diff --git a/contrib/usart-common.c b/contrib/usart-common.c
index 9e4c0dc..5a2aeeb 100644
--- a/contrib/usart-common.c
+++ b/contrib/usart-common.c
@@ -250,7 +250,7 @@ usart_init (uint16_t prio, uintptr_t stack_addr, size_t stack_size,
 
 struct brr_setting {
   uint8_t baud_spec;
-  uint16_t brr_value;
+  uint32_t brr_value;
 };
 #define NUM_BAUD (int)(sizeof (brr_table) / sizeof (struct brr_setting))
 
diff --git a/contrib/usart-stm32l4.c b/contrib/usart-stm32l4.c
new file mode 100644
index 0000000..6f781e6
--- /dev/null
+++ b/contrib/usart-stm32l4.c
@@ -0,0 +1,404 @@
+#include <stdint.h>
+#include <stdlib.h>
+#include <chopstx.h>
+#include <mcu/stm32l.h>
+#include <contrib/usart.h>
+
+
+#define RCC_APB1_1_USART2     (1 << 17)
+#define RCC_APB2_USART1       (1 << 14)
+
+/* Hardware registers */
+struct USART {
+  volatile uint32_t CR1;
+  volatile uint32_t CR2;
+  volatile uint32_t CR3;
+  volatile uint32_t BRR;
+  volatile uint32_t GTPR;
+  volatile uint32_t RTOR;
+  volatile uint32_t RQR;
+  volatile uint32_t ISR;
+  volatile uint32_t ICR;
+  volatile uint32_t RDR;
+  volatile uint32_t TDR;
+};
+
+#define USART1_BASE           (APB2PERIPH_BASE + 0x3800)
+
+#define USART2_BASE           (APB1PERIPH_BASE + 0x4400)
+#define USART2 ((struct USART *)USART2_BASE)
+
+#define USART_ISR_CTS	(1 << 10)
+#define USART_ISR_LBDF	(1 << 8)
+#define USART_ISR_TXE	(1 << 7)
+#define USART_ISR_TC	(1 << 6)
+#define USART_ISR_RXNE	(1 << 5)
+#define USART_ISR_IDLE	(1 << 4)
+#define USART_ISR_ORE	(1 << 3)
+#define USART_ISR_NE	(1 << 2)
+#define USART_ISR_FE	(1 << 1)
+#define USART_ISR_PE	(1 << 0)
+
+#define USART_CR1_M1		(1 << 28)
+#define USART_CR1_M0		(1 << 12)
+#define USART_CR1_WAKE		(1 << 11)
+#define USART_CR1_PCE		(1 << 10)
+#define USART_CR1_PS		(1 <<  9)
+#define USART_CR1_PEIE		(1 <<  8)
+#define USART_CR1_TXEIE		(1 <<  7)
+#define USART_CR1_TCIE		(1 <<  6)
+#define USART_CR1_RXNEIE	(1 <<  5)
+#define USART_CR1_IDLEIE	(1 <<  4)
+#define USART_CR1_TE		(1 <<  3)
+#define USART_CR1_RE		(1 <<  2)
+#define USART_CR1_UESM		(1 <<  1)
+#define USART_CR1_UE		(1 <<  0)
+
+#define USART_CR3_CTSE		(1 <<  9)
+#define USART_CR3_RTSE		(1 <<  8)
+#define USART_CR3_SCEN		(1 <<  5)
+#define USART_CR3_NACK		(1 <<  4)
+
+static struct usart_stat usart2_stat;
+
+static struct chx_intr usart2_intr;
+
+#define BUF_A2H_SIZE 256
+#define BUF_H2A_SIZE 512
+static uint8_t buf_usart2_rb_a2h[BUF_A2H_SIZE];
+static uint8_t buf_usart2_rb_h2a[BUF_H2A_SIZE];
+
+static struct rb usart2_rb_a2h;
+static struct rb usart2_rb_h2a;
+
+static chopstx_poll_cond_t usart2_app_write_event;
+
+/* Global variables so that it can be easier to debug.  */
+static int usart2_tx_ready;
+
+#define INTR_REQ_USART2 38
+
+#define USART_DEVNO_START 2
+#define USART_DEVNO_END   2
+
+struct usart {
+  struct USART *USART;
+  struct usart_stat *stat;
+  struct chx_intr *intr;
+  struct rb *rb_h2a;
+  struct rb *rb_a2h;
+  uint8_t *buf_a2h;
+  uint8_t *buf_h2a;
+  chopstx_poll_cond_t *app_write_event;
+  int *tx_ready;
+  uint8_t irq_num;
+};
+
+
+static const struct usart usart_array[] =
+  {
+   { USART2, &usart2_stat, &usart2_intr, &usart2_rb_a2h, &usart2_rb_h2a,
+     buf_usart2_rb_a2h, buf_usart2_rb_h2a, &usart2_app_write_event,
+     &usart2_tx_ready, INTR_REQ_USART2 },
+  };
+#define NUM_USART ((int)(sizeof (usart_array) / sizeof (struct usart)))
+
+static int handle_intr (struct USART *USARTx, struct rb *rb2a, struct usart_stat *stat);
+static int handle_tx (struct USART *USARTx, struct rb *rb2h, struct usart_stat *stat);
+static void usart_config_recv_enable (struct USART *USARTx, int on);
+
+#include "usart-common.c"
+
+/* We assume 40MHz f_CK */
+
+static const struct brr_setting brr_table[] = {
+  { B600,    66667 },
+  { B1200,   33333 },
+  { B2400,   16667 },
+  { B9600,    4167 },
+  { B19200,   2083 },
+  { B57600,    694 },
+  { B115200,   347 },
+  { B230400,   174 },
+  { B460800,    87 },
+  { B921600,    43 },
+  { BSCARD,   4167 },
+};
+
+void
+usart_config_brr (uint8_t dev_no, uint16_t brr_value)
+{
+  struct USART *USARTx = get_usart_dev (dev_no);
+  uint32_t save_bits;
+
+  save_bits = USARTx->CR1 & (USART_CR1_TE | USART_CR1_RE);
+  USARTx->CR1 &= ~(USART_CR1_TE | USART_CR1_RE | USART_CR1_UE);
+  USARTx->BRR = brr_value;
+  USARTx->CR1 |= (save_bits | USART_CR1_UE);
+}
+
+/* XXX: not sure if needed */
+static void
+usart_config_recv_enable (struct USART *USARTx, int on)
+{
+  if (on)
+    USARTx->CR1 |= USART_CR1_RE;
+  else
+    USARTx->CR1 &= ~USART_CR1_RE;
+}
+
+void
+usart_config_clken (uint8_t dev_no, int on)
+{
+  struct USART *USARTx = get_usart_dev (dev_no);
+
+  if (on)
+    USARTx->CR2 |= (1 << 11);
+  else
+    USARTx->CR2 &= ~(1 << 11);
+}
+
+
+int
+usart_config (uint8_t dev_no, uint32_t config_bits)
+{
+  struct USART *USARTx = get_usart_dev (dev_no);
+  uint8_t baud_spec = (config_bits & MASK_BAUD);
+  int i;
+  uint32_t cr1_config = (USART_CR1_UE | USART_CR1_RXNEIE
+			 | USART_CR1_TE | USART_CR1_RE);
+				/* TXEIE/TCIE will be enabled when
+				   putting char */
+				/* No CTSIE, PEIE, IDLEIE, LBDIE */
+  if (USARTx == NULL)
+    return -1;
+
+  /* Disable USART before configure.  */
+  USARTx->CR1 &= ~USART_CR1_UE;
+
+  if ((config_bits & MASK_CS) == CS7 && !(config_bits & PARENB))
+    cr1_config |=  USART_CR1_M1;
+  else if (((config_bits & MASK_CS) == CS7 && (config_bits & PARENB))
+      || ((config_bits & MASK_CS) == CS8 && (config_bits & PARENB) == 0))
+    ;
+  else if ((config_bits & MASK_CS) == CS8)
+    cr1_config |=  USART_CR1_M0;
+  else
+    return -1;
+
+  if ((config_bits & PARENB))
+    cr1_config |=  (USART_CR1_PCE | USART_CR1_PEIE);
+
+  if ((config_bits & PARODD))
+    cr1_config |=  USART_CR1_PS;
+
+  if ((config_bits & MASK_STOP) == STOP0B5)
+    USARTx->CR2 = (0x1 << 12);
+  else if ((config_bits & MASK_STOP) == STOP1B)
+    USARTx->CR2 = (0x0 << 12);
+  else if ((config_bits & MASK_STOP) == STOP1B5)
+    USARTx->CR2 = (0x3 << 12);
+  else /* if ((config_bits & MASK_STOP) == STOP2B) */
+    USARTx->CR2 = (0x2 << 12);
+
+  for (i = 0; i < NUM_BAUD; i++)
+    if (brr_table[i].baud_spec == baud_spec)
+      break;
+
+  if (i >= NUM_BAUD)
+    return -1;
+
+  USARTx->BRR = brr_table[i].brr_value;
+
+  if ((config_bits & MASK_FLOW))
+    USARTx->CR3 = USART_CR3_CTSE | USART_CR3_RTSE;
+  else
+    USARTx->CR3 = 0;
+
+  if ((config_bits & MASK_MODE))
+    {
+      if ((config_bits & MASK_MODE) == MODE_SMARTCARD)
+	{
+	  USARTx->GTPR = (1 << 8) | 5;
+	  USARTx->CR3 |= (USART_CR3_SCEN | USART_CR3_NACK);
+	}
+      else if ((config_bits & MASK_MODE) == MODE_IRDA)
+	USARTx->CR3 |= (1 << 1);
+      else if ((config_bits & MASK_MODE) == MODE_IRDA_LP)
+	USARTx->CR3 |= (1 << 2) | (1 << 1);
+    }
+
+  USARTx->CR1 = cr1_config;
+
+  return 0;
+}
+
+
+void
+usart_init0 (int (*cb) (uint8_t dev_no, uint16_t notify_bits))
+{
+  int i;
+
+  ss_notify_callback = cb;
+
+  for (i = 0; i < NUM_USART; i++)
+    {
+      usart_array[i].stat->dev_no = i + USART_DEVNO_START;
+      chopstx_claim_irq (usart_array[i].intr, usart_array[i].irq_num);
+    }
+
+  /* Enable USART2 clock, and strobe reset.  */
+  RCC->APB1ENR1 |= (1 << 17);
+  RCC->APB1RSTR1 = (1 << 17);
+  RCC->APB1RSTR1 = 0;
+}
+
+#define UART_STATE_BITMAP_RX_CARRIER (1 << 0)
+#define UART_STATE_BITMAP_TX_CARRIER (1 << 1)
+#define UART_STATE_BITMAP_BREAK      (1 << 2)
+#define UART_STATE_BITMAP_RINGSIGNAL (1 << 3)
+#define UART_STATE_BITMAP_FRAMING    (1 << 4)
+#define UART_STATE_BITMAP_PARITY     (1 << 5)
+#define UART_STATE_BITMAP_OVERRUN    (1 << 6)
+
+static int
+handle_intr (struct USART *USARTx, struct rb *rb2a, struct usart_stat *stat)
+{
+  int tx_ready = 0;
+  uint32_t r = USARTx->ISR;
+  int notify_bits = 0;
+  int smartcard_mode = ((USARTx->CR3 & USART_CR3_SCEN) != 0);
+
+  if (smartcard_mode)
+    {
+      if ((r & USART_ISR_TC))
+	{
+	  tx_ready = 1;
+	  USARTx->CR1 &= ~USART_CR1_TCIE;
+	}
+    }
+  else
+    {
+      if ((r & USART_ISR_TXE))
+	{
+	  tx_ready = 1;
+	  USARTx->CR1 &= ~USART_CR1_TXEIE;
+	}
+    }
+
+  if ((r & USART_ISR_RXNE))
+    {
+      uint32_t data = USARTx->RDR;
+
+      /* RDR register should be accessed even if data is not used.
+       * Its read-access has side effect of clearing error flags.
+       */
+      asm volatile ("" : : "r" (data) : "memory");
+
+      if ((r & USART_ISR_NE))
+	stat->err_rx_noise++;
+      else if ((r & USART_ISR_FE))
+	{
+	  /* NOTE: Noway to distinguish framing error and break  */
+
+	  stat->rx_break++;
+	  notify_bits |= UART_STATE_BITMAP_BREAK;
+	}
+      else if ((r & USART_ISR_PE))
+	{
+	  stat->err_rx_parity++;
+	  notify_bits |= UART_STATE_BITMAP_PARITY;
+	}
+      else
+	{
+	  if ((r & USART_ISR_ORE))
+	    {
+	      stat->err_rx_overrun++;
+	      notify_bits |= UART_STATE_BITMAP_OVERRUN;
+	    }
+
+	  /* XXX: if CS is 7-bit, mask it, or else parity bit in upper layer */
+	  if (rb_ll_put (rb2a, (data & 0xff)) < 0)
+	    stat->err_rx_overflow++;
+	  else
+	    stat->rx++;
+	}
+    }
+  else if ((r & USART_ISR_ORE))
+    {				/* Clear ORE */
+      uint32_t data = USARTx->RDR;
+      asm volatile ("" : : "r" (data) : "memory");
+      stat->err_rx_overrun++;
+      notify_bits |= UART_STATE_BITMAP_OVERRUN;
+    }
+
+  if (notify_bits)
+    {
+      if ((*ss_notify_callback) (stat->dev_no, notify_bits))
+	stat->err_notify_overflow++;
+    }
+
+  return tx_ready;
+}
+
+static int
+handle_tx (struct USART *USARTx, struct rb *rb2h, struct usart_stat *stat)
+{
+  int tx_ready = 1;
+  int c = rb_ll_get (rb2h);
+
+  if (c >= 0)
+    {
+      uint32_t r;
+      int smartcard_mode = ((USARTx->CR3 & USART_CR3_SCEN) != 0);
+
+      USARTx->TDR = (c & 0xff);
+      stat->tx++;
+      r = USARTx->ISR;
+      if (smartcard_mode)
+	{
+	  if ((r & USART_ISR_TC) == 0)
+	    {
+	      tx_ready = 0;
+	      USARTx->CR1 |= USART_CR1_TCIE;
+	    }
+	}
+      else
+	{
+	  if ((r & USART_ISR_TXE) == 0)
+	    {
+	      tx_ready = 0;
+	      USARTx->CR1 |= USART_CR1_TXEIE;
+	    }
+	}
+    }
+
+  return tx_ready;
+}
+
+int
+usart_send_break (uint8_t dev_no)
+{
+  struct USART *USARTx = get_usart_dev (dev_no);
+  if (USARTx == NULL)
+    return -1;
+
+  USARTx->RQR |= 0x02;
+  return 0;
+}
+
+int
+usart_block_sendrecv (uint8_t dev_no, const char *s_buf, uint16_t s_buflen,
+		      char *r_buf, uint16_t r_buflen,
+		      uint32_t *timeout_block_p, uint32_t timeout_char)
+{
+  /* TBD */
+  (void)dev_no;
+  (void)s_buf;
+  (void)s_buflen;
+  (void)r_buf;
+  (void)r_buflen;
+  (void)timeout_block_p;
+  (void)timeout_char;
+  return 0;
+}