The General USB Process
How Does the Host Know a Device’s Requirements?
Software – General Concepts
Endpoint
Descriptor
The endpoint descriptors define what transfer type to use, the maximum packet size and time interval used to poll the frames (1mS for low or full speed devices and 125us for high speed devices). From this the host determines bandwidth requirements.
//Sample Standard Endpoint Descriptor Type
//Definition Fields
Length (7 bytes)
Descriptor Type (ENDPOINT)
End Point Address (indicates what endpoint this descriptor is describing)
Attributes (specifies the transfer type) Maximum Packet Size (indicates the maximum payload size for this endpoint)
Interval (interval for polling endpoint data transfers. Value in frame counts. Ignored for Bulk & Control Endpoints. Isochronous must equal 1 and field may range from 1 to 255 for interrupt endpoints)
