MATLAB: Are there Simulink guidelines for choosing ufix1 vs. boolean

Question

In the past I've tried making all my 1 bit signals in my Simulink models ufix1 or all of them boolean and neither option seemed to work perfectly. I haven't yet found guidelines from MathWorks for choosing the best type in a particular case – are there any? Or perhaps you really can make them all one type or the other, but I did it wrong.

From my perspective, I don't see the need for a ufix1 data type – does anybody know the reason?

Answer 1

A ufix1 type is an arithmetic type--it represents a number. You can add, subtract, etc., with it. It can represent the numeric values 0 and 1. A boolean type a not an arithmetic type (it stores true and false) and doesn't support arithmetic operations. VHDL in particular is strongly typed, and upholds this distinction in its language implementation. HDL Coder in general follows the most restrictive commonalities between VHDL and Verilog, so it honors the VHDL distinction between types.

Simulink and HDL Coder go even further with ufix1, as they support binary point scaling. For example, ufix1_En2 can store either 0 or 0.25, in a single bit. ufix1_E4 can store 0 or 16, also in one bit. And so on. Arithmetic will be performed on these types in bit-true and cycle-accurate form. This is simply the nature of the full-featured fixed-point numeric system that MATLAB and friends support.