wdsc —
Western Digital WD33c93 SCSI Bus Interface Controller
The wdsc driver provides an abstraction layer between
  the SCSI hardware found in multitudinous SGI machines (including Personal Iris
  series, Indigo, Indy, Challenge S, Indigo2, and Challenge M) and the machine
  independent SCSI drivers described in
  scsibus(4).
In addition to sending the required SCSI commands to target
    devices on the SCSI bus, the wdsc driver deals with
    DMA, device interrupts, sync/async negotiation, and target
    disconnects/reconnects.
Wayne Knowles ported the sgimips incarnation of the wdsc
  driver from the amiga and atari ports. It first appeared in
  NetBSD 1.6.