python nican.dll function call error

[ADLMB]

Based on the example in https://knowledge.ni.com/KnowledgeArticleDetails?id=kA03q000000YHbHCAW&l=en-US I am trying

to access the LIN functions of the NI USB-8476 in the following python script:

#!/usr/bin/env python
from ctypes import *
dll = cdll.LoadLibrary("nican.dll")
linName = c_char_p("LIN0")
linPtr = c_void_p()
dll.ncOpenObject.argtypes = [POINTER(c_char_p), POINTER(c_void_p)]
returnValue = dll.ncOpenObject(linName, linPtr)

resulting in the following error message:

Traceback (most recent call last):
  File "./demo.py", line 15, in <module>
    returnValue = dll.ncOpenObject(byref(linName), linPtr)
ValueError: Procedure called with not enough arguments (8 bytes missing) or wrong calling convention

Thanks for any help.

[ADLMB]

Noticing that I had skipped over the ncConfig function call, thinking this may be a prior

error I tried to set up the ncConfig call according to the ctypes tutorial at

http://python.net/crew/theller/ctypes/tutorial.html.  I have been unable

to make the ncConfig function recognize the parameter arrays:

#!/usr/bin/env python
from ctypes import *
dll = cdll.LoadLibrary("nican.dll")
linName = c_char_p("LIN0")
linNumAttr = c_ulong(2)
NC_ATTR_START_ON_OPEN = c_ulong(0x80000006)
NC_ATTR_BAUD_RATE = c_ulong(0x80000007)
class linAttrIdList(Structure):
   _fields_ = [("ncAttrStartOnOpenID", c_ulong),("ncAttrBaudRateID", c_ulong)]
linAttrIdList.ncAttrStartOnOpenID = NC_ATTR_START_ON_OPEN
linAttrIdList.ncAttrBaudRateID = NC_ATTR_BAUD_RATE
class linAttrValueList(Structure):
   _fields_ = [("ncAttrStartOnOpen", c_ulong),("ncAttrBaudRate", c_ulong)]
linAttrIdList.ncAttrStartOnOpen = 0
linAttrIdList.ncAttrBaudRate = 9600
linPtr = c_void_p(0)
returnValue = dll.ncConfig(linName, linNumAttr, linAttrIdList, linAttrValueList)

this causes python output:

Traceback (most recent call last):
  File "./demo.py", line 23, in <module>
    returnValue = dll.ncConfig(linName, linNumAttr, linAttrIdList, linAttrValueList)
ctypes.ArgumentError: argument 3: <class 'TypeError'>: Don't know how to convert parameter 3

Again, any help is appreciated, especially any examples of correct python usage of nican.dll.

[Mr.F]

Hi ADLMB,

Unfortunately the second link you posted is broken. Also, Python is not one of the languages that R&D tests with when designing the NI-CAN driver so there may be more issues like this moving forward with Python. I would encourage you to consider using a more widely adopted language. Looking at the NI-CAN readme, you can use LabWindows/CVI, Visual Basic 6.0, Microsoft C/C++ 6.0 or Borland C/C++. There may be someone of the forums with the specialized knowledge you need, good luck.

[w.persyn@televic.com]

Dear,

  About the access of the nican.dll driver from 'Python'

  Is there already a solution for it.

  We plan to use the NI USB-8473s as hardware interface an drive from a Python program ?

  I also suffer with the same issue like described above here

Thank you for an update,

Wouter

[JordanG]

Hello,

As mentioned above, Python is not one of the languages R&D tests when they design the CAN driver. Again, any language listed in the readme can be used. I've also attached a few other documents you might find useful as well as the documents linked above.

Introduction to Scripting in Perl, Python and Tcl

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA03q000000YHbHCAW&l=en-US

Advanced Scripting in Perl, Python and Tcl

http://zone.ni.com/devzone/cda/tut/p/id/8911 

Call Perl and Python Scripts from LabVIEW

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA03q000000x4PSCAY&l=en-US

I hope this helps! Good luck programming!

Jordan

[medendoc]

Hello all,

Have you had any luck with this?  I am attempting to use the USB-8473 for monitoring CAN traffic, and would be greatful for any help.

Thank you