Add unit_exponent to collection spec (#68)

macros/src/lib.rs

@@ -166,8 +166,9 @@ use packer::{gen_serializer, uses_report_ids};
 /// Note: Parameters are a tuple, so make sure you have a trailing comma if you only have one
 /// parameter.
 ///
-/// The valid parameters are `collection`, `usage_page`, `usage`, `usage_min`, `usage_max`, and
-/// `report_id`. These simply configure parameters that apply to contained items in the report.
+/// The valid parameters are `collection`, `usage_page`, `usage`, `usage_min`, `usage_max`,
+/// `unit_exponent`, and `report_id`.
+/// These simply configure parameters that apply to contained items in the report.
 /// Use of the `collection` parameter automatically creates a collection feature for all items
 /// which are contained within it, and other parameters specified in the same collection-spec
 /// apply to the collection, not directly to the elements of the collection (ie: defining a
@@ -535,6 +536,16 @@ impl DescCompilation {
                 false,
             );
         }
+        if let Some(unit_exponent) = spec.unit_exponent {
+            self.emit_item(
+                elems,
+                ItemType::Global.into(),
+                GlobalItemKind::UnitExponent.into(),
+                unit_exponent as isize,
+                false,
+                false,
+            );
+        }
 
         for name in spec.clone() {
             let f = spec.get(name.clone()).unwrap();

macros/src/spec.rs

@@ -53,6 +53,7 @@ pub struct GroupSpec {
     pub usage_page: Option<u32>,
     pub collection: Option<u32>,
     pub logical_min: Option<u32>,
+    pub unit_exponent: Option<u32>,
 
     // Local items
     pub usage: Vec<u32>,
@@ -113,6 +114,10 @@ impl GroupSpec {
                 self.collection = Some(val);
                 Ok(())
             }
+            "unit_exponent" => {
+                self.unit_exponent = Some(val);
+                Ok(())
+            }
             // Local items.
             "usage" => {
                 self.usage.push(val);