Peripheral Controller Drivers implement the gadget API, and are the only layers that talk directly to hardware. If the controller is connected to a USB host, it will first disconnect. The correct ep0 maxpacket size is also reported, as defined by the underlying controller driver. At least provided that n is non-zero because if it is, returns last requested ID which is now very useful information. Hardware sometimes restricts how software can manage device configurations, in ways that may prevent implemention of multi-function devices, multi-configuration ones, or certain standard USB Device Class specifications. One of the main tasks of a composite bind routine is to add each of the configurations it supports, using this routine. Convenience functions make it easier to test which of the currently configured controller chips is being used.

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A system running inside a USB peripheral normally has at least three layers inside the kernel to handle USB protocol processing, and may have additional layers in user space code. If the gadget driver module is unloaded before the host starts to enumerate, steps before step 7 are skipped.

USB/Linux USB Layers/GadgetFs – Tizen Wiki

The return value is zero, or a negative errno value. Flexible enough to expose more complex USB device capabilities such as multiple configurations, multiple interfaces, composite devices, and alternate interface settings.

Binding configurations assigns global resources including string IDs, and per-configuration resources such as interface IDs and endpoints. There are two other components worth mentioning.


Devices default to reporting self powered operation. At this point the device is logically in the USB ch9 initial state attacheddrawing no power and not usable since it does not yet support enumeration. The APIs are of course different; the peripheral side is much lower overhead, and serves a “slave” role not a “master” one. An example of multiple activations might be a CDC ACM function that supports two or more distinct instances within the same configuration, providing several independent logical data links to a USB host.

It’s designed for flexibility: These could include kernel layers, such as network protocol stacks, as well as user mode applications building on standard POSIX system call Gaadgetfs such as opencloseread and write. Discussions, patches, and similar work should be on the linux-usb-devel mailing list for now. Adding a function involves calling its bind method to allocate resources such as interface and string identifiers and endpoints.

USB/Linux USB Layers/GadgetFs

That also conserves battery power, which is useful even for non-OTG configurations. This function is used to register drivers using the composite driver framework. Convenience functions make it easier to test which of the currently configured controller chips is being used.

Since normal USB devices only have one upstream port, they only have one of these drivers. Peripheral Controller Drivers implement ,inux gadget API, and are the only layers that talk directly to hardware. Controller Drivers Drivers for several different usb device chips are available.

Gadget driver responsibilities include:. Hardware tends to have arbitrary restrictions, relating to transfer types, addressing, packet sizes, buffering, and availability. You should plan on testing these in conjunction with the controller driver and system board you’ll be using. Gadget drivers talk to hardware-specific code indirectly, through ops vectors.

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There will also be an OTG Controller Driverwhich is visible to gadget and device driver developers only indirectly. This eliminates a lot of boilerplate. Handles devices with dozens of endpoints just as well as ones with just gadgetfw fixed-function ones. The driver supports Linux kernel versions 2. Use the API like this: However, there are host side user-mode implementations, such as gPhoto2.

Linux-USB Gadget API Framework

Different controller hardware will need different drivers, which may also need board-specific customization. You can generate a current version of that yourself directly with commands like “make pdfdocs”, or use a pre-generated version which may not be as up-to-date as what you make from current kernel sources.

Roles switch host to peripheral, or vice versa using HNP during USB suspend processing, and SRP can be viewed as a more battery-friendly kind of device wakeup protocol. Those issues may be handled at various points: This is the first such API released on Linux to address a number of important linuux, including:. Drivers use hardware-specific knowledge to configure the usb hardware.