diff --git a/CMSIS/README b/CMSIS/README
index ff42ebe..369c323 100644
--- a/CMSIS/README
+++ b/CMSIS/README
@@ -1,2 +1,14 @@
-The files under this folder are copied from:
+The source codes under this folder are copied from:
 https://github.com/ARM-software/CMSIS_5.git, tag 5.5.0, without modifications.
+
+The prebuilt libraries have two versions:
+ - v5.5.0 for ARMCLANG and GCC compilers
+ - v5.7.0 for IAR compiler
+
+The v5.7.0 libraries for ARMCLANG and GCC have linking issues on Musca_A and
+AN524. So libraries for these two compilers keep using v5.5.0 which has been
+tested and verified.
+
+The IAR libraries of v5.5.0 has a problem and has been updated in CMSIS_5 5.7.0.
+So IAR libraries use v5.7.0.
+