Execute a non Stop Action during others actions

[Romess31]

Hello,

I have a problem with my program. I have developping a communication with the serial port with the example of Labwindows. But it read when the users rest on the button. I would like read the serial port all the time and can do other action in the same time. Can you help me please ?

Thank you,

Regards

[RobertoBozzolo]

Hi romess, here you are with the need of performing several tasks inside the single program. This can be obtained in several ways; here a non-exhaustive list of possible solution, in order of increasing complexity:

• Standard UI timer: inside the callback perform the serial port activity. Given the time of the serial port process, you must define a timer interval so that some time is left for user interface activity
• Asyncronous timer: the same as above, with some multithreading added due to the way async timers are structured. CVI offers a specific instrument (<cvidir>\toolslib\toolbox\asynctmr.fp) to handle such timers; they have the same callback definition of standard UI timers so that what you have developed for the above solution can be portes almost 'as is' to async timers
• Multithreading

When developing programs that have two or more independent tasks, some precautions are to be taken in order to prevent contemporaneous access to shared resources or to internal variables/objects: a good starting point is to read <cvidir>\bin\MultithreadingOverview.pdf document, which even if aimed to pure multithreading structures, nevertheless gives you a conceptual framework on the possible problems you can find and how to prevent them.

[Romess31]

Thank you very much Roberto for your rapid answer.

A person tell me to use ProcessSystemEvents and thread to execute one action un loop all the time and all the action of the program in the same time.

But I dont know if it exist others functions to make this ?

And i dont see how do to realize this ?

Can you help me please ?

Thank you very much

[RobertoBozzolo]

I personally discourage systematic use of ProcessSystemEvents in a program as it may interfere with normal events handling by the system and can cause unpredictable situations.

Before going that way you should at least give a try to some examples that come with CVI: samples\userint\timer.prj to shows you how to use standard UI timers and gives some caveat in their usage.

A step above can be to study  samples\toolbox\asyncdem.prj application, which gives you an immediate comparison between standard UI timers and asynchronous timers.

As per multithreading, I suggest you to use Help >> Find Example menu function and search for "multithreading" keyword: starting from "simple.prj" example listed there you can progressively deep into multithreaded programming.

[Romess31]

Ok Thank you very much. I have found. 🙂

But I have just one last question.

I send in the serial port ascii bytes. But my program must receive just Hexadecimal byte.

Does it exist a function who convert ascii to hexadecimal?

Otherwise how can I do to Convert ?

Thank you for your help.

[RobertoBozzolo]

Don't make the error of considering ascii, int and hex as separate things with need to convert between each other! They are nothing but different representations of the same bit pattern: either you say (int)65 or (octal)101 or (hex)0x41 or (ascii)"A" or (binary)01000001, you are always treating the same exact thing. So unless your external device sends you a message like "0x41" (4 characters), the string you receive in ComRd needs no convertion at all and what you call "hexadecimal bytes"can simply be a hexadecimal representation used in the documentation to make things clear.

Different is the case if you need to pack two or more received bytes into a more complex data type (short, in, float...): if this is your situation, I'd like to know what exactly you need to do with received data before answering in a possibly wrong way.

[Romess31]

In reality, my program say to the user to enter hexadecimal bytes. But when I enter this value, when my programm affich this value, It's not that I like. When I use the program with Hyperterminal, I have create a program who take the ascii value and return the hexadecimal value partner. And I would to do the same thing with my Labwindows program.

[RobertoBozzolo]

That is: you have a string control in which the user enters something like "0x41, 0x42, 0x43" and you want to send to your instrument the string "ABC", right?

So:

char   inS[32], outS[32];

GetCtrlVal (panelHandle, PANEL_STRING, inS);

sscanf (inS, "%x,%x,%x", (int *)&outS[0], (int *)&outS[1], (int *)&outS[2]);

the result of all this is the string "ABC" in outS variable which can be sent through the serial port.

Of course this is just a framework: you must add some check for validity of user input and scan/format appropriately the strings.

[RobertoBozzolo]

As alternatives you can think of using ANSI C strtod () function with base 16 to scan user input, or Scan () function from CVI Formatting and I/O library.