ALSA 0.9.x Developer documentation
The Advanced Linux Sound Architecture comes with a driver API & library API. Our aim is to describe hardware as close as possible in drivers, but in userspace, the alsa-lib covers the hardware differences (if required). It's possible for applications to control all hardware features (if required).
- Click here to view the code online - highlighted syntax
- Extra driver/architecture specific information is available in the http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/alsa/alsa-kernel/Documentation/ alsa-kernel/Documentation dir
Q: Why is ALSA more advanced than OSS?
- kernel-space supports only h/w-level capabilities
- multi-thread safe design
- transparent use of plugin architecture to handle format,rate,channel cnt and many other conversions
- support for non-interleaved interfaces
- user-space software mixing (dmix)
- user-space "loopback/snoop" capabilities
- merging multiple cards into a single virtual device
- hiding non-ALSA-drivers behind a consistent user-space API (e.g. IEEE1394 drivers, or JACK)
- consistent and generic control API for managing h/w controls
- sufficiently flexible mixer architecture to handle modern audio interfaces fully (rather than reducing them to a simplistic device)
- consistent support for multiple instances of the same card
- linked operations of multiple cards
- and more...
Currently we need developers to write docs on the ctl API. Until then you will have to read the code and reference other applications for more advanced info.
- ALSA 0.9.0 HOWTO - Dr Matthias Nagorni has writen a comprehensive tutorial for audio application developers.
- Howto use the ALSA API - Paul Davis has also written a brief explanation.
- ALSA Sequencer (draft) - Frank van de Pol's draft on programming the alsa sequencer.
- Kernel OSS-Emulation - Takashi Iwai has written some notes on how ALSA handles OSS applications.
- Programming ALSA (Espanol) - David Garcia Garzon has written Spanish docs and tutorials
- The LAD meeting in Karlsruhe, April 2003 provided two presentations (among many) from the core ALSA developers Jaroslav and Takashi. You can view slides and listen to .ogg recordings of the presentations.
ALSA Library API
The ALSA lib api is the interface to the ALSA drivers. Developers need to use the functions in this api to achieve native ALSA support for their applications. The ALSA lib documentation is a valuable developer reference to the available functions. In many ways it is a tutorial. The latest on-line documentation is generated from the alsa-lib CVS sources.
You can also generate it yourself. Install the doxygen tool and type 'make doc' in the alsa-lib directory.
The currently designed interfaces are listed below:
- Information Interface (/proc/asound)
- Control Interface (/dev/snd/controlCX)
- Mixer Interface (/dev/snd/mixerCXDX)
- PCM Interface (/dev/snd/pcmCXDX)
- Raw MIDI Interface (/dev/snd/midiCXDX)
- Sequencer Interface (/dev/snd/seq)
- Timer Interface (/dev/snd/timer)
ALSA Driver Documentation
Takashi Iwai has written "Writing an ALSA Driver" - a very comprehensive guide to developing a device driver for ALSA.
The document focuses mainly on the PCI soundcard. In the case of other device types, the API might be different. However the ALSA kernel API is consistent so it will be helpful in that context.
ALSA Driver API
This document gives a complete rundown of the functions in the alsa-driver API.
The ALSA HOWTO/FAQ documentation tries to do the ALSA driver installation easier. If you have any ideas or questions regarding this documentation, please, leave a message on the alsa-devel at lists.sourceforge.net mailing list.
The ALSA-sound-mini-HOWTO describes the installation of the ALSA sound drivers for Linux. This HOWTO is also available from the Linux Documentation Project, take a look at http://metalab.unc.edu/LDP/mirrors.html to find your nearest mirror. You can get this HOWTO in various formats:
- HTML (multiple documents)
- HTML (one document)
- plain text
- sgml source of the HOWTO is also available.
There is also an old ALSA FAQ document from John Fulmer.
ALSA 0.5.x Developer documentation
N.B. The 0.5.x series is considered deprecated and is no longer supported by ALSA developers
The ALSA 0.4.0 Developer documentation describes the internals of the ALSA kernel driver. It is a document for kernel developers and others which want to know more about ALSA internals. It is not for application programmers. Application programmers should use the ALSA library API found in the alsa-lib package. Incomplete documentation for ALSA 0.5.x API is available in HTML format on ALSA WWW server or you may get tarball for off-line reading.