In the HDL co-simulation tutorial provided by Mathworks (page 4-63 of the HDL Verifier User's Guide, R2014A), I read the sentence: "Configure the Simulink solver options for a fixed-step, discrete simulation; this is required for cosimulation operation." For the simple model being described in the tutorial, using the fixed-step solver makes sense. But this sentence makes it sound like the fixed-step solver must be used for all models which include co-simulation blocks. This would mean that co-simulation cannot be applied in models which have blocks with continuous states outside the HDL block. Is this correct? Or is this just a poorly-worded sentence in the tutorial?