diff --git a/cores/arduino/HardwareSerial.cpp b/cores/arduino/HardwareSerial.cpp
index 561127f9f..2523865ef 100644
--- a/cores/arduino/HardwareSerial.cpp
+++ b/cores/arduino/HardwareSerial.cpp
@@ -44,21 +44,33 @@
 #if defined(HAVE_HWSERIAL0)
   void serialEvent() __attribute__((weak));
   bool Serial0_available() __attribute__((weak));
+
+  void serialEvent() { }
+  bool Serial0_available() { return false; }
 #endif
 
 #if defined(HAVE_HWSERIAL1)
   void serialEvent1() __attribute__((weak));
   bool Serial1_available() __attribute__((weak));
+
+  void serialEvent1() { }
+  bool Serial1_available() { return false; }
 #endif
 
 #if defined(HAVE_HWSERIAL2)
   void serialEvent2() __attribute__((weak));
   bool Serial2_available() __attribute__((weak));
+
+  void serialEvent2() { }
+  bool Serial2_available() { return false; }
 #endif
 
 #if defined(HAVE_HWSERIAL3)
   void serialEvent3() __attribute__((weak));
   bool Serial3_available() __attribute__((weak));
+
+  void serialEvent3() { }
+  bool Serial3_available() { return false; }
 #endif
 
 void serialEventRun(void)
diff --git a/cores/arduino/HardwareSerial.h b/cores/arduino/HardwareSerial.h
index 6ff29d0b9..3e12e779f 100644
--- a/cores/arduino/HardwareSerial.h
+++ b/cores/arduino/HardwareSerial.h
@@ -156,6 +156,6 @@ class HardwareSerial : public Stream
   #define HAVE_HWSERIAL3
 #endif
 
-extern void serialEventRun(void) __attribute__((weak));
+extern void serialEventRun(void);
 
 #endif
diff --git a/cores/arduino/main.cpp b/cores/arduino/main.cpp
index 434cd403c..e5b9248c0 100644
--- a/cores/arduino/main.cpp
+++ b/cores/arduino/main.cpp
@@ -44,7 +44,7 @@ int main(void)
     
 	for (;;) {
 		loop();
-		if (serialEventRun) serialEventRun();
+		serialEventRun();
 	}
         
 	return 0;
diff --git a/extras/pack.release.bash b/extras/pack.release.bash
index a2999d505..cf17bb39c 100755
--- a/extras/pack.release.bash
+++ b/extras/pack.release.bash
@@ -26,8 +26,10 @@ THIS_SCRIPT_NAME=`basename $0`
 rm -f avr-$VERSION.tar.bz2
 
 cd ..
-tar --transform "s|$FOLDERNAME|$FOLDERNAME-$VERSION|g"  --exclude=extras/** --exclude=.git* --exclude=.idea -cjf avr-$VERSION.tar.bz2 $FOLDERNAME
+tar --transform "s|$FOLDERNAME|$FOLDERNAME-$VERSION|g"  --exclude=extras/** --exclude=.git* --exclude=.idea -cjf cba-avr-$VERSION.tar.bz2 $FOLDERNAME
 cd -
 
-mv ../avr-$VERSION.tar.bz2 .
+mv ../cba-avr-$VERSION.tar.bz2 .
+echo "SHA256: $(sha256sum cba-avr-${VERSION}.tar.bz2)"
+echo "size: $(stat -c%s cba-avr-${VERSION}.tar.bz2)"
 
diff --git a/platform.txt b/platform.txt
index df5ddb712..5a9dfd76f 100644
--- a/platform.txt
+++ b/platform.txt
@@ -5,8 +5,8 @@
 # For more info:
 # https://arduino.github.io/arduino-cli/latest/platform-specification/
 
-name=Arduino AVR Boards
-version=1.8.6
+name=ClangBuiltArduino AVR Boards
+version=1.0.0
 
 # AVR compile variables
 # ---------------------
@@ -18,23 +18,23 @@ compiler.warning_flags.more=-Wall
 compiler.warning_flags.all=-Wall -Wextra
 
 # Default "compiler.path" is correct, change only if you want to override the initial value
-compiler.path={runtime.tools.avr-gcc.path}/bin/
-compiler.c.cmd=avr-gcc
-compiler.c.flags=-c -g -Os {compiler.warning_flags} -std=gnu11 -ffunction-sections -fdata-sections -MMD -flto -fno-fat-lto-objects
-compiler.c.elf.flags={compiler.warning_flags} -Os -g -flto -fuse-linker-plugin -Wl,--gc-sections
-compiler.c.elf.cmd=avr-gcc
-compiler.S.flags=-c -g -x assembler-with-cpp -flto -MMD
-compiler.cpp.cmd=avr-g++
-compiler.cpp.flags=-c -g -Os {compiler.warning_flags} -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto
-compiler.ar.cmd=avr-gcc-ar
+compiler.path={runtime.tools.cba-llvm.path}/bin/
+compiler.c.cmd=clang
+compiler.c.flags=--target=avr -c -g -Os {compiler.warning_flags} --sysroot={runtime.tools.cba-avr-sysroot.path} -std=gnu11 -ffunction-sections -fdata-sections -MMD -flto -fno-fat-lto-objects
+compiler.c.elf.flags=--target=avr -mno-relax {compiler.warning_flags} --sysroot={runtime.tools.cba-avr-sysroot.path} -Os -g -flto -fuse-linker-plugin -ffunction-sections -fdata-sections -Wl,--gc-sections --bfd-dir={runtime.tools.cba-avr-bfd.path} --llvmgold-dir={runtime.tools.cba-llvmgold.path}
+compiler.c.elf.cmd=clang++-wrapper
+compiler.S.flags=--target=avr --sysroot={runtime.tools.cba-avr-sysroot.path} -c -g -x assembler-with-cpp -flto -MMD
+compiler.cpp.cmd=clang++
+compiler.cpp.flags=--target=avr -c -g -Os {compiler.warning_flags} --sysroot={runtime.tools.cba-avr-sysroot.path} -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fno-rtti -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -flto -MMD
+compiler.ar.cmd=llvm-ar
 compiler.ar.flags=rcs
-compiler.objcopy.cmd=avr-objcopy
-compiler.objcopy.eep.flags=-O ihex -j .eeprom --set-section-flags=.eeprom=alloc,load --no-change-warnings --change-section-lma .eeprom=0
+compiler.objcopy.cmd=llvm-objcopy
+compiler.objcopy.eep.flags=-O ihex -j .eeprom --set-section-flags=.eeprom=alloc,load
 compiler.elf2hex.flags=-O ihex -R .eeprom
-compiler.elf2hex.cmd=avr-objcopy
+compiler.elf2hex.cmd=llvm-objcopy
 compiler.ldflags=
 compiler.libraries.ldflags=
-compiler.size.cmd=avr-size
+compiler.size.cmd=llvm-size
 
 # This can be overridden in boards.txt
 build.extra_flags=