Can you share a sample model?
It sounds like you have parts of the design that do not need to be updated at 20e-9s, if that is the case, variable step discrete solver should help with the simulation time if you are trying to speeding up the Simulink simulation of the model intended for HDL code generation.
However, there are some aspects of HDL test bench generation that would not work with this. Please reach out to tech support for additional help.
