audiodriverslinux-kernel
I have headphones with three buttons on it which allow me to control my music player. I want to write a driver to make it control my music player on my pc (Ubuntu Linux).
So I think I should write a special program for my device. I have some basic knowledge about kernel programming and Linux device drivers. Who can tell me where I can find the default driver for headphones, or some ideas and suggestion are also appreciated.
Was the idea behind the controller to be able to control devices from a different manufacturers with the same driver?
No. The primary purpose is to provide part of the interface between devices and the processor. A controller has its own driver; this is in addition to any drivers necessary for the devices connected to it.
The reason the interface is necessary is that the processor is highly specialized; controllers are sort of translators from the specialized world of the processor to the multiverse of devices. The processor only has one physical data connection to the outside (the bus), not a variety of them, and in fact, generally intermediary between controllers and the processor are bridges which connect the processor to the motherboard. Device controllers are then connected to the motherboard and communicate via a bridge. So there are four discrete physical entities in the chain: processor -> bridge -> controller -> device, all of which involve their own software drivers (a driver for the processor, for the bridge chipset, then for each of the controllers, and for each of the devices).
If you look at the diagram below from this wikipedia article, the blue boxes at the bottom represent device controllers.
[By Alexander Taubenkorb, Creative Commons Attribution-Share Alike 3.0]
Files in /dev are mostly created by the udev process which receives events from the kernel by listening to the netlink socket for NETLINK_KOBJECT_UEVENT (see man 7 netlink). The events are sent when a new kernel object (kobject) is created. These objects are also seen in the /sys sysfs filesystem. In particular, files named dev in the /sys/devices subtree hold the major and minor number of the node to use for a given device. Eg
$ cat /sys/devices/pnp0/00:05/tty/ttyS0/dev
4:64
This is explained in this online chapter 14 pdf of Linux Device Drivers, Third Edition
from 2005, The Linux Device Model. It is a little outdated and does not mention netlink for example.
Best Answer
If you don't have a USB headset your headset is typically handled by your normal audio driver, e.g. if you plug your headset in the driver will typically mute the speakers and use the headset output instead. Audio drivers nowadays are typically Alsa drivers and can be found in the
sounddirectory of the Linux kernel.If you have a USB headset it will be a dedicated soundcard and you would need to modify the driver for your specific USB headset.
To determine the specific driver for your soundcard use
and have a look at the
Kernel driver in use: snd_hda_intelline or uselsmodto list your modules and determine your audio driver.