pub fn fields(
fields: &[&Field],
register: &Register,
name_uc_spec: &Ident,
all_registers: &[&Register],
peripheral: &Peripheral,
all_peripherals: &[Peripheral],
rty: &Ident,
access: Access,
properties: &RegisterProperties,
mod_items: &mut TokenStream,
r_impl_items: &mut TokenStream,
w_impl_items: &mut TokenStream,
config: &Config
) -> Result<()>