pymetawear/c++: Delay after import required?
When I tried to create a counter data processor that counts events from a switch I ran into an interesting problem: apparently my code only runs when I add a delay after importing the MetaWearClient class. Otherwise I get a segmentation fault.
Here is my code:
from pymetawear.client import MetaWearClient
# Pause required after this line!
from pymetawear import libmetawear
from ctypes import cast, POINTER, c_uint
from pymetawear.mbientlab.metawear.core import Fn_VoidPtr, Fn_DataPtr, DataTypeId
c = MetaWearClient('D9:1B:01:B3:A9:01', 'pygatt')
switch_signal = libmetawear.mbl_mw_switch_get_state_data_signal(c.board)
# Callback: print the data
assert(data.contents.type_id == DataTypeId.UINT32)
data_ptr = cast(data.contents.value, POINTER(c_uint))
callback_print = 
# Callback: counter is created, now subscribe to it
Now there are actually two parts which I dont understand:
1. When I subscribe the sensor_data_print_uint32() function to the counters data signal, I have to store the Fn_DataPtr to an array (callback_print.append...) and then access it through the array. Otherwise It will not work.
I do not understand why this is the case (maybe something with pythons garbage collection...)
2. My main concern is the pymetawear.client.MetaWearClient import. I noticed that the code above only runs when I execute the first import statement in an interactive python shell, and when it is imported paste the rest of the code. Running the whole code as a script will result in a Segmentation Fault, just as pasting the script as a whole into an interactive python shell. In both cases the Segmentation Fault occurs right before libmetawear.mbl_mw_dataprocessor_counter_create(...) is called. Any idea why this is happening?
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