diff --git a/ChangeLog b/ChangeLog
index bfbe8b7..af86d2d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2017-11-16  NIIBE Yutaka  <gniibe@fsij.org>
+
+	* chopstx-cortex-m.c (idle): Support WFE.
+	* mcu/usb-stm32f103.c (usb_lld_init): Use event.
+	* usb_lld.h (INTR_REQ_USB_WAKEUP): Remove.
+
 2017-11-15  NIIBE Yutaka  <gniibe@fsij.org>
 
 	* usb_lld.h (INTR_REQ_USB_WAKEUP): New.
diff --git a/chopstx-cortex-m.c b/chopstx-cortex-m.c
index ffad3ec..cc28311 100644
--- a/chopstx-cortex-m.c
+++ b/chopstx-cortex-m.c
@@ -237,7 +237,11 @@ idle (void)
   for (;;)
     {
       asm ("ldr	%0, %1" : "=r" (sleep_enabled): "m" (chx_allow_sleep));
-      if (sleep_enabled)
+      if (!sleep_enabled)
+	continue;
+      if ((sleep_enabled & 0x80))
+	asm volatile ("wfe" : : : "memory");
+      else
 	asm volatile ("wfi" : : : "memory");
     }
 }
@@ -737,31 +741,31 @@ struct PWR
   volatile uint32_t CSR;
 };
 static struct PWR *const PWR = ((struct PWR *)0x40007000);
-#define PWR_CR_LPDS 0x0001
-#define PWR_CR_PDDS 0x0002
-#define PWR_CR_CWUF 0x0004
+#define PWR_CR_LPDS 0x0001	/* Low-power deepsleep  */
+#define PWR_CR_PDDS 0x0002	/* Power down deepsleep */
+#define PWR_CR_CWUF 0x0004	/* Clear wakeup flag    */
 
 void
-chx_sleep_mode (int enable_sleep)
+chx_sleep_mode (int how)
 {
-  if (enable_sleep == 0)
+  if (how == 0)
     ;
   else
     {
-      if (enable_sleep == 1)
+      if (how == 1)
 	/* sleep only */
 	SCB->SCR &= ~SCB_SCR_SLEEPDEEP;
       else
 	{
 	  PWR->CR |= PWR_CR_CWUF;
-	
-	  if (enable_sleep == 2 || enable_sleep == 3)
+
+	  if (how == 2 || how == 3)
 	    {
 	      PWR->CR &= ~PWR_CR_PDDS;
-	      if (enable_sleep == 3)
+	      if (how == 3)
 		PWR->CR |= PWR_CR_LPDS;
 	    }
-	  else /* enable_sleep == 4 */
+	  else /* how == 4 */
 	    PWR->CR |= PWR_CR_PDDS;
 
 	  SCB->SCR |= SCB_SCR_SLEEPDEEP;
diff --git a/chopstx.c b/chopstx.c
index 387847b..31a0d0c 100644
--- a/chopstx.c
+++ b/chopstx.c
@@ -1485,11 +1485,10 @@ chopstx_setpriority (chopstx_prio_t prio_new)
  *
  * Behavior of @enable_sleep >= 1 depends on MCU.
  *
- * For STM32F103, it's like following.
- *    1: Sleep   (CPU clock OFF only)
- *    2: Stop    Wakeup by EXTI  (voltage regulator on)
- *    3: Stop    Wakeup by EXTI  (voltage regulator low-power)
- *    4: Standby Wakeup by RESET (voltage regulator off)
+ * For STM32F103, 1 for Sleep (CPU clock OFF only), 2 for Stop (Wakeup
+ * by EXTI, voltage regulator on), 3 for Stop (Wakeup by EXTI, voltage
+ * regulator low-power), 4 for Standby (Wakeup by RESET, voltage
+ * regulator off), and 128 is or-ed to ask WFE instead of WFI.
  *
  * Return previous value of @enable_sleep.
  */
@@ -1501,7 +1500,7 @@ chopstx_conf_idle (int enable_sleep)
   chx_spin_lock (&chx_enable_sleep_lock);
   r = chx_allow_sleep;
   chx_allow_sleep = enable_sleep;
-  chx_sleep_mode (enable_sleep);
+  chx_sleep_mode ((enable_sleep & 0x7f));
   chx_spin_unlock (&chx_enable_sleep_lock);
 
   return r;
diff --git a/mcu/usb-stm32f103.c b/mcu/usb-stm32f103.c
index 6a8fddf..77ffe55 100644
--- a/mcu/usb-stm32f103.c
+++ b/mcu/usb-stm32f103.c
@@ -343,10 +343,9 @@ void usb_lld_init (struct usb_dev *dev, uint8_t feature)
   st103_set_cntr (CNTR_CTRM | CNTR_OVRM | CNTR_ERRM
 		  | CNTR_WKUPM | CNTR_SUSPM | CNTR_RESETM);
 
-  /* Setting of EXTI wakeup interrupt to break sleep mode.  */
+  /* Setting of EXTI wakeup event to break sleep on WFE.    */
   EXTI->RTSR |= (1 << 18);	/* Rising trigger selection */
-  EXTI->PR   |= (1 << 18);	/* Clear pending bit */
-  EXTI->IMR  |= (1 << 18);	/* Interrupt mask disabled */
+  EXTI->EMR  |= (1 << 18);	/* Event mask cleared       */
 }
 
 void usb_lld_prepare_shutdown (void)
diff --git a/usb_lld.h b/usb_lld.h
index c8e6944..ce08f73 100644
--- a/usb_lld.h
+++ b/usb_lld.h
@@ -153,7 +153,6 @@ void usb_lld_setup_endp (struct usb_dev *dev, int ep_num, int rx_en, int tx_en);
 void usb_lld_stall_tx (int ep_num);
 void usb_lld_stall_rx (int ep_num);
 #else
-#define INTR_REQ_USB_WAKEUP 42
 #define INTR_REQ_USB 20
 /* EP_TYPE[1:0] EndPoint TYPE */
 #define EP_BULK        (0x0000) /* EndPoint BULK        */