The Endpoint Descriptor (USB_ENDPOINT_DESCRIPTOR) specifies the transfer type, direction, polling interval, and maximum packet size for each endpoint. Endpoint 0 (zero), the default endpoint, is always assumed to be a control endpoint and never has a descriptor.

Offset	Field	Type	Size	Value	Description
0	bLength	uint8_t	1	Number	Size of this descriptor in bytes.
1	bDescriptorType	uint8_t	1	Constant	Endpoint Descriptor Type = 5.
2	bEndpointAddress	uint8_t	1	Endpoint	The address of the endpoint on the USB device described by this descriptor. The address is encoded as follows: Bit 3...0: The endpoint number Bit 6...4: Reserved, reset to zero Bit 7: Direction, ignored for control endpoints. 0 = OUT endpoint 1 = IN endpoint
3	bmAttributes	uint8_t	1	Bitmap	The endpoint attribute when configured through bConfigurationValue. Bits 1..0: Transfer Type 00 = Control 01 = Isochronous 10 = Bulk 11 = Interrupt For non-isochronous endpoints, bits 5..2 must be set to zero. For isochronous endpoints, they are defined as: Bits 3..2: Synchronization Type 00 = No Synchronization 01 = Asynchronous 10 = Adaptive 11 = Synchronous Bits 5..4: Usage Type 00 = Data 01 = Feedback 10 = Implicit feedback 11 = Reserved All other bits are reserved and must be reset to zero.
4	wMaxPacketSize	uint16_t	2	Number	Is the maximum packet size of this endpoint. For isochronous endpoints, this value is used to reserve the time on the bus, required for the per-(micro)frame data payloads. Bits 10..0 = max. packet size (in bytes). For high-speed isochronous and interrupt endpoints: Bits 12..11 = number of additional transaction opportunities per micro-frame: 00 = None (1 transaction per micro-frame) 01 = 1 additional (2 per micro-frame) 10 = 2 additional (3 per micro-frame) 11 = Reserved Bits 15..13 are reserved and must be set to zero.
6	bInterval	uint8_t	1	Number	Interval for polling endpoint for data transfers. Expressed in frames or micro-frames depending on the operating speed (1ms, or 125μs units). For full-/high-speed isochronous endpoints, this value must be in the range from 1 to 16. The bInterval value is used as the exponent for a 2^bInterval-1 value; For example, a bInterval of 4 means a period of 8 (2^4-1). For full-/low-speed interrupt endpoints, the value of this field may be from 1 to 255. For high-speed interrupt endpoints, the bInterval value is used as the exponent for a 2^bInterval-1 value; For Example, a bInterval of 4 means a period of 8 (2^4-1). This value must be from 1 to 16. For high-speed bulk/control OUT endpoints, the bInterval must specify the maximum NAK rate of the endpoint. A value of 0 indicates the endpoint never NAKs. Other values indicate at most 1 NAK each bInterval number of microframes. This value must be in the range from 0 to 255.