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esstee

esstee is an interpreter written in C (GNU C99), currently under work, for the Structured Text (ST) programming language. Structured Text is one of the five languages defined in the IEC-61131-3 standard, and used a lot in the automation industry.

The aim of esstee is to provide a, "free as in freedom", platform for building better testing and debug tools for ST applications.

esstee is licensed under GPLv3. Besides Bison and Flex, esstee has no external dependencies besides the header libraries included in the source. Compiling has so far only been tested under Debian, but should work without problems in any Linux distro.

Quick Start

The first milestone of esstee is to provide a library that allows ST syntax to be parsed into a representation which can be stepped/run. The public interface to the library is defined in src/esstee/esstee.h.

Currently, the parsing step of the library is complete (Flex and Bison grammar). In addition there is support for types (elementary, derived and complex), all statements and expressions, however it is not yet properly tested (automatic integration tests not ready), and should be considered as under work.

A simple test program using the library interface (and building all the current code) can be built by;

make build/program-tester

The program parses ST syntax from a file, then executes possible "pre" queries on the runnable representation, runs N cycles and finally executes possible "post" queries. A query is either a variable reference or an assignment. The program takes the following options:

• file the file to parse
• program the PROGRAM in the file that is to be run (a file may contain multiple programs)
• pre-run-queries the queries to run right after parsing
• run-cycles number of cycles to run (default 1)
• post-run-queries the queries to run after the cycles have been run

In pre and post queries, access the program variables by prefixing with [name-of-program].

An example:

./build/program-tester --file="src/tests/programs/example.ST" --program="testprgm" --pre-run-queries="[testprgm].a:=10*5+1" --post-run-queries="[testprgm].a"