USB

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Descriptors

One of the most complex things when developing USB is the descriptors. Descriptors are used by a USB Gadgets to inform the USB Host about it's capabilities.

Overall, USB Descriptors is a hierarchy of descriptors organised like this:

USB Descriptor Hierarchy.png

A USB device (or gadget) can only have one device descriptor.

When a USB host enumerates a USB device, the device and configuration descriptors are analysed and one configuration is enabled. Only one configuration can be active at any time.

While it _is_ possible for a host to switch configuration on a device offering more than one, it is very rare for devices to offer more than one configuration.

Device Descriptors

Configuration Descriptors

Configuration Descriptor.png

Interface Descriptors

Endpoint Descriptors

String Descriptors

Miscellaneous Links