From d33639a2fcaddc6a0cfc3eb9aee0a119e03047b6 Mon Sep 17 00:00:00 2001
From: bsdevlin <bsdevlin@gmail.com>
Date: Sun, 6 Sep 2020 18:50:06 -0400
Subject: [PATCH] update barret mod overflow control

---
 ip_cores/util/src/rtl/barret_mod.sv | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/ip_cores/util/src/rtl/barret_mod.sv b/ip_cores/util/src/rtl/barret_mod.sv
index e90a029..9a3f940 100644
--- a/ip_cores/util/src/rtl/barret_mod.sv
+++ b/ip_cores/util/src/rtl/barret_mod.sv
@@ -24,7 +24,7 @@ module barret_mod #(
   parameter                CTL_BITS = 8,
   parameter                IN_BITS = 512,
   parameter [OUT_BITS-1:0] P = 256'hFFFFFFFF_FFFFFFFF_FFFFFFFF_FFFFFFFE_BAAEDCE6_AF48A03B_BFD25E8C_D0364141,
-  parameter                K = $clog2(P),
+  parameter                K = OUT_BITS,
   parameter                MULTIPLIER = "EXTERNAL" // [ACCUM_MULT || KARATSUBA || EXTERNAL]
 )(
   input                       i_clk,
@@ -48,11 +48,12 @@ logic [2:0][CTL_BITS-1:0] ctl_r;
 if_axi_stream #(.DAT_BITS(2*(OUT_BITS+2))) mult_in_if(i_clk);
 if_axi_stream #(.DAT_BITS(2*(OUT_BITS+2))) mult_out_if(i_clk);
 
-logic [MAX_IN_BITS:0] c1, c2, c3, c4, c2_, P_;
+logic [MAX_IN_BITS:0] c1, c2, c3, c4, P_;
+logic c4_grt;
 
 always_comb begin
-  P_ = 0;
-  P_[OUT_BITS-1:0] = P; 
+  P_ = {{(MAX_IN_BITS-OUT_BITS-1){1'b0}}, P}; 
+  c4_grt  = c4 >= P_;
 end
 
 typedef enum {IDLE, S0, S1, S2, FINISHED, WAIT_MULT} state_t;
@@ -88,7 +89,6 @@ always_ff @ (posedge i_clk) begin
           mult_in_if.dat[0 +: OUT_BITS+1] <= i_dat >> (K-1);
           mult_in_if.dat[OUT_BITS+1 +: OUT_BITS+1] <= U;
           prev_state <= S0;
-          c2_ <= (i_dat >> (K - 1))*U; // Using multiplier interface
         end
       end
       {S0}: begin
@@ -105,8 +105,9 @@ always_ff @ (posedge i_clk) begin
         ctl_r[2] <= ctl_r[1];
       end
       {S2}: begin
-        if (c4 >= P_) begin
+        if (c4_grt) begin
           c4 <= c4 - P_;
+          state <= S2;
         end else begin
           state <= FINISHED;
           o_dat <= c4;
@@ -128,9 +129,14 @@ always_ff @ (posedge i_clk) begin
           case(prev_state)
             S0: c2 <= mult_out_if.dat;
             S2: c4 <= c4 - mult_out_if.dat;
+            default: begin end     
           endcase
         end
       end
+      default: begin
+        o_val <= 0;
+        state <= IDLE;
+      end
     endcase
   end
 end
@@ -205,4 +211,4 @@ generate
 endgenerate
 initial assert (IN_BITS <= MAX_IN_BITS) else $fatal(1, "%m ERROR: IN_BITS[%d] > MAX_IN_BITS[%d] in barret_mod", IN_BITS, MAX_IN_BITS);
 
-endmodule
\ No newline at end of file
+endmodule