Writing a linux usb driver for your specific device

In addition to the kernel driver I introduce a simple user-space tool that can be used to control the device. Although I have to delve into the specifics of a particular device, the process can be applied to other USB devices as well. Introduction Recently, I found a fancy device while searching eBay:

Writing a linux usb driver for your specific device

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.

writing a linux usb driver for your specific device

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Some vendors are open with their USB protocols and help with the creation of Linux drivers, while others do not publish them, and developers are forced to reverse-engineer.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.

Writing USB driver for Android - Stack Overflow

Because each different protocol causes a new driver to be created, I have written a generic USB driver skeleton, modelled after the pci-skeleton. 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.

It can be found, along with many other useful documents, at the USB home page see Resources. 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.

It is used in informational messages printed to the system log.

writing a linux usb driver for your specific device

The fops and minor variables are optional. These types of drivers register themselves with the other kernel subsystem, and any user-space interactions are provided through that interface. But for drivers that do not have a matching kernel subsystem, such as MP3 players or scanners, a method of interacting with user space is needed.

The following code tells the hotplug scripts that this module supports a single device with a specific vendor and product ID: If so, it returns 0. 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. 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: 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: This function is called when the urb is finished by the USB subsystem. The callback function is called in interrupt context, so caution must be taken not to do very much processing at that time.

The read function works a bit differently from the write function in that we do not use an urb to transfer data from the device to the driver. If the timeout period expires without receiving any data from the device, the function will fail and return an error message. This can be shown with the following code: When the user program releases the file handle that it has been using to talk to the device, the release function in the driver is called.

In this function we decrement our private usage count and wait for possible pending writes: It needs to be able to shut down any current reads and writes and notify the user-space programs that the device is no longer there.

For every read, write, release and other functions that expect a device to be present, the driver first checks this flag to see if the device is still present. Interrupt data is sent almost exactly as bulk data is, with a few minor exceptions.

Drivers - How can I write raw data to a USB device - Unix & Linux Stack Exchange

Isochronous data works differently with continuous streams of data being sent to or from the device. The audio and video camera drivers are very good examples of drivers that handle isochronous data and will be useful if you also need to do this.The first goal in trying to write a driver for a device is to determine how to control the device.

Delcom Engineering is nice enough to ship the entire USB protocol specification their devices use with the product, and it also is available on-line for free.

Writing Linux USB device drivers is not a difficult task as the usb-skeleton driver shows. This driver, combined with the other current USB drivers, should provide enough examples to help a beginning author create a working driver in a minimal amount of.

Apr 03,  · Introduction to Linux - A Hands on Guide This guide was created as an overview of the Linux Operating System, geared toward new users as an exploration tour and getting started guide, with exercises at the end of each chapter. An Introduction to Device Drivers - vetconnexx.com is.

May 12,  · Hello all, I have a IC CY7C USB SX2 of Cypress semiconductors. The driver for this IC was given from Cypress semiconductor for Win XP, which functions properly on XP. Now i want to import(run) my Usb device on Linux.

Apr 03,  · Introduction to Linux - A Hands on Guide This guide was created as an overview of the Linux Operating System, geared toward new users as an exploration tour and getting started guide, with exercises at the end of each chapter. Under the Linux Operating System, creating a MODULE_DEVICE_TABLE that contains the vendor specific product ID will enable the Linux-hotplug system for that specific device only. The codes contained in this table will instruct the hotplug script on how to handle the USB-based device. May 12,  · Hello all, I have a IC CY7C USB SX2 of Cypress semiconductors. The driver for this IC was given from Cypress semiconductor for Win XP, which functions properly on XP. Now i want to import(run) my Usb device on Linux.

static void __exit usb_skel_exit(void) { /* deregister this driver with the USB subsystem */ usb_deregister(&skel_driver); } module_exit(usb_skel_exit); To enable the linux-hotplug system to load the driver automatically when the device is plugged in, you need to create a MODULE_DEVICE_TABLE.

Writing a USB driver in linux