libregister: add macro for multi-bit RO fields

libregister/src/lib.rs

@@ -290,6 +290,19 @@ macro_rules! register_bits {
             }
         }
     );
+
+    ($mod_name: ident, $(#[$outer:meta])* $name: ident, $type: ty, $bit_begin: expr, $bit_end: expr, RO) => (
+        impl $mod_name::Read {
+            #[allow(unused)]
+            #[inline]
+            $(#[$outer])*
+            pub fn $name(&self) -> $type {
+                use bit_field::BitField;
+
+                self.inner.get_bits($bit_begin..=$bit_end) as $type
+            }
+        }
+    );
 }
 
 /// Define a multi-bit field of a register, coerced to a certain type