SALSA-Lib - Small ALSA Library

GENERAL

SALSA-Lib is a small, light-weight, hot and spicy version of the ALSA library, mainly for embedded systems with limited resources. The library is designed to be source-level compatible with ALSA library API for limited contents. Most of function calls are inlined, and accesses directly to the hardware via system calls. Some components like ALSA sequencer aren't supported, and most of all, the alsa-lib plugins and configurations are completely dropped. Thus, neither dmix nor format conversion is available with SALSA-lib.

The current features are found in the sections below.

CONFIG

• All functions snd_config_*() are replaced with dummy ones since SALSA-Lib doesn't support the configuration files. The apps accessing config stuff won't work properly as expected.
• Disabled as default

PCM

• Supports only the hw layer, i.e. no up/down-mixing, format conversion, rate conversion, etc, and no external plug-in
• Accepts the limited PCM name, hw, default, default:x, and hw:x,y,z
• Some of snd_pcm_mmap_read/write*() functions are declared but not implemented (returns -ENXIO)
• The support of async handlers can be built in via configure option, --enable-async. For simplicity, SALSA-lib supports only one async handler per PCM handler.

CONTROL

• Supports only the hw layer, no plug-in
• Some H-control functions are not included
• The support of async handlers via --enable-async as well as PCM async handlers.

MIXER

• No sort with weight as default, sorted in the order of numid
• Simple-none layer only
• "Capture Source" isn't split to switches but handled as an enum (I personally like this better :-)
• dB support can be selected via configure option
• Linear <-> log dB conversion enabled via configure option

TIMER

• No query interface (returns errors)
• No async handler (returns -ENXIO)
• Disabled as default

RAWMIDI

• Should work
• Disabled as default

HWDEP

• Should work
• Disabled as default

SEQUENCER

• All replaced with dummy functions. The apps using sequencer won't work properly.
• Disabled as default

INSTRUMENT LAYER

• No APIs are provided

UCM

• Not supported yet at all

MISC

• The API functions that are not supported but defined have deprecated attribute. You'll get compile warnings when compiling the code using such functions. (The same is true for the all components below.) They are just warnings that you can usually ignore. The warnings are given so that you can find the non-functional features easily. If warnings really matter, remove the deprecated attribute via --disable-deprecated configure option.

INSTALLATION

Some configure options are available to reduce the binary size. As default, rawmidi, hwdep, timer, conf and seq components are disabled. They can be enabled via --enable-xxx option, such as --enable-rawmidi. The PCM and mixer components are enabled as default, and can be disabled via --disable-pcm and --disable-mixer option, respectively.

The dB range support can be enabled via --enable-tlv option. It's disabled as default. For enabling the floating-point math calculation used in dB <-> linear conversion for the mixer, pass --enable-float option as well.

The support for user-space control elements is enabled as default to keep the compatibility with the older salsa-lib releases. But now it can be disabled via --disable-user-elem configure option, too.

The async handler support can be enabled via --enable-async option. It's disabled as default.

The PCM chmap API support is also optional, can be enabled via --enable-chmap option.

With option --enable-abi-compat, libasound.so will be created as an opt-in ABI-compatible library with the genuine ALSA-lib.

When --enable-abicheck is given, each open function checks the ABI compatibility with the installed library.

When --enable-time64 is passed, the library enforces to use the 64bit timespec and 64bit-compatible PCM ioctls even if the libc is still with 32bit time. It's good for testing the 64bit time support.

All these options can be enabled via a single option, --enable-everything, for your convenience.

For disabling the deprecated attribute for non-working functions (see the description of "MISC" in the section "GENERAL"), pass --disable-deprecated option.

For enabling the support for the string buffer with snd_output_*() function (e.g. used by PulseAudio), pass --enable-output-buffer option.

The alsa-library version to be compatible can be given explicitly via --with-compat-version option. As default, 1.2.5 is set.

If the ALSA device files are not in /dev/snd, another directory can be specified with the --with-alsa-devdir option.

The library is installed as $LIBDIR/libsalsa.so.*. This package provides also the compatible alsa.m4 and alsa.pc. If the other packages can be autoreconf'ed, you'll be able to link libsalsa as it is.

The C header files are installed into $INCLUDEDIR/alsa. The alsa/asoundlib.h should be compatible with the normal alsa-lib's one.

CROSS-COMPILATION

For compiling the library with a cross compiler, run like the following:

% CC=arm-linux-gcc \
  ./configure --target=arm-linux --host=i686-linux

Don't forget to add -linux to the host option value. Otherwise configure script won't detect the host type correctly, and the shared library won't be built properly.

DOCUMENTATION

See alsa-lib reference. It's compatible!

KNOWN PROBLEMS

• Incomplete MMAP mode

  snd_pcm_mmap_*() are only partially implemented, and the mmap-mode is less tested, so far.

• When built without --enable-output-buffer, the buffer output via snd_output_*() functions doesn't work. And, the last close argument in snd_input_stdio_attach() and snd_output_stdio_attach() is ignored and the attached IO is always closed.

LICENSE

Distributed under LGPL. See COPYING file.