Beckhoff TwinCAT IEC 61131-3 Lark-based Structured Text Tools

Or for short, blark. B(eckhoff)-lark. It sounded good in my head, at least.

The Grammar

The grammar uses Lark's Earley parser algorithm.

The grammar itself is not perfect. It may not reliably parse your source code or produce useful Python instances just yet.

See issues for further details.

The plan

As a fun side project, blark isn't at the top of my priority list.

Once I get around to it, I hope to:

• Introduce user-friendly Python dataclasses for all PLC constructs
• Create a lark Transformer to take tokenized PLC code and map them onto those dataclasses
• Fix the grammar and improve it as I go
• Python black-style automatic code formatter?
• Documentation generator in markdown?
• Syntax highlighted source code output?

Requirements

• lark (for grammar-based parsing)
• pytmc (for directly loading TwinCAT projects)

How to use it

1. Preferably using non-system Python, set up an environment using, e.g., miniconda:

$ conda create -n blark-env python=3.7
$ conda activate blark-env

2. Install the library (using conda or otherwise, these steps are the same)

$ pip install blark

3. Run the parser or experimental formatter utility. Supported file types include those from TwinCAT3 projects ( .tsproj, .sln, .TcPOU, .TcGVL).

$ blark parse -vvv blark/tests/POUs/F_SetStateParams.TcPOU
iec_source
  function_declaration
    F_SetStateParams
    BOOL
    function_var_blocks
      input_declarations
        None
        var1_init_decl
          var1_list
            var1
              variable_name
                nStateRef
                None
              None
          simple_spec_init
            None
            UDINT
            None
... (clipped) ...

To interact with the Python dataclasses directly, use:

$ blark parse --interactive blark/tests/POUs/F_SetStateParams.TcPOU
# Assuming IPython is installed, the following prompt will come up:

In [1]: result.items[0].name
Out[1]: Token('IDENTIFIER', 'F_SetStateParams')

Dump out a parsed and reformatted set of source code:

$ blark format blark/tests/POUs/F_SetStateParams.TcPOU
FUNCTION F_SetStateParams : BOOL
    VAR_INPUT
        nStateRef : UDINT;
        rPosition : REAL;
        rTolerance : REAL;
        stBeamParams : ST_BeamParams;
    END_VAR
    VAR_IN_OUT
        Table : FB_LinearDeviceStateTable;
    END_VAR
    VAR
        stDeviceState : ST_DeviceState;
    END_VAR
    stDeviceState.nStateRef := nStateRef;
    stDeviceState.rPosition := rPosition;
    stDeviceState.rTolerance := rTolerance;
    stDeviceState.stReqBeamParam := stBeamParams;
    Table.A_Add(key := nStateRef, putValue := stDeviceState);
    F_SetStateParams := Table.bOk;
END_FUNCTION

If you want to use the tokenized source for your own purposes, you'll have to dig into the source code from there.

Acknowledgements

Originally based on Volker Birk's IEC 61131-3 grammar iec2xml (GitHub fork here) and A Syntactic Specification for the Programming Languages of theIEC 61131-3 Standard by Flor Narciso et al. Many aspects of the grammar have been added to, modified, and in cases entirely rewritten to better support lark grammars and transformers.