USB_Init() no longer calls sei() to enable global interrupts - this must now be done in the user application once all init code has run.

LUFA/Drivers/USB/LowLevel/LowLevel.c

@@ -103,8 +103,6 @@ void USB_Init(
 	#endif
 
 	USB_IsInitialized = true;
-
-	sei();
 }
 
 void USB_ShutDown(void)

LUFA/Drivers/USB/LowLevel/LowLevel.h

@@ -236,8 +236,12 @@
 			 *  allow for device connection to a host when in device mode, or for device enumeration while in
 			 *  host mode.
 			 *
-			 *  As the USB library relies on USB interrupts for some of its functionality, this routine will
-			 *  enable global interrupts.
+			 *  As the USB library relies on interrupts for the device and host mode enumeration processes,
+			 *  the user must enable global interrupts before or shortly after this function is called. In
+			 *  device mode, interrupts must be enabled within 500ms of this function being called to ensure
+			 *  that the host does not time out whilst enumerating the device. In host mode, interrupts may be
+			 *  enabled at the application's leisure however enumeration will not begin of an attached device
+			 *  until after this has occurred.
 			 *
 			 *  Calling this function when the USB interface is already initialized will cause a complete USB
 			 *  interface reset and re-enumeration.

LUFA/ManPages/ChangeLog.txt

@@ -28,6 +28,7 @@
   *  - Added LIBUSB_FILTERDRV_COMPAT compile time option to the AVRISP programmer project to make the code compatible with Windows
   *    builds of avrdude at the expense of AVRStudio compatibility
   *  - Removed two-step endpoint/pipe bank clear and switch sequence for smaller, faster endpoint/pipe code
+  *  - The USB_Init() function no longer calls sei() - the user is now responsible for enabling interrupts when they are ready
   *
   *  <b>Fixed:</b>
   *  - Fixed software PDI/TPI programming mode in the AVRISP project not correctly toggling just the clock pin

LUFA/ManPages/MigrationInformation.txt

@@ -16,6 +16,18 @@
  *    - The \ref TWI_StartTransmission() function now takes in a timeout period, expressed in milliseconds, within which the addressed
  *      device must respond or the function will abort.
  *
+ *  <b>Device Mode</b>
+ *    - The \ref USB_Init() function no longer calls sei() to enable global interrupts, as the user application may need
+ *      to perform other initialization before it is ready to handle global interrupts. The user application is now responsible
+ *      for enabling global interrupts before or shortly after calling \ref USB_Init() to ensure that the enumeration process
+ *      functions correctly.
+ *
+ *  <b>Host Mode</b>
+ *    - The \ref USB_Init() function no longer calls sei() to enable global interrupts, as the user application may need
+ *      to perform other initialization before it is ready to handle global interrupts. The user application is now responsible
+ *      for enabling global interrupts before or shortly after calling \ref USB_Init() to ensure that the enumeration process
+ *      functions correctly.
+ *
  * \section Sec_Migration100219 Migrating from 091223 to 100219
  *
  *  <b>Non-USB Library Components</b>