Manual Pages  — ATTIMER

attimer – i8254 Programmable Interval Timer (AT Timer) driver

SYNOPSIS DESCRIPTION SEE ALSO

This driver uses i8254 Programmable Interval Timer (AT Timer) hardware to supply the kernel with one timecounter and one event timer, and to generate sound tones for the system speaker. This hardware includes three channels. Each channel includes a 16 bit counter which decreases with a known, platform-dependent frequency. Counters can operate in several different modes, including periodic and one-shot. The output of each channel has platform-defined wiring: one channel is wired to the interrupt controller and may be used as event timer, one channel is wired to the speaker and used to generate sound tones, and one timer is reserved for platform purposes.

The attimer driver uses a single hardware channel to provide both time counter and event timer functionality. To make this possible, the respective counter must be running in periodic mode. As a result, the one-shot event timer mode is supported only when time counter functionality is disabled.

The event timer provided by the driver is irrelevant to CPU power states.