diff --git a/hardware/arduino/sam/cores/arduino/USB/USBAPI.h b/hardware/arduino/sam/cores/arduino/USB/USBAPI.h
index 97e8ad6fe..ee9739cb5 100644
--- a/hardware/arduino/sam/cores/arduino/USB/USBAPI.h
+++ b/hardware/arduino/sam/cores/arduino/USB/USBAPI.h
@@ -131,7 +131,7 @@ bool	CDC_Setup(USBSetup& setup);
 void USBD_InitControl(int end);
 int USBD_SendControl(uint8_t flags, const void* d, uint32_t len);
 int USBD_RecvControl(void* d, uint32_t len);
-int USBD_SendInterfaces(void);
+uint8_t USBD_SendInterfaces(void);
 bool USBD_ClassInterfaceRequest(USBSetup& setup);
 
 
diff --git a/hardware/arduino/sam/cores/arduino/USB/USBCore.cpp b/hardware/arduino/sam/cores/arduino/USB/USBCore.cpp
index 421b48f7e..6631ec006 100644
--- a/hardware/arduino/sam/cores/arduino/USB/USBCore.cpp
+++ b/hardware/arduino/sam/cores/arduino/USB/USBCore.cpp
@@ -101,7 +101,7 @@ const DeviceDescriptor USB_DeviceDescriptor =
 const DeviceDescriptor USB_DeviceDescriptorA =
 	D_DEVICE(0xEF,0x02,0x01,64,USB_VID,USB_PID,0x100,IMANUFACTURER,IPRODUCT,0,1);
 
-const DeviceDescriptor USB_DeviceQualifier =
+const QualifierDescriptor USB_DeviceQualifier =
 	D_QUALIFIER(0x00,0x00,0x00,64,1);
 
 //! 7.1.20 Test Mode Support
@@ -130,7 +130,7 @@ class LockEP
 {
 	irqflags_t flags;
 public:
-	LockEP(uint32_t ep) : flags(cpu_irq_save())
+	LockEP(uint32_t ep __attribute__ ((unused))) : flags(cpu_irq_save())
 	{
 	}
 	~LockEP()
@@ -219,8 +219,8 @@ uint32_t USBD_Send(uint32_t ep, const void* d, uint32_t len)
 	return r;
 }
 
-int _cmark;
-int _cend;
+uint16_t _cmark;
+uint16_t _cend;
 
 void USBD_InitControl(int end)
 {
@@ -229,7 +229,7 @@ void USBD_InitControl(int end)
 }
 
 //	Clipped by _cmark/_cend
-int USBD_SendControl(uint8_t flags, const void* d, uint32_t len)
+int USBD_SendControl(uint8_t flags __attribute__ ((unused)), const void* d, uint32_t len)
 {
 	const uint8_t* data = (const uint8_t*)d;
 	uint32_t length = len;
@@ -302,7 +302,7 @@ bool USBD_ClassInterfaceRequest(USBSetup& setup)
 	return false;
 }
 
-int USBD_SendInterfaces(void)
+uint8_t USBD_SendInterfaces(void)
 {
 	uint8_t interfaces = 0;
 
@@ -318,7 +318,7 @@ int USBD_SendInterfaces(void)
 	return interfaces;
 }
 
-int USBD_SendOtherInterfaces(void)
+uint8_t USBD_SendOtherInterfaces(void)
 {
 	uint8_t interfaces = 0;
 
@@ -342,7 +342,7 @@ static bool USBD_SendConfiguration(int maxlen)
 	//	Count and measure interfaces
 	USBD_InitControl(0);
 	//TRACE_CORE(printf("=> USBD_SendConfiguration _cmark1=%d\r\n", _cmark);)
-	int interfaces = USBD_SendInterfaces();
+	uint8_t interfaces = USBD_SendInterfaces();
 	//TRACE_CORE(printf("=> USBD_SendConfiguration _cmark2=%d\r\n", _cmark);)
 	//TRACE_CORE(printf("=> USBD_SendConfiguration sizeof=%d\r\n", sizeof(ConfigDescriptor));)
 
@@ -365,7 +365,7 @@ static bool USBD_SendOtherConfiguration(int maxlen)
 	//	Count and measure interfaces
 	USBD_InitControl(0);
 	//TRACE_CORE(printf("=> USBD_SendConfiguration _cmark1=%d\r\n", _cmark);)
-	int interfaces = USBD_SendOtherInterfaces();
+	uint8_t interfaces = USBD_SendOtherInterfaces();
 	//TRACE_CORE(printf("=> USBD_SendConfiguration _cmark2=%d\r\n", _cmark);)
 	//TRACE_CORE(printf("=> USBD_SendConfiguration sizeof=%d\r\n", sizeof(ConfigDescriptor));)
 
diff --git a/hardware/arduino/sam/cores/arduino/USB/USBCore.h b/hardware/arduino/sam/cores/arduino/USB/USBCore.h
index 10df90ba7..893d84fcb 100644
--- a/hardware/arduino/sam/cores/arduino/USB/USBCore.h
+++ b/hardware/arduino/sam/cores/arduino/USB/USBCore.h
@@ -149,6 +149,18 @@ typedef struct {
 	uint8_t	maxPower;
 } ConfigDescriptor;
 
+//	Device Qualifier (only needed for USB2.0 devices)
+typedef struct {
+	uint8_t	bLength;
+	uint8_t	dtype;
+	uint16_t bDescriptorType;
+	uint8_t	bDeviceClass;
+	uint8_t	bDeviceSubClass;
+	uint8_t	bDeviceProtocol;
+	uint8_t	bMaxPacketSize0;
+	uint8_t	bNumConfigurations;
+} QualifierDescriptor;
+
 //	String
 
 //	Interface
@@ -257,16 +269,16 @@ _Pragma("pack()")
 	{ 18, 1, 0x200, _class,_subClass,_proto,_packetSize0,_vid,_pid,_version,_im,_ip,_is,_configs }
 
 #define D_CONFIG(_totalLength,_interfaces) \
-	{ 9, 2, _totalLength,_interfaces, 1, 0, USB_CONFIG_SELF_POWERED, USB_CONFIG_POWER_MA(500) }
+	{ 9, 2, (uint16_t)(_totalLength),_interfaces, 1, 0, USB_CONFIG_SELF_POWERED, USB_CONFIG_POWER_MA(500) }
 
 #define D_OTHERCONFIG(_totalLength,_interfaces) \
-	{ 9, 7, _totalLength,_interfaces, 1, 0, USB_CONFIG_SELF_POWERED, USB_CONFIG_POWER_MA(500) }
+	{ 9, 7, (uint16_t)(_totalLength),_interfaces, 1, 0, USB_CONFIG_SELF_POWERED, USB_CONFIG_POWER_MA(500) }
 
 #define D_INTERFACE(_n,_numEndpoints,_class,_subClass,_protocol) \
 	{ 9, 4, _n, 0, _numEndpoints, _class,_subClass, _protocol, 0 }
 
 #define D_ENDPOINT(_addr,_attr,_packetSize, _interval) \
-	{ 7, 5, _addr,_attr,_packetSize, _interval }
+	{ 7, 5, (uint8_t)(_addr),_attr,_packetSize, _interval }
 
 #define D_QUALIFIER(_class,_subClass,_proto,_packetSize0,_configs) \
 	{ 10, 6, 0x200, _class,_subClass,_proto,_packetSize0,_configs }