From 5a4b5a312a7bcedff0514b410541f95b266d406a Mon Sep 17 00:00:00 2001
From: Yuri Tatishchev <itatishch@gmail.com>
Date: Tue, 8 Oct 2024 00:05:19 -0700
Subject: [PATCH] lab-04: gate level model for 32-bit signed multiplier

Gate level implementation for the following components:
- MULT32_U
- MULT32
- MUX32_2x1
---
 TESTBENCH/mult_tb.v |  2 ++
 logic_32_bit.v      | 16 ++++++++++++++
 mult.v              | 53 +++++++++++++++++++++++++++++++++++++++++++--
 mux.v               | 20 +++++++++++++++--
 4 files changed, 87 insertions(+), 4 deletions(-)

diff --git a/TESTBENCH/mult_tb.v b/TESTBENCH/mult_tb.v
index 3111ef0..cd44040 100644
--- a/TESTBENCH/mult_tb.v
+++ b/TESTBENCH/mult_tb.v
@@ -36,6 +36,8 @@ A=10; B=20;     // Y = 10 * 20 = 200
 #1 result[i] = {HI,LO}; i=i+1;
 #1 A=10; B=19; 	// Y = 10 * 19 = 190
 #1 result[i] = {HI,LO}; i=i+1;
+#1 A=32'h00d96027; B=32'h7c32b43c; 	// Y = 0x0d96027 * 0x7c32b43c = 0x 006975a0 b62bf524
+#1 result[i] = {HI,LO}; i=i+1;
 #1 A=32'h70000000; B=32'h70000000; 
 #1 result[i] = {HI,LO}; i=i+1;
 #1 
diff --git a/logic_32_bit.v b/logic_32_bit.v
index d02d6ce..df558e3 100755
--- a/logic_32_bit.v
+++ b/logic_32_bit.v
@@ -80,3 +80,19 @@ generate
     end
 endgenerate
 endmodule
+
+// 32-bit buffer
+module BUF32_1x1(Y,A);
+//output 
+output [31:0] Y;
+//input
+input [31:0] A;
+
+genvar i;
+generate
+    for (i = 0; i < 32; i = i + 1)
+    begin : buf32_gen_loop
+        buf buf32_inst(Y[i], A[i]);
+    end
+endgenerate
+endmodule
diff --git a/mult.v b/mult.v
index ddb65d8..9e03d0f 100644
--- a/mult.v
+++ b/mult.v
@@ -27,7 +27,25 @@ output [31:0] LO;
 input [31:0] A;
 input [31:0] B;
 
-// TBD
+wire [31:0] A_neg, B_neg;
+TWOSCOMP32 A_twoscomp(A_neg, A);
+TWOSCOMP32 B_twoscomp(B_neg, B);
+
+wire [31:0] A_abs, B_abs;
+MUX32_2x1 A_mux(A_abs, A, A_neg, A[31]);
+MUX32_2x1 B_mux(B_abs, B, B_neg, B[31]);
+
+wire [31:0] HI_abs, LO_abs;
+MULT32_U mult_abs(HI_abs, LO_abs, A_abs, B_abs);
+
+wire [31:0] HI_neg, LO_neg;
+TWOSCOMP64 mult_neg({HI_neg,LO_neg}, {HI_abs,LO_abs});
+
+wire sign;
+xor (sign, A[31], B[31]);
+
+MUX32_2x1 HI_mux(HI, HI_abs, HI_neg, sign);
+MUX32_2x1 LO_mux(LO, LO_abs, LO_neg, sign);
 
 endmodule
 
@@ -39,6 +57,37 @@ output [31:0] LO;
 input [31:0] A;
 input [31:0] B;
 
-// TBD
+// partial sums
+wire [31:0] Y [31:0];
+
+// first partial is just
+AND32_2x1 partial_1(Y[0], A, {32{B[0]}});
+// put lowest bit from first partial into result
+buf (LO[0], Y[0][0]);
+
+
+// carries from partial adders
+wire CI[31:0];
+// first carry is always 0
+buf (CI[0], 0);
+
+genvar i;
+generate
+    for (i = 0; i < 31; i = i + 1)
+    begin : mult32u_gen_loop
+        // multiply A by a single digit in B
+        wire [31:0] A_and;
+        AND32_2x1 partial_and_inst(A_and, A, {32{B[i+1]}});
+
+        // calc the next partial and carry (i + 1)
+        RC_ADD_SUB_32 partial_add_inst(.Y(Y[i+1]), .CO(CI[i+1]), .A(A_and), .B({CI[i],Y[i][31:1]}), .SnA(1'b0));
+
+        // put lowest bit from calc into result
+        buf (LO[i+1], Y[i+1][0]);
+    end
+endgenerate
+
+// last carry and partial is HI
+BUF32_1x1 buf_hi(HI, {CI[31],Y[31][31:1]});
 
 endmodule
diff --git a/mux.v b/mux.v
index b2af14d..0cdaeab 100644
--- a/mux.v
+++ b/mux.v
@@ -102,7 +102,20 @@ input [31:0] I0;
 input [31:0] I1;
 input S;
 
-// TBD
+// only need 1 not gate
+not (S_not, S);
+
+wire [31:0] x0, x1;
+
+genvar i;
+generate
+    for (i = 0; i < 32; i = i + 1)
+    begin : mux32_gen_loop
+        and (x0[i], S_not, I0[i]);
+        and (x1[i], S, I1[i]);
+        or (Y[i], x0[i], x1[i]);
+    end
+endgenerate
 
 endmodule
 
@@ -113,6 +126,9 @@ output Y;
 //input list
 input I0, I1, S;
 
-// TBD
+not (S_not, S);
+and (x0, S_not, I0);
+and (x1, S, I1);
+or (Y, x0, x1);
 
 endmodule