refactor USB init functions to minimize API

src/machine/machine_atsamd51.go

@@ -1974,7 +1974,7 @@ func (tcc *TCC) Set(channel uint8, value uint32) {
 	}
 }
 
-func InitUSBIO() {
+func initUSB() {
 	// Configure USB D+/D- pins.
 	USBCDC_DM_PIN.Configure(PinConfig{Mode: PinCom})
 	USBCDC_DP_PIN.Configure(PinConfig{Mode: PinCom})

src/machine/usb-cdc.go

@@ -7,8 +7,7 @@ import "machine/usb"
 
 var USB = &usb.CDC{}
 
-func InitUSB(port int) {
-	InitUSBIO()
-	USB.Port = port
+func InitUSB() {
+	initUSB()
 	USB.Configure(usb.CDCConfig{})
 }

src/machine/usb-hid.go

@@ -7,8 +7,7 @@ import "machine/usb"
 
 var USB = &usb.HID{}
 
-func InitUSB(port int) {
-	InitUSBIO()
-	USB.Port = port
+func InitUSB() {
+	initUSB()
 	USB.Configure(usb.HIDConfig{})
 }

src/machine/usb/dhw_atsamd51.go

@@ -497,6 +497,9 @@ func (d *dhw) controlTransferContinue(endpoint uint8, count, total uint32) {
 	if xfer, ok := d.ep[num][dir].activeTransfer(); ok {
 		data, size := xfer.packetComplete(count)
 		d.endpointTransfer(endpoint, data, size)
+		if size == 0 || size < xfer.maxPacketSize {
+			d.controlTransferComplete(endpoint, count, total)
+		}
 	}
 }
 

src/runtime/runtime_atsamd51.go

@@ -33,7 +33,7 @@ func init() {
 	//	machine.USB.Configure(usb.UARTConfig{})
 	//}
 
-	machine.InitUSB(0)
+	machine.InitUSB()
 }
 
 func putchar(c byte) {