The Suppress generation of default cases… configuration option was introduced in R2011b. Prior to that release, a default case was generated for all charts with multiple child states, and that default could theoretically be unreachable. When the option was first introduced, users could instead have Stateflow generate code with only case statements, and no defaults.
However, the behavior of this option was changed starting in R2012a. Now this configuration option will have an effect on the generated code only from charts which contain local events. In their absence, the default case is always the last child state (in alphabetical order), is always reachable, and is always generated. In the presence of local events, you can use the configuration option to suppress the generation of the default case, if desired.
It is important to note that the statement “if unreachable” in the option name refers to the possibility of reaching the default case itself, not any sort of unreachable states in the Stateflow chart. Stateflow is designed to always optimize unreachable states out of the generated code entirely.
