diff --git a/headers/os/drivers/USB_spec.h b/headers/os/drivers/USB_spec.h
index 0f07a1ed7c..e0619eda1e 100644
--- a/headers/os/drivers/USB_spec.h
+++ b/headers/os/drivers/USB_spec.h
@@ -40,11 +40,17 @@
 #define USB_REQUEST_SYNCH_FRAME				12
 
 /* Used by {set|get}_descriptor() */
-#define USB_DESCRIPTOR_DEVICE				1
-#define USB_DESCRIPTOR_CONFIGURATION		2
-#define USB_DESCRIPTOR_STRING				3
-#define USB_DESCRIPTOR_INTERFACE			4
-#define USB_DESCRIPTOR_ENDPOINT				5
+#define USB_DESCRIPTOR_DEVICE				0x01
+#define USB_DESCRIPTOR_CONFIGURATION		0x02
+#define USB_DESCRIPTOR_STRING				0x03
+#define USB_DESCRIPTOR_INTERFACE			0x04
+#define USB_DESCRIPTOR_ENDPOINT				0x05
+/* conventional class-specific descriptors */
+#define USB_DESCRIPTOR_CS_DEVICE			0x21
+#define USB_DESCRIPTOR_CS_CONFIGURATION		0x22
+#define USB_DESCRIPTOR_CS_STRING			0x23
+#define USB_DESCRIPTOR_CS_INTERFACE			0x24
+#define USB_DESCRIPTOR_CS_ENDPOINT			0x25
 
 /* Used by {set|clear}_feature() */
 #define USB_FEATURE_DEVICE_REMOTE_WAKEUP	1
diff --git a/headers/os/drivers/usb/USB_cdc.h b/headers/os/drivers/usb/USB_cdc.h
index 575561eb4c..5736328334 100644
--- a/headers/os/drivers/usb/USB_cdc.h
+++ b/headers/os/drivers/usb/USB_cdc.h
@@ -53,8 +53,8 @@ typedef struct usb_cdc_cm_functional_descriptor {
 } _PACKED usb_cdc_cm_functional_descriptor;
 
 enum { // Call Management Functional Descriptor capabilities bitmap
-	USB_CDC_CM_DOES_CALL_MANAGEMENT = 0x00,
-	USB_CDC_CM_OVER_DATA_INTERFACE	= 0x01
+	USB_CDC_CM_DOES_CALL_MANAGEMENT = 0x01,
+	USB_CDC_CM_OVER_DATA_INTERFACE	= 0x02
 };
 
 typedef struct usb_cdc_acm_functional_descriptor {
@@ -64,11 +64,11 @@ typedef struct usb_cdc_acm_functional_descriptor {
 	uint8	capabilities;
 } _PACKED usb_cdc_acm_functional_descriptor;
 
-enum { // Abstract Control Model Functional Descriptor capabilities bitmap
-	USB_CDC_ACM_HAS_COMM_FEATURES 		= 0x00,
-	USB_CDC_ACM_HAS_LINE_CONTROL		= 0x01,
-	USB_CDC_ACM_HAS_SEND_BREAK			= 0x02,
-	USB_CDC_ACM_HAS_NETWORK_CONNECTION	= 0x04
+enum { // Abstract Control Model Functional Descriptor capabilities bitmap (p36)
+	USB_CDC_ACM_HAS_COMM_FEATURES 		= 0x01,
+	USB_CDC_ACM_HAS_LINE_CONTROL		= 0x02,
+	USB_CDC_ACM_HAS_SEND_BREAK			= 0x04,
+	USB_CDC_ACM_HAS_NETWORK_CONNECTION	= 0x08
 };
 
 typedef struct usb_cdc_union_functional_descriptor {
diff --git a/headers/os/drivers/usb/USB_midi.h b/headers/os/drivers/usb/USB_midi.h
index 4ff46b1c12..2eb8d7ed04 100644
--- a/headers/os/drivers/usb/USB_midi.h
+++ b/headers/os/drivers/usb/USB_midi.h
@@ -17,4 +17,107 @@ typedef struct {	// USB MIDI Event Packet
 	uint8	midi[3];
 } _PACKED usb_midi_event_packet;
 
+
+// MIDIStreaming (ms) insterface descriptors (p20)
+
+enum { // MIDI Streaming descriptors subtypes
+	USB_MS_HEADER_DESCRIPTOR = 0x01,
+	USB_MS_MIDI_IN_JACK_DESCRIPTOR,
+	USB_MS_MIDI_OUT_JACK_DESCRIPTOR,
+	USB_MS_ELEMENT_DESCRIPTOR
+};
+
+typedef struct usb_midi_interface_header_descriptor {
+	uint8	length;
+	uint8	descriptor_type;
+	uint8	descriptor_subtype;	// USB_MS_HEADER_DESCRIPTOR
+	uint16	ms_version;
+	uint16	total_length;
+} _PACKED usb_midi_interface_header_descriptor;
+
+
+enum {
+	USB_MIDI_EMBEDDED_JACK = 0x01,
+	USB_MIDI_EXTERNAL_JACK
+};
+
+typedef struct usb_midi_in_jack_descriptor {
+	uint8	length;
+	uint8	descriptor_type;
+	uint8	descriptor_subtype;	// USB_MS_MIDI_IN_JACK_DESCRIPTOR
+	uint8	type;	// USB_MIDI_{EMBEDDED | EXTERNAL}_JACK
+	uint8	id;
+	uint8	string_descriptor;
+} _PACKED usb_ms_midi_in_jack_descriptor;
+
+
+typedef struct usb_midi_source {
+	uint8	source_id;
+	uint8	source_pin;
+} _PACKED usb_midi_source;
+
+typedef struct usb_midi_out_jack_descriptor {
+	uint8	length;
+	uint8	descriptor_type;
+	uint8	descriptor_subtype;	// USB_MS_MIDI_OUT_JACK_DESCRIPTOR
+	uint8	type;	// USB_MIDI_{EMBEDDED | EXTERNAL}_JACK
+	uint8	id;
+	uint8	inputs_count;
+	usb_midi_source input_source[0];	// inputs_count times
+	// uint8	string_descriptor;
+} _PACKED usb_midi_out_jack_descriptor;
+
+
+enum { // USB Element Capabilities bitmap (p23,25)
+	USB_MS_ELEMENT_CUSTOM_UNDEFINED		= 0x0001,
+	USB_MS_ELEMENT_MIDI_CLOCK			= 0x0002,
+	USB_MS_ELEMENT_MIDI_TIME_CODE		= 0x0004,
+	USB_MS_ELEMENT_MTC	= USB_MS_ELEMENT_MIDI_TIME_CODE,
+	USB_MS_ELEMENT_MIDI_MACHINE_CONTROL	= 0x0008,
+	USB_MS_ELEMENT_MMC	= USB_MS_ELEMENT_MIDI_MACHINE_CONTROL,
+	// General MIDI System Level 1 compatible
+	USB_MS_ELEMENT_GM1					= 0x0010,
+	// General MIDI System Level 2 compatible
+	USB_MS_ELEMENT_GM2					= 0x0020,
+	// GS Format compatible (Roland)
+	USB_MS_ELEMENT_GS					= 0x0040,
+	// XG compatibily (Yamaha)
+	USB_MS_ELEMENT_XG					= 0x0080,
+	USB_MS_ELEMENT_EFX					= 0x0100,
+	// internal MIDI Patcher or Router
+	USB_MS_ELEMENT_MIDI_PATCH_BAY		= 0x0200,
+	// Downloadable Sounds Standards Level 1 compatible
+	USB_MS_ELEMENT_DLS1					= 0x0400,
+	// Downloadable Sounds Standards Level 2 compatible
+	USB_MS_ELEMENT_DLS2					= 0x0800
+};
+
+typedef struct usb_midi_element_descriptor {
+	uint8	length;
+	uint8	descriptor_type;
+	uint8	descriptor_subtype;	// USB_MS_ELEMENT_DESCRIPTOR
+	uint8	id;
+	uint8	inputs_count;
+	usb_midi_source input_source[0];	// inputs_count times
+	// uint8	outputs_count;
+	// uint8	input_terminal_id;
+	// uint8	output_terminal_id;
+	// uint8	capabilities_size;
+	// uint8	capabilities[0];	// capabilities_size bytes
+	// uint8	string_descriptor;	// see USB_MS_ELEMENT_* enum above
+} _PACKED usb_midi_element_descriptor;
+
+// Class-Specific MIDIStream Bulk Data Endpoint descriptor (p26)
+
+#define USB_MS_GENERAL_DESCRIPTOR	0x01
+
+typedef struct usb_midi_endpoint_descriptor {
+	uint8	length;
+	uint8	descriptor_type;	// USB_DESCRIPTOR_CS_ENDPOINT
+	uint8	descriptor_subtype;	// USB_MS_GENERAL_DESCRIPTOR
+	uint8	jacks_count;
+	uint8	jacks_id[0];		// jacks_count times
+} _PACKED usb_midi_endpoint_descriptor;
+
+
 #endif	// USB_MIDI_H