Making C++ module support variable number of input C messages

[GorgiAstro]

Hi folks,

I am having trouble writing a new module whose input is a variable number of
IMUSensorBodyMsgPayload messages. I've read the documentation on how to do that, and I've read the eclipse example, but still I am getting an error message about the module getting a IMUSensorBodyMsg_C pointer instead of a IMUSensorBodyMsgPayload pointer.

The C++ module is in the attached ZIP file: VectorVoter_bsk.zip

The Python code calling the external module is the following:

from Basilisk.ExternalModules import VectorVoter_bsk
vector_voter = VectorVoter_bsk.VectorVoter_bsk()
vector_voter.ModelTag = "IMU Voter"
for i_imu, imu_defs in imu_df.iterrows():
     vector_voter.addSensorToVoter(imu_defs['imuCommConfig'].imuSensorOutMsg)
scSim.AddModelToTask(att_det_task_name, vector_voter)

gives

-------------------------------------------------------------------------- TypeError Traceback (most recent call last) Cell In [19], line 5 3 vector_voter.ModelTag = "IMU Voter" 4 for i_imu, imu_defs in imu_df.iterrows(): ----> 5 vector_voter.addSensorToVoter(imu_defs['imuCommConfig'].imuSensorOutMsg) 6 scSim.AddModelToTask(att_det_task_name, vector_voter) File /media/ssd/git/basilisk/dist3/Basilisk/ExternalModules/VectorVoter_bsk.py:109, in VectorVoter_bsk.addSensorToVoter(self, tmpVecMsg) 108 def addSensorToVoter(self, tmpVecMsg): --> 109 return _VectorVoter_bsk.VectorVoter_bsk_addSensorToVoter(self, tmpVecMsg) TypeError: in method 'VectorVoter_bsk_addSensorToVoter', argument 2 of type 'Message< IMUSensorBodyMsgPayload > *'

where
print(imu_defs['imuCommConfig'].imuSensorOutMsg)
gives

<Basilisk.architecture.messaging.IMUSensorBodyMsgPayload.IMUSensorBodyMsg_C; proxy of <Swig Object of type 'IMUSensorBodyMsg_C *' at 0x7fbaffb7e010> >

I suspect that it's because ImuComm is a C module. If I understood correctly (I am still a Basilisk beginner), when calling subscribeTo, it does not matter if it's a C or C++ module, it's hidden in messaging.h. However, this seems not to be the case when subscribing manually to the multiple input messages in my module's cpp file (method
addSensorToVoter).

Cheers
Clément

[schaubh]

In a C module the message is a structure that contains the payload message structure, the message header structure, and pointers to the payload and header. These are defined as imuSensorOutMsg_C and automatically created when you run python conanfile.h. In C++ the message container is a C++ class, not a C structure. When you subscribe from one to another, yes, there I magic under the hood that recognizes if you are connecting a C++ msg to C msg reader, or vise versa, and makes the correct connections to the msg payload and header structures.

In your case, your module is a C++ module and you are making a standard message of C++ msg objects. There should be nothing special to connect to.

[GorgiAstro]

Thank you for the information.

I still didn't manage to solve the issue:

• my C++ module expects a pointer to a Message<IMUSensorBodyMsgPayload> object
  (method void VectorVoter_bsk::addSensorToVoter(Message<IMUSensorBodyMsgPayload> *tmpVecMsg))
• The IMU comm config object has an attribute imuSensorOutMsg, but in Python it is a proxy of a IMUSensorBodyMsg_C pointer and not of a Message<IMUSensorBodyMsgPayload>: <Basilisk.architecture.messaging.IMUSensorBodyMsgPayload.IMUSensorBodyMsg_C; proxy of <Swig Object of type 'IMUSensorBodyMsg_C *' at 0x7f012e022f40> >

How to get a pointer to a Message<IMUSensorBodyMsgPayload> from an IMU comm object in Python to make my C++ module subscribe to a variable number of IMU comm modules? I looked at the imuCommWrap but it does not have this message either.

[schaubh]

Mm, I think I'm seeing the issue. If you followed the guidance at http://hanspeterschaub.info/basilisk/Learn/makingModules/cppModules/cppModules-3.html your command addSensorToVoter() is expecting a C++ message object. however, the imu output message is a C-wrapped output message. You are trying to add the C-wrapped MSG object to the new BSK module and getting the swig errors.

Basilisk doesn't do any magic conversion here between the message types. You would have to rewrite your addSensorToVoter() method to accept a structure of type IMUSensorBodyMsg_C in this case, and then store these in a vector. To read them, you wold use the IMUSensorBodyMsg_C_read() command as you do in a C-module. You need to include the proper *.h files of course as you do in a C BSK module.