diff --git a/cores/arduino/CDC.cpp b/cores/arduino/CDC.cpp
index d694a2d..7c7eacf 100644
--- a/cores/arduino/CDC.cpp
+++ b/cores/arduino/CDC.cpp
@@ -49,8 +49,8 @@ const CDCDescriptor _cdcInterface =
 
 	//	CDC data interface
 	D_INTERFACE(CDC_DATA_INTERFACE,2,CDC_DATA_INTERFACE_CLASS,0,0),
-	D_ENDPOINT(USB_ENDPOINT_OUT(CDC_ENDPOINT_OUT),USB_ENDPOINT_TYPE_BULK,0x40,0),
-	D_ENDPOINT(USB_ENDPOINT_IN (CDC_ENDPOINT_IN ),USB_ENDPOINT_TYPE_BULK,0x40,0)
+	D_ENDPOINT(USB_ENDPOINT_OUT(CDC_ENDPOINT_OUT),USB_ENDPOINT_TYPE_BULK,USB_EP_SIZE,0),
+	D_ENDPOINT(USB_ENDPOINT_IN (CDC_ENDPOINT_IN ),USB_ENDPOINT_TYPE_BULK,USB_EP_SIZE,0)
 };
 
 int CDC_GetInterface(u8* interfaceNum)
@@ -92,11 +92,24 @@ bool CDC_Setup(USBSetup& setup)
 			// with a relatively long period so it can finish housekeeping tasks
 			// like servicing endpoints before the sketch ends
 
+#ifndef MAGIC_KEY
+#define MAGIC_KEY 0x7777
+#endif
+#ifndef MAGIC_KEY_POS
+#define MAGIC_KEY_POS 0x0800
+#endif
+
 			// We check DTR state to determine if host port is open (bit 0 of lineState).
 			if (1200 == _usbLineInfo.dwDTERate && (_usbLineInfo.lineState & 0x01) == 0)
 			{
-				*(uint16_t *)(RAMEND-1) = *(uint16_t *)0x0800;
-				*(uint16_t *)0x0800 = 0x7777;
+#if MAGIC_KEY_POS != (RAMEND-1)
+				*(uint16_t *)(RAMEND-1) = *(uint16_t *)MAGIC_KEY_POS;
+				*(uint16_t *)MAGIC_KEY_POS = MAGIC_KEY;
+#else
+				// for future boards save the key in the inproblematic RAMEND
+				// which is reserved for the main() return value (which will never return)
+				*(uint16_t *)MAGIC_KEY_POS = MAGIC_KEY;
+#endif
 				wdt_enable(WDTO_120MS);
 			}
 			else
@@ -108,7 +121,11 @@ bool CDC_Setup(USBSetup& setup)
 
 				wdt_disable();
 				wdt_reset();
-				*(uint16_t *)0x0800 = *(uint16_t *)(RAMEND-1);
+#if MAGIC_KEY_POS != (RAMEND-1)
+				*(uint16_t *)MAGIC_KEY_POS = *(uint16_t *)(RAMEND-1);
+#else
+				*(uint16_t *)MAGIC_KEY_POS = 0x0000;
+#endif
 			}
 		}
 		return true;
diff --git a/cores/arduino/USBAPI.h b/cores/arduino/USBAPI.h
index 4abd961..7f468a6 100644
--- a/cores/arduino/USBAPI.h
+++ b/cores/arduino/USBAPI.h
@@ -32,6 +32,12 @@ typedef unsigned long u32;
 
 #include "Arduino.h"
 
+// This definitions is usefull if you want to reduce the EP_SIZE to 16
+// at the moment only 64 and 16 as EP_SIZE for all EPs are supported except the control endpoint
+#ifndef USB_EP_SIZE
+#define USB_EP_SIZE 64
+#endif
+
 #if defined(USBCON)
 
 #include "USBDesc.h"
@@ -41,13 +47,13 @@ typedef unsigned long u32;
 //================================================================================
 //	USB
 
-#define EP_TYPE_CONTROL				0x00
-#define EP_TYPE_BULK_IN				0x81
-#define EP_TYPE_BULK_OUT			0x80
-#define EP_TYPE_INTERRUPT_IN		0xC1
-#define EP_TYPE_INTERRUPT_OUT		0xC0
-#define EP_TYPE_ISOCHRONOUS_IN		0x41
-#define EP_TYPE_ISOCHRONOUS_OUT		0x40
+#define EP_TYPE_CONTROL				(0x00)
+#define EP_TYPE_BULK_IN				((1<<EPTYPE1) | (1<<EPDIR))
+#define EP_TYPE_BULK_OUT			(1<<EPTYPE1)
+#define EP_TYPE_INTERRUPT_IN		((1<<EPTYPE1) | (1<<EPTYPE0) | (1<<EPDIR))
+#define EP_TYPE_INTERRUPT_OUT		((1<<EPTYPE1) | (1<<EPTYPE0))
+#define EP_TYPE_ISOCHRONOUS_IN		((1<<EPTYPE0) | (1<<EPDIR))
+#define EP_TYPE_ISOCHRONOUS_OUT		(1<<EPTYPE0)
 
 class USBDevice_
 {
diff --git a/cores/arduino/USBCore.cpp b/cores/arduino/USBCore.cpp
index 8237ccb..f12d326 100644
--- a/cores/arduino/USBCore.cpp
+++ b/cores/arduino/USBCore.cpp
@@ -110,7 +110,7 @@ static inline void ClearOUT(void)
 	UEINTX = ~(1<<RXOUTI);
 }
 
-void Recv(volatile u8* data, u8 count)
+static inline void Recv(volatile u8* data, u8 count)
 {
 	while (count--)
 		*data++ = UEDATX;
@@ -253,7 +253,7 @@ u8 USB_SendSpace(u8 ep)
 	LockEP lock(ep);
 	if (!ReadWriteAllowed())
 		return 0;
-	return 64 - FifoByteCount();
+	return USB_EP_SIZE - FifoByteCount();
 }
 
 //	Blocking Send of data to an endpoint
@@ -326,6 +326,7 @@ u8 _initEndpoints[] =
 
 #define EP_SINGLE_64 0x32	// EP0
 #define EP_DOUBLE_64 0x36	// Other endpoints
+#define EP_SINGLE_16 0x12
 
 static
 void InitEP(u8 index, u8 type, u8 size)
@@ -344,7 +345,13 @@ void InitEndpoints()
 		UENUM = i;
 		UECONX = (1<<EPEN);
 		UECFG0X = _initEndpoints[i];
+#if USB_EP_SIZE == 16
+		UECFG1X = EP_SINGLE_16;
+#elif USB_EP_SIZE == 64
 		UECFG1X = EP_DOUBLE_64;
+#else
+#error Unsupported value for USB_EP_SIZE
+#endif
 	}
 	UERST = 0x7E;	// And reset them
 	UERST = 0;
@@ -620,13 +627,19 @@ void USB_Flush(u8 ep)
 
 static inline void USB_ClockDisable()
 {
+#if defined(OTGPADE)
 	USBCON = (USBCON & ~(1<<OTGPADE)) | (1<<FRZCLK); // freeze clock and disable VBUS Pad
+#else // u2 Series
+	USBCON = (1 << FRZCLK); // freeze clock
+#endif
 	PLLCSR &= ~(1<<PLLE);  // stop PLL
 }
 
 static inline void USB_ClockEnable()
 {
+#if defined(UHWCON)
 	UHWCON |= (1<<UVREGE);			// power internal reg
+#endif
 	USBCON = (1<<USBE) | (1<<FRZCLK);	// clock frozen, usb enabled
 
 // ATmega32U4
@@ -639,6 +652,16 @@ static inline void USB_ClockEnable()
 #error "Clock rate of F_CPU not supported"
 #endif
 
+#elif defined(__AVR_AT90USB82__) || defined(__AVR_AT90USB162__) || defined(__AVR_ATmega32U2__) || defined(__AVR_ATmega16U2__) || defined(__AVR_ATmega8U2__)
+	// for the u2 Series the datasheet is confusing. On page 40 its called PINDIV and on page 290 its called PLLP0
+#if F_CPU == 16000000UL
+	// Need 16 MHz xtal
+	PLLCSR |= (1 << PLLP0);
+#elif F_CPU == 8000000UL
+	// Need 8 MHz xtal
+	PLLCSR &= ~(1 << PLLP0);
+#endif
+
 // AT90USB646, AT90USB647, AT90USB1286, AT90USB1287
 #elif defined(PLLP2)
 #if F_CPU == 16000000UL
@@ -670,10 +693,18 @@ static inline void USB_ClockEnable()
 	// strange behaviors when the board is reset using the serial
 	// port touch at 1200 bps. This delay fixes this behavior.
 	delay(1);
+#if defined(OTGPADE)
 	USBCON = (USBCON & ~(1<<FRZCLK)) | (1<<OTGPADE);	// start USB clock, enable VBUS Pad
+#else
+	USBCON &= ~(1 << FRZCLK);	// start USB clock
+#endif
 
 #if defined(RSTCPU)
+#if defined(LSM)
 	UDCON &= ~((1<<RSTCPU) | (1<<LSM) | (1<<RMWKUP) | (1<<DETACH));	// enable attach resistor, set full speed mode
+#else // u2 Series
+	UDCON &= ~((1 << RSTCPU) | (1 << RMWKUP) | (1 << DETACH));	// enable attach resistor, set full speed mode
+#endif
 #else
 	// AT90USB64x and AT90USB128x don't have RSTCPU
 	UDCON &= ~((1<<LSM) | (1<<RMWKUP) | (1<<DETACH));	// enable attach resistor, set full speed mode
diff --git a/libraries/HID/HID.cpp b/libraries/HID/HID.cpp
index 0d2133e..c629eb9 100644
--- a/libraries/HID/HID.cpp
+++ b/libraries/HID/HID.cpp
@@ -43,7 +43,7 @@ static u8 HID_INTERFACE;
 HIDDescriptor _hidInterface;
 
 static HIDDescriptorListNode* rootNode = NULL;
-static uint8_t sizeof_hidReportDescriptor = 0;
+static uint16_t sizeof_hidReportDescriptor = 0;
 static uint8_t modules_count = 0;
 //================================================================================
 //================================================================================
@@ -59,7 +59,7 @@ int HID_GetInterface(u8* interfaceNum)
 	{
 		D_INTERFACE(HID_INTERFACE,1,3,0,0),
 		D_HIDREPORT(sizeof_hidReportDescriptor),
-		D_ENDPOINT(USB_ENDPOINT_IN (HID_ENDPOINT_INT),USB_ENDPOINT_TYPE_INTERRUPT,0x40,0x01)
+		D_ENDPOINT(USB_ENDPOINT_IN (HID_ENDPOINT_INT),USB_ENDPOINT_TYPE_INTERRUPT,USB_EP_SIZE,0x01)
 	};
 	return USB_SendControl(0,&_hidInterface,sizeof(_hidInterface));
 }
@@ -91,7 +91,7 @@ void HID_::AppendDescriptor(HIDDescriptorListNode *node)
 		current->next = node;
 	}
 	modules_count++;
-	sizeof_hidReportDescriptor += node->cb->length;
+	sizeof_hidReportDescriptor += (uint16_t)node->cb->length;
 }
 
 void HID_::SendReport(u8 id, const void* data, int len)
diff --git a/libraries/HID/HID.h b/libraries/HID/HID.h
index 89832a9..b9f29b4 100644
--- a/libraries/HID/HID.h
+++ b/libraries/HID/HID.h
@@ -45,7 +45,7 @@
 #define HID_PHYSICAL_DESCRIPTOR_TYPE    0x23
 
 typedef struct __attribute__((packed)) {
-  u8 length;
+  uint16_t length;
   const void* descriptor;
 } HID_Descriptor;
 
@@ -88,10 +88,10 @@ typedef struct
 #define HID_TX HID_ENDPOINT_INT
 
 #define D_HIDREPORT(_descriptorLength) \
-  { 9, 0x21, 0x1, 0x1, 0, 1, 0x22, _descriptorLength, 0 }
+  { 9, 0x21, 0x1, 0x1, 0, 1, 0x22, _descriptorLength & 0xFF, _descriptorLength >> 8 }
 
 #define WEAK __attribute__ ((weak))
 
 #endif
 
-#endif
\ No newline at end of file
+#endif