blockmem1rw1.v
+// --------------
+// Synchronous block memory with one read and one write port.
+// The data size is the same for both read and write operations.
+//
+// The memory is used in the modexp core.
+//
+//
+// Author: Joachim Strombergson
+// Copyright (c) 2015, NORDUnet A/S 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.
+//
+// - 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.
+//
+// - 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.
+//
+// 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.
+//
+//======================================================================
+
+module blockmem1r1w(
+                    input wire           clk,
+
+                    input wire  [07 : 0] read_addr,
+                    output wire [31 : 0] read_data,
+
+                    input wire           wr,
+                    input wire  [07 : 0] write_addr,
+                    input wire  [31 : 0] write_data
+                   );
+
+  reg [31 : 0] mem [0 : 255];
+  reg [31 : 0] tmp_read_data;
+
+  assign read_data = tmp_read_data;
+
+  always @ (posedge clk)
+    begin : reg_mem
+      if (wr)
+        mem[write_addr] <= write_data;
+
+      tmp_read_data <= mem[read_addr];
+    end
+
+endmodule // blockmem1r1w
+
+//======================================================================
+// EOF blockmem1r1w.v
+//======================================================================
diff --git a/src/rtl/blockmem2r1w.v b/src/rtl/blockmem2r1w.v
new file mode 100644
index 0000000..252764f
--- /dev/null
+++ b/src/rtl/blockmem2r1w.v
@@ -0,0 +1,76 @@
+//======================================================================
+//
+// blockmem2r1w.v
+// --------------
+// Synchronous block memory with two read ports and one write port.
+// The data size is the same for both read and write operations.
+//
+// The memory is used in the modexp core.
+//
+//
+// Author: Joachim Strombergson
+// Copyright (c) 2015, NORDUnet A/S 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.
+//
+// - 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.
+//
+// - 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.
+//
+// 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.
+//
+//======================================================================
+
+module blockmem2r1w(
+                    input wire           clk,
+
+                    input wire  [07 : 0] read_addr0,
+                    output wire [31 : 0] read_data0,
+
+                    input wire  [07 : 0] read_addr1,
+                    output wire [31 : 0] read_data1,
+
+                    input wire           wr,
+                    input wire  [07 : 0] write_addr,
+                    input wire  [31 : 0] write_data
+                   );
+
+  reg [31 : 0] mem [0 : 255];
+  reg [31 : 0] tmp_read_data0;
+  reg [31 : 0] tmp_read_data1;
+
+  assign read_data0 = tmp_read_data0;
+  assign read_data1 = tmp_read_data1;
+
+  always @ (posedge clk)
+    begin : reg_mem
+      if (wr)
+        mem[write_addr] <= write_data;
+
+      tmp_read_data0 <= mem[read_addr0];
+      tmp_read_data1 <= mem[read_addr1];
+    end
+
+endmodule // blockmem2r1w
+
+//======================================================================
+// EOF blockmem2r1w.v
+//======================================================================
diff --git a/src/rtl/modexp.v b/src/rtl/modexp.v
new file mode 100644
index 0000000..b0e8aa3
--- /dev/null
+++ b/src/rtl/modexp.v
@@ -0,0 +1,807 @@
+//======================================================================
+//
+// modexp.v
+// --------
+// Modular exponentiation core for implementing public key algorithms
+// such as RSA, DH, ElGamal etc.
+//
+// The core calculates the following function:
+//
+//   C = M ** e mod N
+//
+//   M is a message with a length of n bits
+//   e is the exponent with a length of at most 32 bits
+//   N is the modulus  with a length of n bits
+//   n is can be 32 and up to and including 8192 bits in steps
+//   of 32 bits.
+//
+// The core has a 32-bit memory like interface, but provides
+// status signals to inform the system that a given operation
+// has is done. Additionally, any errors will also be asserted.
+//
+//
+// Author: Peter Magnusson, Joachim Strombergson
+// Copyright (c) 2015, NORDUnet A/S 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.
+//
+// - 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.
+//
+// - 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.
+//
+// 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.
+//
+//======================================================================
+
+module modexp(
+              input wire           clk,
+              input wire           reset_n,
+
+              input wire           cs,
+              input wire           we,
+
+              input wire  [11 : 0] address,
+              input wire  [31 : 0] write_data,
+              output wire [31 : 0] read_data
+             );
+
+
+  //----------------------------------------------------------------
+  // Internal constant and parameter definitions.
+  //----------------------------------------------------------------
+  localparam GENERAL_PREFIX      = 4'h0;
+  localparam ADDR_NAME0          = 8'h00;
+  localparam ADDR_NAME1          = 8'h01;
+  localparam ADDR_VERSION        = 8'h02;
+
+  localparam ADDR_MODSIZE        = 8'h10;
+  localparam ADDR_EXPONENT       = 8'h20;
+
+  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 MESSAGE_PREFIX      = 4'h3;
+  localparam MESSAGE_START       = 8'h00;
+  localparam MESSAGE_END         = 8'hff;
+
+  localparam RESULT_PREFIX       = 4'h4;
+  localparam RESULT_START        = 8'h00;
+  localparam RESULT_END          = 8'hff;
+
+  localparam LENGTH_PREFIX       = 4'h5;
+
+  localparam DEFAULT_MODLENGTH   = 8'h80;
+  localparam DEFAULT_EXPLENGTH   = 8'h80;
+
+  localparam MONTPROD_SELECT_ONE_NR = 3'h0;
+  localparam MONTPROD_SELECT_X_NR   = 3'h1;
+  localparam MONTPROD_SELECT_Z_P    = 3'h2;
+  localparam MONTPROD_SELECT_P_P    = 3'h3;
+  localparam MONTPROD_SELECT_ONE_Z  = 3'h4;
+
+  localparam MONTPROD_DEST_Z        = 2'b00;
+  localparam MONTPROD_DEST_P        = 2'b01;
+  localparam MONTPROD_DEST_NOWHERE  = 2'b10;
+
+  localparam CTRL_IDLE           = 4'h0;
+  localparam CTRL_RESIDUE        = 4'h1;
+  localparam CTRL_CALCULATE_Z0   = 4'h2;
+  localparam CTRL_CALCULATE_P0   = 4'h3;
+  localparam CTRL_ITERATE        = 4'h4;
+  localparam CTRL_ITERATE_Z_P    = 4'h5;
+  localparam CTRL_ITERATE_P_P    = 4'h6;
+  localparam CTRL_ITERATE_END    = 4'h7;
+  localparam CTRL_CALCULATE_ZN   = 4'h8;
+  localparam CTRL_DONE           = 4'h9;
+
+  localparam CORE_NAME0          = 32'h72736120; // "rsa "
+  localparam CORE_NAME1          = 32'h38313932; // "8192"
+  localparam CORE_VERSION        = 32'h302e3031; // "0.01"
+
+
+  //----------------------------------------------------------------
+  // Registers including update variables and write enable.
+  //----------------------------------------------------------------
+  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;
+  wire [31 : 0] result_mem_int_rd_data;
+  reg  [07 : 0] result_mem_int_wr_addr;
+  reg  [31 : 0] result_mem_int_wr_data;
+  reg           result_mem_int_we;
+
+  reg          residue_calculator_start; //TODO not implemented yet
+  reg          residue_calculator_ready; //TODO not implemented yet
+
+  reg  [31 : 0] residue_mem [0 : 255];
+  reg  [07 : 0] residue_mem_rd_addr;
+  wire [31 : 0] residue_mem_rd_data;
+  reg  [07 : 0] residue_mem_wr_addr;
+  reg  [31 : 0] residue_mem_wr_data;
+  reg           residue_mem_we;
+
+
+  reg  [07 : 0] p_mem_rd0_addr;
+  wire [31 : 0] p_mem_rd0_data;
+  reg  [07 : 0] p_mem_rd1_addr;
+  wire [31 : 0] p_mem_rd1_data;
+  reg  [07 : 0] p_mem_wr_addr;
+  reg  [31 : 0] p_mem_wr_data;
+  reg           p_mem_we;
+
+  reg [07 : 0] length_reg;
+  reg [07 : 0] length_m1_reg;
+  reg [07 : 0] length_new;
+  reg [07 : 0] length_m1_new;
+  reg          length_we;
+
+  reg          start_reg;
+  reg          start_new;
+  reg          start_we;
+
+  reg          ready_reg;
+  reg          ready_new;
+  reg          ready_we;
+
+  reg [2 : 0]  montprod_select_reg;
+  reg [2 : 0]  montprod_select_new;
+  reg          montprod_select_we;
+  reg [1 : 0]  montprod_dest_reg;
+  reg [1 : 0]  montprod_dest_new;
+  reg [1 : 0]  montprod_dest_we;
+
+  reg [3 : 0]  modexp_ctrl_reg;
+  reg [3 : 0]  modexp_ctrl_new;
+  reg          modexp_ctrl_we;
+
+  reg [31 : 0] one;
+  reg [31 : 0] one_new;
+
+  reg [12 : 0] loop_counter_reg;
+  reg [12 : 0] loop_counter_new;
+  reg [12 : 0] loop_counter_we;
+  reg [07 : 0] E_word_index;
+  reg [04 : 0] E_bit_index;
+  reg          last_iteration;
+  reg          ei_reg;
+  reg          ei_new;
+  reg          ei_we;
+
+  //----------------------------------------------------------------
+  // Wires.
+  //----------------------------------------------------------------
+  reg [31 : 0]  tmp_read_data;
+  reg           tmp_error;
+
+  reg           montprod_calc;
+  wire          montprod_ready;
+  reg [07 : 0]  montprod_length;
+
+  wire [07 : 0] montprod_opa_addr;
+  reg [31 : 0]  montprod_opa_data;
+
+  wire [07 : 0] montprod_opb_addr;
+  reg [31 : 0]  montprod_opb_data;
+
+  wire [07 : 0] montprod_opm_addr;
+  reg [31 : 0]  montprod_opm_data;
+
+  wire [07 : 0] montprod_result_addr;
+  wire [31 : 0] montprod_result_data;
+  wire          montprod_result_we;
+
+
+  //----------------------------------------------------------------
+  // Concurrent connectivity for ports etc.
+  //----------------------------------------------------------------
+  assign read_data = tmp_read_data;
+
+
+  //----------------------------------------------------------------
+  // core instantiations.
+  //----------------------------------------------------------------
+  montprod montprod_inst(
+                         .clk(clk),
+                         .reset_n(reset_n),
+
+                         .calculate(montprod_calc),
+                         .ready(montprod_ready),
+
+                         .length(montprod_length),
+
+                         .opa_addr(montprod_opa_addr),
+                         .opa_data(montprod_opa_data),
+
+                         .opb_addr(montprod_opb_addr),
+                         .opb_data(montprod_opb_data),
+
+                         .opm_addr(montprod_opm_addr),
+                         .opm_data(message_mem_int_rd_data),
+
+                         .result_addr(montprod_result_addr),
+                         .result_data(montprod_result_data),
+                         .result_we(montprod_result_we)
+                        );
+
+
+  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)
+                         );
+
+  blockmem2r1w p_mem(
+                           .clk(clk),
+                           .read_addr0(p_mem_rd0_addr),
+                           .read_data0(p_mem_rd0_data),
+                           .read_addr1(p_mem_rd1_addr),
+                           .read_data1(p_mem_rd1_data),
+                           .wr(p_mem_we),
+                           .write_addr(p_mem_wr_addr),
+                           .write_data(p_mem_wr_data)
+                           );
+
+
+  //----------------------------------------------------------------
+  // reg_update
+  //
+  // Update functionality for all registers in the core.
+  // All registers are positive edge triggered with asynchronous
+  // active low reset. All registers have write enable.
+  //----------------------------------------------------------------
+  always @ (posedge clk or negedge reset_n)
+    begin
+      if (!reset_n)
+        begin
+          ready_reg           <= 1'b1;
+          montprod_select_reg <= MONTPROD_SELECT_ONE_NR;
+          montprod_dest_reg   <= MONTPROD_DEST_NOWHERE;
+          modexp_ctrl_reg     <= CTRL_IDLE;
+          one                 <= 32'h0;
+          length_reg          <= 8'h0;
+          length_m1_reg       <= 8'h0;
+          loop_counter_reg    <= 13'b0;
+          ei_reg              <= 1'b0;
+        end
+      else
+        begin
+          if (ready_we)
+            ready_reg <= ready_new;
+
+          if (montprod_select_we)
+            montprod_select_reg <= montprod_select_new;
+
+          if (montprod_dest_we)
+            montprod_dest_reg <= montprod_dest_new;
+
+          if (modexp_ctrl_we)
+            modexp_ctrl_reg <= modexp_ctrl_new;
+
+          if (length_we)
+            begin
+              length_reg <= length_new;
+              length_m1_reg <= length_m1_new;
+            end
+
+          if (loop_counter_we)
+            loop_counter_reg <= loop_counter_new;
+
+          if (ei_we)
+            ei_reg <= ei_new;
+
+          one <= one_new;
+        end
+    end // reg_update
+
+
+  //----------------------------------------------------------------
+  // api
+  //
+  // The interface command decoding logic.
+  //----------------------------------------------------------------
+  always @*
+    begin : api
+      modulus_mem_api_we  = 1'b0;
+      exponent_mem_api_we = 1'b0;
+      message_mem_api_we  = 1'b0;
+      tmp_read_data       = 32'h00000000;
+
+      length_new = write_data[7 : 0];
+      length_m1_new = write_data[7 : 0] - 8'h1;
+      length_we = 1'b0;
+
+      if (cs)
+        begin
+          case (address[11 : 8])
+            GENERAL_PREFIX:
+              begin
+//                if (we)
+//                  begin
+//                    case (address)
+//                      // Write operations.
+//                      ADDR_MODSIZE:
+//                        begin
+//                          modsize_we  = 1;
+//                        end
+//
+//                      ADDR_EXPONENT:
+//                        begin
+//                          exponent_we = 1;
+//                        end
+//
+//                      default:
+//                        begin
+//                          tmp_error = 1;
+//                        end
+//                    endcase // case (addr)
+//                  end // if (write_read)
+//                else
+//                  begin
+//                    case (address)
+//                      // Read operations.
+//                      ADDR_NAME0:
+//                        begin
+//                          tmp_read_data = CORE_NAME0;
+//                        end
+//
+//                      ADDR_NAME1:
+//                        begin
+//                          tmp_read_data = CORE_NAME1;
+//                        end
+//
+//                      ADDR_VERSION:
+//                        begin
+//                          tmp_read_data = CORE_VERSION;
+//                        end
+//
+//                      ADDR_MODSIZE:
+//                        begin
+//                          tmp_read_data = {28'h0000000, modsize_reg};
+//                        end
+//
+//                      default:
+//                        begin
+//                          tmp_error = 1;
+//                        end
+//                    endcase // case (addr)
+//                  end
+              end
+
+            MODULUS_PREFIX:
+              begin
+                if (we)
+                  begin
+                    modulus_mem_api_we = 1'b1;
+                  end
+                else
+                  begin
+                    tmp_read_data = modulus_mem_api_rd_data;
+                  end
+              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
+
+            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
+
+            RESULT_PREFIX:
+              begin
+                tmp_read_data = result_mem_api_rd_data;
+              end
+
+            LENGTH_PREFIX:
+              begin
+                if (we)
+                  length_we = 1'b1;
+              end
+
+//            RESULT_PREFIX:
+//              begin
+//                if (we)
+//                  begin
+//                    modulus_mem_api_we = 1'b1;
+//                  end
+//                else
+//                  begin
+//                    tmp_read_data = modulus_mem_int_rd_data;
+//                  end
+//              end
+
+            default:
+              begin
+
+              end
+          endcase // case (address[11 : 8])
+        end // if (cs)
+    end // api
+
+
+  //----------------------------------------------------------------
+  // montprod_op_select
+  //
+  // Select operands used during montprod calculations depending
+  // on what operation we want to do
+  //----------------------------------------------------------------
+  always @*
+    begin : montprod_op_select
+      message_mem_int_rd_addr  = montprod_opa_addr;
+      p_mem_rd0_addr           = montprod_opa_addr;
+
+      residue_mem_rd_addr      = montprod_opb_addr;
+      p_mem_rd1_addr           = montprod_opb_addr;
+
+      modulus_mem_int_rd_addr  = montprod_opm_addr;
+
+      montprod_opa_data        = 32'h00000000;
+      montprod_opb_data        = 32'h00000000;
+
+      if (montprod_opa_addr == length_m1_reg)
+        one_new = 32'h00000001;
+      else
+        one_new = 32'h00000000;
+
+      case (montprod_select_reg)
+        MONTPROD_SELECT_ONE_NR:
+          begin
+            montprod_opa_data       = one;
+            montprod_opb_data       = residue_mem_rd_data;
+          end
+
+        MONTPROD_SELECT_X_NR:
+          begin
+            montprod_opa_data       = message_mem_int_rd_data;
+            montprod_opb_data       = residue_mem_rd_data;
+          end
+
+        MONTPROD_SELECT_Z_P:
+          begin
+            montprod_opa_data       = result_mem_int_rd_data;
+            montprod_opb_data       = p_mem_rd1_data;
+          end
+
+        MONTPROD_SELECT_P_P:
+          begin
+            montprod_opa_data       = p_mem_rd0_data;
+            montprod_opb_data       = p_mem_rd1_data;
+          end
+
+        MONTPROD_SELECT_ONE_Z:
+          begin
+            montprod_opa_data       = one;
+            montprod_opb_data       = result_mem_int_rd_data;
+          end
+
+        default:
+          begin
+          end
+      endcase // case (montprod_selcect_reg)
+    end
+
+  //----------------------------------------------------------------
+  // memory write mux
+  //
+  // direct memory write signals to correct memory
+  //----------------------------------------------------------------
+  always @*
+    begin : memory_write_process
+      result_mem_int_wr_addr = montprod_result_addr;
+      result_mem_int_wr_data = montprod_result_data;
+      result_mem_int_we      = 1'b0;
+
+      p_mem_wr_addr = montprod_result_addr;
+      p_mem_wr_data = montprod_result_data;
+      p_mem_we      = 1'b0;
+
+      case (montprod_dest_reg)
+        MONTPROD_DEST_Z:
+          result_mem_int_we = montprod_result_we;
+        MONTPROD_DEST_P:
+          p_mem_we = montprod_result_we;
+        default:
+          begin
+          end
+      endcase
+
+      // inhibit Z=Z*P when ei = 0
+      if (modexp_ctrl_reg == CTRL_ITERATE_Z_P)
+        result_mem_int_we = result_mem_int_we & ei_reg;
+    end
+
+  //----------------------------------------------------------------
+  // loop_counter
+  //
+  // Calculate the loop counter and related variables
+  //----------------------------------------------------------------
+  always @*
+    begin : loop_counters_process
+      E_bit_index      = loop_counter_reg[ 04 : 0 ];
+
+      if (loop_counter_reg == { length_m1_reg, 5'b11111 })
+        last_iteration = 1'b1;
+      else
+        last_iteration = 1'b0;
+
+      case (modexp_ctrl_reg)
+        CTRL_CALCULATE_P0:
+          begin
+            loop_counter_new = 13'b0;
+            loop_counter_we  = 1'b1;
+          end
+
+        CTRL_ITERATE_END:
+          begin
+            loop_counter_new = loop_counter_reg + 1'b1;
+            loop_counter_we  = 1'b1;
+          end
+
+        default:
+          begin
+            loop_counter_new = 13'b0;
+            loop_counter_we  = 1'b0;
+          end
+
+      endcase
+    end
+
+  //----------------------------------------------------------------
+  // exponent
+  //
+  // reads the exponent
+  //----------------------------------------------------------------
+  always @*
+    begin : exponent_process
+      // accessing new instead of reg - pick up update at CTRL_ITERATE_NEW to remove a pipeline stall
+      E_word_index  = loop_counter_new[ 12 : 5 ];
+
+      exponent_mem_int_rd_addr = E_word_index;
+
+      ei_new = exponent_mem_int_rd_data[ E_bit_index ];
+
+      if (modexp_ctrl_reg == CTRL_ITERATE)
+        ei_we = 1'b1;
+      else
+        ei_we = 1'b0;
+    end
+
+  //----------------------------------------------------------------
+  // modexp_ctrl
+  //
+  // Control FSM logic needed to perform the modexp operation.
+  //----------------------------------------------------------------
+  always @*
+    begin
+      ready_new           = 0;
+      ready_we            = 0;
+      montprod_select_new = MONTPROD_SELECT_ONE_NR;
+      montprod_select_we  = 0;
+      montprod_dest_new   = MONTPROD_DEST_NOWHERE;
+      montprod_dest_we    = 0;
+      montprod_calc       = 0;
+      modexp_ctrl_new     = CTRL_IDLE;
+      modexp_ctrl_we      = 0;
+
+      residue_calculator_start = 1'b0;
+
+      case (modexp_ctrl_reg)
+        CTRL_IDLE:
+          begin
+            ready_new           = 0;
+            ready_we            = 1;
+            if (start_reg == 1'b1)
+              begin
+                modexp_ctrl_new = CTRL_RESIDUE;
+                modexp_ctrl_we  = 1;
+                residue_calculator_start = 1'b1;
+              end
+          end
+
+        CTRL_RESIDUE:
+          begin
+            if (residue_calculator_ready == 1'b1)
+              begin
+                montprod_select_new = MONTPROD_SELECT_ONE_NR;
+                montprod_select_we  = 1;
+                montprod_dest_new   = MONTPROD_DEST_Z;
+                montprod_dest_we    = 1;
+                montprod_calc       = 1;
+                modexp_ctrl_new = CTRL_CALCULATE_Z0;
+                modexp_ctrl_we  = 1;
+              end
+          end
+
+        CTRL_CALCULATE_Z0:
+          begin
+            if (montprod_ready == 1'b1)
+              begin
+                montprod_select_new = MONTPROD_SELECT_X_NR;
+                montprod_select_we  = 1;
+                montprod_dest_new   = MONTPROD_DEST_P;
+                montprod_dest_we    = 1;
+                montprod_calc       = 1;
+                modexp_ctrl_new = CTRL_CALCULATE_P0;
+                modexp_ctrl_we  = 1;
+              end
+          end
+
+        CTRL_CALCULATE_P0:
+          begin
+            if (montprod_ready == 1'b1)
+              begin
+                modexp_ctrl_new = CTRL_ITERATE;
+                modexp_ctrl_we  = 1;
+              end
+          end
+
+        CTRL_ITERATE:
+          begin
+            montprod_select_new = MONTPROD_SELECT_Z_P;
+            montprod_select_we  = 1;
+            montprod_dest_new   = MONTPROD_DEST_Z;
+            montprod_dest_we    = 1;
+            montprod_calc       = 1;
+            modexp_ctrl_new = CTRL_ITERATE_Z_P;
+            modexp_ctrl_we  = 1;
+          end
+
+        CTRL_ITERATE_Z_P:
+            if (montprod_ready == 1'b1)
+              begin
+                montprod_select_new = MONTPROD_SELECT_P_P;
+                montprod_select_we  = 1;
+                montprod_dest_new   = MONTPROD_DEST_P;
+                montprod_dest_we    = 1;
+                montprod_calc       = 1;
+                modexp_ctrl_new = CTRL_ITERATE_P_P;
+                modexp_ctrl_we  = 1;
+              end
+
+        CTRL_ITERATE_P_P:
+            if (montprod_ready == 1'b1)
+              begin
+                modexp_ctrl_new = CTRL_ITERATE_END;
+                modexp_ctrl_we  = 1;
+              end
+
+        CTRL_ITERATE_END:
+          begin
+            if (last_iteration == 1'b0)
+              begin
+                modexp_ctrl_new = CTRL_ITERATE;
+                modexp_ctrl_we  = 1;
+              end
+            else
+              begin
+                montprod_select_new = MONTPROD_SELECT_ONE_Z;
+                montprod_select_we  = 1;
+                montprod_calc       = 1;
+                modexp_ctrl_new = CTRL_CALCULATE_ZN;
+                modexp_ctrl_we  = 1;
+              end
+          end
+
+        CTRL_CALCULATE_ZN:
+          begin
+            if (montprod_ready == 1'b1)
+              begin
+                modexp_ctrl_new = CTRL_DONE;
+                modexp_ctrl_we  = 1;
+              end
+          end
+
+        CTRL_DONE:
+          begin
+            ready_new           = 1;
+            ready_we            = 1;
+            modexp_ctrl_new     = CTRL_IDLE;
+            modexp_ctrl_we      = 1;
+          end
+
+        default:
+          begin
+          end
+
+      endcase // case (modexp_ctrl_reg)
+    end
+
+endmodule // modexp
+
+//======================================================================
+// EOF modexp.v
+//======================================================================
diff --git a/src/rtl/montprod.v b/src/rtl/montprod.v
new file mode 100644
index 0000000..32bbdec
--- /dev/null
+++ b/src/rtl/montprod.v
@@ -0,0 +1,590 @@
+//======================================================================
+//
+// montprod.v
+// ---------
+// Montgomery product calculator for the modular exponentiantion core.
+//
+//
+// Author: Peter Magnusson, Joachim Strombergson
+// Copyright (c) 2015, NORDUnet A/S 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.
+//
+// - 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.
+//
+// - 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.
+//
+// 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.
+//
+//======================================================================
+
+module montprod(
+                input wire           clk,
+                input wire           reset_n,
+
+                input wire           calculate,
+                output wire          ready,
+
+                input   [7 : 0]      length,
+
+                output wire [7 : 0]  opa_addr,
+                input wire [31 : 0]  opa_data,
+
+                output wire [7 : 0]  opb_addr,
+                input wire [31 : 0]  opb_data,
+
+                output wire [7 : 0]  opm_addr,
+                input wire [31 : 0]  opm_data,
+
+                output wire [7 : 0]  result_addr,
+                output wire [31 : 0] result_data,
+                output wire          result_we
+               );
+
+
+  //----------------------------------------------------------------
+  // Internal constant and parameter definitions.
+  //----------------------------------------------------------------
+  localparam CTRL_IDLE           = 4'h0;
+  localparam CTRL_INIT_S         = 4'h1;
+  localparam CTRL_LOOP_INIT      = 4'h2;
+  localparam CTRL_LOOP_ITER      = 4'h3;
+  localparam CTRL_LOOP_BQ        = 4'h4;
+  localparam CTRL_L_CALC_SM      = 4'h5;
+  localparam CTRL_L_STALLPIPE_SM = 4'h6;
+  localparam CTRL_L_CALC_SA      = 4'h7;
+  localparam CTRL_L_STALLPIPE_SA = 4'h8;
+  localparam CTRL_L_CALC_SDIV2   = 4'h9;
+  localparam CTRL_L_STALLPIPE_D2 = 4'hA;
+  localparam CTRL_L_STALLPIPE_ES = 4'hB;
+  localparam CTRL_EMIT_S         = 4'hC;
+  localparam CTRL_DONE           = 4'hD;
+
+  localparam SMUX_0            = 2'h0;
+  localparam SMUX_ADD_SM       = 2'h1;
+  localparam SMUX_ADD_SA       = 2'h2;
+  localparam SMUX_SHR          = 2'h3;
+
+  //----------------------------------------------------------------
+  // Registers including update variables and write enable.
+  //----------------------------------------------------------------
+
+  reg [07 : 0] opa_addr_reg;
+  reg [07 : 0] opb_addr_reg;
+  reg [07 : 0] opm_addr_reg;
+
+  reg [07 : 0] result_addr_reg;
+  reg [31 : 0] result_data_reg;
+
+  reg          ready_reg;
+  reg          ready_new;
+  reg          ready_we;
+
+  reg [3 : 0]  montprod_ctrl_reg;
+  reg [3 : 0]  montprod_ctrl_new;
+  reg          montprod_ctrl_we;
+
+  reg  [1 : 0] s_mux_new;
+  reg  [1 : 0] s_mux_reg;
+
+  reg [31 : 0] s_mem_new;
+  reg          s_mem_we;
+  reg          s_mem_we_new;
+  reg [07 : 0] s_mem_addr;
+  reg [07 : 0] s_mem_wr_addr;
+  wire [31 : 0] s_mem_read_data;
+
+  reg          q; //q = (s - b * A) & 1
+  reg          q_reg;
+  reg          b; //b: bit of B
+  reg          b_reg;
+
+  reg [12 : 0] loop_counter;
+  reg [12 : 0] loop_counter_new;
+  reg [12 : 0] loop_counter_dec;
+  reg [07 : 0] B_word_index; //loop counter as a word index
+  reg [04 : 0] B_bit_index; //loop counter as a bit index
+  reg [04 : 0] B_bit_index_reg; //loop counter as a bit index
+
+  reg [07 : 0] word_index; //register of what word is being read
+  reg [07 : 0] word_index_new; //calculation of what word to be read
+  reg [07 : 0] word_index_prev; //register of what word was read previously (result address to emit)
+  reg [07 : 0] length_m1;
+
+  reg          add_carry_in_sa;
+  reg          add_carry_new_sa;
+  reg          add_carry_in_sm;
+  reg          add_carry_new_sm;
+
+  reg          shr_carry_in;
+  reg          shr_carry_new;
+
+  reg          reset_word_index_LSW;
+  reg          reset_word_index_MSW;
+
+
+  //----------------------------------------------------------------
+  // Wires.
+  //----------------------------------------------------------------
+  reg           tmp_result_we;
+  wire [31 : 0] add_result_sa;
+  wire          add_carry_out_sa;
+  wire [31 : 0] add_result_sm;
+  wire          add_carry_out_sm;
+
+  wire          shr_carry_out;
+  wire [31 : 0] shr_adiv2;
+
+
+  //----------------------------------------------------------------
+  // Concurrent connectivity for ports etc.
+  //----------------------------------------------------------------
+  assign opa_addr    = opa_addr_reg;
+  assign opb_addr    = opb_addr_reg;
+  assign opm_addr    = opm_addr_reg;
+
+  assign result_addr = result_addr_reg;
+  assign result_data = result_data_reg;
+  assign result_we   = tmp_result_we;
+
+  assign ready       = ready_reg;
+
+
+  //----------------------------------------------------------------
+  // Instantions
+  //----------------------------------------------------------------
+
+  blockmem1r1w s_mem(
+                     .clk(clk),
+                     .read_addr(s_mem_addr),
+                     .read_data(s_mem_read_data),
+                     .wr(s_mem_we),
+                     .write_addr(s_mem_wr_addr),
+                     .write_data(s_mem_new)
+                    );
+
+
+  adder32 s_adder_sa(
+    .a(s_mem_read_data),
+    .b(opa_data),
+    .carry_in(add_carry_in_sa),
+    .sum(add_result_sa),
+    .carry_out(add_carry_out_sa)
+  );
+
+  adder32 s_adder_sm(
+    .a(s_mem_read_data),
+    .b(opm_data),
+    .carry_in(add_carry_in_sm),
+    .sum(add_result_sm),
+    .carry_out(add_carry_out_sm)
+  );
+
+  shr32 shifter(
+     .a( s_mem_read_data ),
+     .carry_in( shr_carry_in ),
+     .adiv2( shr_adiv2 ),
+     .carry_out( shr_carry_out )
+  );
+
+  always @*
+    begin : s_mux
+      case (s_mux_reg)
+        SMUX_0:
+          s_mem_new = 32'b0;
+        SMUX_ADD_SA:
+          s_mem_new = add_result_sa;
+        SMUX_ADD_SM:
+          s_mem_new = add_result_sm;
+        SMUX_SHR:
+          s_mem_new = shr_adiv2;
+      endcase
+      $display("SMUX%x: %x", s_mux_reg, s_mem_new);
+    end
+
+  //----------------------------------------------------------------
+  // reg_update
+  //
+  // Update functionality for all registers in the core.
+  // All registers are positive edge triggered with asynchronous
+  // active low reset. All registers have write enable.
+  //----------------------------------------------------------------
+  always @ (posedge clk or negedge reset_n)
+    begin : reg_update
+      if (!reset_n)
+        begin
+          ready_reg         <= 1'b0;
+          loop_counter      <= 13'h0;
+          word_index        <= 8'h0;
+          word_index_prev   <= 8'h0;
+          add_carry_in_sa   <= 1'b0;
+          add_carry_in_sm   <= 1'b0;
+          shr_carry_in      <= 1'b0;
+          montprod_ctrl_reg <= CTRL_IDLE;
+          b_reg             <= 1'b0;
+          q_reg             <= 1'b0;
+          s_mux_reg         <= SMUX_0;
+          s_mem_we          <= 1'b0;
+          s_mem_wr_addr     <= 8'h0;
+          B_bit_index_reg   <= 5'h0;
+        end
+      else
+        begin
+          if (ready_we)
+            ready_reg <= ready_new;
+
+          if (montprod_ctrl_we)
+            begin
+               montprod_ctrl_reg <= montprod_ctrl_new;
+             end
+
+          s_mem_wr_addr <= s_mem_addr;
+
+          s_mem_we <= s_mem_we_new;
+
+          word_index <= word_index_new;
+          word_index_prev <= word_index;
+
+          loop_counter <= loop_counter_new;
+          shr_carry_in <= shr_carry_new;
+          add_carry_in_sa <= add_carry_new_sa;
+          add_carry_in_sm <= add_carry_new_sm;
+
+          B_bit_index_reg <= B_bit_index;
+          q_reg <= q;
+          b_reg <= b;
+
+          s_mux_reg <= s_mux_new;
+      end
+    end // reg_update
+
+  always @*
+   begin : bq_process
+      b = b_reg;
+      q = q_reg;
+      if (montprod_ctrl_reg == CTRL_LOOP_BQ)
+         begin
+           b = opb_data[ B_bit_index_reg ];
+           //opa_addr will point to length-1 to get A LSB.
+           //s_read_addr will point to length-1
+           q = s_mem_read_data[0] ^ (opa_data[0] & b);
+           $display("s_mem_read_data: %x opa_data %x b %x q %x B_bit_index_reg %x", s_mem_read_data, opa_data, b, q, B_bit_index_reg);
+        end
+   end
+
+
+  //----------------------------------------------------------------
+  // Process for iterating the loop counter and setting related B indexes
+  //----------------------------------------------------------------
+  always @*
+   begin : loop_counter_process
+      length_m1        = length - 1'b1;
+      loop_counter_dec = loop_counter - 1'b1;
+      B_word_index     = loop_counter[12:5];
+      B_bit_index      = B_bit_index_reg;
+
+      case (montprod_ctrl_reg)
+        CTRL_LOOP_INIT:
+          loop_counter_new = {length, 5'b00000}-1;
+
+        CTRL_LOOP_ITER:
+          begin
+            B_word_index     = loop_counter[12:5];
+            B_bit_index      = 5'h1f - loop_counter[4:0];
+          end
+
+        CTRL_L_STALLPIPE_D2:
+            loop_counter_new = loop_counter_dec;
+
+        default:
+          loop_counter_new = loop_counter;
+      endcase
+    end
+
+
+  //----------------------------------------------------------------
+  // prodcalc
+  //----------------------------------------------------------------
+  always @*
+    begin : prodcalc
+
+      case (montprod_ctrl_reg)
+        CTRL_LOOP_ITER:
+          //q = (s[length-1] ^ A[length-1]) & 1;
+          opa_addr_reg = length_m1;
+
+        default:
+          opa_addr_reg = word_index;
+       endcase
+
+       opb_addr_reg = B_word_index;
+       opm_addr_reg = word_index;
+
+      case (montprod_ctrl_reg)
+        CTRL_LOOP_ITER:
+          s_mem_addr = length_m1;
+        default:
+          s_mem_addr = word_index;
+      endcase
+
+
+
+
+      result_addr_reg  = word_index_prev;
+      result_data_reg  = s_mem_read_data;
+
+      case (montprod_ctrl_reg)
+        CTRL_EMIT_S:
+           tmp_result_we = 1'b1;
+        default:
+           tmp_result_we = 1'b0;
+      endcase
+
+
+      if (reset_word_index_LSW == 1'b1)
+        word_index_new = length_m1;
+      else if (reset_word_index_MSW == 1'b1)
+        word_index_new = 8'h0;
+      else if (montprod_ctrl_reg == CTRL_L_CALC_SDIV2)
+        word_index_new = word_index + 1'b1;
+      else
+        word_index_new = word_index - 1'b1;
+    end // prodcalc
+
+
+  always @*
+    begin : s_writer_process
+      shr_carry_new    = 1'b0;
+      s_mux_new        = SMUX_0;
+
+      s_mem_we_new  = 1'b0;
+      case (montprod_ctrl_reg)
+        CTRL_INIT_S:
+          begin
+            s_mem_we_new = 1'b1;
+            s_mux_new    = SMUX_0; // write 0
+          end
+
+        CTRL_L_CALC_SM:
+          begin
+            //s = (s + q*M + b*A) >>> 1;, if(q==1) S+= M. Takes (1..length) cycles.
+            s_mem_we_new     = q_reg;
+            s_mux_new        = SMUX_ADD_SM;
+          end
+
+        CTRL_L_CALC_SA:
+          begin
+            //s = (s + q*M + b*A) >>> 1;, if(b==1) S+= A. Takes (1..length) cycles.
+            s_mem_we_new     = b_reg;
+            s_mux_new        = SMUX_ADD_SA;
+          end
+
+        CTRL_L_CALC_SDIV2:
+          begin
+            //s = (s + q*M + b*A) >>> 1; s>>=1.  Takes (1..length) cycles.
+            s_mux_new     = SMUX_SHR;
+            s_mem_we_new  = 1'b1;
+          end
+
+        default:
+          begin
+          end
+      endcase
+
+      add_carry_new_sa = 1'b0;
+      add_carry_new_sm = 1'b0;
+
+      case (s_mux_reg)
+        SMUX_ADD_SM:
+          add_carry_new_sm = add_carry_out_sm;
+
+        SMUX_ADD_SA:
+          add_carry_new_sa = add_carry_out_sa;
+
+        SMUX_SHR:
+          shr_carry_new = shr_carry_out;
+
+        default:
+          begin
+          end
+      endcase
+
+    end // prodcalc
+
+
+  //----------------------------------------------------------------
+  // montprod_ctrl
+  //
+  // Control FSM for the montgomery product calculator.
+  //----------------------------------------------------------------
+  always @*
+    begin : montprod_ctrl
+      ready_new         = 1'b0;
+      ready_we          = 1'b0;
+      montprod_ctrl_new = CTRL_IDLE;
+      montprod_ctrl_we  = 1'b0;
+
+      reset_word_index_LSW = 1'b0;
+      reset_word_index_MSW = 1'b0;
+
+      case (montprod_ctrl_reg)
+        CTRL_IDLE:
+          begin
+            if (calculate)
+              begin
+                ready_new = 1'b0;
+                ready_we  = 1'b1;
+                montprod_ctrl_new = CTRL_INIT_S;
+                montprod_ctrl_we = 1'b1;
+                reset_word_index_LSW = 1'b1;
+              end
+            else
+              begin
+                ready_new = 1'b1;
+                ready_we  = 1'b1;
+              end
+          end
+
+        CTRL_INIT_S:
+          begin
+            if (word_index == 8'h0)
+              begin
+                 montprod_ctrl_new = CTRL_LOOP_INIT;
+                 montprod_ctrl_we = 1'b1;
+              end
+          end
+
+
+        CTRL_LOOP_INIT:
+          begin
+            montprod_ctrl_new = CTRL_LOOP_ITER;
+            montprod_ctrl_we  = 1'b1;
+          end
+
+        //calculate q = (s - b * A) & 1;.
+        // Also abort loop if done.
+        CTRL_LOOP_ITER:
+          begin
+            reset_word_index_LSW = 1'b1;
+            montprod_ctrl_new = CTRL_LOOP_BQ;
+            montprod_ctrl_we  = 1'b1;
+          end
+
+        CTRL_LOOP_BQ:
+          begin
+            reset_word_index_LSW = 1'b1;
+            montprod_ctrl_new = CTRL_L_CALC_SM;
+            montprod_ctrl_we  = 1'b1;
+          end
+
+        CTRL_L_CALC_SM:
+          begin
+            if (word_index == 8'h0)
+              begin
+                reset_word_index_LSW  = 1'b1;
+                montprod_ctrl_we  = 1'b1;
+                montprod_ctrl_new = CTRL_L_STALLPIPE_SM;
+              end
+          end
+
+        CTRL_L_STALLPIPE_SM:
+          begin
+            montprod_ctrl_new = CTRL_L_CALC_SA;
+            montprod_ctrl_we = 1'b1;
+            reset_word_index_LSW = 1'b1;
+          end
+
+        CTRL_L_CALC_SA:
+          begin
+            if (word_index == 8'h0)
+              begin
+                reset_word_index_LSW  = 1'b1;
+                montprod_ctrl_new = CTRL_L_STALLPIPE_SA;
+                montprod_ctrl_we = 1'b1;
+              end
+          end
+
+        CTRL_L_STALLPIPE_SA:
+          begin
+            montprod_ctrl_new = CTRL_L_CALC_SDIV2;
+            montprod_ctrl_we = 1'b1;
+            reset_word_index_MSW = 1'b1;
+          end
+
+        CTRL_L_CALC_SDIV2:
+          begin
+            if (word_index == length_m1)
+              begin
+                montprod_ctrl_new = CTRL_L_STALLPIPE_D2;
+                montprod_ctrl_we = 1'b1;
+                //reset_word_index = 1'b1;
+              end
+          end
+
+        CTRL_L_STALLPIPE_D2:
+          begin
+            montprod_ctrl_new = CTRL_LOOP_ITER; //loop
+            montprod_ctrl_we = 1'b1;
+            reset_word_index_LSW = 1'b1;
+            if (loop_counter == 0)
+              begin
+                montprod_ctrl_new = CTRL_L_STALLPIPE_ES;
+                montprod_ctrl_we = 1'b1;
+              end
+          end
+
+        CTRL_L_STALLPIPE_ES:
+          begin
+            montprod_ctrl_new = CTRL_EMIT_S;
+            montprod_ctrl_we = 1'b1;
+            //reset_word_index_LSW = 1'b1;
+          end
+
+        CTRL_EMIT_S:
+           begin
+             $display("EMIT_S word_index: %d", word_index);
+             if (word_index_prev == 8'h0)
+               begin
+                 montprod_ctrl_new = CTRL_DONE;
+                 montprod_ctrl_we  = 1'b1;
+               end
+           end
+
+        CTRL_DONE:
+          begin
+            ready_new         = 1'b1;
+            ready_we          = 1'b1;
+            montprod_ctrl_new = CTRL_IDLE;
+            montprod_ctrl_we  = 1'b1;
+          end
+
+        default:
+          begin
+          end
+
+      endcase // case (montprod_ctrl_reg)
+    end // montprod_ctrl
+
+endmodule // montprod
+
+//======================================================================
+// EOF montprod.v
+//======================================================================
diff --git a/src/rtl/residue.v b/src/rtl/residue.v
new file mode 100644
index 0000000..2991dd6
--- /dev/null
+++ b/src/rtl/residue.v
@@ -0,0 +1,224 @@
+//======================================================================
+//
+// residue.v
+// ---------
+// Modulus 2**2N residue calculator for montgomery calculations.
+//
+// m_residue_2_2N_array( N, M, Nr)
+//   Nr = 00...01 ; Nr = 1 == 2**(2N-2N)
+//   for (int i = 0; i < 2 * N; i++)
+//     Nr = Nr shift left 1
+//     if (Nr less than M) continue;
+//     Nr = Nr - M
+// return Nr
+//
+//
+//
+// Author: Peter Magnusson
+// Copyright (c) 2015, NORDUnet A/S 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.
+//
+// - 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.
+//
+// - 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.
+//
+// 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.
+//
+//======================================================================
+
+module residue(
+  input wire clk,
+  input wire reset_n,
+
+  input wire  calculate,
+  output wire ready,
+
+  input wire  [07 : 0] nn,
+  input wire  [07 : 0] length,
+
+  output wire [07 : 0] opa_rd_addr,
+  input wire  [31 : 0] opa_rd_data,
+  output wire [07 : 0] opa_wr_addr,
+  output wire [31 : 0] opa_wr_data,
+  output wire          opa_wr_we,
+
+  output wire [07 : 0] opm_addr,
+  input wire  [31 : 0] opm_data
+
+);
+
+//----------------------------------------------------------------
+// Internal constant and parameter definitions.
+//----------------------------------------------------------------
+
+
+localparam CTRL_IDLE          = 4'h0;
+localparam CTRL_INIT          = 4'h1;
+localparam CTRL_INIT_STALL    = 4'h2;
+localparam CTRL_SHL           = 4'h3;
+localparam CTRL_SHL_STALL     = 4'h4;
+localparam CTRL_COMPARE       = 4'h5;
+localparam CTRL_COMPARE_STALL = 4'h6;
+localparam CTRL_SUB           = 4'h7;
+localparam CTRL_SUB_STALL     = 4'h8;
+localparam CTRL_LOOP          = 4'h9;
+
+//----------------------------------------------------------------
+// Registers including update variables and write enable.
+//----------------------------------------------------------------
+
+reg [07 : 0] opa_rd_addr_reg;
+reg [07 : 0] opa_wr_addr_reg;
+reg [31 : 0] opa_wr_data_reg;
+reg          opa_wr_we_reg;
+reg [07 : 0] opm_addr_reg;
+reg          ready_reg;
+reg          ready_new;
+reg          ready_we;
+reg [03 : 0] residue_ctrl_reg;
+reg [03 : 0] residue_ctrl_new;
+reg          residue_ctrl_we;
+reg          reset_word_index;
+reg          reset_n_counter;
+reg [07 : 0] word_index;
+
+//----------------------------------------------------------------
+// Concurrent connectivity for ports etc.
+//----------------------------------------------------------------
+assign opa_rd_addr = opa_rd_addr_reg;
+assign opa_wr_addr = opa_wr_addr_reg;
+assign opa_wr_data = opa_wr_data_reg;
+assign opm_addr    = opm_addr_reg;
+assign ready       = ready_reg;
+
+
+
+
+  //----------------------------------------------------------------
+  // reg_update
+  //----------------------------------------------------------------
+  always @ (posedge clk or negedge reset_n)
+    begin
+      if (!reset_n)
+        begin
+          residue_ctrl_reg <= CTRL_IDLE;
+        end
+      else
+        begin
+          if (residue_ctrl_we)
+            residue_ctrl_reg <= residue_ctrl_new;
+        end
+    end // reg_update
+
+
+  //----------------------------------------------------------------
+  //----------------------------------------------------------------
+  always @*
+    begin : process_1_to_2n
+    end
+
+  //----------------------------------------------------------------
+  //----------------------------------------------------------------
+  always @*
+    begin : word_index_process
+    end
+
+//----------------------------------------------------------------
+// residue_ctrl
+//
+// Control FSM for residue
+//----------------------------------------------------------------
+always @*
+  begin : residue_ctrl
+    ready_new = 1'b0;
+    ready_we  = 1'b0;
+    residue_ctrl_new = CTRL_IDLE;
+    residue_ctrl_we  = 1'b0;
+    reset_word_index = 1'b0;
+    reset_n_counter  = 1'b0;
+
+    case (residue_ctrl_reg)
+      CTRL_IDLE:
+        if (calculate)
+          begin
+            ready_new = 1'b0;
+            ready_we  = 1'b1;
+            residue_ctrl_new = CTRL_INIT;
+            residue_ctrl_we  = 1'b1;
+            reset_word_index = 1'b1;
+          end
+
+      CTRL_INIT:
+        if (word_index == 8'h0)
+          begin
+            residue_ctrl_new = CTRL_INIT_STALL;
+            residue_ctrl_we  = 1'b1;
+          end
+
+      CTRL_INIT_STALL:
+        begin
+          reset_word_index = 1'b1;
+          reset_n_counter  = 1'b1;
+          residue_ctrl_new = CTRL_COMPARE;
+          residue_ctrl_we  = 1'b1;
+        end
+
+      CTRL_COMPARE:
+        begin
+        end
+
+      CTRL_COMPARE_STALL:
+        begin
+        end
+
+      CTRL_SUB:
+        begin
+        end
+
+      CTRL_SUB_STALL:
+        begin
+        end
+
+      CTRL_SHL:
+        begin
+        end
+
+      CTRL_SHL_STALL:
+        begin
+        end
+
+      CTRL_LOOP:
+        begin
+        end
+
+      default:
+        begin
+        end
+
+    endcase
+  end
+
+endmodule // residue
+
+//======================================================================
+// EOF residue.v
+//======================================================================
diff --git a/src/rtl/shr32.v b/src/rtl/shr32.v
new file mode 100644
index 0000000..840f9df
--- /dev/null
+++ b/src/rtl/shr32.v
@@ -0,0 +1,53 @@
+//======================================================================
+//
+// shr32.v
+// ---------
+// 32bit shifter with carry in / carry out
+//
+//
+// Author: Peter Magnusson
+// Copyright (c) 2015, NORDUnet A/S 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.
+//
+// - 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.
+//
+// - 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.
+//
+// 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.
+//
+//======================================================================
+
+
+module shr32(
+   input       [31 : 0] a,
+   input                carry_in,
+   output wire [31 : 0] adiv2,
+   output wire          carry_out);
+
+   reg [32 : 0] shr_result;
+
+   assign adiv2     = shr_result[32:1];
+   assign carry_out = shr_result[0];
+
+   always @(a, carry_in)
+     shr_result = { carry_in, a };
+endmodule