coder . cl

I need to work with a hierarchical state machine. The main problem that I am currently facing is how to pass messages or trigger events on each event transition. Since I am using C Plus Plus, I will use class methods. In this case, I will use a hardware device class method. On each state transition, an event will be thrown, and the given event should trigger an action — in this case a class method — that will complete the state transition. The advantage of the hierarchical state machine is the fact that you can manage composite hardware devices without problems, because each sub-device can be handled individually with its own state, but increases the complexity of the program.

As I have discussed on a previous blog post, static typing helps on correctness by providing well-typed programs through type checking algorithms. Compiler warning messages and compiler error messages are not thrown as they were made by a capricious developer. Almost all of them are following a language definition, and they help if you want to build better programs. The more strict are your compiler flags, better are your programs. Using language extensions, which are not present on their standard definitions is not so cool as it seems. That depends on the language, sometimes there is very long time after certain language extensions are passed to the language definition. So, you should try to look on how can you write better code for that language without abusing of its extensions and extra features provided by the compiler.

Base conversion can be used to compress number representations, and can be used to hide the real number representation. The algorithm is well known, anyone can program that algorithm, and it is not so hard to handle. I was playing with Haskell writing that algorithm to check how effective is that algorithm to create URL shorteners. My idea is quite simple, you have an URL database ID, which is an integer number, indexed as many entries on the database, but once the database starts growing, the number can reach a length that is not so easy to remember. For example the ID 999 999 999 999 is not so easy to remember.

Standar ML is defined as safe using the following definition «ML is safe, in that a program that passes the type-checker cannot dump core, access private fields of abstract data types, mistake integers for pointers, or otherwise “go wrong.”». A type-checker verifies that each term used in the programming language should have the correct type once it is used. For example if a function is defined to receive an integer type, once it is called, an integer term should be used, otherwise the compiler may throw an error and the execution “goes wrong”. If the type-checking algorithm accepts the program, then it is well-typed. When a programming language has a type-checking algorithm on its compiler, we call it statically-typed. Dynamic typing does not have a type checker on its compiler, you can write the same function, it will not have any sentence defining an input type, and it will be able to receive a string when an integer is required.

The basic definition of a state machine is a set of states S, with a subset of initial states I, another subset of final states F, and a set of transitions between states T, and every state s’ ∈ S ∧ s” ∈ S where I ⊆ S ∧ F ⊆ S, and each element on T { s’, s”, h }, with s’ as the current state, s” as the next state and h as the state action. On my current automation project where I am using ProView, I have each device controlled by state machines, and each user or automatic control request is queued on a priority queue, where the highest priority is executed replacing any previous execution state, because we have only one communication channel. So the basic state machine definition is not enough to hold every environmental variable that we are using to control each device.

How to choose between C and C++?. The answer is pretty clear. C allows powerful data type abstractions using three star and two star pointers, C++ only allows one star pointers. Also void pointers on C are more powerful once you try to pass abstract parameters to functions and procedures. The abstractions on C++ are built on top of virtual classes and templates, not its data types as C does. So, if you need to create complex data types, for example to handle hardware buffers, you should use C rather than C++, but if you want to create abstractions to manage real life objects, an object oriented interface like C++ does have is pretty good, enough to support almost any object oriented abstraction that you want to implement.

We are doing pretty good advances on the ICS/DCS that we are doing. The current code base is using the STL std::priority_queue as operation request queue, but we are changing the task request priority each time that the communication channel is being used by any transition that requests the Profibus channel. We cannot saturate the communication channel with requests, because it runs on a very low bandwidth connection, so each request should be correctly measured, where all operations on the machinery is being directed by states machines with dynamic priorities of execution, and the STL priority queue is doing a good job. But was a little bit complex to think in terms of source code with the model presented as state diagrams and flow control diagrams on a whiteboard, and took me about one week to finish the final skeleton of the primary source code.