diff --git a/builder/frameworks/arduino.py b/builder/frameworks/arduino.py
index 3d150e1..d2e0d40 100644
--- a/builder/frameworks/arduino.py
+++ b/builder/frameworks/arduino.py
@@ -34,7 +34,7 @@ for f in family.inheritance:
     code = f"{f.code}_arduino"
     path = join("$CORES_DIR", f.name, "arduino")
 
-    found = found or env.AddCoreSources(queue, name=code, path=join(path, "src"))
+    found = env.AddCoreSources(queue, name=code, path=join(path, "src")) or found
     env.AddArduinoLibraries(queue, name=code, path=join(path, "libraries"))
 
     if f.short_name:
diff --git a/cores/beken-72xx/arduino/libraries/Serial/Serial.cpp b/cores/beken-72xx/arduino/libraries/Serial/Serial.cpp
index 6e90c20..50f7bbc 100644
--- a/cores/beken-72xx/arduino/libraries/Serial/Serial.cpp
+++ b/cores/beken-72xx/arduino/libraries/Serial/Serial.cpp
@@ -1,18 +1,6 @@
 /* Copyright (c) Kuba Szczodrzyński 2022-06-23. */
 
-#include "Serial.h"
-
-#include <Arduino.h>
-
-extern "C" {
-
-#include <uart_pub.h>
-
-extern void bk_send_byte(uint8_t uport, uint8_t data);
-extern void uart_hw_set_change(uint8_t uport, bk_uart_config_t *uart_config);
-extern int uart_rx_callback_set(int uport, uart_callback callback, void *param);
-
-} // extern "C"
+#include "SerialPrivate.h"
 
 #if HAS_SERIAL1
 SerialClass Serial1(UART1_PORT);
@@ -21,39 +9,22 @@ SerialClass Serial1(UART1_PORT);
 SerialClass Serial2(UART2_PORT);
 #endif
 
-SerialClass::SerialClass(uint8_t port) {
-	this->port = port;
-	this->buf  = NULL;
-}
-
-#if LT_AUTO_DOWNLOAD_REBOOT
-static uint8_t adrState		  = 0;
-static const uint8_t adrCmd[] = {0x01, 0xE0, 0xFC, 0x01, 0x00};
-
-static void adrParse(uint8_t c) {
-	// parse and respond to link check command (CMD_LinkCheck=0)
-	adrState = (adrState + 1) * (c == adrCmd[adrState]);
-	if (adrState == 5) {
-		LT_I("Auto download mode: rebooting");
-		LT.restart();
-	}
-}
-#endif
-
 static void callback(int port, void *param) {
-	RingBuffer *buf = (RingBuffer *)param;
 	int ch;
 	while ((ch = uart_read_byte(port)) != -1) {
-#if LT_AUTO_DOWNLOAD_REBOOT && defined(PIN_SERIAL1_RX)
+#if LT_AUTO_DOWNLOAD_REBOOT && defined(LT_UART_ADR_PATTERN) && defined(PIN_SERIAL1_RX)
 		// parse UART protocol commands on UART1
 		if (port == UART1_PORT)
-			adrParse(ch);
+			SerialClass::adrParse(ch);
 #endif
-		buf->store_char(ch);
+		pBUF->store_char(ch);
 	}
 }
 
 void SerialClass::begin(unsigned long baudrate, uint16_t config) {
+	this->data = new SerialData();
+	this->buf  = &BUF;
+
 	uint8_t dataWidth = ((config & SERIAL_DATA_MASK) >> 8) - 1;				  // 0x100..0x400 -> 0..3
 	uint8_t parity	  = 3 - (config & SERIAL_PARITY_MASK);					  // 0x3..0x1 -> 0..2
 	uint8_t stopBits  = (config & SERIAL_STOP_BIT_MASK) == SERIAL_STOP_BIT_2; // 0x10..0x30 -> 0..1
@@ -66,14 +37,8 @@ void SerialClass::begin(unsigned long baudrate, uint16_t config) {
 		.flow_control = FLOW_CTRL_DISABLED,
 	};
 
-	if (this->buf) {
-		this->buf->clear();
-	} else {
-		this->buf = new RingBuffer();
-	}
-
 	uart_hw_set_change(port, &cfg);
-	uart_rx_callback_set(port, callback, this->buf);
+	uart_rx_callback_set(port, callback, &BUF);
 }
 
 void SerialClass::end() {
@@ -86,19 +51,8 @@ void SerialClass::end() {
 			uart2_exit();
 			break;
 	}
-	delete this->buf;
-}
-
-int SerialClass::available() {
-	return buf->available();
-}
-
-int SerialClass::peek() {
-	return buf->peek();
-}
-
-int SerialClass::read() {
-	return buf->read_char();
+	this->buf = NULL;
+	delete DATA;
 }
 
 void SerialClass::flush() {
diff --git a/cores/beken-72xx/arduino/libraries/Serial/SerialPrivate.h b/cores/beken-72xx/arduino/libraries/Serial/SerialPrivate.h
new file mode 100644
index 0000000..c481237
--- /dev/null
+++ b/cores/beken-72xx/arduino/libraries/Serial/SerialPrivate.h
@@ -0,0 +1,14 @@
+/* Copyright (c) Kuba Szczodrzyński 2023-05-24. */
+
+#pragma once
+
+#include <Arduino.h>
+#include <sdk_private.h>
+
+typedef struct {
+	RingBuffer buf;
+} SerialData;
+
+#define DATA ((SerialData *)data)
+#define BUF	 (DATA->buf)
+#define pBUF ((RingBuffer *)param)
diff --git a/cores/beken-72xx/base/lt_family.h b/cores/beken-72xx/base/lt_family.h
index 4484a1d..fce1aa6 100644
--- a/cores/beken-72xx/base/lt_family.h
+++ b/cores/beken-72xx/base/lt_family.h
@@ -14,3 +14,7 @@
 #error "No serial port is available"
 #endif
 #endif
+
+// Auto-download-reboot detection pattern
+// Link check command (CMD_LinkCheck=0)
+#define LT_UART_ADR_PATTERN 0x01, 0xE0, 0xFC, 0x01, 0x00
diff --git a/cores/beken-72xx/base/sdk_extern.h b/cores/beken-72xx/base/sdk_extern.h
new file mode 100644
index 0000000..08452ac
--- /dev/null
+++ b/cores/beken-72xx/base/sdk_extern.h
@@ -0,0 +1,24 @@
+/* Copyright (c) Kuba Szczodrzyński 2023-05-24. */
+
+#pragma once
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif // __cplusplus
+
+#include <uart_pub.h>
+
+// SDK
+extern uint8_t system_mac[];
+extern int uart_print_port;
+uint32_t wdt_ctrl(uint32_t cmd, void *param);
+void bk_send_byte(uint8_t uport, uint8_t data);
+void uart_hw_set_change(uint8_t uport, bk_uart_config_t *uart_config);
+int uart_rx_callback_set(int uport, uart_callback callback, void *param);
+
+#ifdef __cplusplus
+} // extern "C"
+#endif
diff --git a/cores/beken-72xx/base/sdk_private.h b/cores/beken-72xx/base/sdk_private.h
index 41d6a56..044e2cb 100644
--- a/cores/beken-72xx/base/sdk_private.h
+++ b/cores/beken-72xx/base/sdk_private.h
@@ -19,9 +19,7 @@ extern "C" {
 #include <wdt_pub.h>
 #include <wlan_ui_pub.h>
 
-extern uint8_t system_mac[];
-extern uint32_t wdt_ctrl(uint32_t cmd, void *param);
-extern int uart_print_port;
+#include <sdk_extern.h>
 
 // conflict with stl_algobase.h
 #undef min
diff --git a/cores/common/arduino/libraries/api/Serial/Serial.cpp b/cores/common/arduino/libraries/api/Serial/Serial.cpp
new file mode 100644
index 0000000..2f64f42
--- /dev/null
+++ b/cores/common/arduino/libraries/api/Serial/Serial.cpp
@@ -0,0 +1,34 @@
+/* Copyright (c) Kuba Szczodrzyński 2023-05-23. */
+
+#include "Serial.h"
+
+SerialClass::SerialClass(uint32_t port) {
+	this->port = port;
+	this->buf  = NULL;
+	this->data = NULL;
+}
+
+#if LT_AUTO_DOWNLOAD_REBOOT && defined(LT_UART_ADR_PATTERN)
+static uint8_t adrState = 0;
+static uint8_t adrCmd[] = {LT_UART_ADR_PATTERN};
+
+void SerialClass::adrParse(uint8_t c) {
+	adrState = (adrState + 1) * (c == adrCmd[adrState]);
+	if (adrState == sizeof(adrCmd) / sizeof(uint8_t)) {
+		LT_I("Auto download mode: rebooting");
+		LT.restartDownloadMode();
+	}
+}
+#endif
+
+int SerialClass::available() {
+	return this->buf && this->buf->available();
+}
+
+int SerialClass::peek() {
+	return this->buf ? this->buf->peek() : -1;
+}
+
+int SerialClass::read() {
+	return this->buf ? this->buf->read_char() : -1;
+}
diff --git a/cores/beken-72xx/arduino/libraries/Serial/Serial.h b/cores/common/arduino/libraries/api/Serial/Serial.h
similarity index 72%
rename from cores/beken-72xx/arduino/libraries/Serial/Serial.h
rename to cores/common/arduino/libraries/api/Serial/Serial.h
index 5c77c4d..ca46229 100644
--- a/cores/beken-72xx/arduino/libraries/Serial/Serial.h
+++ b/cores/common/arduino/libraries/api/Serial/Serial.h
@@ -2,7 +2,7 @@
 
 #pragma once
 
-#include <api/ArduinoAPI.h>
+#include <Arduino.h>
 #include <api/HardwareSerial.h>
 #include <api/RingBuffer.h>
 
@@ -10,11 +10,14 @@ using namespace arduino;
 
 class SerialClass : public HardwareSerial {
   private:
-	uint8_t port;
+	uint32_t port;
 	RingBuffer *buf;
 
   public:
-	SerialClass(uint8_t port);
+	void *data;
+
+  public:
+	SerialClass(uint32_t port);
 
 	inline void begin(unsigned long baudrate) {
 		begin(baudrate, SERIAL_8N1);
@@ -32,5 +35,12 @@ class SerialClass : public HardwareSerial {
 		return !!buf;
 	}
 
+  public:
+#if LT_AUTO_DOWNLOAD_REBOOT
+	static void adrParse(uint8_t c);
+#endif
+
 	using Print::write;
 };
+
+#define HAS_SERIAL_CLASS 1
diff --git a/cores/common/arduino/src/Arduino.h b/cores/common/arduino/src/Arduino.h
index dec3c7e..7e3e184 100644
--- a/cores/common/arduino/src/Arduino.h
+++ b/cores/common/arduino/src/Arduino.h
@@ -42,6 +42,7 @@ using std::min;
 #if defined(__cplusplus) && LT_ARD_HAS_SERIAL
 #include <Serial.h>
 
+#if HAS_SERIAL_CLASS
 #if HAS_SERIAL0
 extern SerialClass Serial0;
 #endif
@@ -51,6 +52,7 @@ extern SerialClass Serial1;
 #if HAS_SERIAL2
 extern SerialClass Serial2;
 #endif
+#endif
 
 #define SerialN(x) Serial##x
 #define SerialM(x) SerialN(x)
diff --git a/cores/common/arduino/src/wiring_custom.h b/cores/common/arduino/src/wiring_custom.h
index 4dd43f1..392e280 100644
--- a/cores/common/arduino/src/wiring_custom.h
+++ b/cores/common/arduino/src/wiring_custom.h
@@ -21,6 +21,8 @@ extern "C" {
 #define PIN_SWD	 (1 << 10)
 #define PIN_UART (1 << 11)
 
+#define PIN_INVALID 255
+
 typedef struct {
 	/**
 	 * @brief GPIO name in the family SDK.
diff --git a/cores/realtek-amb/arduino/libraries/Serial/Serial.cpp b/cores/realtek-amb/arduino/libraries/Serial/Serial.cpp
deleted file mode 100644
index c387d47..0000000
--- a/cores/realtek-amb/arduino/libraries/Serial/Serial.cpp
+++ /dev/null
@@ -1,146 +0,0 @@
-/* Copyright (c) Kuba Szczodrzyński 2022-07-03. */
-
-#include "Serial.h"
-
-#include <Arduino.h>
-#include <sdk_private.h>
-
-#if HAS_SERIAL0
-SerialClass Serial0(UART0_DEV, UART0_IRQ, PIN_SERIAL0_RX, PIN_SERIAL0_TX);
-#endif
-#if HAS_SERIAL1
-SerialClass Serial1(UART1_DEV, UART1_IRQ, PIN_SERIAL1_RX, PIN_SERIAL1_TX);
-#endif
-#if HAS_SERIAL2
-SerialClass Serial2(UART2_DEV, UART_LOG_IRQ, PIN_SERIAL2_RX, PIN_SERIAL2_TX);
-#endif
-
-SerialClass::SerialClass(void *uart, uint8_t irq, pin_size_t rx, pin_size_t tx) {
-	data.uart = uart;
-	data.buf  = NULL;
-	this->irq = irq;
-	this->rx  = rx;
-	this->tx  = tx;
-}
-
-#if LT_AUTO_DOWNLOAD_REBOOT
-static uint8_t adrState = 0;
-
-// clang-format off
-// Family ID, big-endian
-static const uint8_t adrCmd[] = {
-	0x55, 0xAA,
-	(FAMILY >> 24) & 0xFF,
-	(FAMILY >> 16) & 0xFF,
-	(FAMILY >> 8) & 0xFF,
-	(FAMILY >> 0) & 0xFF
-};
-
-// clang-format on
-
-static void adrParse(uint8_t c) {
-	adrState = (adrState + 1) * (c == adrCmd[adrState]);
-	if (adrState == 6) {
-		LT_I("Auto download mode: rebooting");
-		LT.restartDownloadMode();
-	}
-}
-#endif
-
-static uint32_t callback(void *param) {
-	SerialData *data   = (SerialData *)param;
-	UART_TypeDef *uart = (UART_TypeDef *)data->uart;
-
-	uint32_t intcr	= uart->DLH_INTCR;
-	uart->DLH_INTCR = 0;
-
-	uint8_t c;
-	while (UART_Readable(uart)) {
-		UART_CharGet(uart, &c);
-#if LT_AUTO_DOWNLOAD_REBOOT && defined(PIN_SERIAL2_RX)
-		// parse UART protocol commands on UART2
-		if (uart == UART2_DEV)
-			adrParse(c);
-#endif
-		data->buf->store_char(c);
-	}
-
-	uart->DLH_INTCR = intcr;
-	return 0;
-}
-
-void SerialClass::begin(unsigned long baudrate, uint16_t config) {
-	// RUART_WLS_7BITS / RUART_WLS_8BITS
-	uint8_t dataWidth = (config & SERIAL_DATA_MASK) == SERIAL_DATA_8;
-	// RUART_PARITY_DISABLE / RUART_PARITY_ENABLE
-	uint8_t parity = (config & SERIAL_PARITY_MASK) != SERIAL_PARITY_NONE;
-	// RUART_ODD_PARITY / RUART_EVEN_PARITY
-	uint8_t parityType = (config & SERIAL_PARITY_MASK) == SERIAL_PARITY_EVEN;
-	// RUART_STOP_BIT_1 / RUART_STOP_BIT_2
-	uint8_t stopBits = (config & SERIAL_STOP_BIT_MASK) == SERIAL_STOP_BIT_2;
-
-	switch ((uint32_t)data.uart) {
-		case UART0_REG_BASE:
-			RCC_PeriphClockCmd(APBPeriph_UART0, APBPeriph_UART0_CLOCK, ENABLE);
-			break;
-		case UART1_REG_BASE:
-			RCC_PeriphClockCmd(APBPeriph_UART1, APBPeriph_UART1_CLOCK, ENABLE);
-			break;
-	}
-
-	Pinmux_Config(pinInfo(this->rx)->gpio, PINMUX_FUNCTION_UART);
-	Pinmux_Config(pinInfo(this->tx)->gpio, PINMUX_FUNCTION_UART);
-	PAD_PullCtrl(pinInfo(this->rx)->gpio, GPIO_PuPd_UP);
-
-	UART_InitTypeDef cfg;
-	UART_StructInit(&cfg);
-	cfg.WordLen	   = dataWidth;
-	cfg.Parity	   = parity;
-	cfg.ParityType = parityType;
-	cfg.StopBit	   = stopBits;
-	UART_Init((UART_TypeDef *)data.uart, &cfg);
-	UART_SetBaud((UART_TypeDef *)data.uart, baudrate);
-
-	if (data.buf) {
-		data.buf->clear();
-	} else {
-		data.buf = new RingBuffer();
-	}
-
-	VECTOR_IrqUnRegister(this->irq);
-	VECTOR_IrqRegister(callback, this->irq, (uint32_t)&data, 10);
-	VECTOR_IrqEn(this->irq, 10);
-
-	UART_RxCmd((UART_TypeDef *)data.uart, ENABLE);
-	UART_INTConfig((UART_TypeDef *)data.uart, RUART_IER_ERBI, ENABLE);
-}
-
-void SerialClass::end() {
-	if (data.uart == UART2_DEV) {
-		// restore command line mode
-		DIAG_UartReInit((IRQ_FUN)UartLogIrqHandle);
-	}
-	delete data.buf;
-}
-
-int SerialClass::available() {
-	return data.buf->available();
-}
-
-int SerialClass::peek() {
-	return data.buf->peek();
-}
-
-int SerialClass::read() {
-	return data.buf->read_char();
-}
-
-void SerialClass::flush() {
-	UART_WaitBusy((UART_TypeDef *)data.uart, 10);
-}
-
-size_t SerialClass::write(uint8_t c) {
-	while (UART_Writable((UART_TypeDef *)data.uart) == 0) {}
-	UART_CharPut((UART_TypeDef *)data.uart, c);
-	return 1;
-}
diff --git a/cores/realtek-amb/arduino/libraries/Serial/Serial.h b/cores/realtek-amb/arduino/libraries/Serial/Serial.h
deleted file mode 100644
index aa0a78b..0000000
--- a/cores/realtek-amb/arduino/libraries/Serial/Serial.h
+++ /dev/null
@@ -1,44 +0,0 @@
-/* Copyright (c) Kuba Szczodrzyński 2022-07-03. */
-
-#pragma once
-
-#include <api/ArduinoAPI.h>
-#include <api/HardwareSerial.h>
-#include <api/RingBuffer.h>
-
-using namespace arduino;
-
-typedef struct {
-	void *uart; // UART_TypeDef
-	RingBuffer *buf;
-} SerialData;
-
-class SerialClass : public HardwareSerial {
-  private:
-	// data accessible to IRQ handler
-	SerialData data;
-	uint8_t irq; // IRQn
-	pin_size_t rx;
-	pin_size_t tx;
-
-  public:
-	SerialClass(void *uart, uint8_t irq, pin_size_t rx, pin_size_t tx);
-
-	inline void begin(unsigned long baudrate) {
-		begin(baudrate, SERIAL_8N1);
-	}
-
-	void begin(unsigned long baudrate, uint16_t config);
-	void end();
-	int available();
-	int peek();
-	int read();
-	void flush();
-	size_t write(uint8_t c);
-
-	operator bool() {
-		return !!data.buf;
-	}
-
-	using Print::write;
-};
diff --git a/cores/realtek-amb/arduino/src/lt_defs.h b/cores/realtek-amb/arduino/src/lt_defs.h
index 2083962..948ea56 100644
--- a/cores/realtek-amb/arduino/src/lt_defs.h
+++ b/cores/realtek-amb/arduino/src/lt_defs.h
@@ -4,13 +4,5 @@
 
 #define LT_ARD_HAS_WIFI		  1
 #define LT_ARD_HAS_SOFTSERIAL 1
-#define LT_ARD_HAS_SERIAL	  1
-
-#define LT_ARD_MD5_POLARSSL 1
 
 #define ARDUINO_AMEBA
-
-// the SDK declares bool if not defined before
-// which conflicts with C++ built-in bool
-// so it's either -fpermissive or this:
-#define bool bool
diff --git a/cores/realtek-amb/base/fixups/basic_types.h b/cores/realtek-amb/base/fixups/basic_types.h
index 8b00424..c9a7f10 100644
--- a/cores/realtek-amb/base/fixups/basic_types.h
+++ b/cores/realtek-amb/base/fixups/basic_types.h
@@ -7,6 +7,9 @@
 
 #include <stdbool.h>
 
+// the SDK declares bool if not defined before
+// which conflicts with C++ built-in bool
+// so it's either -fpermissive or this:
 #ifndef bool
 #define bool bool
 #endif
diff --git a/cores/realtek-amb/base/fixups/cmsis_ipsr.c b/cores/realtek-amb/base/fixups/cmsis_ipsr.c
index d6307fd..7819c32 100644
--- a/cores/realtek-amb/base/fixups/cmsis_ipsr.c
+++ b/cores/realtek-amb/base/fixups/cmsis_ipsr.c
@@ -4,9 +4,8 @@
 
 // for some reason, cmsis_os.c does not link properly when this method is inlined in core_cmFunc.h
 // (or I am too stupid to understand this)
-__attribute__((weak)) uint32_t __get_IPSR()
-{
+__attribute__((weak)) uint32_t __get_IPSR() {
 	uint32_t result;
-    asm volatile ("MRS %0, ipsr" : "=r" (result) );
+	asm volatile("MRS %0, ipsr" : "=r"(result));
 	return result;
 }
diff --git a/cores/realtek-ambz/arduino/libraries/Serial/Serial.cpp b/cores/realtek-ambz/arduino/libraries/Serial/Serial.cpp
new file mode 100644
index 0000000..c4bbde3
--- /dev/null
+++ b/cores/realtek-ambz/arduino/libraries/Serial/Serial.cpp
@@ -0,0 +1,142 @@
+/* Copyright (c) Kuba Szczodrzyński 2022-07-03. */
+
+#include "SerialPrivate.h"
+
+#if HAS_SERIAL0
+SerialClass Serial0(0);
+#endif
+#if HAS_SERIAL1
+SerialClass Serial1(1);
+#endif
+#if HAS_SERIAL2
+SerialClass Serial2(2);
+#endif
+
+static UART_TypeDef *PORT_UART[3]  = {UART0_DEV, UART1_DEV, UART2_DEV};
+static const IRQn PORT_IRQ[3]	   = {UART0_IRQ, UART1_IRQ, UART_LOG_IRQ};
+static const pin_size_t PORT_RX[3] = {
+#ifdef PIN_SERIAL0_RX
+	PIN_SERIAL0_RX,
+#else
+	PIN_INVALID,
+#endif
+#ifdef PIN_SERIAL1_RX
+	PIN_SERIAL1_RX,
+#else
+	PIN_INVALID,
+#endif
+#ifdef PIN_SERIAL2_RX
+	PIN_SERIAL2_RX,
+#else
+	PIN_INVALID,
+#endif
+};
+static const pin_size_t PORT_TX[3] = {
+#ifdef PIN_SERIAL0_TX
+	PIN_SERIAL0_TX,
+#else
+	PIN_INVALID,
+#endif
+#ifdef PIN_SERIAL1_TX
+	PIN_SERIAL1_TX,
+#else
+	PIN_INVALID,
+#endif
+#ifdef PIN_SERIAL2_TX
+	PIN_SERIAL2_TX,
+#else
+	PIN_INVALID,
+#endif
+};
+
+static uint32_t callback(void *param) {
+	UART_TypeDef *uart = pdUART;
+
+	uint32_t intcr	= uart->DLH_INTCR;
+	uart->DLH_INTCR = 0;
+
+	uint8_t c;
+	while (UART_Readable(uart)) {
+		UART_CharGet(uart, &c);
+#if LT_AUTO_DOWNLOAD_REBOOT && defined(LT_UART_ADR_PATTERN) && defined(PIN_SERIAL2_RX)
+		// parse UART protocol commands on UART2
+		if (uart == UART2_DEV)
+			SerialClass::adrParse(c);
+#endif
+		pdBUF.store_char(c);
+	}
+
+	uart->DLH_INTCR = intcr;
+	return 0;
+}
+
+void SerialClass::begin(unsigned long baudrate, uint16_t config) {
+	this->data = new SerialData();
+	this->buf  = &BUF;
+	DATA->uart = PORT_UART[this->port];
+	DATA->irq  = PORT_IRQ[this->port];
+	DATA->rx   = PORT_RX[this->port];
+	DATA->tx   = PORT_TX[this->port];
+
+	// RUART_WLS_7BITS / RUART_WLS_8BITS
+	uint8_t dataWidth = (config & SERIAL_DATA_MASK) == SERIAL_DATA_8;
+	// RUART_PARITY_DISABLE / RUART_PARITY_ENABLE
+	uint8_t parity = (config & SERIAL_PARITY_MASK) != SERIAL_PARITY_NONE;
+	// RUART_ODD_PARITY / RUART_EVEN_PARITY
+	uint8_t parityType = (config & SERIAL_PARITY_MASK) == SERIAL_PARITY_EVEN;
+	// RUART_STOP_BIT_1 / RUART_STOP_BIT_2
+	uint8_t stopBits = (config & SERIAL_STOP_BIT_MASK) == SERIAL_STOP_BIT_2;
+
+	switch ((uint32_t)DATA->uart) {
+		case UART0_REG_BASE:
+			RCC_PeriphClockCmd(APBPeriph_UART0, APBPeriph_UART0_CLOCK, ENABLE);
+			break;
+		case UART1_REG_BASE:
+			RCC_PeriphClockCmd(APBPeriph_UART1, APBPeriph_UART1_CLOCK, ENABLE);
+			break;
+	}
+
+	if (DATA->tx != PIN_INVALID) {
+		Pinmux_Config(DATA->tx, PINMUX_FUNCTION_UART);
+	}
+	if (DATA->rx != PIN_INVALID) {
+		Pinmux_Config(DATA->rx, PINMUX_FUNCTION_UART);
+		PAD_PullCtrl(DATA->rx, GPIO_PuPd_UP);
+	}
+
+	UART_InitTypeDef cfg;
+	UART_StructInit(&cfg);
+	cfg.WordLen	   = dataWidth;
+	cfg.Parity	   = parity;
+	cfg.ParityType = parityType;
+	cfg.StopBit	   = stopBits;
+	UART_Init(UART, &cfg);
+	UART_SetBaud(UART, baudrate);
+
+	if (DATA->rx != PIN_INVALID) {
+		VECTOR_IrqUnRegister(DATA->irq);
+		VECTOR_IrqRegister(callback, DATA->irq, (uint32_t)&data, 10);
+		VECTOR_IrqEn(DATA->irq, 10);
+		UART_RxCmd(UART, ENABLE);
+		UART_INTConfig(UART, RUART_IER_ERBI, ENABLE);
+	}
+}
+
+void SerialClass::end() {
+	if (UART == UART2_DEV) {
+		// restore command line mode
+		DIAG_UartReInit((IRQ_FUN)UartLogIrqHandle);
+	}
+	this->buf = NULL;
+	delete DATA;
+}
+
+void SerialClass::flush() {
+	UART_WaitBusy(UART, 10);
+}
+
+size_t SerialClass::write(uint8_t c) {
+	while (UART_Writable(UART) == 0) {}
+	UART_CharPut(UART, c);
+	return 1;
+}
diff --git a/cores/realtek-ambz/arduino/libraries/Serial/SerialPrivate.h b/cores/realtek-ambz/arduino/libraries/Serial/SerialPrivate.h
new file mode 100644
index 0000000..aba22e7
--- /dev/null
+++ b/cores/realtek-ambz/arduino/libraries/Serial/SerialPrivate.h
@@ -0,0 +1,21 @@
+/* Copyright (c) Kuba Szczodrzyński 2023-05-23. */
+
+#pragma once
+
+#include <Arduino.h>
+#include <sdk_private.h>
+
+typedef struct {
+	UART_TypeDef *uart;
+	IRQn irq;
+	pin_size_t rx;
+	pin_size_t tx;
+	RingBuffer buf;
+} SerialData;
+
+#define DATA   ((SerialData *)data)
+#define pDATA  ((SerialData *)param)
+#define BUF	   (DATA->buf)
+#define pdBUF  (pDATA->buf)
+#define UART   (DATA->uart)
+#define pdUART (pDATA->uart)
diff --git a/cores/realtek-ambz/arduino/src/lt_defs.h b/cores/realtek-ambz/arduino/src/lt_defs.h
new file mode 100644
index 0000000..aff5c9b
--- /dev/null
+++ b/cores/realtek-ambz/arduino/src/lt_defs.h
@@ -0,0 +1,7 @@
+#pragma once
+
+#error "Don't include this file directly"
+
+#define LT_ARD_HAS_SERIAL 1
+
+#define LT_ARD_MD5_POLARSSL 1
diff --git a/cores/realtek-ambz/base/lt_family.h b/cores/realtek-ambz/base/lt_family.h
index 9723ffb..3a25b48 100644
--- a/cores/realtek-ambz/base/lt_family.h
+++ b/cores/realtek-ambz/base/lt_family.h
@@ -16,3 +16,13 @@
 #error "No serial port is available"
 #endif
 #endif
+
+// clang-format off
+// Auto-download-reboot detection pattern
+// Family ID, big-endian
+#define LT_UART_ADR_PATTERN 0x55, 0xAA, \
+	(FAMILY >> 24) & 0xFF, \
+	(FAMILY >> 16) & 0xFF, \
+	(FAMILY >> 8) & 0xFF, \
+	(FAMILY >> 0) & 0xFF
+// clang-format on
diff --git a/cores/realtek-ambz/base/sdk_extern.h b/cores/realtek-ambz/base/sdk_extern.h
index b03191a..131f623 100644
--- a/cores/realtek-ambz/base/sdk_extern.h
+++ b/cores/realtek-ambz/base/sdk_extern.h
@@ -2,12 +2,15 @@
 
 #pragma once
 
+#include <stdbool.h>
+#include <stdint.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif // __cplusplus
 
-int LOGUART_SetBaud(uint32_t BaudRate);			  // from fixups/log_uart.c
-extern void DumpForOneBytes(void *addr, int cnt); // cnt max 0x70!
+int LOGUART_SetBaud(uint32_t BaudRate);	   // from fixups/log_uart.c
+void DumpForOneBytes(void *addr, int cnt); // cnt max 0x70!
 
 #ifdef __cplusplus
 } // extern "C"
diff --git a/cores/realtek-ambz2/base/port/printf.c b/cores/realtek-ambz2/base/port/printf.c
index 1ec6a0b..f3aa09b 100644
--- a/cores/realtek-ambz2/base/port/printf.c
+++ b/cores/realtek-ambz2/base/port/printf.c
@@ -19,7 +19,7 @@ void putchar_(char c) {
 }
 
 void putchar_p(char c, unsigned long port) {
-	while (uart_dev[port]->lsr_b.txfifo_empty == 0) {}
+	while ((uart_dev[port]->tflvr & 0x1F) > 15) {}
 	uart_dev[port]->thr = c;
 }
 
diff --git a/docs/TODO.md b/docs/TODO.md
index 937adbc..1d69e48 100644
--- a/docs/TODO.md
+++ b/docs/TODO.md
@@ -43,7 +43,6 @@ Explicit is better than implicit.
 
 ### Other
 
-- refactor `SerialClass` to have a shared header `Serial.h` in the common core (and `SerialData`, just like WiFi). Move ADR to common core
 - implement Wire on BK, refactor the API and class
 - watchdog API
 - `Preferences` library