Expanded micro-operation parameters (added dedicated control bit to force the B input of

the modular multiplier to 1, this is necessary to bring numbers out of Montgomery domain).

1 files changed, 20 insertions, 6 deletions

diff --git a/rtl/modexpng_mmm_dual.v b/rtl/modexpng_mmm_dual.v
index babd565..b9b41e8 100644
--- a/rtl/modexpng_mmm_dual.v
+++ b/rtl/modexpng_mmm_dual.v
@@ -7,6 +7,7 @@ module modexpng_mmm_dual
     ladder_mode,
     word_index_last,
     word_index_last_minus1,
+    force_unity_b,
     
     sel_wide_in, sel_narrow_in,
     
@@ -70,7 +71,8 @@ module modexpng_mmm_dual
     input                   ladder_mode;
     input [7:0] word_index_last;
     input [7:0] word_index_last_minus1;
-    
+    input       force_unity_b;
+        
     input [BANK_ADDR_W-1:0] sel_wide_in;
     input [BANK_ADDR_W-1:0] sel_narrow_in;
     
@@ -708,13 +710,22 @@ module modexpng_mmm_dual
     // DSP Feed Logic
     //
     reg dsp_merge_xy_b;
+    reg dsp_merge_xy_b_first;
     
-    always @(posedge clk)
+    always @(posedge clk) begin
         //
         case (fsm_state)
             FSM_STATE_MULT_SQUARE_COL_0_TRIG:   dsp_merge_xy_b <= 1'b1;
             FSM_STATE_MULT_TRIANGLE_COL_0_TRIG: dsp_merge_xy_b <= 1'b0;
         endcase
+        //
+        case (fsm_state)
+            FSM_STATE_MULT_SQUARE_COL_0_TRIG,
+            FSM_STATE_MULT_SQUARE_COL_N_TRIG: dsp_merge_xy_b_first <= 1'b1;
+            default:                          dsp_merge_xy_b_first <= 1'b0;
+        endcase
+        //
+    end
 
     //
     // On-the-fly Carry Recombination
@@ -723,6 +734,9 @@ module modexpng_mmm_dual
     wire [17:0] rd_narrow_y_dout_carry = rd_narrow_y_dout + {{16{1'b0}}, dsp_xy_b_carry};
     wire [17:0] rd_narrow_xy_dout_carry_mux = ladder_mode ? rd_narrow_y_dout_carry : rd_narrow_x_dout_carry;
   
+    wire [15:0] rd_narrow_xy_dout_carry_mux_or_unity = !force_unity_b ?
+        rd_narrow_xy_dout_carry_mux[15:0] : dsp_merge_xy_b_first ? WORD_ONE : WORD_ZERO;
+  
     always @(posedge clk)
         //
         if (narrow_xy_ena_dly2) begin // rewrite
@@ -732,15 +746,15 @@ module modexpng_mmm_dual
                 dsp_y_b <= rd_narrow_y_dout[15:0];
                 dsp_xy_b_carry <= 2'b00;
             end else begin
-                dsp_x_b <= rd_narrow_xy_dout_carry_mux[15:0];
-                dsp_y_b <= rd_narrow_xy_dout_carry_mux[15:0];
+                dsp_x_b <= rd_narrow_xy_dout_carry_mux_or_unity;
+                dsp_y_b <= rd_narrow_xy_dout_carry_mux_or_unity;
                 dsp_xy_b_carry <= rd_narrow_xy_dout_carry_mux[17:16];
             end                 
             //
         end else begin
             //
-            dsp_x_b <= {16{1'bX}};
-            dsp_y_b <= {16{1'bX}};
+            dsp_x_b <= WORD_DNC;
+            dsp_y_b <= WORD_DNC;
             //
             dsp_xy_b_carry <= 2'b00;
             //