Model Composer allows many black boxes to share a common Questa co-simulation session. For example, many black boxes can be set to use the same Questa block. In this case, Model Composer automatically combines all black box HDL components into a single shared top-level co-simulation component, which is transparent to the user. However, only one Questa simulation license is needed to co-simulate several black boxes in the Simulink® simulation.
Multiple black boxes can also be co-simulated with the Vivado simulator by selecting Vivado Simulator as the option for Simulation mode on each black box.