Modify EndpointInfo to provide meaningful data rather than raw USB

descriptor values. E.g. for the user, the distinction between
MaxIsoPkt and MaxPktSize is irrelevant, only the calculated max packet
size matters.

usb/constants.go

@@ -144,23 +144,32 @@ func (ist IsoSyncType) String() string {
 	return isoSyncTypeDescription[ist]
 }
 
-type IsoUsageType uint8
+type UsageType uint8
 
 const (
-	IsoUsageTypeData     IsoUsageType = C.LIBUSB_ISO_USAGE_TYPE_DATA << 4
-	IsoUsageTypeFeedback IsoUsageType = C.LIBUSB_ISO_USAGE_TYPE_FEEDBACK << 4
-	IsoUsageTypeImplicit IsoUsageType = C.LIBUSB_ISO_USAGE_TYPE_IMPLICIT << 4
-	IsoUsageTypeMask                  = 0x30
+	// Note: USB3.0 defines usage type for both isochronous and interrupt
+	// endpoints, with the same constants representing different usage types.
+	// UsageType constants do not correspond to bmAttribute values.
+	UsageTypeMask                = 0x30
+	UsageTypeUndefined UsageType = iota
+	IsoUsageTypeData
+	IsoUsageTypeFeedback
+	IsoUsageTypeImplicit
+	InterruptUsageTypePeriodic
+	InterruptUsageTypeNotification
 )
 
-var isoUsageTypeDescription = map[IsoUsageType]string{
-	IsoUsageTypeData:     "data",
-	IsoUsageTypeFeedback: "feedback",
-	IsoUsageTypeImplicit: "implicit data",
+var usageTypeDescription = map[UsageType]string{
+	UsageTypeUndefined:             "undefined usage",
+	IsoUsageTypeData:               "data",
+	IsoUsageTypeFeedback:           "feedback",
+	IsoUsageTypeImplicit:           "implicit data",
+	InterruptUsageTypePeriodic:     "periodic",
+	InterruptUsageTypeNotification: "notification",
 }
 
-func (iut IsoUsageType) String() string {
-	return isoUsageTypeDescription[iut]
+func (ut UsageType) String() string {
+	return usageTypeDescription[ut]
 }
 
 type RequestType uint8