Using pixelink software development kit with labview

Question

hi,
i am currently using the pixelink camera pl b741 f, however i am facing a problem when i use the "get frame dll" in labview.
my program works when in highlight execution mode, however when i run it in normal mode i get the following message:
Labview: an exception occurred within the external code called by a library node function node. This might have corrupted labview's memory. Save any work to a new location and restart labview. VI "amol_getimage.vi" was stopped at node "" at a call to "MEPU- acquisition-getframe .vi"
can you please help me!
thanks
amol

Answer 1

amolchoudhary wrote:
hi,
i am currently using the pixelink camera pl b741 f, however i am facing a problem when i use the "get frame dll" in labview.
my program works when in highlight execution mode, however when i run it in normal mode i get the following message:
Labview: an exception occurred within the external code called by a library node function node. This might have corrupted labview's memory. Save any work to a new location and restart labview. VI "amol_getimage.vi" was stopped at node "" at a call to "MEPU- acquisition-getframe .vi"
can you please help me!
It's simple! You made an error in the configuration of your Call Library Node. It could be a number of reasons but the two most likely ones are that you get a variable wrong to be passed by Value while it should be by Reference or vice versa, or that you call the function which expects a buffer it can write in the results (the image frame is a likely candiate) and didn't create a large enough buffer in LabVIEW to be passed to the function.
I actually think this last one is by far the most likely reason here and in fact the number 1 error done by most people that try to interface to a DLL through the Call Library Node. DLLs come from the C world and want to be called like that and one important rule there is that memory buffers to be filled, must always be created by the caller. This is different in LabVIEW itself since LabVIEW manages all the memory for you and allocates it whenver necessary but this can't work for calling DLLs as LabVIEW has ABSOLUTELY no way to know what a DLL function might need as memory buffer.
You can create such a buffer by either executing the Initialize Array function with the correct parameters or in LabVIEW 8.2 you can directly configure array and string parameters in the Call Library Node configuration to create the necessary buffer. I prefer the Initialize Array variant since the other one is a LabVIEW 8.2 only feature and creates a fixed size buffer while for your frame buffer you will likely have to allocate a memory buffer whose minimum size depends on the bitmap format and bitmap size the function is going to return.
Rolf Kalbermatter
Message Edited by rolfk on 06-29-2007 07:27 PM
Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions