How does call library / .dll file work?

I'm helping someone troubleshoot their machine / LabVIEW program. I'm fairly new to LabVIEW, and I'm not sure what part of the program is doing. I've attached the .vi in question. In the middle of the page there is a sub.vi with a blank icon with two dots in it (peak_detect_dll.vi). This sub.vi has a call library function node, which I understand calls the file it points to in the config: s3ilvutils.dll (also attached). I don't understand what this file does. I've searched the help and the discussion board. Can anyone explain to me what this is doing?
Jeremy Backer
CLAD
Attachments:
count.vi ‏31 KB
peak_detect_dll.vi ‏8 KB
s3ilvutils.zip ‏3 KB

Well I typed too slowly! See that you have a bunch of other answers in the time I took. It was probably written in another language, but dll's can be created in LabVIEW as well. The "C" calling convention only describes a interface convention, doesn't guarantee that C was the language it was developed in, although it probably is a good bet that it was C/C++. I don't think there is an "easy" was to reverse engineer what is in the dll, that is one reasons some functions are put in them, to protect the Intellectual Property, another is to encapsulate a bunch of functionality in a portable block, although yours only has three calls, so that isn't "a bunch".
Starting with the "peak_detect_dll.vi": this vi encapsulates a call to the s3livutils.dll, which appears to take a data array from a unit (S3?), pass in this data and parameters for a threshold level and minimum signal width (obviously, the vi's names agree with those of the dll). It returns an array of dbl's, which are apparently the detected peaks above the threshold, and a I32 giving the number of these peaks, which in the highest level vi is not used. This information can be seen if you right click on the "call library function" in the peak_detect_dll.vi and select "configure". Dll's are used like for a number of reasons, usually because there is an existing library call, written in another language, or a developer felt that the algorithm used was more efficient than native C. If you right click and select configure you will see (under the pulldown "Function name") that there is additional functionality contained in the dll that may (or may not) be used elsewhere in the program in another dll call.
Not sure what exactly you need, but this is just a snippet of code that apparently finds peak values in the input array above some threshold.
Message Edited by LV_Pro on 10-19-2009 08:42 AM
Putnam
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