From c0448c8663a0513d2060d974e153a6b93e4bfa4e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Joachim=20Stro=CC=88mbergson?= <joachim@secworks.se>
Date: Thu, 18 Jun 2015 11:00:31 +0200
Subject: Restored version of montprod to a version that actually works.

---
 src/rtl/montprod.v | 53 +++++++++++++++++++++++++++++++++++------------------
 1 file changed, 35 insertions(+), 18 deletions(-)

(limited to 'src')

diff --git a/src/rtl/montprod.v b/src/rtl/montprod.v
index f505d0c..9748b09 100644
--- a/src/rtl/montprod.v
+++ b/src/rtl/montprod.v
@@ -127,7 +127,7 @@ module montprod(
 
   reg [04 : 0] b_bit_index_reg;
   reg [04 : 0] b_bit_index_new;
-  reg          b_bit_index_we;
+  reg [04 : 0] b_bit_index_we;
 
   reg [07 : 0] word_index_reg; //register of what word is being read
   reg [07 : 0] word_index_new; //calculation of what word to be read
@@ -157,7 +157,7 @@ module montprod(
   wire [31 : 0] add_result_sm;
   wire          add_carry_out_sm;
 
-  reg  [31 : 0] shr_data_in;
+  reg           shr_data_in;
   wire          shr_carry_out;
   wire [31 : 0] shr_data_out;
 
@@ -331,19 +331,44 @@ module montprod(
   //----------------------------------------------------------------
   always @*
     begin : s_select_write
-      sa_adder_data_in    = 32'h0;
-      shr_carry_in_new    = 1'b0;
+      shr_carry_in_new = 1'b0;
+      s_mux_new        = SMUX_0;
+      s_mem_we_new     = 1'b0;
+      sa_adder_data_in = 32'h0;
+
+      case (montprod_ctrl_reg)
+        CTRL_INIT_S:
+          begin
+            s_mux_new    = SMUX_0; // write 0
+            s_mem_we_new = 1'b1;
+          end
+
+        CTRL_L_CALC_SA:
+          begin
+            //s = (s + q*M + b*A) >>> 1;, if(b==1) S+= A. Takes (1..length) cycles.
+            s_mux_new    = SMUX_ADD_SA;
+            s_mem_we_new = b_reg | q_reg;
+          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
+
+      s_mem_new           = 32'h0;
       add_carry_in_sa_new = 1'b0;
       add_carry_in_sm_new = 1'b0;
-      s_mem_new           = 32'h0;
-      s_mem_we_new        = 1'b0;
 
       case (s_mux_reg)
         SMUX_0:
-          begin
-            s_mem_new = 32'h0;
-            s_mem_we_new = 1'b1;
-          end
+          s_mem_new = 32'h0;
 
         SMUX_ADD_SA:
           begin
@@ -359,7 +384,6 @@ module montprod(
 
             add_carry_in_sa_new = add_carry_out_sa;
             add_carry_in_sm_new = add_carry_out_sm;
-            s_mem_we_new = b_reg | q_reg;
           end
 
         SMUX_SHR:
@@ -367,7 +391,6 @@ module montprod(
             shr_data_in      = s_mem_read_data;
             s_mem_new        = shr_data_out;
             shr_carry_in_new = shr_carry_out;
-            s_mem_we_new  = 1'b1;
           end
 
         default:
@@ -460,8 +483,6 @@ module montprod(
 
         CTRL_INIT_S:
           begin
-            s_mux_new = SMUX_0;
-
             if (word_index_reg == 8'h0)
               begin
                 loop_ctr_set  = 1'b1;
@@ -496,8 +517,6 @@ module montprod(
 
         CTRL_L_CALC_SA:
           begin
-            s_mux_new = SMUX_ADD_SA;
-
             if (word_index_reg == 8'h0)
               begin
                 reset_word_index_lsw = 1'b1;
@@ -515,8 +534,6 @@ module montprod(
 
         CTRL_L_CALC_SDIV2:
           begin
-            s_mux_new     = SMUX_SHR;
-
             if (word_index_reg == length_m1)
               begin
                 montprod_ctrl_new = CTRL_L_STALLPIPE_D2;
-- 
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