Difference between revisions of "USB"
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[[File:USB Descriptor Hierarchy.png|1000px]] | [[File:USB Descriptor Hierarchy.png|1000px]] | ||
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| + | A USB device (or gadget) can only have '''one''' device descriptor. | ||
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| + | 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. | ||
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| + | 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 === | === Device Descriptors === | ||
=== Configuration Descriptors === | === Configuration Descriptors === | ||
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| + | [[File:Configuration Descriptor.png|800px]] | ||
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=== Interface Descriptors === | === Interface Descriptors === | ||
=== Endpoint Descriptors === | === Endpoint Descriptors === | ||
=== String Descriptors === | === String Descriptors === | ||
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== Miscellaneous Links == | == Miscellaneous Links == | ||
* [https://beyondlogic.org/usbnutshell/usb5.shtml USB In a Nutshell]] | * [https://beyondlogic.org/usbnutshell/usb5.shtml USB In a Nutshell]] | ||
Revision as of 07:21, 30 August 2021
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:
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
