Inital commit

.gitignore

@@ -0,0 +1 @@
+work/*

LICENSE.md

@@ -0,0 +1,166 @@
+#GNU LESSER GENERAL PUBLIC LICENSE
+Version 3, 29 June 2007
+
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+
+  This version of the GNU Lesser General Public License incorporates
+the terms and conditions of version 3 of the GNU General Public
+License, supplemented by the additional permissions listed below.
+
+#### 0. Additional Definitions.
+
+  As used herein, "this License" refers to version 3 of the GNU Lesser
+General Public License, and the "GNU GPL" refers to version 3 of the GNU
+General Public License.
+
+  "The Library" refers to a covered work governed by this License,
+other than an Application or a Combined Work as defined below.
+
+  An "Application" is any work that makes use of an interface provided
+by the Library, but which is not otherwise based on the Library.
+Defining a subclass of a class defined by the Library is deemed a mode
+of using an interface provided by the Library.
+
+  A "Combined Work" is a work produced by combining or linking an
+Application with the Library.  The particular version of the Library
+with which the Combined Work was made is also called the "Linked
+Version".
+
+  The "Minimal Corresponding Source" for a Combined Work means the
+Corresponding Source for the Combined Work, excluding any source code
+for portions of the Combined Work that, considered in isolation, are
+based on the Application, and not on the Linked Version.
+
+  The "Corresponding Application Code" for a Combined Work means the
+object code and/or source code for the Application, including any data
+and utility programs needed for reproducing the Combined Work from the
+Application, but excluding the System Libraries of the Combined Work.
+
+#### 1. Exception to Section 3 of the GNU GPL.
+
+  You may convey a covered work under sections 3 and 4 of this License
+without being bound by section 3 of the GNU GPL.
+
+#### 2. Conveying Modified Versions.
+
+  If you modify a copy of the Library, and, in your modifications, a
+facility refers to a function or data to be supplied by an Application
+that uses the facility (other than as an argument passed when the
+facility is invoked), then you may convey a copy of the modified
+version:
+
+   a) under this License, provided that you make a good faith effort to
+   ensure that, in the event an Application does not supply the
+   function or data, the facility still operates, and performs
+   whatever part of its purpose remains meaningful, or
+
+   b) under the GNU GPL, with none of the additional permissions of
+   this License applicable to that copy.
+
+#### 3. Object Code Incorporating Material from Library Header Files.
+
+  The object code form of an Application may incorporate material from
+a header file that is part of the Library.  You may convey such object
+code under terms of your choice, provided that, if the incorporated
+material is not limited to numerical parameters, data structure
+layouts and accessors, or small macros, inline functions and templates
+(ten or fewer lines in length), you do both of the following:
+
+   a) Give prominent notice with each copy of the object code that the
+   Library is used in it and that the Library and its use are
+   covered by this License.
+
+   b) Accompany the object code with a copy of the GNU GPL and this license
+   document.
+
+#### 4. Combined Works.
+
+  You may convey a Combined Work under terms of your choice that,
+taken together, effectively do not restrict modification of the
+portions of the Library contained in the Combined Work and reverse
+engineering for debugging such modifications, if you also do each of
+the following:
+
+   a) Give prominent notice with each copy of the Combined Work that
+   the Library is used in it and that the Library and its use are
+   covered by this License.
+
+   b) Accompany the Combined Work with a copy of the GNU GPL and this license
+   document.
+
+   c) For a Combined Work that displays copyright notices during
+   execution, include the copyright notice for the Library among
+   these notices, as well as a reference directing the user to the
+   copies of the GNU GPL and this license document.
+
+   d) Do one of the following:
+
+   *0) Convey the Minimal Corresponding Source under the terms of this
+      License, and the Corresponding Application Code in a form
+      suitable for, and under terms that permit, the user to
+      recombine or relink the Application with a modified version of
+      the Linked Version to produce a modified Combined Work, in the
+      manner specified by section 6 of the GNU GPL for conveying
+      Corresponding Source.*
+
+   *1) Use a suitable shared library mechanism for linking with the
+       Library.  A suitable mechanism is one that (a) uses at run time
+       a copy of the Library already present on the user's computer
+       system, and (b) will operate properly with a modified version
+       of the Library that is interface-compatible with the Linked
+       Version.*
+
+   e) Provide Installation Information, but only if you would otherwise
+   be required to provide such information under section 6 of the
+   GNU GPL, and only to the extent that such information is
+   necessary to install and execute a modified version of the
+   Combined Work produced by recombining or relinking the
+   Application with a modified version of the Linked Version. (If
+   you use option 4d0, the Installation Information must accompany
+   the Minimal Corresponding Source and Corresponding Application
+   Code. If you use option 4d1, you must provide the Installation
+   Information in the manner specified by section 6 of the GNU GPL
+   for conveying Corresponding Source.)
+
+#### 5. Combined Libraries.
+
+  You may place library facilities that are a work based on the
+Library side by side in a single library together with other library
+facilities that are not Applications and are not covered by this
+License, and convey such a combined library under terms of your
+choice, if you do both of the following:
+
+   a) Accompany the combined library with a copy of the same work based
+   on the Library, uncombined with any other library facilities,
+   conveyed under the terms of this License.
+
+   b) Give prominent notice with the combined library that part of it
+   is a work based on the Library, and explaining where to find the
+   accompanying uncombined form of the same work.
+
+#### 6. Revised Versions of the GNU Lesser General Public License.
+
+  The Free Software Foundation may publish revised and/or new versions
+of the GNU Lesser General Public License from time to time. Such new
+versions will be similar in spirit to the present version, but may
+differ in detail to address new problems or concerns.
+
+  Each version is given a distinguishing version number. If the
+Library as you received it specifies that a certain numbered version
+of the GNU Lesser General Public License "or any later version"
+applies to it, you have the option of following the terms and
+conditions either of that published version or of any later version
+published by the Free Software Foundation. If the Library as you
+received it does not specify a version number of the GNU Lesser
+General Public License, you may choose any version of the GNU Lesser
+General Public License ever published by the Free Software Foundation.
+
+  If the Library as you received it specifies that a proxy can decide
+whether future versions of the GNU Lesser General Public License shall
+apply, that proxy's public statement of acceptance of any version is
+permanent authorization for you to choose that version for the
+Library.

README.md

@@ -0,0 +1,6 @@
+# formal_verification
+
+Tests and examples of using formal verification to check correctness of digital hardware designs. All tests are done with SymbiYosys, a free formal verification tool based on Yosys. Some examples use the VHDL/SystemVerilog parser plugin by Verific which isn't free SW and nit included in the free Yosys version. See on the [Symbiotic EDA website](https://www.symbioticeda.com) for more information. 
+
+### alu
+A simple ALU design in VHDL, together with a formal testbench written in SystemVerilog. The testbench contains various simple properties for assert & cover directives which are proved with the SymbiYosys tool.

alu/.gitignore

@@ -0,0 +1 @@
+*/work/*

alu/Makefile

@@ -0,0 +1,2 @@
+alu: alu.vhd alu_t.v alu_f.sby
+	sby -f -d work alu_f.sby

alu/alu.vhd

@@ -0,0 +1,54 @@
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+
+
+
+entity alu is
+  port (
+    Reset_n_i  : in  std_logic;
+    Clk_i      : in  std_logic;
+    Opc_i      : in  std_logic_vector(1 downto 0);
+    DinA_i     : in  std_logic_vector(31 downto 0);
+    DinB_i     : in  std_logic_vector(31 downto 0);
+    Dout_o     : out std_logic_vector(31 downto 0);
+    OverFlow_o : out std_logic
+  );
+end entity alu;
+
+
+
+architecture rtl of alu is
+
+
+  constant c_add : std_logic_vector(1 downto 0) := "00";
+  constant c_sub : std_logic_vector(1 downto 0) := "01";
+  constant c_and : std_logic_vector(1 downto 0) := "10";
+  constant c_or  : std_logic_vector(1 downto 0) := "11";
+
+
+begin
+
+
+  process (Reset_n_i, Clk_i) is
+  begin
+    if (Reset_n_i = '0') then
+      Dout_o <= (others => '0');
+    elsif (rising_edge(Clk_i)) then
+      case Opc_i is
+        when c_add => (OverFlow_o, Dout_o) <=
+	  std_logic_vector(resize(unsigned(DinA_i), Dout_o'length+1) +
+	                   resize(unsigned(DinB_i), Dout_o'length+1));
+        when c_sub => (OverFlow_o, Dout_o) <=
+	  std_logic_vector(resize(unsigned(DinA_i), Dout_o'length+1) -
+	                   resize(unsigned(DinB_i), Dout_o'length+1));
+	when c_and => Dout_o <= DinA_i and DinB_i;
+	when c_or  => Dout_o <= DinA_i or DinB_i;
+	when others => null;
+      end case;
+    end if;
+  end process;
+
+
+end architecture rtl;
+

alu/alu_f.sby

@@ -0,0 +1,16 @@
+[options]
+mode prove
+#mode bmc
+#depth 20
+
+[engines]
+smtbmc
+
+[script]
+verific -vhdl alu.vhd
+verific -formal alu_t.sv
+prep -top alu_t
+
+[files]
+alu.vhd
+alu_t.sv

alu/alu_t.sv

@@ -0,0 +1,57 @@
+module alu_t (
+    inout        Reset_n_i,
+    input        Clk_i,
+    input  [1:0] Opc_i,
+    input  [31:0] DinA_i,
+    input  [31:0] DinB_i,
+    output [31:0] Dout_o,
+    output       OverFlow_o
+);
+
+
+  alu alu_i (
+    .Reset_n_i(Reset_n_i),
+    .Clk_i(Clk_i),
+    .Opc_i(Opc_i),
+    .DinA_i(DinA_i),
+    .DinB_i(DinB_i),
+    .Dout_o(Dout_o),
+    .OverFlow_o(OverFlow_o)
+  );
+
+  const logic [1:0] OPC_ADD = 0;
+  const logic [1:0] OPC_SUB = 1;
+  const logic [1:0] OPC_AND = 2;
+  const logic [1:0] OPC_OR  = 3;
+
+  initial begin
+    assume (!Reset_n_i);
+  end
+
+  bit unsigned [32:0] dina, dinb;
+
+  assign dina = DinA_i;
+  assign dinb = DinB_i;
+
+  assert property (@(posedge Clk_i) disable iff (!Reset_n_i) Opc_i == OPC_ADD |=> Dout_o == ($past(DinA_i) + $past(DinB_i)));
+  assert property (@(posedge Clk_i) disable iff (!Reset_n_i) Opc_i == OPC_ADD && (dina + dinb) > 2**32-1 |=> OverFlow_o);
+  assert property (@(posedge Clk_i) disable iff (!Reset_n_i) Opc_i == OPC_SUB |=> Dout_o == ($past(DinA_i) - $past(DinB_i)));
+  assert property (@(posedge Clk_i) disable iff (!Reset_n_i) Opc_i == OPC_SUB && (dina - dinb) > 2**32-1 |=> OverFlow_o);
+  assert property (@(posedge Clk_i) disable iff (!Reset_n_i) Opc_i == OPC_AND |=> Dout_o == ($past(DinA_i) & $past(DinB_i)));
+  assert property (@(posedge Clk_i) disable iff (!Reset_n_i) Opc_i == OPC_OR |=> Dout_o == ($past(DinA_i) | $past(DinB_i)));
+
+  assert property (@(posedge Clk_i or negedge Clk_i) !Reset_n_i |-> Dout_o == 0);
+
+  property cover_opc (opc);
+    @(posedge Clk_i)
+      disable iff (!Reset_n_i) Opc_i == opc;
+  endproperty
+
+  cover property (cover_opc(OPC_ADD));
+  cover property (cover_opc(OPC_SUB));
+  cover property (cover_opc(OPC_AND));
+  cover property (cover_opc(OPC_OR));
+
+
+endmodule
+