How to solve this warning: This property will be converted to datatype "double" in the Simulink bus.

I'm a new bee to Simulink and ROS2. When I followed the tutorial to study ROS2 Custom Message Support, I changed the data type of "int_property" from "uint32" to "uint64". Then I genmsg from this example. I haven't had any problems until here.

Then I try to use this custom message in Simulink. I open ros2GetStartedExample.slx, change the Blank Message from "geometry_msgs/Point" to "example_b_msgs/Standalone" and fix some compile bug. Finally, I simplified the model like this.

Then I got this warning.

warning: The property "int_property" in ROS message type "example_b_msgs/Standalone" has an unsupported datatype (uint64). This property
will be converted to datatype "double" in the Simulink bus. 

So, how can I prevent Simulink to do this convertion? I find this convertion is type cast in generated C++ code, which may cause loss of accuracy like this.

c++ code:

#include<iostream>

using namespace std;

int main(){
    uint64_t test1 = 1311768467463790329;

    double test2 = (double)test1;

    uint64_t test3 = (uint64_t)test2;
    cout << test1 << endl;
    cout << test2 << endl;
    cout << test3 << endl;

    return 0;
}
$ g++ test.cpp -std=c++11 -o test
$ ./test
1311768467463790329
1.31177e+18
1311768467463790336

matlab comand:

>> uint64(1311768467463790329)

ans =

  uint64

   1311768467463790329

>> uint64(double(uint64(1311768467463790329)))

ans =

  uint64

   1311768467463790336

[Zheng Zhang]

I also have the same warning. Do you solve it?

Answer 1

[Josh Chen]

Hi An and Zheng,

This auto conversion from int64 to double is to align with standard Simuilnk datatype by default. To avoid such conversion, you would need to do the following two steps before generating the code:

1. Use the following command to enable 'Int64' mode for Simulink Buses:

>> ros.slros.internal.bus.Util.setInt64SLBusMode(<model_name>,true)

2. Navigate to 'Hardware Implementation' and check 'Support long long':

Hope this helps,

Thanks.

Josh