You need to create a bus object. You can do this by calling
myStruct = struct('field1',0,'field2',0);
busInfo = Simulink.Bus.createObject(myStruct);
MyDataStructureType = eval(busInfo.busName);
Then you can export the bus definition to a file by running
Then in your simulink model, you can use a bus creator block with the output data type set to "Bus: MyDataStructureType". Or you can create a subsystem with one outport connected to a ground and set the output data type of the output port to "Bus: MyDataStructureType". Then you can use the Bus Assignment block to assign elements to the bus. If you have an existing c-header file that you would like to use as the structure definition in the generated code, you can set the MyDataStructureType.HeaderFile = ''; to your specific header file in the "MyBusDefinitions.m"