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sby/docs/source/reference.rst
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.. role:: sby(code)
:language: sby
Reference for .sby file format
==============================
A ``.sby`` file consists of sections. Each section start with a single-line
section header in square brackets. The order of sections in a ``.sby`` file is
for the most part irrelevant, but by convention the usual order is
:sby:`[tasks]`, :sby:`[options]`, :sby:`[engines]`, :sby:`[script]`, and
:sby:`[files]`.
Tasks section
-------------
The optional :sby:`[tasks]` section can be used to configure multiple
verification tasks in a single ``.sby`` file. Each line in the :sby:`[tasks]`
section configures one task. For example:
.. code-block:: sby
[tasks]
task1 task_1_or_2 task_1_or_3
task2 task_1_or_2
task3 task_1_or_3
Each task can be assigned additional group aliases, such as ``task_1_or_2``
and ``task_1_or_3`` in the above example.
One or more tasks can be specified as additional command line arguments when
calling ``sby`` on a ``.sby`` file:
.. code-block:: text
sby example.sby task2
If no task is specified then all tasks in the :sby:`[tasks]` section are run.
After the :sby:`[tasks]` section individual lines can be specified for specific
tasks or task groups:
.. code-block:: sby
[options]
task_1_or_2: mode bmc
task_1_or_2: depth 100
task3: mode prove
If the tag ``<taskname>:`` is used on a line by itself then the conditional string
extends until the next conditional block or ``--`` on a line by itself.
.. code-block:: sby
[options]
task_1_or_2:
mode bmc
depth 100
task3:
mode prove
--
The tag ``~<taskname>:`` can be used for a line or block that should not be used when
the given task is active:
.. code-block:: sby
[options]
~task3:
mode bmc
depth 100
task3:
mode prove
--
The following example demonstrates how to configure safety and liveness checks for all
combinations of some host implementations A and B and device implementations X and Y:
.. code-block:: sby
[tasks]
prove_hAdX prove hostA deviceX
prove_hBdX prove hostB deviceX
prove_hAdY prove hostA deviceY
prove_hBdY prove hostB deviceY
live_hAdX live hostA deviceX
live_hBdX live hostB deviceX
live_hAdY live hostA deviceY
live_hBdY live hostB deviceY
[options]
prove: mode prove
live: mode live
[engines]
prove: abc pdr
live: aiger suprove
[script]
hostA: read -sv hostA.v
hostB: read -sv hostB.v
deviceX: read -sv deviceX.v
deviceY: read -sv deviceY.v
...
The :sby:`[tasks]` section must appear in the ``.sby`` file before the first
``<taskname>:`` or ``~<taskname>:`` tag.
The command ``sby --dumptasks <sby_file>`` prints the list of all tasks defined in
a given ``.sby`` file.
Options section
---------------
The :sby:`[options]` section contains lines with key-value pairs. The ``mode``
option is mandatory. The possible values for the ``mode`` option are:
========= ===========
Mode Description
========= ===========
``bmc`` Bounded model check to verify safety properties (``assert(...)`` statements)
``prove`` Unbounded model check to verify safety properties (``assert(...)`` statements)
``live`` Unbounded model check to verify liveness properties (``assert(s_eventually ...)`` statements)
``cover`` Generate set of shortest traces required to reach all cover() statements
========= ===========
..
``equiv`` Formal equivalence checking (usually to verify pre- and post-synthesis equivalence)
``synth`` Reactive Synthesis (synthesis of circuit from safety properties)
All other options have default values and thus are optional. The available
options are:
+-------------------+------------+---------------------------------------------------------+
| Option | Modes | Description |
+===================+============+=========================================================+
| ``expect`` | All | Expected result as comma-separated list of the tokens |
| | | ``pass``, ``fail``, ``unknown``, ``error``, and |
| | | ``timeout``. Unexpected results yield a nonzero return |
| | | code . Default: ``pass`` |
+-------------------+------------+---------------------------------------------------------+
| ``timeout`` | All | Timeout in seconds. Default: ``none`` (i.e. no timeout) |
+-------------------+------------+---------------------------------------------------------+
| ``multiclock`` | All | Create a model with multiple clocks and/or asynchronous |
| | | logic. Values: ``on``, ``off``. Default: ``off`` |
+-------------------+------------+---------------------------------------------------------+
| ``wait`` | All | Instead of terminating when the first engine returns, |
| | | wait for all engines to return and check for |
| | | consistency. Values: ``on``, ``off``. Default: ``off`` |
+-------------------+------------+---------------------------------------------------------+
| ``vcd`` | All | Write VCD traces for counter-example or cover traces. |
| | | Values: ``on``, ``off``. Default: ``on`` |
+-------------------+------------+---------------------------------------------------------+
| ``vcd_sim`` | All | When generating VCD traces, use Yosys's ``sim`` |
| | | command. Replaces the engine native VCD output. |
| | | Values: ``on``, ``off``. Default: ``off`` |
+-------------------+------------+---------------------------------------------------------+
| ``fst`` | All | Generate FST traces using Yosys's sim command. |
| | | Values: ``on``, ``off``. Default: ``off`` |
+-------------------+------------+---------------------------------------------------------+
| ``aigsmt`` | All | Which SMT2 solver to use for converting AIGER witnesses |
| | | to counter example traces. Use ``none`` to disable |
| | | conversion of AIGER witnesses. Default: ``yices`` |
+-------------------+------------+---------------------------------------------------------+
| ``tbtop`` | All | The top module for generated Verilog test benches, as |
| | | hierarchical path relative to the design top module. |
+-------------------+------------+---------------------------------------------------------+
| ``make_model`` | All | Force generation of the named formal models. Takes a |
| | | comma-separated list of model names. For a model |
| | | ``<name>`` this will generate the |
| | | ``model/design_<name>.*`` files within the working |
| | | directory, even when not required to run the task. |
+-------------------+------------+---------------------------------------------------------+
| ``smtc`` | ``bmc``, | Pass this ``.smtc`` file to the smtbmc engine. All |
| | ``prove``, | other engines are disabled when this option is used. |
| | ``cover`` | Default: None |
+-------------------+------------+---------------------------------------------------------+
| ``depth`` | ``bmc``, | Depth of the bounded model check. Only the specified |
| | ``cover`` | number of cycles are considered. Default: ``20`` |
| +------------+---------------------------------------------------------+
| | ``prove`` | Depth for the k-induction performed by the ``smtbmc`` |
| | | engine. Other engines ignore this option in ``prove`` |
| | | mode. Default: ``20`` |
+-------------------+------------+---------------------------------------------------------+
| ``skip`` | ``bmc``, | Skip the specified number of time steps. Only valid |
| | ``cover`` | with smtbmc engine. All other engines are disabled when |
| | | this option is used. Default: None |
+-------------------+------------+---------------------------------------------------------+
| ``append`` | ``bmc``, | When generating a counter-example trace, add the |
| | ``prove``, | specified number of cycles at the end of the trace. |
| | ``cover`` | Default: ``0`` |
+-------------------+------------+---------------------------------------------------------+
| ``append_assume`` | ``bmc``, | Uphold assumptions when appending cycles at the end of |
| | ``prove``, | the trace. Depending on the engine and options used |
| | ``cover`` | this may be implicitly on or not supported (as |
| | | indicated in SBY's log output). |
| | | Values: ``on``, ``off``. Default: ``on`` |
+-------------------+------------+---------------------------------------------------------+
| ``cover_assert`` | ``cover`` | Check for assertion properties during ``cover`` mode. |
| | | Values: ``on``, ``off``. Default: ``off`` |
+-------------------+------------+---------------------------------------------------------+
Cancelledby section
-------------------
At times it may be desirable for one task to be able to stop another task early,
such as when a ``prove`` task and a ``bmc`` task are testing the same properties
and the ``prove`` task finishes first, making the ``bmc`` task redundant. This
is where the optional ``[cancelledby]`` section comes in. Each line corresponds
to the name of a task which, if finished, will cancel the current task. No
distinction is made for whether the task finished successfully, only that
it is finished. Remember that tags can be used to control which tasks contain a
given configuration line.
Example:
.. code-block:: sby
[cancelledby]
task1:
task2
task3
task2:
task3
task4
In this example, ``task1`` can be cancelled by ``task2`` or ``task3``, while
``task2`` can be cancelled by ``task3`` or ``task4``. If ``task4`` is the first
to finish, then ``task2`` will be cancelled, which in turn leads to ``task1``
being cancelled. A task can only be cancelled if it has not yet finished, and
will check the finished tasks before starting and periodically while the
attached engines are running.
Normally, only the current taskloop is checked for finished tasks. This means
that intertask cancellations are not possible across separate SBY invocations or
when using the ``--sequential`` flag. By providing SBY with the
``--statuscancels`` flag however the status database will be used, allowing
tasks to be cancelled independently of taskloop. Note that this also means that
a task may be cancelled by a previous invocation unless ``--statusreset`` is
called first.
Example:
.. code-block:: shell
sby $sbyfile --statusreset
sby $sbyfile a b &
sby $sbyfile c d --statuscancels
In this example, the ``a`` and ``b`` tasks can only be cancelled by each other,
while the ``c`` and ``d`` tasks can be cancelled by any task.
Engines section
---------------
The ``[engines]`` section configures which engines should be used to solve the
given problem. Each line in the ``[engines]`` section specifies one engine. When
more than one engine is specified then the result returned by the first engine
to finish is used.
Each engine configuration consists of an engine name followed by engine options,
usually followed by a solver name and solver options.
Example:
.. code-block:: sby
[engines]
smtbmc --syn --nopresat z3 rewriter.cache_all=true opt.enable_sat=true
abc sim3 -W 15
In the first line ``smtbmc`` is the engine, ``--syn --nopresat`` are engine options,
``z3`` is the solver, and ``rewriter.cache_all=true opt.enable_sat=true`` are
solver options.
In the 2nd line ``abc`` is the engine, there are no engine options, ``sim3`` is the
solver, and ``-W 15`` are solver options.
The following mode/engine/solver combinations are currently supported:
+-----------+--------------------------+
| Mode | Engine |
+===========+==========================+
| ``bmc`` | ``smtbmc [all solvers]`` |
| | |
| | ``btor btormc`` |
| | |
| | ``btor pono`` |
| | |
| | ``abc bmc3`` |
| | |
| | ``abc sim3`` |
| | |
| | ``aiger aigbmc`` |
+-----------+--------------------------+
| ``prove`` | ``smtbmc [all solvers]`` |
| | |
| | ``abc pdr`` |
| | |
| | ``aiger avy`` |
| | |
| | ``aiger rIC3`` |
| | |
| | ``aiger suprove`` |
+-----------+--------------------------+
| ``cover`` | ``smtbmc [all solvers]`` |
| | |
| | ``btor btormc`` |
+-----------+--------------------------+
| ``live`` | ``aiger suprove`` |
+-----------+--------------------------+
``smtbmc`` engine
~~~~~~~~~~~~~~~~~
The ``smtbmc`` engine supports the ``bmc``, ``prove``, and ``cover`` modes and supports
the following options:
+------------------+---------------------------------------------------------+
| Option | Description |
+==================+=========================================================+
| ``--nomem`` | Don't use the SMT theory of arrays to model memories. |
| | Instead synthesize memories to registers and address |
| | logic. |
+------------------+---------------------------------------------------------+
| ``--syn`` | Synthesize the circuit to a gate-level representation |
| | instead of using word-level SMT operators. This also |
| | runs some low-level logic optimization on the circuit. |
+------------------+---------------------------------------------------------+
| ``--stbv`` | Use large bit vectors (instead of uninterpreted |
| | functions) to represent the circuit state. |
+------------------+---------------------------------------------------------+
| ``--stdt`` | Use SMT-LIB 2.6 datatypes to represent states. |
+------------------+---------------------------------------------------------+
| ``--nopresat`` | Do not run "presat" SMT queries that make sure that |
| | assumptions are non-conflicting (and potentially |
| | warmup the SMT solver). |
+------------------+---------------------------------------------------------+
| ``--keep-going`` | In BMC mode, continue after the first failed assertion |
| | and report further failed assertions. |
+------------------+---------------------------------------------------------+
| ``--unroll``, | Disable/enable unrolling of the SMT problem. The |
| ``--nounroll`` | default value depends on the solver being used. |
+------------------+---------------------------------------------------------+
| ``--dumpsmt2`` | Write the SMT2 trace to an additional output file. |
| | (Useful for benchmarking and troubleshooting.) |
+------------------+---------------------------------------------------------+
| ``--progress`` | Enable Yosys-SMTBMC timer display. |
+------------------+---------------------------------------------------------+
Any SMT2 solver that is compatible with ``yosys-smtbmc`` can be passed as
argument to the ``smtbmc`` engine. The solver options are passed to the solver
as additional command line options.
The following solvers are currently supported by ``yosys-smtbmc``:
* yices
* boolector
* bitwuzla
* z3
* mathsat
* cvc4
* cvc5
Any additional options after ``--`` are passed to ``yosys-smtbmc`` as-is.
``btor`` engine
~~~~~~~~~~~~~~~
The ``btor`` engine supports hardware modelcheckers that accept btor2 files.
The engine supports no engine options and supports the following solvers:
+-------------------------------+---------------------------------+
| Solver | Modes |
+===============================+=================================+
| ``btormc`` | ``bmc``, ``cover`` |
+-------------------------------+---------------------------------+
| ``pono`` | ``bmc`` |
+-------------------------------+---------------------------------+
Solver options are passed to the solver as additional command line options.
``aiger`` engine
~~~~~~~~~~~~~~~~
The ``aiger`` engine is a generic front-end for hardware modelcheckers that are capable
of processing AIGER files. The engine supports no engine options and supports the following
solvers:
+-------------------------------+---------------------------------+
| Solver | Modes |
+===============================+=================================+
| ``suprove`` | ``prove``, ``live`` |
+-------------------------------+---------------------------------+
| ``avy`` | ``prove`` |
+-------------------------------+---------------------------------+
| ``rIC3`` | ``prove`` |
+-------------------------------+---------------------------------+
| ``aigbmc`` | ``bmc`` |
+-------------------------------+---------------------------------+
Solver options are passed to the solver as additional command line options.
``abc`` engine
~~~~~~~~~~~~~~
The ``abc`` engine is a front-end for the functionality in Berkeley ABC. It
currently supports no engine options and supports the following
solvers:
+------------+-----------------+---------------------------------+
| Solver | Modes | ABC Command |
+============+=================+=================================+
| ``bmc3`` | ``bmc`` | ``bmc3 -F <depth> -v`` |
+------------+-----------------+---------------------------------+
| ``sim3`` | ``bmc`` | ``sim3 -F <depth> -v`` |
+------------+-----------------+---------------------------------+
| ``pdr`` | ``prove`` | ``pdr`` |
+------------+-----------------+---------------------------------+
Solver options are passed as additional arguments to the ABC command
implementing the solver.
``none`` engine
~~~~~~~~~~~~~~~
The ``none`` engine does not run any solver. It can be used together with the
``make_model`` option to manually generate any model supported by one of the
other engines. This makes it easier to use the same models outside of sby.
Script section
--------------
The :sby:`[script]` section contains the Yosys script that reads and elaborates
the design under test. For example, for a simple project contained in a single
design file ``mytest.sv`` with the top-module ``mytest``:
.. code-block:: sby
[script]
read -sv mytest.sv
prep -top mytest
Or explicitly using the Verific SystemVerilog parser (default for ``read -sv``
when Yosys is built with Verific support):
.. code-block:: sby
[script]
verific -sv mytest.sv
verific -import mytest
prep -top mytest
Or explicitly using the native Yosys Verilog parser (default for ``read -sv``
when Yosys is not built with Verific support):
.. code-block:: sby
[script]
read_verilog -sv mytest.sv
prep -top mytest
Run ``yosys`` in a terminal window and enter ``help`` on the Yosys prompt
for a command list. Run ``help <command>`` for a detailed description of the
command, for example ``help prep``.
Files section
-------------
The files section lists the source files for the proof, meaning all the
files Yosys will need to access when reading the design, including for
example data files for ``$readmemh`` and ``$readmemb``.
``sby`` copies these files to ``<outdir>/src/`` before running the Yosys
script. When the Yosys script is executed, it will use the copies in
``<outdir>/src/``. (Alternatively absolute filenames can be used in the
Yosys script for files not listed in the files section.)
For example:
.. code-block:: sby
[files]
top.sv
../common/defines.vh
/data/prj42/modules/foobar.sv
Will copy these files as ``top.v``, ``defines.vh``, and ``foobar.sv``
to ``<outdir>/src/``.
If the name of the file in ``<outdir>/src/`` should be different from the
basename of the specified file, then the new file name can be specified before
the source file name. For example:
.. code-block:: sby
[files]
top.sv
defines.vh ../common/defines_footest.vh
foo/bar.sv /data/prj42/modules/foobar.sv
File sections
-------------
File sections can be used to create additional files in ``<outdir>/src/`` from
the literal content of the :sby:`[file <filename>]` section ("here document").
For example:
.. code-block:: sby
[file params.vh]
`define RESET_LEN 42
`define FAULT_CYCLE 57
Pycode blocks
-------------
Blocks enclosed in ``--pycode-begin--`` and ``--pycode-end--`` lines are interpreted
as Python code. The function ``output(line)`` can be used to add configuration
file lines from the python code. The variable ``task`` contains the current task name,
if any, and ``None`` otherwise. The variable ``tags`` contains a set of all tags
associated with the current task.
.. code-block:: sby
[tasks]
--pycode-begin--
for uut in "rotate reflect".split():
for op in "SRL SRA SLL SRO SLO ROR ROL FSR FSL".split():
output("%s_%s %s %s" % (uut, op, uut, op))
--pycode-end--
...
[script]
--pycode-begin--
for op in "SRL SRA SLL SRO SLO ROR ROL FSR FSL".split():
if op in tags:
output("read -define %s" % op)
--pycode-end--
rotate: read -define UUT=shifter_rotate
reflect: read -define UUT=shifter_reflect
read -sv test.v
read -sv shifter_reflect.v
read -sv shifter_rotate.v
prep -top test
...
The command ``sby --dumpcfg <sby_file>`` can be used to print the configuration without
specialization for any particular task, and ``sby --dumpcfg <sby_file> <task_name>`` can
be used to print the configuration with specialization for a particular task.
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