The
attimer driver handles the so-called AT Timer device, initially found as chip model 8253. It is used as the main counter for the clock on the i386 port, but also offers control over the pitch of the PC speaker.
The
attimer driver currently only implements the access to the ISA register “TIMER1” which controls the pitch of the PC speaker, and should be configured along with
pcppi(4) to be of any actual use.