diff --git a/builder/frameworks/_bare.py b/builder/frameworks/_bare.py
index 4fd489e..a083fa9 100644
--- a/builder/frameworks/_bare.py
+++ b/builder/frameworks/_bare.py
@@ -21,7 +21,12 @@ from SCons.Script import DefaultEnvironment
 env = DefaultEnvironment()
 
 env.Append(
-    ASFLAGS=["-x", "assembler-with-cpp"],
+    ASFLAGS=[
+        "-mthumb",
+    ],
+    ASPPFLAGS=[
+        "-x", "assembler-with-cpp",
+    ],
 
     CCFLAGS=[
         "-Os",  # optimize for size
@@ -54,6 +59,9 @@ env.Append(
 
 if "BOARD" in env:
     env.Append(
+        ASFLAGS=[
+            "-mcpu=%s" % env.BoardConfig().get("build.cpu")
+        ],
         CCFLAGS=[
             "-mcpu=%s" % env.BoardConfig().get("build.cpu")
         ],
@@ -61,6 +69,3 @@ if "BOARD" in env:
             "-mcpu=%s" % env.BoardConfig().get("build.cpu")
         ]
     )
-
-# copy CCFLAGS to ASFLAGS (-x assembler-with-cpp mode)
-env.Append(ASFLAGS=env.get("CCFLAGS", [])[:])
diff --git a/builder/frameworks/arduino/mbed-core b/builder/frameworks/arduino/mbed-core
index 36ee4ff..ed9a345 160000
--- a/builder/frameworks/arduino/mbed-core
+++ b/builder/frameworks/arduino/mbed-core
@@ -1 +1 @@
-Subproject commit 36ee4ff8adb0d80d6ff15e03b34e7b10a147b4d0
+Subproject commit ed9a3458e336660fdf2b1d4a4c828a2ddfd214ad