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https://github.com/YosysHQ/mcy

Mutation Cover with Yosys (MCY)
https://github.com/YosysHQ/mcy

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Mutation Cover with Yosys (MCY)

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README 

        
# Mutation Cover with Yosys



MCY is a new tool to help digital designers and project managers understand and improve testbench coverage.



*If you have a testbench, and it fails, you know you have a problem. But if it passes, you know nothing if you don’t know what your testbench is actually testing for.*



![MCY Overview Diagram](https://github.com/YosysHQ/mcy/raw/main/docs/images/mcy.png)



Given a self checking testbench, MCY generates 1000s of mutations by modifying individual signals in a post synthesis netlist. These mutations are then filtered using Formal Verification techniques, keeping only those that can cause an important change in the design’s output.



All mutated designs are run against the testbench to check that the testbench will detect and fail for a relevant mutation. The testbench can then be improved to get 100% complete coverage.



`mcy gui` can be used to explore the results and find where coverage needs improvement.



![MCY GUI Screenshot](https://github.com/YosysHQ/mcy/raw/main/docs/images/mcy-gui.png)



`mcy dash` provides at a glance overview as the tool runs. It is browser-based to easily take advantage of cloud compute.



![MCY Dash Screenshot](https://github.com/YosysHQ/mcy/raw/main/docs/images/mcy-dash.png)



**For more information please contact [email protected]**



## Getting Started

### Installing Tabby CAD Suite or OSS CAD Suite



MCY is part of the [Tabby CAD Suite](https://www.yosyshq.com/tabby-cad-datasheet) and the [OSS CAD Suite](https://github.com/YosysHQ/oss-cad-suite-build)! The easiest way to use MCY is to install the binary software suite, which contains all required dependencies.



* [Contact YosysHQ](https://www.yosyshq.com/contact) for a [Tabby CAD Suite](https://www.yosyshq.com/tabby-cad-datasheet) Evaluation License and download link

* OR go to https://github.com/YosysHQ/oss-cad-suite-build/releases to download the free OSS CAD Suite

* Follow the [Install Instructions on GitHub](https://github.com/YosysHQ/oss-cad-suite-build#installation)



Make sure to get a Tabby CAD Suite Evaluation License if you need features such as industry-grade SystemVerilog and VHDL parsers!



For more information about the difference between Tabby CAD Suite and the OSS CAD Suite, please visit https://www.yosyshq.com/tabby-cad-datasheet.



### Installing from Source



Install [SBY](http://symbiyosys.readthedocs.io/) and its dependencies first.



Install MCY:



```

sudo make install

```



Install requirements:



```

pip install click flask

```



Run an example project (may run for a while):



```

cd examples/bitcnt

mcy init

mcy run -j8

```



The examples additionally require Icarus Verilog (https://github.com/steveicarus/iverilog) to run the testbench under test.



## Documentation



The full MCY documentation can be found at https://mcy.readthedocs.io/.



See also [YosysHQ AppNote 400: Introduction to Mutation Coverage with Yosys (MCY)](https://yosyshq.readthedocs.io/projects/ap400/en/latest/)



## Short Tutorial



Create a new directory with a `config.mcy` file. For example:



```

[options]

size 100



[script]

read_verilog verilog/picorv32.v

prep -top picorv32



[files]

picorv32.v



[logic]

if result("sim_simple") == "FAIL":

    tag("COVERED")

    return



if result("eq_sim3 10") == "FAIL":

    tag("UNCOVERED")

    return



if result("eq_bmc") == "FAIL":

    tag("UNCOVERED")

    return



if result("eq_sim3 500") == "FAIL":

    tag("UNCOVERED")

    return



tag("NOC")



[report]

if tags("!NOC"):

    print("Coverage: %.2f%%" % (100.0*tags("COVERED")/tags("!NOC")))



[test sim_simple]

maxbatchsize 10

expect PASS FAIL

run bash $PRJDIR/scripts/sim_simple.sh



[test eq_bmc]

maxbatchsize 10

expect PASS FAIL

run bash $PRJDIR/scripts/eq_bmc.sh



[test eq_sim3]

maxbatchsize 10

expect TIMEOUT FAIL

run bash $PRJDIR/scripts/eq_sim3.sh

```



Create the referenced files and run `mcy init`.



This will create a `database/` directory, run the Yosys script and create

`database/design.il`, create `size` mutations and store them in `database/db.sqlite3`.



Running `mcy reset` re-runs the `[logic]` section for all mutations, imports

additional mutations if the value of the `size` option has been increased,

resets the "running" status of all tests, removes the `tasks/` directory, and

prints some statistics.



Running `mcy status` prints the statistics from `mcy reset` but will

not make any changes to the database.



Running `mcy list` will list all mutations and their current tags.



Running `mcy list --details` will print more details for each mutation.



Running `mcy run -j8` will run the mutation cover analysis, with a maximum

of 8 concurently running jobs.



Running `mcy task [-v] [-k]  ..` will (re-)run the specified

test with the given mutations. This is mostly used during development of test

scripts. `-v` displays the command and its output on the console, and with `-k`

the task directory `tasks/` will not be removed when the task

completes.



Running `mcy source ` prints the original HDL source, annotated with

coverage information. (This is hardcoded to use the tags `COVERED` and

`UNCOVERED`.) This is using the copy of the specified source file that was

placed in the database on `mcy init`. (This requires a `[files]` corresponding

entry in the config file.) Use `mcy source  `

to use a source file from the file system instead.



Running `mcy dash` launches a web-based dashboard that can be used to launch

jobs and monitor progress.



Running `mcy gui` launches a GUI application that can be used to investigate

the database.



Finally, `mcy purge` removes the `database/` and `tasks/` directories.



### Logic



The `[logic]` section contains python code that defines how MCY should

run the individual tests. The following special functions are available:



`tag(tagname)`: Mark the current mutation with the specified tag



`result(test_with_args)`: Run the specified test and return the

result, or use a cached result if the test had been run previously.



`rng(N)`: Return a deterministic pseudo-random integer in the range 0..N-1.



### Report



The `[report]` section contains python code for printing a report based

on the data collect via the tagging mechanism described above.



`tags()` returns the total number of mutations that have any tag assigned

to them.



`tags("FOO")` returns the number of mutations that have the tag `FOO` assigned.



`tags("!FOO")` returns the number of mutations that have at least one tag

assigned, but not the `FOO` tag.



### Tests



Each test has its own configuration file section, `[test testname]`.



If `maxbatchsize` is set to a value > 1 then MCY will automatically create

batches of up to the specified number of mutations, and then pass them all

to a single invocation of the test. (The default `maxbatchsize` value is `1`.)



Running the test means running the command specified with `run`, with any

additional arguments to the test appended to the command.



The command is run in the `tasks/` subdirectory, with the environment

variable `TASK` set to the task id, `TASKDIR` set to the directory, and `PRJDIR`

set to the project directory.



The environment variable `KEEPDIR` will be set to `1` if the task is run with

`mcy task -k`, and `0` otherwise. This can be used for example to only create

VCD traces if the task directory is kept.



The command is then given an input in `input.txt`, formatted as following:



```

1 

2 

3 

...

```



And it will procude an output in `output.txt`, formatted as following:



```

1 

2 

3 

...

```



The numbers are not mutation IDs but a task-local numbering, starting fresh

at 1 for each task. The order of the output lines does not matter.



The environment variable `MUTATIONS` contains the list of mutation IDs for the

task. This is mostly useful for debug purposes. Ideally a test should not

need to know the mutation IDs of the mutations it tests.



Standard output of the command will be redirected to `logfile.txt`, unless

the command is run from `mcy task -v`. Standard error always stays connected

to the console.



A test with `expect` setting will cause a runtime error if the test returns

anything else than one of the expected values.