Macro group_peripherals 

macro_rules! group_peripherals {
    (
        $(#[$outer:meta])*
        $group:ident {
            $(
                $(#[$inner:meta])*
                $peripheral_name:ident : $peripherals:path
            ),*
            $(,)?
        }
    ) => { ... };
}

This macro allows to group peripheral structs defined with define_peripherals! into a single peripheral struct.