Scripting in Yosys ------------------ On the previous page we went through a synthesis script, running each command in the interactive Yosys shell. On this page, we will be introducing the script file format and how you can make your own synthesis scripts. Yosys script files typically use the :file:`.ys` extension and contain a set of commands for Yosys to run sequentially. These commands are the same ones we were using on the previous page like `read_verilog` and `hierarchy`. Script parsing ~~~~~~~~~~~~~~ As with the interactive shell, each command consists of the command name, and an optional whitespace separated list of arguments. Commands are terminated with the newline character, and anything after a hash sign ``#`` is a comment (i.e. it is ignored). It is also possible to terminate commands with a semicolon ``;``. This is particularly useful in conjunction with the ``-p `` command line option, where ```` can be a string with multiple commands separated by semicolon. In-line comments can also be made with the colon ``:``, where the end of the comment is a semicolon ``;`` or a new line. .. code-block:: :caption: Using the ``-p`` option $ yosys -p "read_verilog fifo.v; :this is a comment; prep" .. warning:: The space after the semicolon is required for correct parsing. ``log a;log b;`` for example will display ``a;log b`` instead of ``a`` and ``b`` as might be expected. Another special character that can be used in Yosys scripts is the bang ``!``. Anything after the bang will be executed as a shell command. This can only be terminated with a new line. Any semicolons, hashes, or other special characters will be passed to the shell. If an error code is returned from the shell it will be raised by Yosys. `exec` provides a much more flexible way of executing commands, allowing the output to be logged and more control over when to generate errors. The synthesis starter script ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. role:: yoscrypt(code) :language: yoscrypt All of the images and console output used in :doc:`/getting_started/example_synth` were generated by Yosys, using Yosys script files found in :file:`docs/source/code_examples/fifo`. If you haven't already, let's take a look at some of those script files now. .. literalinclude:: /code_examples/fifo/fifo.ys :language: yoscrypt :lineno-match: :start-at: echo on :end-before: design -reset :caption: A section of :file:`fifo.ys`, generating the images used for :ref:`addr_gen_example` :name: fifo-ys The first command there, :yoscrypt:`echo on`, uses `echo` to enable command echoes on. This is how we generated the code listing for :ref:`hierarchy_output`. Turning command echoes on prints the ``yosys> hierarchy -top addr_gen`` line, making the output look the same as if it were an interactive terminal. :yoscrypt:`hierarchy -top addr_gen` is of course the command we were demonstrating, including the output text and an image of the design schematic after running it. We briefly touched on `select` when it came up in `synth_ice40`, but let's look at it more now. .. _select_intro: Selections intro ^^^^^^^^^^^^^^^^ The `select` command is used to modify and view the list of selected objects: .. literalinclude:: /code_examples/fifo/fifo.out :language: doscon :start-at: yosys> select :end-before: yosys> show When we call :yoscrypt:`select -module addr_gen` we are changing the currently active selection from the whole design, to just the ``addr_gen`` module. Notice how this changes the ``yosys`` at the start of each command to ``yosys [addr_gen]``? This indicates that any commands we run at this point will *only* operate on the ``addr_gen`` module. When we then call :yoscrypt:`select -list` we get a list of all objects in the ``addr_gen`` module, including the module itself, as well as all of the wires, inputs, outputs, processes, and cells. Next we perform another selection, :yoscrypt:`select t:*`. The ``t:`` part signifies we are matching on the *cell type*, and the ``*`` means to match anything. For this (very simple) selection, we are trying to find all of the cells, regardless of their type. The active selection is now shown as ``[addr_gen]*``, indicating some sub-selection of the ``addr_gen`` module. This gives us the `$add` and `$eq` cells, which we want to highlight for the :ref:`addr_gen_hier` image. .. _select_new_cells: We can assign a name to a selection with :yoscrypt:`select -set`. In our case we are using the name ``new_cells``, and telling it to use the current selection, indicated by the ``%`` symbol. We can then use this named selection by referring to it as ``@new_cells``, which we will see later. Then we clear the selection so that the following commands can operate on the full design. While we split that out for this document, we could have done the same thing in a single line by calling :yoscrypt:`select -set new_cells addr_gen/t:*`. If we know we only have the one module in our design, we can even skip the ``addr_gen/`` part. Looking further down :ref:`the fifo.ys code ` we can see this with :yoscrypt:`select -set new_cells t:$mux t:*dff`. We can also see in that command that selections don't have to be limited to a single statement. Many commands also support an optional ``[selection]`` argument which can be used to override the currently selected objects. We could, for example, call :yoscrypt:`clean addr_gen` to have `clean` operate on *just* the ``addr_gen`` module. Detailed documentation of the select framework can be found under :doc:`/using_yosys/more_scripting/selections` or in the command reference at :doc:`/cmd/select`. .. _show_intro: Displaying schematics ^^^^^^^^^^^^^^^^^^^^^ While the `select` command is very useful, sometimes nothing beats being able to see a design for yourself. This is where `show` comes in. Note that this document is just an introduction to the `show` command, only covering the basics. For more information, including a guide on what the different symbols represent, see :ref:`interactive_show` and the :doc:`/using_yosys/more_scripting/interactive_investigation` page. .. figure:: /_images/code_examples/fifo/addr_gen_show.* :class: width-helper invert-helper :name: addr_gen_show Calling :yoscrypt:`show addr_gen` after `hierarchy` .. note:: The `show` command requires a working installation of `GraphViz`_ and `xdot`_ for displaying the actual circuit diagrams. .. _GraphViz: http://www.graphviz.org/ .. _xdot: https://github.com/jrfonseca/xdot.py This is the first :yoscrypt:`show` command we called in :file:`fifo.ys`, :ref:`as we saw above `. If we look at the log output for this image we see the following: .. literalinclude:: /code_examples/fifo/fifo.out :language: doscon :start-at: -prefix addr_gen_show :end-before: yosys> show Calling `show` with :yoscrypt:`-format dot` tells it we want to output a :file:`.dot` file rather than opening it for display. The :yoscrypt:`-prefix addr_gen_show` option indicates we want the file to be called :file:`addr_gen_show.{*}`. Remember, we do this in :file:`fifo.ys` because we need to store the image for displaying in the documentation you're reading. But if you just want to display the images locally you can skip these two options. The ``-format`` option internally calls the ``dot`` command line program from GraphViz to convert to formats other than :file:`.dot`. Check `GraphViz output docs`_ for more on available formats. .. _GraphViz output docs: https://graphviz.org/docs/outputs/ .. note:: If you are using a POSIX based version of Yosys (such as for Mac or Linux), xdot will be opened in the background and Yosys can continue to be used. If it it still open, future calls to :yoscrypt:`show` will use the same xdot instance. The ``addr_gen`` at the end tells it we only want the ``addr_gen`` module, just like when we called :yoscrypt:`select -module addr_gen` in :ref:`select_intro`. That last parameter doesn't have to be a module name, it can be any valid selection string. Remember when we :ref:`assigned a name to a selection` and called it ``new_cells``? We saw in the :yoscrypt:`select -list` output that it contained two cells, an `$add` and an `$eq`. We can call `show` on that selection just as easily: .. figure:: /_images/code_examples/fifo/new_cells_show.* :class: width-helper invert-helper :name: new_cells_show Calling :yoscrypt:`show -notitle @new_cells` We could have gotten the same output with :yoscrypt:`show -notitle t:$add t:$eq` if we didn't have the named selection. By adding the :yoscrypt:`-notitle` flag there we can also get rid of the ``addr_gen`` title that would have been automatically added. The last two images were both added for this introduction. The next image is the first one we saw in :doc:`/getting_started/example_synth`: showing the full ``addr_gen`` module while also highlighting ``@new_cells`` and the two ``PROC`` blocks. To achieve this highlight, we make use of the :yoscrypt:`-color` option: .. figure:: /_images/code_examples/fifo/addr_gen_hier.* :class: width-helper invert-helper Calling :yoscrypt:`show -color maroon3 @new_cells -color cornflowerblue p:* -notitle` As described in the the `help` output for `show` (or by clicking on the `show` link), colors are specified as :yoscrypt:`-color `. Color names for the ```` portion can be found on the `GraphViz color docs`_. Unlike the final `show` parameter which can have be any selection string, the ```` part must be a single selection expression or named selection. That means while we can use ``@new_cells``, we couldn't use ``t:$eq t:$add``. In general, if a command lists ``[selection]`` as its final parameter it can be any selection string. Any selections that are not the final parameter, such as those used in options, must be a single expression instead. .. _GraphViz color docs: https://graphviz.org/doc/info/colors For all of the options available to `show`, check the command reference at :doc:`/cmd/show`. .. seealso:: :ref:`interactive_show` on the :doc:`/using_yosys/more_scripting/interactive_investigation` page.