What is the acpi_pm linux clocksource used for, what hardware implements it?

Question

The file /sys/devices/system/clocksource/clocksource0/available_clocksource in my Linux box lists the following clock sources:

tsc hpet acpi_pm

I know that tsc is the Timestamp Counter Register in the Processer. I know the hpet is the High Precision event timer.

I do not know what the acpi_pm is and what hardware implements it? Is this the PIT (programmable interval timer)?

Answer 1

That's ACPI power management timer.

The ACPI Power Management Timer (or ACPI PMT) is yet another clock device included in almost all ACPI-based motherboards. Its clock signal has a fixed frequency of roughly 3.58 MHz. The device is actually a simple counter increased at each clock tick

(from Understanding the Linux Kernel)