Every signal in Simulink must be of specific type, and fixed point values of different length are considered different data types. The consistency checking is done at the time the model is to be built, but the building process compiles in specific internal routines and lengths.
Options include:
- Permitting your user to choose only one of a limited number of widths and build distinct subsystems for every permitted width that hold all of the blocks that need to know about that width, with the block boundaries at the point where the computations no longer rely upon the width;
- Variant controls https://www.mathworks.com/help/simulink/ug/switching-between-variants.html
- there might be options about busses that carry around the length and an array of bytes and then at each point you switch on the length to choose the appropriate instruction and push the results back into a bus again.
