Macro ctl_code 

macro_rules! ctl_code {
    ($device_type:expr, $function:expr, $method:expr, $access:expr) => { ... };
}

macro_rules! spelling of ctl_code, mirroring the C CTL_CODE macro for call sites that prefer macro syntax. Both forms expand to the same value; the const fn is preferred in const definitions because it is type-checked.