From 7ad179151bc444eb7ee664b2145b41de199c4920 Mon Sep 17 00:00:00 2001
From: Ahmed Irfan <irfan@levert.(none)>
Date: Fri, 3 Apr 2015 16:20:29 +0200
Subject: appnote for verilog to btor

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+
+% IEEEtran howto:
+% http://ftp.univie.ac.at/packages/tex/macros/latex/contrib/IEEEtran/IEEEtran_HOWTO.pdf
+\documentclass[9pt,technote,a4paper]{IEEEtran}
+
+\usepackage[T1]{fontenc}   % required for luximono!
+\usepackage[scaled=0.8]{luximono}  % typewriter font with bold face
+
+% To install the luximono font files:
+% getnonfreefonts-sys --all        or
+% getnonfreefonts-sys luximono
+%
+% when there are trouble you might need to:
+% - Create /etc/texmf/updmap.d/99local-luximono.cfg
+%   containing the single line: Map ul9.map
+% - Run update-updmap followed by mktexlsr and updmap-sys
+%
+% This commands must be executed as root with a root environment
+% (i.e. run "sudo su" and then execute the commands in the root
+% shell, don't just prefix the commands with "sudo").
+
+\usepackage[unicode,bookmarks=false]{hyperref}
+\usepackage[english]{babel}
+\usepackage[utf8]{inputenc}
+\usepackage{amssymb}
+\usepackage{amsmath}
+\usepackage{amsfonts}
+\usepackage{units}
+\usepackage{nicefrac}
+\usepackage{eurosym}
+\usepackage{graphicx}
+\usepackage{verbatim}
+\usepackage{algpseudocode}
+\usepackage{scalefnt}
+\usepackage{xspace}
+\usepackage{color}
+\usepackage{colortbl}
+\usepackage{multirow}
+\usepackage{hhline}
+\usepackage{listings}
+\usepackage{float}
+
+\usepackage{tikz}
+\usetikzlibrary{calc}
+\usetikzlibrary{arrows}
+\usetikzlibrary{scopes}
+\usetikzlibrary{through}
+\usetikzlibrary{shapes.geometric}
+
+\lstset{basicstyle=\ttfamily,frame=trBL,xleftmargin=2em,xrightmargin=1em,numbers=left}
+
+\begin{document}
+
+\title{Yosys Application Note 012: \\ Converting Verilog to BTOR}
+\author{Ahmed Irfan and Clifford Wolf \\ November 2014}
+\maketitle
+
+\begin{abstract}
+Verilog-2005 is a powerful Hardware Description Language (HDL) that
+can be used to easily create complex designs from small HDL code.
+BTOR~\cite{btor} is a bit-precise word-level format for model
+checking.  It is simple format and easy to parse.  It allows to model
+the model checking problem over theory of bit-vectors with
+one-dimensional arrays, thus enabling to model verilog designs with
+registers and memories.  Yosys \cite{yosys} is an Open-Source Verilog
+synthesis tool that can be used to convert Verilog designs with simple
+assertions to BTOR format.
+
+\end{abstract}
+
+\section{Installation}
+
+Yosys written in C++ (using features from C++11) and is tested on
+modern Linux.  It should compile fine on most UNIX systems with a
+C++11 compiler. The README file contains useful information on
+building Yosys and its prerequisites.
+
+Yosys is a large and feature-rich program with some dependencies. For
+this work, we may deactivate other extra features that are {\tt TCL},
+{\tt Qt}, {\tt MiniSAT}, and {\tt yosys-abc} support in the {\tt
+  Makefile}.
+
+\bigskip
+
+This Application Note is based on GIT Rev. {\tt d3c67ad} from
+2014-09-22 of Yosys \cite{yosys}.
+%The Verilog sources used for the examples are taken from
+%yosys-bigsim \cite{bigsim}, a collection of real-world designs used for
+%regression testing Yosys.
+
+\section{Quick Start}
+
+We assume that the Verilog design is synthesizable and we also assume
+that the design does not have multi-dimensional memories.  As BTOR
+implicitly initializes registers to zero value and memories stay
+uninitilized, we assume that the the Verilog design does
+not contain initial block. For more details about the BTOR format,
+please refer to~\cite{btor}.
+
+We provide a shell script {\tt verilog2btor.sh} which can be used to
+convert a Verilog design to BTOR.  The script can be found in {\tt
+  backends/btor} directory.  Following example shows its usage:
+
+\begin{figure}[H]
+\begin{lstlisting}[language=sh]
+verilog2btor.sh fsm.v fsm.btor test
+\end{lstlisting}
+ \renewcommand{\figurename}{Listing}
+\caption{Using verilog2btor script}
+\end{figure}
+
+The script {\tt verilog2btor.sh} takes three parameters.  In the above
+example, first parameter {\tt fsm.v} is the input design, second
+parameter {\tt fsm.btor} is the file name of BTOR output, and third
+parameter {\tt test} is the name of top module in the design.
+
+To specify the properties (that need to be checked), we have two
+options:
+\begin{itemize}
+\item We can use simple {\tt assert} command in the procedural block
+  or continuous block of the Verilog design, as shown in
+  Listing~\ref{specifying_property_assert}. This is preferred option.
+\item We can use a output wire (single bit), whose name starts with
+  {\tt safety}.  The value of this output wire needs to be handled in
+  the Verilog code, as shown in
+  Listing~\ref{specifying_property_output}.
+\end{itemize}
+
+\begin{figure}[H]
+\begin{lstlisting}[language=Verilog]
+module test(input clk, input rst, output y);
+reg [2:0] state;
+output safety1;
+always @(posedge clk) begin
+  if (rst || state == 3) begin
+    state <= 0;
+  end else begin
+    assert(state < 3);
+    state <= state + 1;
+  end
+end
+assign y = state[2];
+assert property (y !== 1'b1);
+endmodule
+\end{lstlisting}
+\renewcommand{\figurename}{Listing}
+\caption{Specifying property in Verilog design with {\tt assert}}
+\label{specifying_property_assert}
+\end{figure}
+
+\begin{figure}[H]
+\begin{lstlisting}[language=Verilog]
+module test(input clk, input rst, output y, 
+  output safety1);
+reg [2:0] state;
+output safety1;
+always @(posedge clk) begin
+  if (rst || state == 3)
+    state <= 0;
+  else
+    state <= state + 1;
+end
+assign y = state[2];
+always @(*)
+begin
+  if (y !== 1'b1)
+    safety1 <= 1;
+  else
+    safety1 <= 0;
+end
+endmodule
+\end{lstlisting}
+\renewcommand{\figurename}{Listing}
+\caption{Specifying property in Verilog design with output wire}
+\label{specifying_property_output}
+\end{figure}
+
+We can run Boolector~$1.4$~\cite{boolector} on the generated BTOR
+file.  The url for boolector provided in the references, contains
+installation and usage guide.
+
+We can also run nuXmv~\cite{nuxmv} but on the BTOR designs that does
+not have memories. With the next release of nuXmv, we will be also
+able to verify the designs with memories.
+
+\section{Detailed Flow}
+
+Yosys is able to synthesize the Verilog designs up to the gate level.
+We are interested in keeping registers and memories when synthesizing
+the design. For this purpose, we describe a customized Yosys synthesis
+flow, that is also provided as a script {\tt verilog2btor.sh} in Yosys
+distribution. The following script shows the operations that are
+performed in {\tt verilog2btor.sh}:
+
+\begin{figure}[H]
+\begin{lstlisting}[language=sh]
+read_verilog -sv $1; 
+hierarchy -top $3; hierarchy -libdir $DIR; 
+hierarchy -check; 
+proc; opt; 
+opt_const -mux_undef; opt;
+rename -hide;;;
+splice; opt;
+memory_dff -wr_only; memory_collect;;
+flatten;;
+memory_unpack; 
+splitnets -driver;
+setundef -zero -undriven;
+opt;;;
+write_btor $2;
+\end{lstlisting}
+ \renewcommand{\figurename}{Listing}
+\caption{Synthesis Flow for BTOR with memories}
+\label{btor_script_memory}
+\end{figure}
+
+Here is short description of what is happening in the script line by
+line:
+
+\begin{enumerate}
+\item Reading the input file.
+\item Setting the top module in the hierarchy and trying to read
+  automatically the files which are given as {\tt include} in the file
+  read in first line.
+\item Checking the design heirarchy.
+\item Converting processes to multiplexers (muxs) and flip-flops.
+\item Removing undef signals from muxs.
+\item Hiding the signals that are not used.
+\item Explicit type conversion, by introducing slice and concat cells
+  in the circuit.
+\item Converting write memories to synchronuos memories, and
+  collecting the memories to multiport memories.
+\item Flattening the design to get only one module.
+\item Separating read and write memories.
+\item Splitting the signals that are partially assigned 
+\item Setting undef to zero value.
+\item Final optimization pass.
+\item Writing BTOR file.
+\end{enumerate}
+
+For detailed description of the commands mentioned above, please refer
+to documentation of Yosys~\cite{yosys}.
+
+The script presented earlier can be easily modified to have a BTOR
+file that does not contain memories. This is done by removing the line
+number~8 and 10, and introduces a new command {\tt memory} at line
+number~8.  Following is the modified yosys script file:
+
+\begin{figure}[H]
+\begin{lstlisting}[language=sh]
+read_verilog -sv $1; 
+hierarchy -top $3; hierarchy -libdir $DIR; 
+hierarchy -check; 
+proc; opt; 
+opt_const -mux_undef; opt;
+rename -hide;;;
+splice; opt;
+memory;;
+flatten;;
+splitnets -driver;
+setundef -zero -undriven;
+opt;;;
+write_btor $2;
+\end{lstlisting}
+ \renewcommand{\figurename}{Listing}
+\caption{Synthesis Flow for BTOR without memories}
+\label{btor_script_without_memory}
+\end{figure}
+
+\section{Example}
+
+Here is an example verilog design that we want to convert to BTOR:
+
+\begin{figure}[H]
+\begin{lstlisting}[language=Verilog]
+module array(input clk);
+reg [7:0] counter;
+reg [7:0] mem [7:0];
+always @(posedge clk) begin
+  counter <= counter + 8'd1;
+  mem[counter] <= counter;
+end
+assert property (!(counter > 8'd0) || 
+  mem[counter - 8'd1] == counter - 8'd1);
+endmodule
+\end{lstlisting}
+\renewcommand{\figurename}{Listing}
+\caption{Example - Verilog Design}
+\label{example_verilog}
+\end{figure}
+
+The generated BTOR file that contain memories, using the script shown
+in Listing~\ref{btor_script_memory}:
+\begin{figure}[H]
+\begin{lstlisting}[numbers=none]
+1 var 1 clk
+2 array 8 3
+3 var 8 $auto$rename.cc:150:execute$20
+4 const 8 00000001
+5 sub 8 3 4
+6 slice 3 5 2 0
+7 read 8 2 6
+8 slice 3 3 2 0
+9 add 8 3 4
+10 const 8 00000000
+11 ugt 1 3 10
+12 not 1 11
+13 const 8 11111111
+14 slice 1 13 0 0
+15 one 1
+16 eq 1 1 15
+17 and 1 16 14
+18 write 8 3 2 8 3
+19 acond 8 3 17 18 2
+20 anext 8 3 2 19
+21 eq 1 7 5
+22 or 1 12 21
+23 const 1 1
+24 one 1
+25 eq 1 23 24
+26 cond 1 25 22 24
+27 root 1 -26
+28 cond 8 1 9 3
+29 next 8 3 28
+\end{lstlisting}
+\renewcommand{\figurename}{Listing}
+\caption{Example - Converted BTOR with memory}
+\label{example_btor}
+\end{figure}
+
+Here is the BTOR file obtained by the script shown in
+Listing~\ref{btor_script_without_memory} which expands the memory
+into individual elements:
+\begin{figure}[H]
+\begin{lstlisting}[numbers=none]
+1 var 1 clk
+2 var 8 mem[0]
+3 var 8 $auto$rename.cc:150:execute$20
+4 slice 3 3 2 0
+5 slice 1 4 0 0
+6 not 1 5
+7 slice 1 4 1 1
+8 not 1 7
+9 slice 1 4 2 2
+10 not 1 9
+11 and 1 8 10
+12 and 1 6 11
+13 cond 8 12 3 2
+14 cond 8 1 13 2
+15 next 8 2 14
+16 const 8 00000001
+17 add 8 3 16
+18 const 8 00000000
+19 ugt 1 3 18
+20 not 1 19
+21 var 8 mem[2]
+22 and 1 7 10
+23 and 1 6 22
+24 cond 8 23 3 21
+25 cond 8 1 24 21
+26 next 8 21 25
+27 sub 8 3 16
+.
+.
+.
+54 cond 1 53 50 52
+55 root 1 -54
+.
+.
+.
+77 cond 8 76 3 44
+78 cond 8 1 77 44
+79 next 8 44 78
+\end{lstlisting}
+\renewcommand{\figurename}{Listing}
+\caption{Example - Converted BTOR without memory}
+\label{example_btor}
+\end{figure}
+
+\section{Limitations}
+
+BTOR does not support initialization of memories and registers are
+implicitly initialized to value zero, so the initial block for
+memories need to be removed when converting to BTOR. This should be
+also kept in consideration that BTOR does not handle multi-dimensional
+memories, and does not support {\tt x} or {\tt z} value of Verilog.
+
+
+\section{Conclusion}
+
+Using the described flow, we can use Yosys to generate word-level
+verification benchmarks with or without memories from Verilog design.
+
+\begin{thebibliography}{9}
+
+\bibitem{yosys}
+Clifford Wolf. The Yosys Open SYnthesis Suite. \\
+\url{http://www.clifford.at/yosys/}
+
+%\bibitem{bigsim}
+%yosys-bigsim, a collection of real-world Verilog designs for regression testing purposes. \\
+%\url{https://github.com/cliffordwolf/yosys-bigsim}
+
+%\bibitem{navre}
+%Sebastien Bourdeauducq. Navré AVR clone (8-bit RISC). \\
+%\url{http://opencores.org/project,navre}
+
+%\bibitem{amber}
+%Conor Santifort. Amber ARM-compatible core. \\
+%\url{http://opencores.org/project,amber}
+
+%\bibitem{ABC}
+%Berkeley Logic Synthesis and Verification Group. ABC: A System for Sequential Synthesis and Verification. \\
+%\url{http://www.eecs.berkeley.edu/~alanmi/abc/}
+
+\bibitem{boolector}
+Robert Brummayer and Armin Biere, Boolector: An Efficient SMT Solver for Bit-Vectors and Arrays\\
+\url{http://fmv.jku.at/boolector/}
+
+\bibitem{btor}
+Robert Brummayer and Armin Biere and Florian Lonsing, BTOR:
+Bit-Precise Modelling of Word-Level Problems for Model Checking\\
+\url{http://fmv.jku.at/papers/BrummayerBiereLonsing-BPR08.pdf}
+
+\bibitem{nuxmv} 
+Roberto Cavada and Alessandro Cimatti and Michele Dorigatti and
+Alberto Griggio and Alessandro Mariotti and Andrea Micheli and Sergio
+Mover and Marco Roveri and Stefano Tonetta, The nuXmv Symbolic Model
+Checker\\
+\url{https://es-static.fbk.eu/tools/nuxmv/index.php}
+
+\end{thebibliography}
+
+
+\end{document}
-- 
cgit v1.2.3

