1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
|
\section{Yosys by example -- Beyond Synthesis}
\begin{frame}
\sectionpage
\end{frame}
\begin{frame}{Overview}
This section contains 2 subsections:
\begin{itemize}
\item Interactive Design Investigation
\item Symbolic Model Checking
\end{itemize}
\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Interactive Design Investigation}
\begin{frame}
\subsectionpage
\subsectionpagesuffix
\end{frame}
\begin{frame}{\subsecname}
Yosys can also be used to investigate designs (or netlists created
from other tools).
\begin{itemize}
\item
The selection mechanism (see slides ``Using Selections''), especially patterns such
as {\tt \%ci} and {\tt \%co}, can be used to figure out how parts of the design
are connected.
\item
Commands such as {\tt submod}, {\tt expose}, {\tt splice}, \dots can be used
to transform the design into an equivalent design that is easier to analyse.
\item
Commands such as {\tt eval} and {\tt sat} can be used to investigate the
behavior of the circuit.
\end{itemize}
\end{frame}
\begin{frame}[t, fragile]{Example: Reorganizing a module}
\begin{columns}
\column[t]{4cm}
\lstinputlisting[basicstyle=\ttfamily\fontsize{6pt}{7pt}\selectfont, language=verilog]{PRESENTATION_ExOth/scrambler.v}
\column[t]{7cm}
\begin{lstlisting}[basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont, language=ys, frame=single]
read_verilog scrambler.v
hierarchy; proc;;
cd scrambler
submod -name xorshift32 \
xs %c %ci %D %c %ci:+[D] %D \
%ci*:-$dff xs %co %ci %d
\end{lstlisting}
\end{columns}
\hfil\includegraphics[width=11cm,trim=0 0cm 0 1.5cm]{PRESENTATION_ExOth/scrambler_p01.pdf}
\hfil\includegraphics[width=11cm,trim=0 0cm 0 2cm]{PRESENTATION_ExOth/scrambler_p02.pdf}
\end{frame}
\begin{frame}[t, fragile]{Example: Analysis of circuit behavior}
\begin{lstlisting}[basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont, language=ys]
> read_verilog scrambler.v
> hierarchy; proc;; cd scrambler
> submod -name xorshift32 xs %c %ci %D %c %ci:+[D] %D %ci*:-$dff xs %co %ci %d
> cd xorshift32
> rename n2 in
> rename n1 out
> eval -set in 1 -show out
Eval result: \out = 270369.
> eval -set in 270369 -show out
Eval result: \out = 67634689.
> sat -set out 632435482
Signal Name Dec Hex Bin
-------------------- ---------- ---------- -------------------------------------
\in 745495504 2c6f5bd0 00101100011011110101101111010000
\out 632435482 25b2331a 00100101101100100011001100011010
\end{lstlisting}
\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Symbolic Model Checking}
\begin{frame}
\subsectionpage
\subsectionpagesuffix
\end{frame}
\begin{frame}{\subsecname}
Symbolic Model Checking (SMC) is used to formally prove that a circuit has
(or has not) a given property.
\bigskip
One application is Formal Equivalence Checking: Proving that two circuits
are identical. For example this is a very useful feature when debugging custom
passes in Yosys.
\bigskip
Other applications include checking if a module conforms to interface
standards.
\bigskip
The {\tt sat} command in Yosys can be used to perform Symbolic Model Checking.
\end{frame}
\begin{frame}[t]{Example: Formal Equivalence Checking (1/2)}
Remember the following example?
\vskip1em
\vbox to 0cm{
\vskip-0.3cm
\lstinputlisting[basicstyle=\ttfamily\fontsize{6pt}{7pt}\selectfont, language=verilog]{PRESENTATION_ExSyn/techmap_01_map.v}
}\vbox to 0cm{
\vskip-0.5cm
\lstinputlisting[xleftmargin=5cm, basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont, frame=single, language=verilog]{PRESENTATION_ExSyn/techmap_01.v}
\lstinputlisting[xleftmargin=5cm, basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont, language=ys, frame=single]{PRESENTATION_ExSyn/techmap_01.ys}}
\vskip5cm\hskip5cm
Lets see if it is correct..
\end{frame}
\begin{frame}[t, fragile]{Example: Formal Equivalence Checking (2/2)}
\begin{lstlisting}[basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont, language=ys, frame=single]
# read test design
read_verilog techmap_01.v
hierarchy -top test
# create two version of the design: test_orig and test_mapped
copy test test_orig
rename test test_mapped
# apply the techmap only to test_mapped
techmap -map techmap_01_map.v test_mapped
# create a miter circuit to test equivalence
miter -equiv -make_assert -make_outputs test_orig test_mapped miter
flatten miter
# run equivalence check
sat -verify -prove-asserts -show-inputs -show-outputs miter
\end{lstlisting}
\dots
\begin{lstlisting}[basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont]
Solving problem with 945 variables and 2505 clauses..
SAT proof finished - no model found: SUCCESS!
\end{lstlisting}
\end{frame}
\begin{frame}[t, fragile]{Example: Symbolic Model Checking (1/2)}
\small
The following AXI4 Stream Master has a bug. But the bug is not exposed if the
slave keeps {\tt tready} asserted all the time. (Something a test bench might do.)
\medskip
Symbolic Model Checking can be used to expose the bug and find a sequence
of values for {\tt tready} that yield the incorrect behavior.
\vskip-1em
\begin{columns}
\column[t]{5cm}
\lstinputlisting[basicstyle=\ttfamily\fontsize{5pt}{6pt}\selectfont, language=verilog]{PRESENTATION_ExOth/axis_master.v}
\column[t]{5cm}
\lstinputlisting[basicstyle=\ttfamily\fontsize{5pt}{6pt}\selectfont, language=verilog]{PRESENTATION_ExOth/axis_test.v}
\end{columns}
\end{frame}
\begin{frame}[t, fragile]{Example: Symbolic Model Checking (2/2)}
\begin{lstlisting}[basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont, language=ys, frame=single]
read_verilog -sv axis_master.v axis_test.v
hierarchy -top axis_test
proc; flatten;;
sat -seq 50 -prove-asserts
\end{lstlisting}
\bigskip
\dots with unmodified {\tt axis\_master.v}:
\begin{lstlisting}[basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont]
Solving problem with 159344 variables and 442126 clauses..
SAT proof finished - model found: FAIL!
\end{lstlisting}
\bigskip
\dots with fixed {\tt axis\_master.v}:
\begin{lstlisting}[basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont]
Solving problem with 159144 variables and 441626 clauses..
SAT proof finished - no model found: SUCCESS!
\end{lstlisting}
\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Summary}
\begin{frame}{\subsecname}
\begin{itemize}
\item Yosys provides useful features beyond synthesis.
\item The commands {\tt sat} and {\tt eval} can be used to analyse the behavior of a circuit.
\item The {\tt sat} command can also be used for symbolic model checking.
\item This can be useful for debugging and testing designs and Yosys extensions alike.
\end{itemize}
\bigskip
\bigskip
\begin{center}
Questions?
\end{center}
\bigskip
\bigskip
\begin{center}
\url{http://www.clifford.at/yosys/}
\end{center}
\end{frame}
|
