ctypes uint64 conversion error

Question

I got the following problem :

I load via c types the nicaiu.dll to control a NI-USB6218 Data Acquisition Pad and i have to call several function to initialise it (DAQmxCreateTask(), DAQmxCreateAIVoltageChan() and DAQmxCfgSampClkTiming() ).

The first two calls work but DAQmxCfgSampClkTiming() raises this error

Traceback (most recent call last):
File "C:/*********/Voltage.py", line 68, in <module>
values)
ctypes.ArgumentError: argument 6: <type 'exceptions.TypeError'>: Don't know how to convert
parameter 6

Parameter 6 should be uint64 see Doc This is my function call:

DAQmx_Val_Rising = 10280 #see NIDAQmx.h
DAQmx_Val_FiniteSamps = 10178 # see NIDAQmx.h
values = uint64(40000) #numpy function
dll.DAQmxCfgSampClkTiming(taskHandle, "OnboardClock", c_float(4000.0), DAQmx_Val_Rising, DAQmx_Val_FiniteSamps,
                                    values)

I also tried values = c_uint64(40000) but it did not work.

Edit1: The dll is located in System32 folder (Win7)

dll = cdll.nicaiu

E.g this function call works (returnvalue = 0)

DAQmx_Val_Diff = 10106
DAQmx_Val_RSE = 10083
DAQmx_Val_Volts = 10348
returnvalue = dll.DAQmxCreateAIVoltageChan(taskHandle, "Dev1/ai1", taskName, DAQmx_Val_RSE,
                                           c_float(-1.0),c_float(1.0), DAQmx_Val_Volts, None)

Edit2:

Added argtypes line

dll.DAQmxCfgSampClkTiming.argtypes = [c_int, c_char_p, c_float, c_int32, c_int32, c_uint64]
returnvalue = dll.DAQmxCfgSampClkTiming(taskHandle, None, c_float(4000.0), DAQmx_Val_Rising,
                                        DAQmx_Val_FiniteSamps,values)

Still get Error Code -200077 Definition of this code is :

nierror code = -200077
Requested value is not a supported value for this property. The property value may be invalid
because it conflicts with another property.

Can you post more code? How are you opening the DLL? It looks like you aren't using `argtypes`. — 101, Oct 29 '14 at 20:59

score 2 · Accepted Answer · answered Oct 30 '14 at 09:44

2

I can't test it as I don't have that instrument, but I would start with something like:

samp_clk_timing = dll.DAQmxCfgSampClkTiming
samp_clk_timing.restype = c_int32
samp_clk_timing.argtypes = (TaskHandle,
                            c_char_p,          
                            c_double,         
                            c_int32,
                            c_int32,           
                            c_uint64)

return_val = samp_clk_timing(taskHandle,
                             "OnboardClock",
                             c_double(4000),
                             c_int32(10106),
                             c_int32(10178),
                             c_uint64(40000))

answered Oct 30 '14 at 09:44

101

8,514
6
43
69

now it works :D i had to change the first argtype to c_int and at the function call the 4th and 5th to the right values for Rising Edge and Finite Samples Thx a lot :D – Gora Oct 30 '14 at 10:06
Strictly speaking TaskHandle should probably be a structure, but if it's only and int then nevermind :) – 101 Oct 30 '14 at 11:07
yeah initially it is defined as a void * but by calling DAQmxCreateTask it gets a memory address (i saw somewhere long long ) – Gora Oct 30 '14 at 11:14

ctypes uint64 conversion error

1 Answers1