AC'97 codecs contain the analog-to-digital (A/D), digital-to-analog
(D/A), and mixing circuitry of many modern sound cards.
AC'97 codecs, for the most part, do not talk to host buses like the PCI bus
Instead, they communicate through an interface chip, called
the host controller.
The Ensoniq AudioPCI 97 (see
is an example of such a host controller.
Unlike many drivers, the
driver does not appear in the configuration file.
Instead, the driver is automatically attached by the drivers that require it.
driver does not keep track of the current user settings and instead
relies on the hardware to do this.
driver could do more to detect mixer channels that don't work and cull
them from the list.