Python with NI-SCOPE DLL

Question

Hi, I'm trying to use ctypes in Python to import the NI-SCOPE_32.DLL and interface with a 5105 and 5124.
So far, I have successfully (I think) created a new session with the 5124. I can't do anything else as trying to access any constants results in an error such as "AtrributeError: function 'NISCOPE_VAL_NORMAL' not found" when trying to access any of these constants. I can look in the niscope.h file and see that they are #defined, but it seems the compiled DLL doesn't contain these definitions, or I can't access them for some reasons. Has anybody got this to work correctly or have any advice?

Answer 1

snelltaylor wrote:
Thanks for the input. I had been looking for the #define's in the headers, and found them, but the definitions were just to other strings - such as IVISCOPE_VAL_NORMAL.
Where would I go about finding what the values these represent are? Do I just have to chase them down through the headers?
Also, what kind of value should I be getting back from the niScope_init function? Right now, it gives a return value of -10something, maybe 5 or 6 digits, but the viSession pointer (which I pass using ctypes.byref()) ends up with a value of 0. The two booleans that are passed were just Python's False, so the function call looked like:
import ctypes
scope = ctypes.cdll.niscope_32
viSession = ctypes.c_long() #do I need a value here for an actual variable rather than null?
scope.niScope_init("PXI2::13::INSTR",False,False,ctypes.byref(viSession))
Does this seem reasonable? Am I missing something big here?
Thanks,
Sean
Sean,
As far as deciphering the various #define's, you will have to look at niscope.h, iviscope.h, and perhaps even ivi.h. Namley, anything IVISCOPE_VAL_xxx will most likely be defined in iviscope.h, and anything IVI_VAL_xxx should be in ivi.h. There might be some definitions elsewhere, but little grep-ing ought to get you all you need. This is where the type library information would come in very handy, but again, I am not sure how to do this in Python.
NI-Scope functions will return a ViStatus (a signed 32-bit integer). Value of 0 means that the function succeeds without an error, a negative value indicates an error, while a positive indicates a warning - one can usually ignore the warnings, while the errors usually mean some run-time condition that will prevent further predictable execution.
In you specific case (from the code snippet), I believe that the first parameter is invalid ("PXI2::13::INSTR"), and niScope_init() function does not generate a valid session - hence the value of 0 for ViSession (by the way, your ViSession definition is just fine). Specifically, the first  parameter for niScope_init() needs to be the device name that you see in MAX under Devices and Interfaces >> NI-DAQmx Devices (something like "Dev1", or "PXI1Slot5", or something similar - you can also give it your own name (both 5105 and 5124 are DAQmx devices). Refer to the NI-Scope (a.k.a. NI High Speed Digitizers Help) for more details on the functions and their parameters.
Hope this helps.
Regrads,
Sead Suskic
National Instruments