Selections ---------- .. role:: yoscrypt(code) :language: yoscrypt The selection framework ~~~~~~~~~~~~~~~~~~~~~~~ The :cmd:ref:`select` command can be used to create a selection for subsequent commands. For example: .. code:: yoscrypt select foobar # select the module foobar delete # delete selected objects Normally the :cmd:ref:`select` command overwrites a previous selection. The commands :yoscrypt:`select -add` and :yoscrypt:`select -del` can be used to add or remove objects from the current selection. The command :yoscrypt:`select -clear` can be used to reset the selection to the default, which is a complete selection of everything in the current module. This selection framework can also be used directly in many other commands. Whenever a command has ``[selection]`` as last argument in its usage help, this means that it will use the engine behind the :cmd:ref:`select` command to evaluate additional arguments and use the resulting selection instead of the selection created by the last :cmd:ref:`select` command. For example, the command :cmd:ref:`delete` will delete everything in the current selection; while :yoscrypt:`delete foobar` will only delete the module foobar. If no :cmd:ref:`select` command has been made, then the "current selection" will be the whole design. .. note:: Many of the examples on this page make use of the :cmd:ref:`show` command to visually demonstrate the effect of selections. For a more detailed look at this command, refer to :ref:`interactive_show`. How to make a selection ~~~~~~~~~~~~~~~~~~~~~~~ Selection by object name ^^^^^^^^^^^^^^^^^^^^^^^^ The easiest way to select objects is by object name. This is usually only done in synthesis scripts that are hand-tailored for a specific design. .. code:: yoscrypt select foobar # select module foobar select foo* # select all modules whose names start with foo select foo*/bar* # select all objects matching bar* from modules matching foo* select */clk # select objects named clk from all modules Module and design context ^^^^^^^^^^^^^^^^^^^^^^^^^ Commands can be executed in *module/* or *design/* context. Until now all commands have been executed in design context. The :cmd:ref:`cd` command can be used to switch to module context. In module context, all commands only effect the active module. Objects in the module are selected without the ``/`` prefix. For example: .. code:: yoscrypt cd foo # switch to module foo delete bar # delete object foo/bar cd mycpu # switch to module mycpu dump reg_* # print details on all objects whose names start with reg_ cd .. # switch back to design Note: Most synthesis scripts never switch to module context. But it is a very powerful tool which we explore more in :doc:`/using_yosys/more_scripting/interactive_investigation`. Selecting by object property or type ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Special patterns can be used to select by object property or type. For example: - select all wires whose names start with ``reg_``: :yoscrypt:`select w:reg_*` - select all objects with the attribute ``foobar`` set: :yoscrypt:`select a:foobar` - select all objects with the attribute ``foobar`` set to 42: :yoscrypt:`select a:foobar=42` - select all modules with the attribute ``blabla`` set: :yoscrypt:`select A:blabla` - select all $add cells from the module foo: :yoscrypt:`select foo/t:$add` A complete list of pattern expressions can be found in :doc:`/cmd/select`. Operations on selections ~~~~~~~~~~~~~~~~~~~~~~~~ Combining selections ^^^^^^^^^^^^^^^^^^^^ The :cmd:ref:`select` command is actually much more powerful than it might seem at first glance. When it is called with multiple arguments, each argument is evaluated and pushed separately on a stack. After all arguments have been processed it simply creates the union of all elements on the stack. So :yoscrypt:`select t:$add a:foo` will select all ``$add`` cells and all objects with the ``foo`` attribute set: .. literalinclude:: /code_examples/selections/foobaraddsub.v :caption: Test module for operations on selections :name: foobaraddsub :language: verilog .. code-block:: :caption: Output for command ``select t:$add a:foo -list`` on :numref:`foobaraddsub` yosys> select t:$add a:foo -list foobaraddsub/$add$foobaraddsub.v:6$3 foobaraddsub/$sub$foobaraddsub.v:5$2 foobaraddsub/$add$foobaraddsub.v:4$1 In many cases simply adding more and more stuff to the selection is an ineffective way of selecting the interesting part of the design. Special arguments can be used to combine the elements on the stack. For example the ``%i`` arguments pops the last two elements from the stack, intersects them, and pushes the result back on the stack. So :yoscrypt:`select t:$add a:foo %i` will select all ``$add`` cells that have the ``foo`` attribute set: .. code-block:: :caption: Output for command ``select t:$add a:foo %i -list`` on :numref:`foobaraddsub` yosys> select t:$add a:foo %i -list foobaraddsub/$add$foobaraddsub.v:4$1 Some of the special ``%``-codes: - ``%u``: union of top two elements on stack -- pop 2, push 1 - ``%d``: difference of top two elements on stack -- pop 2, push 1 - ``%i``: intersection of top two elements on stack -- pop 2, push 1 - ``%n``: inverse of top element on stack -- pop 1, push 1 See :doc:`/cmd/select` for the full list. Expanding selections ^^^^^^^^^^^^^^^^^^^^ The listing in :numref:`sumprod` uses the Yosys non-standard ``{... *}`` syntax to set the attribute ``sumstuff`` on all cells generated by the first assign statement. (This works on arbitrary large blocks of Verilog code an can be used to mark portions of code for analysis.) .. literalinclude:: /code_examples/selections/sumprod.v :caption: Another test module for operations on selections :name: sumprod :language: verilog Selecting ``a:sumstuff`` in this module will yield the following circuit diagram: .. figure:: /_images/code_examples/selections/sumprod_00.* :class: width-helper :name: sumprod_00 Output of ``show a:sumstuff`` on :numref:`sumprod` As only the cells themselves are selected, but not the temporary wire ``$1_Y``, the two adders are shown as two disjunct parts. This can be very useful for global signals like clock and reset signals: just unselect them using a command such as :yoscrypt:`select -del clk rst` and each cell using them will get its own net label. In this case however we would like to see the cells connected properly. This can be achieved using the ``%x`` action, that broadens the selection, i.e. for each selected wire it selects all cells connected to the wire and vice versa. So :yoscrypt:`show a:sumstuff %x` yields the diagram shown in :numref:`sumprod_01`: .. figure:: /_images/code_examples/selections/sumprod_01.* :class: width-helper :name: sumprod_01 Output of ``show a:sumstuff %x`` on :numref:`sumprod` .. _selecting_logic_cones: Selecting logic cones ^^^^^^^^^^^^^^^^^^^^^ :numref:`sumprod_01` shows what is called the ``input cone`` of ``sum``, i.e. all cells and signals that are used to generate the signal ``sum``. The ``%ci`` action can be used to select the input cones of all object in the top selection in the stack maintained by the :cmd:ref:`select` command. As with the ``%x`` action, these commands broaden the selection by one "step". But this time the operation only works against the direction of data flow. That means, wires only select cells via output ports and cells only select wires via input ports. The following sequence of diagrams demonstrates this step-wise expansion: .. figure:: /_images/code_examples/selections/sumprod_02.* :class: width-helper Output of ``show prod`` on :numref:`sumprod` .. figure:: /_images/code_examples/selections/sumprod_03.* :class: width-helper Output of ``show prod %ci`` on :numref:`sumprod` .. figure:: /_images/code_examples/selections/sumprod_04.* :class: width-helper Output of ``show prod %ci %ci`` on :numref:`sumprod` .. figure:: /_images/code_examples/selections/sumprod_05.* :class: width-helper Output of ``show prod %ci %ci %ci`` on :numref:`sumprod` When selecting many levels of logic, repeating ``%ci`` over and over again can be a bit dull. So there is a shortcut for that: the number of iterations can be appended to the action. So for example the action ``%ci3`` is identical to performing the ``%ci`` action three times. The action ``%ci*`` performs the ``%ci`` action over and over again until it has no effect anymore. .. _advanced_logic_cones: Advanced logic cone selection ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ In most cases there are certain cell types and/or ports that should not be considered for the ``%ci`` action, or we only want to follow certain cell types and/or ports. This can be achieved using additional patterns that can be appended to the ``%ci`` action. Lets consider :numref:`memdemo_src`. It serves no purpose other than being a non-trivial circuit for demonstrating some of the advanced Yosys features. This code is available in ``docs/source/code_examples/selections`` of the Yosys source repository. .. literalinclude:: /code_examples/selections/memdemo.v :caption: ``memdemo.v`` :name: memdemo_src :language: verilog The script ``memdemo.ys`` is used to generate the images included here. Let's look at the first section: .. literalinclude:: /code_examples/selections/memdemo.ys :caption: Synthesizing :ref:`memdemo_src` :name: memdemo_ys :language: yoscrypt :end-at: opt This loads :numref:`memdemo_src` and synthesizes the included module. Note that this code can be copied and run directly in a Yosys command line session, provided ``memdemo.v`` is in the same directory. We can now change to the ``memdemo`` module with ``cd memdemo``, and call :cmd:ref:`show` to see the diagram in :numref:`memdemo_00`. .. figure:: /_images/code_examples/selections/memdemo_00.* :class: width-helper :name: memdemo_00 Complete circuit diagram for the design shown in :numref:`memdemo_src` .. TODO:: :ref:`memdemo_01` and :ref:`memdemo_02` are the same, probably change the example so they aren't. There's a lot going on there, but maybe we are only interested in the tree of multiplexers that select the output value. Let's start by just showing the output signal, ``y``, and its immediate predecessors. Remember `Selecting logic cones`_ from above, we can use :yoscrypt:`show y %ci2`: .. figure:: /_images/code_examples/selections/memdemo_01.* :class: width-helper :name: memdemo_01 Output of :yoscrypt:`show y %ci2` From this we would learn that ``y`` is driven by a ``$dff cell``, that ``y`` is connected to the output port ``Q``, that the ``clk`` signal goes into the ``CLK`` input port of the cell, and that the data comes from a auto-generated wire into the input ``D`` of the flip-flop cell. As we are not interested in the clock signal we add an additional pattern to the ``%ci`` action :yoscrypt:`show y %ci2:+$dff[Q,D]`, that tells it to only follow ports ``Q`` and ``D`` of ``$dff`` cells: .. figure:: /_images/code_examples/selections/memdemo_02.* :class: width-helper :name: memdemo_02 Output of :yoscrypt:`show y %ci2:+$dff[Q,D]` To add a pattern we add a colon followed by the pattern to the ``%ci`` action. The pattern itself starts with ``-`` or ``+``, indicating if it is an include or exclude pattern, followed by an optional comma separated list of cell types, followed by an optional comma separated list of port names in square brackets. Since we know that the only cell considered in this case is a ``$dff`` cell, we could as well only specify the port names, :yoscrypt:`show y %ci2:+[Q,D]`. Or we could decide to tell the ``%ci`` action to not follow the ``CLK`` input, :yoscrypt:`show y %ci2:-[CLK]`. Next we would investigate the next logic level by adding another ``%ci2`` to the command, :yoscrypt:`show y %ci2:-[CLK] %ci2`: .. figure:: /_images/code_examples/selections/memdemo_03.* :class: width-helper :name: memdemo_03 Output of :yoscrypt:`show y %ci2:-[CLK] %ci2` From this we would learn that the next cell is a ``$mux`` cell and we would add an additional pattern to narrow the selection on the path we are interested. In the end we would end up with a command such as :yoscrypt:`show y %ci2:+$dff[Q,D] %ci*:-$mux[S]:-$dff` in which the first ``%ci`` jumps over the initial d-type flip-flop and the 2nd action selects the entire input cone without going over multiplexer select inputs and flip-flop cells. The diagram produced by this command is shown in :numref:`memdemo_04`. .. figure:: /_images/code_examples/selections/memdemo_04.* :class: width-helper :name: memdemo_04 Output of ``show y %ci2:+$dff[Q,D] %ci*:-$mux[S]:-$dff`` Similar to ``%ci`` exists an action ``%co`` to select output cones that accepts the same syntax for pattern and repetition. The ``%x`` action mentioned previously also accepts this advanced syntax. These actions for traversing the circuit graph, combined with the actions for boolean operations such as intersection (``%i``) and difference (``%d``) are powerful tools for extracting the relevant portions of the circuit under investigation. Again, see :doc:`/cmd/select` for full documentation of these expressions. Incremental selection ^^^^^^^^^^^^^^^^^^^^^ Sometimes a selection can most easily be described by a series of add/delete operations. As mentioned previously, the commands :yoscrypt:`select -add` and :yoscrypt:`select -del` respectively add or remove objects from the current selection instead of overwriting it. .. code:: yoscrypt select -none # start with an empty selection select -add reg_* # select a bunch of objects select -del reg_42 # but not this one select -add state %ci # and add more stuff Within a select expression the token ``%`` can be used to push the previous selection on the stack. .. code:: yoscrypt select t:$add t:$sub # select all $add and $sub cells select % %ci % %d # select only the input wires to those cells Storing and recalling selections ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. todo:: reflow for not presentation The current selection can be stored in memory with the command ``select -set ``. It can later be recalled using ``select @``. In fact, the ``@`` expression pushes the stored selection on the stack maintained by the :cmd:ref:`select` command. So for example :yoscrypt:`select @foo @bar %i` will select the intersection between the stored selections ``foo`` and ``bar``. In larger investigation efforts it is highly recommended to maintain a script that sets up relevant selections, so they can easily be recalled, for example when Yosys needs to be re-run after a design or source code change. The :cmd:ref:`history` command can be used to list all recent interactive commands. This feature can be useful for creating such a script from the commands used in an interactive session. Remember that select expressions can also be used directly as arguments to most commands. Some commands also accept a single select argument to some options. In those cases selection variables must be used to capture more complex selections. Example: .. literalinclude:: /code_examples/selections/select.v :language: verilog :caption: ``docs/source/code_examples/selections/select.v`` .. literalinclude:: /code_examples/selections/select.ys :language: yoscrypt :caption: ``docs/source/code_examples/selections/select.ys`` :name: select_ys .. figure:: /_images/code_examples/selections/select.* :class: width-helper Circuit diagram produced by :numref:`select_ys`