All the relevant code lives in
/usr/src/sys/dev/sound/, except for the
public ioctl interface definitions, found in
/usr/src/sys/sys/soundcard.h
Under /usr/src/sys/dev/sound/, the
pcm/ directory holds the central code,
while the pci/, isa/
and usb/ directories have the drivers
for PCI and ISA boards, and for USB audio devices.
This, and other documents, can be downloaded from ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/
For questions about FreeBSD, read the
documentation before
contacting <questions@FreeBSD.org>.
For questions about this documentation, e-mail <doc@FreeBSD.org>.