diff --git a/include/etl/integral_limits.h b/include/etl/integral_limits.h
index f30f63a58..8ac9aa804 100644
--- a/include/etl/integral_limits.h
+++ b/include/etl/integral_limits.h
@@ -460,7 +460,7 @@ namespace etl
     ETL_CONSTANT bool statics_char32_t<T>::is_signed;
 #endif
 
-#ifdef ETL_20_BIT
+#if ETL_USING_20BIT_TYPES
 template <typename T = void>
     struct statics___int20
     {
@@ -604,11 +604,12 @@ template <typename T = void>
   struct integral_limits<unsigned long long> : public private_integral_limits::statics_unsigned_long_long<>
   {
   };
-  #ifdef ETL_20_BIT
-    //***************************************************************************
+
+  #if ETL_USING_20BIT_TYPES
+  //***************************************************************************
   ///\ingroup integral_limits
   //***************************************************************************
-    template <>
+  template <>
   struct integral_limits<__int20> : public private_integral_limits::statics___int20<>
   {
   };
diff --git a/include/etl/platform.h b/include/etl/platform.h
index 17c7961d5..f89ede6fb 100644
--- a/include/etl/platform.h
+++ b/include/etl/platform.h
@@ -117,6 +117,17 @@ SOFTWARE.
 
 #define ETL_8BIT_SUPPORT (CHAR_BIT == 8) // Deprecated
 
+//*************************************
+// Some targets support 20bit types.
+#if defined(ETL_USE_20BIT_TYPES)
+  #define ETL_USING_20BIT_TYPES     1
+  #define ETL_NOT_USING_20BIT_TYPES 0
+#else
+  #define ETL_USING_20BIT_TYPES     0
+  #define ETL_NOT_USING_20BIT_TYPES 1
+#endif
+
+
 //*************************************
 // Helper macro for ETL_NO_64BIT_TYPES.
 #if defined(ETL_NO_64BIT_TYPES)
diff --git a/support/Release notes.txt b/support/Release notes.txt
index cc50700d0..c65f3142f 100644
--- a/support/Release notes.txt	
+++ b/support/Release notes.txt	
@@ -1,4 +1,40 @@
 ===============================================================================
+20.39.0
+
+Refactored:
+Breaking change.
+Modified io_port classes so that they are not derived from iterator types.
+    Added iterator and const_iterator types.
+    Added iter() and citer() member functions to get an iterator.
+    Added &= |= ^= <<= >>= and ~ operators (only available for io_port_rw and io_port_wos types)
+    Added static asserts to only allow integral types.
+
+Fixes:
+#921 unique_ptr reset
+#923 Missing equality operator for class expected 
+#930 Unused parameter warnings
+#931 Using etl::make_vector to make a vector of two pairs causes a compile error
+
+Features:
+#918 Request for additional operator support for etl::io_port_*
+#919 callback_timer: expose callback_timer_data::is_active() as icallback_timer public method 
+#920 Define ETL_USING_LEGACY_VARIANT as a convenience macro for code that tries to support both new and legacy variants
+
+Pull Requests
+#909 fix c++20-compat false positive
+#914 Fix doc comment for pool::allocate()
+#924 Add an etl::nullptr_t type to <etl/nullptr.h>
+#925 Add equality operators for class expected
+#926 Fix issue #923 equality operator for class expected
+#927 Fix missing partial specialisation equal operators
+#928 Add missing swap implementations for expected
+#929 Fix run-tests.sh script
+#932 Fix issue #931 Using etl::make_vector to make a vector of two pairs causes a compile error
+#934 Fixes compiler detection with Wundef
+#935 Added 20 bit integral limits (MSP430 devices)
+     New configuration macro, ETL_USE_20BIT_TYPES, which controls the definition of ETL_USING_20BIT_TYPES and ETL_NOT_USING_20BIT_TYPES.
+
+===============================================================================
 20.38.17
 
 #895 Removed std algorithm calls from algorithm.h