This directory contains the middle layer which is the heart of ALSA drivers. In this directory, the native ALSA modules are stored. The sub-directories contain different modules and are dependent upon the kernel config.
The codes for PCM and mixer OSS emulation modules are stored
in this directory. The rawmidi OSS emulation is included in
the ALSA rawmidi code since it's quite small. The sequencer
code is stored in core/seq/oss directory (see
below).
This directory contains the 32bit-ioctl wrappers for 64bit architectures such like x86-64, ppc64 and sparc64. For 32bit and alpha architectures, these are not compiled.
This directory and its sub-directories are for the ALSA
sequencer. This directory contains the sequencer core and
primary sequencer modules such like snd-seq-midi,
snd-seq-virmidi, etc. They are compiled only when
CONFIG_SND_SEQUENCER is set in the kernel
config.