diff --git a/arduino/libretuya/common/main.cpp b/arduino/libretuya/common/main.cpp
new file mode 100644
index 0000000..e2a11f1
--- /dev/null
+++ b/arduino/libretuya/common/main.cpp
@@ -0,0 +1,40 @@
+/* Copyright (c) Kuba Szczodrzyński 2022-06-19. */
+
+#include <Arduino.h>
+#include <api/HardwareSerial.h>
+
+using namespace arduino;
+
+// Weak empty variant initialization function.
+// May be redefined by variant files.
+void initVariant() __attribute__((weak));
+
+// Initialize C library
+extern "C" void __libc_init_array(void);
+
+void main_task(const void *arg) {
+	setup();
+
+	for (;;) {
+		loop();
+		if (serialEventRun)
+			serialEventRun();
+		yield();
+	}
+}
+
+int main(void) {
+	// print a startup banner
+	LT_BANNER();
+	// initialize Arduino framework
+	init();
+	// initialize C library
+	__libc_init_array();
+	// optionally initialize per-variant code
+	initVariant();
+	// start the main task and OS kernel
+	startMainTask();
+
+	while (1) {}
+	return 0;
+}
diff --git a/arduino/libretuya/common/serial_event.cpp b/arduino/libretuya/common/serial_event.cpp
new file mode 100644
index 0000000..85a0822
--- /dev/null
+++ b/arduino/libretuya/common/serial_event.cpp
@@ -0,0 +1,11 @@
+/* Copyright (c) Kuba Szczodrzyński 2022-06-19. */
+
+#include <Arduino.h>
+
+void serialEvent() __attribute__((weak));
+bool Serial_available() __attribute__((weak));
+
+void serialEventRun(void) {
+	if (Serial_available && serialEvent && Serial_available())
+		serialEvent();
+}
diff --git a/arduino/libretuya/core/LibreTuyaAPI.h b/arduino/libretuya/core/LibreTuyaAPI.h
index 8d74318..18d91f9 100644
--- a/arduino/libretuya/core/LibreTuyaAPI.h
+++ b/arduino/libretuya/core/LibreTuyaAPI.h
@@ -2,6 +2,11 @@
 
 #pragma once
 
+// C standard libraries
+#include <stdarg.h>
+#include <stddef.h>
+#include <stdint.h>
+
 // LibreTuya version macros
 #ifndef LT_VERSION
 #define LT_VERSION 1.0.0
diff --git a/arduino/libretuya/core/LibreTuyaCustom.h b/arduino/libretuya/core/LibreTuyaCustom.h
index 7119fd2..205f726 100644
--- a/arduino/libretuya/core/LibreTuyaCustom.h
+++ b/arduino/libretuya/core/LibreTuyaCustom.h
@@ -1,11 +1,24 @@
 /* Copyright (c) Kuba Szczodrzyński 2022-06-06. */
 
+#pragma once
+
 #include "LibreTuyaAPI.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+/**
+ * @brief Run main_task & start OS kernel (family-defined)
+ */
+extern bool startMainTask();
+
+/**
+ * @brief Main setup() and loop() task.
+ * Not to be called directly.
+ */
+extern void main_task(const void *arg);
+
 #define PIN_NONE (1 << 0)
 #define PIN_GPIO (1 << 1)
 #define PIN_IRQ	 (1 << 2)
diff --git a/arduino/libretuya/libraries/MD5/MD5.h b/arduino/libretuya/libraries/MD5/MD5.h
index 593d72a..4aae25e 100644
--- a/arduino/libretuya/libraries/MD5/MD5.h
+++ b/arduino/libretuya/libraries/MD5/MD5.h
@@ -2,6 +2,7 @@
 
 #pragma once
 
+#include <Arduino.h>
 #include <MD5Impl.h>
 
 // available built-in implementations
diff --git a/arduino/libretuya/libraries/MD5/MD5PolarSSLImpl.cpp b/arduino/libretuya/libraries/MD5/MD5PolarSSLImpl.cpp
index f03ddb7..fe5b032 100644
--- a/arduino/libretuya/libraries/MD5/MD5PolarSSLImpl.cpp
+++ b/arduino/libretuya/libraries/MD5/MD5PolarSSLImpl.cpp
@@ -1,14 +1,9 @@
 /* Copyright (c) Kuba Szczodrzyński 2022-06-03. */
 
-// check if impl defines LT_MD5_USE_POLARSSL
-extern "C" {
-#include <MD5Impl.h>
-}
+#include "MD5.h"
 
 #if LT_MD5_USE_POLARSSL
 
-#include "MD5PolarSSLImpl.h"
-
 extern "C" {
 
 void MD5Init(LT_MD5_CTX_T *context) {
diff --git a/arduino/libretuya/libraries/MD5/MD5PolarSSLImpl.h b/arduino/libretuya/libraries/MD5/MD5PolarSSLImpl.h
index 7cad1fc..778d526 100644
--- a/arduino/libretuya/libraries/MD5/MD5PolarSSLImpl.h
+++ b/arduino/libretuya/libraries/MD5/MD5PolarSSLImpl.h
@@ -12,5 +12,3 @@ extern "C" {
 #ifdef __cplusplus
 } // extern "C"
 #endif
-
-#include "MD5.h"
diff --git a/arduino/realtek-ambz/cores/arduino/WVariant.h b/arduino/realtek-ambz/cores/arduino/WVariant.h
index 6e7e5ac..71902f3 100644
--- a/arduino/realtek-ambz/cores/arduino/WVariant.h
+++ b/arduino/realtek-ambz/cores/arduino/WVariant.h
@@ -1,9 +1,5 @@
 #pragma once
 
-#include <stdarg.h>
-#include <stddef.h>
-#include <stdint.h>
-
 #ifdef __cplusplus
 extern "C" {
 #endif
diff --git a/arduino/realtek-ambz/cores/arduino/main.cpp b/arduino/realtek-ambz/cores/arduino/main.cpp
index 8a02de6..39804c5 100644
--- a/arduino/realtek-ambz/cores/arduino/main.cpp
+++ b/arduino/realtek-ambz/cores/arduino/main.cpp
@@ -22,53 +22,13 @@
 #include <Arduino.h>
 #include <cmsis_os.h>
 
-// Weak empty variant initialization function.
-// May be redefined by variant files.
-void initVariant() __attribute__((weak));
-
-void initVariant() {}
-
-// Initialize C library
-extern "C" void __libc_init_array(void);
-
 osThreadId main_tid = 0;
 
-void main_task(const void *arg) {
-	setup();
-
-	for (;;) {
-		loop();
-		if (serialEventRun)
-			serialEventRun();
-		yield();
-	}
-}
-
-int main(void) {
-	LT_BANNER();
-	init();
-
-	__libc_init_array();
-
-	initVariant();
-
+bool startMainTask() {
 	osThreadDef(main_task, osPriorityRealtime, 1, 4096 * 4);
 	main_tid = osThreadCreate(osThread(main_task), NULL);
-
 	osKernelStart();
-
-	while (1)
-		;
-
-	return 0;
-}
-
-void serialEvent() __attribute__((weak));
-bool Serial_available() __attribute__((weak));
-
-void serialEventRun(void) {
-	if (Serial_available && serialEvent && Serial_available())
-		serialEvent();
+	return true;
 }
 
 void wait_for_debug() {
diff --git a/arduino/realtek-ambz/cores/arduino/sdk_extern.h b/arduino/realtek-ambz/cores/arduino/sdk_extern.h
index 09ea421..da658dd 100644
--- a/arduino/realtek-ambz/cores/arduino/sdk_extern.h
+++ b/arduino/realtek-ambz/cores/arduino/sdk_extern.h
@@ -2,9 +2,8 @@
 
 #pragma once
 
+// va_list is declared by SDK and conflicting
 #include <stdarg.h>
-#include <stddef.h>
-#include <stdint.h>
 
 // disable typedef in basic_types.h
 #define boolean boolean_rtl
diff --git a/arduino/realtek-ambz/libraries/MD5/MD5Impl.h b/arduino/realtek-ambz/libraries/MD5/MD5Impl.h
index ba7753f..e9bb3d8 100644
--- a/arduino/realtek-ambz/libraries/MD5/MD5Impl.h
+++ b/arduino/realtek-ambz/libraries/MD5/MD5Impl.h
@@ -2,6 +2,4 @@
 
 #pragma once
 
-#include <sdk_extern.h>
-
 #define LT_MD5_USE_POLARSSL 1