At this writing, there are people at work on drivers in this framework for several other USB device controllers, with plans to make many of them be widely available. This function chooses the right descriptors for a given endpoint according to gadget speed and saves it in the endpoint desc field. Functions may have static tables of descriptors, which are used as templates and customized with identifiers for interfaces, strings, endpoints, and more as needed by a given function instance. Use the API like this: Recent versions of this API have improved and grown the collection of gadget driver library helper functions.
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This is the lowest software level.
The gadget API is used by the middle layer to interact with the lowest level which directly handles hardware. Other operating systems use other names for this component, perhaps labeling the API plus its libraries as a “Platform Independent Layer” and its implementation as a “Platform Specific Layer”. Peripheral Controller Drivers implement the gadget API, and are the only layers that talk directly to hardware.
These generate and consume the data that the gadget driver transfers to the host through lniux controller driver. Convenience functions make yadgetfs easier to test which of the currently configured controller chips is being used.
USB/Linux USB Layers/GadgetFs
Systems need specialized hardware support to implement OTG, notably including a special Mini-AB jack and associated transceiver to support Dual-Role operation: CDC WMC devices are an example where functions often depend on other functions, with some functions subsidiary to others. Bug fixes, gadget drivers especially “class” driversand new USB device controller drivers will all be of interest.
When the gadget driver module is being unloaded, the driver unbind callback is issued. It’s easy to backport current 2.
For example, some controllers have more endpoints than others, many don’t support high speed or isochronous transfers, and sometimes endpoints have fixed configurations. You can think of that hadgetfs as being the virtual hardware to which the higher level drivers are written. Drivers must make sure the endpoint descriptors match any hardware constraints.
Such issues are in the domain of gadget drivers, including knowing about implementation constraints imposed by gadgefts USB controllers or understanding that composite devices might happen to be built by integrating reusable components.
Configurations are building blocks for gadget drivers structured around function drivers. Sometimes it will be the only option; there are Linux devices that rely on USB even for their power supplies. Other steps are handled by the gadget driver. There is also support for user mode gadget drivers, using gadgetfs.
There may be other public trees with controller or gadget drivers too. The return value is zero, or a negative errno value.
Recent kernels substantially simplify the work involved in supporting new hardware, by autoconfiguring endpoints automatically for many bulk-oriented drivers. It a good base for integrating and re-using this type of driver code.
Linux-USB Gadget API Framework
If this is not big enough to hold the entire configuration descriptor, an error code will be returned. Hardware tends to have arbitrary restrictions, relating to transfer types, addressing, packet sizes, buffering, and availability.
Devices which rely on bus powered operation should report this in their bind method. But when you’re putting together embedded Linux systems, a USB peripheral controller option is routine; it’s often integrated into processors. After initialization, each configuration must have one or more functions gagetfs to it. It can act like a net, a pxa25x, or an sa11x0 in terms of available endpoints and device speeds; and it simulates control, bulk, and to some extent interrupt transfers.
That also conserves battery power, which is useful even for non-OTG configurations.
USB/Linux USB Layers/GadgetFs – Tizen Wiki
Examples that have seen some degree of light include:. Gadget drivers talk to hardware-specific code indirectly, through ops vectors. This function chooses the right descriptors for a given endpoint according to gadget speed and saves it in the endpoint desc field. Recent versions of this API have improved and grown the collection of gadget driver library helper functions. The Linux-USB host-side and peripheral-side driver stacks are directly analagous, except that only the host side has a mid layer.
Other than providing an additional OTG descriptor in each configuration, only the HNP-related differences are particularly visible to driver code.