AC97(4) Kernel Interfaces Manual AC97(4)
ac97 -- generic AC97 codec driver
AC97 codecs contain the analog-to-digital (A/D), digital-to-analog (D/A),
and mixing circuitry of many modern sound cards. AC97 codecs, for the
most part, do not talk to host busses like the PCI bus directly.
Instead, they communicate through an interface chip, called the host
controller. The Ensoniq AudioPCI 97 (see eap(4)) is an example of such a
Unlike many drivers, the ac97 driver does not appear in the configuration
file. Instead, the driver is automatically attached by the drivers that
auacer(4), auich(4), auixp(4), autri(4), auvia(4), clcs(4), clct(4),
eap(4), emuxki(4), esa(4), esm(4), fms(4), neo(4), yds(4)
The ac97 driver does not keep track of the current user settings and
instead relies on the hardware to do this.
The ac97 driver could do more to detect mixer channels that don't work
and cull them from the list.
NetBSD 6.1.5 October 7, 1999 NetBSD 6.1.5