Introduction The Linux USB subsystem has grown from supporting only two different types of devices in the 2.2.7 kernel (mice and keyboards), to over 20 different types of devices in the 2.4 kernel. Linux currently supports almost all USB class devices (standard types of devices like keyboards, mice, modems, printers and speakers) and an ever-growing number of vendor-specific devices (such as USB to serial converters, digital cameras, Ethernet devices and MP3 players). For a full list of the different USB devices currently supported, see Resources. The remaining kinds of USB devices that do not have support on Linux are almost all vendor-specific devices. Each vendor decides to implement a custom protocol to talk to their device, so a custom driver usually needs to be created. Some vendors are open with their USB protocols and help with the creation of Linux drivers, while others do not publish them, and developers are forced to reverse-engineer. See Resources for some links to handy reverse-engineering tools.

Because each different protocol causes a new driver to be created, I have written a generic USB driver skeleton, modelled after the pci-skeleton.c file in the kernel source tree upon which many PCI network drivers have been based. This USB skeleton can be found at drivers/usb/usb-skeleton.c in the kernel source tree. In this article I will walk through the basics of the skeleton driver, explaining the different pieces and what needs to be done to customize it to your specific device. Linux USB Basics If you are going to write a Linux USB driver, please become familiar with the USB protocol specification. It can be found, along with many other useful documents, at the USB home page (see Resources). An excellent introduction to the Linux USB subsystem can be found at the USB Working Devices List (see Resources). It explains how the Linux USB subsystem is structured and introduces the reader to the concept of USB urbs (USB Request Blocks), which are essential to USB drivers.

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Linux; News & reviews; Softpedia > Drivers > Sound Card > REALTEK > Realtek USB Audio Driver 6.3.9600.17. Usually, Windows operating systems apply a generic audio driver that allows computers to recognize the sound card component and make use of its basic functions. Apr 7, 2015 - Windows needs manufacturer-provided hardware drivers before your hardware will work. Linux and other operating systems also need.

The first thing a Linux USB driver needs to do is register itself with the Linux USB subsystem, giving it some information about which devices the driver supports and which functions to call when a device supported by the driver is inserted or removed from the system. All of this information is passed to the USB subsystem in the usb_driver structure. The skeleton driver declares a usb_driver as. Static int skel_probe ( struct usb_interface * interface, const struct usb_device_id * id ) The driver now needs to verify that this device is actually one that it can accept. If so, it returns 0. If not, or if any error occurs during initialization, an errorcode (such as -ENOMEM or -ENODEV) is returned from the probe function.

In the skeleton driver, we determine what end points are marked as bulk-in and bulk-out. We create buffers to hold the data that will be sent and received from the device, and a USB urb to write data to the device is initialized. Conversely, when the device is removed from the USB bus, the disconnect function is called with the device pointer. The driver needs to clean any private data that has been allocated at this time and to shut down any pending urbs that are in the USB system. Now that the device is plugged into the system and the driver is bound to the device, any of the functions in the file_operations structure that were passed to the USB subsystem will be called from a user program trying to talk to the device. The first function called will be open, as the program tries to open the device for I/O.

We increment our private usage count and save a pointer to our internal structure in the file structure. This is done so that future calls to file operations will enable the driver to determine which device the user is addressing.

All of this is done with the following code. /* increment our usage count for the module */ ++ skel -> open_count; /* save our object in the file's private structure */ file -> private_data = dev; After the open function is called, the read and write functions are called to receive and send data to the device. In the skel_write function, we receive a pointer to some data that the user wants to send to the device and the size of the data. The function determines how much data it can send to the device based on the size of the write urb it has created (this size depends on the size of the bulk out end point that the device has). Then it copies the data from user space to kernel space, points the urb to the data and submits the urb to the USB subsystem. This can be seen in the following code.