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The General USB Process
How Does the Host Know a Device’s 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)
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.