There is however an optional framework which makes it easier to reuse and combine functions. These are directly analagous to host side “interface drivers”, except for multi-function “composite” gadget drivers. A gadget driver implements one or more “functions”, each providing a different capability to the USB host, such as a network link or speakers. Useful when assembling descriptors for an associated set of interfaces used as part of configuring a composite device; or in other cases where sets of descriptors need to be marshaled. The USB host side needs such a layer to multiplex potentially hundreds of peripherals and drivers; the peripheral side has no such requirement.
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USB/Linux USB Layers/GadgetFs
These aren’t a separate library or midlayer, they’re just object files optionally linked with gadget drivers that want their functions. It’s designed for flexibility: The USB host side needs such a layer to multiplex potentially hundreds of peripherals and drivers; the peripheral side has no such requirement. The core API is sufficient for writing drivers for composite USB devices with more than one function in a given configurationand also multi-configuration devices also more than lunux function, but not necessarily sharing a given linud.
Linux users with embedded systems gadgetffs more likely to have USB peripheral hardware. They are implemented on 2. Other steps are handled by the gadget driver. Note that the lifecycle above can be slightly different for OTG devices. Returns length of descriptor always even or negative errno.
Gadget Drivers At this writing there are several public “gadget drivers”, each implementing a single common USB function so it will work with virtually any USB peripheral controller. Note that at this lowest level there are no policies about how ep0 configuration logic is implemented, except that it should obey USB specifications. The core API does not expose every possible hardware feature, only the most widely available ones.
Use the API like this: Most of those are full speed controllers.
Such simulators can help debug subsystems where the runtime hardware is unfriendly to software development, or is not yet available. Mentor Graphics supplies a preliminary GPL’d high speed stackbuilding on the gadget API and used with chips integrating their silicon design. One of the standards for cable lunux interoperability even specifies the use of this ethernet model gadgtfs one of two mandatory options. In addition to Gadget Zero used primarily for testing and development with drivers for usb controller hardwareother gadget drivers exist.
HNP support should be reported through a user interface two LEDs could sufficeand is triggered in some cases when the host suspends the peripheral. These provide a software “gadget” device, visible in sysfs. Support for other controllers is expected to lunux developed and contributed over time, as this driver framework evolves.
This work has been supported by patches, feedback, bug reports, hardware, and other contributions from many groups and individuals. You can think of that device as being the virtual hardware to which the higher level drivers are written. Some hardware also constrains other descriptors.
Over time, reusable utilities are linix to help make some gadget driver tasks simpler. Except for the driver data, all fields in this structure are read-only to the gadget driver. Peripheral Controller Drivers implement the gadget API, and are the only layers that talk directly to hardware.
Linux-USB Gadget API Framework
It provides an overview of the API structure, and shows how that gadgetfe into a system development project. At this point the device is logically in the USB ch9 initial state attacheddrawing no power gadgtefs not usable since it does not yet support enumeration. Examples that have seen some degree of light include:.
The gadget API does support such drivers. However, some may need to change modes when the host is not longer directing those activities.
Not all controllers support isochronous transfers, as needed for audio and video class drivers. Configurations are building blocks for gadget drivers structured around function drivers. They share common definitions for the standard USB Chapter 9 messages, structures, and constants. That lets you develop some parts of a gadget driver on a normal PC, without any special hardware, and perhaps with the assistance of tools such as GDB running with User Mode Linux.
When the gadget driver module is being unloaded, the driver unbind callback is issued.