Mexfile ode45 codegen

I am tring the create a MEX file for the function ode45 for it to run faster using the codegen method but I am not sure on how to specify the size, class and complexity of that function.

I tried:

codegen ode45 -args {[1 1],'struct',0}

But there is definitely something wrong.

I obtain the following error message: ??? Top-level function cannot have varargout.

Can you please help me for how the specify inputs for a codegen (especially ode45) or else do you have another method for speeding up ode45?

Thanks