Macro build_register_state 

macro_rules! build_register_state {
    (
        $(#[$($reg_attrs:tt)*])*
        $reg:ident, $reg_num_bits:expr ;
        $(
            $(#[$($field_attrs:tt)*])*
            $field:ident : $num_bits:expr, $reset:expr
        ),+ $(,)*
    ) => { ... };
}