bba —
IOASIC Baseboard Audio device driver
bba0 at ioasic? offset ?
audio* at audiobus?
The bba driver provides support for the IOASIC baseboard
  audio found on DEC 3000/300, 3000/500 (NetBSD/alpha)
  and DEC Personal DECstation (NetBSD/pmax) systems. The
  baseboard audio driver is based on the AMD 79c30 ISDN and audio interface. The
  interface is only capable of playing and recording 8kHz mu-law audio.
The bba device driver appeared in
  NetBSD 1.5. The name for the driver was adopted from
  the same driver in ULTRIX.