Development: How to develop drivers for USB based devices
This article is meant to serve as an introduction to the task of developing a driver for a usb based dvb device. Currently, in terms of this subject, there are a number of scattered resources available that, when organized together, could form the basis of a howto suitable for the noice developer. Hence, it might be very worthwile documenting the process.
The very first thing you would want to do is to identify the components used in your device. Refer to the section entitled "Gathering Information About Your Unidentified/Unsupported Device" for some clues on how to proceed with that task.
The next logical step would be to try to obtain technical datasheets on the components. Many chip manufacturers make this documentation readiablily available, while in other cases a google search for the chip's part or model number is necessary to track down other sources for such documentation.
Familiarizing yourself with a USB driver
To start with, there are some great Linux USB tutorials on Linux Journal:
- start here: How to Write a Linux USB Device Driver
- then here: Writing a Simple USB Driver
- here: Hot Plug
- and then here: Snooping the USB Data Stream
In addition, get the source code for the LinuxTV V4L-DVB driver set. You will find that USB based DVB drivers are contained within the ./v4l-dvb/linux/drivers/media/dvb/dvb-usb directory. Have a bit of a browse through them while you're reading through the first article listed above, and try to get a feel for how the driver is put together (note: there is also a procedure about this that is described in a thread found here). Sometimes you can get a good head start in your own development efforts by attempting to leverage parts of earlier released code -- that which may have been written specifically for the exact same chip as contained in your own device or via code for a near similar chip, such as say from a previous production generation. Simply, modifying existing code to suite your own endeavour can greatly expediate the process of driver development.
Some useful tools
- usbsnoop - a Windows USB sniffer utilitly, which adheres to the WDM architecture
- also see SniffUSB 2.0 - a usbsnoop derivative
- parser.pl - a script for parsing the huge usbsniff log file
- USB Replay - allows one to replay parsed usbsnoop logfiles on a Linux system
- also see this M920x specific script for some ideas
- Usbmon2usbsnoop - a script that converts the output from usbmon to a format that is compatible with USB Replay