ACPI PM

ACPI PM is a timer in the power management system. The most common abbreviations are ACPI PM and ACPI PMT. ACPI means Advanced Configuration and Power Interface, PMT means Power Management Timer. However, it’s a common practice to call it ACPI PM, PMC, or just Power Management Timer.

By aspi-specifications (Section 4.8.2.1), the frequency of this timer is always 3.579545 MHz. Both HPETHPET and ACPI PM use the same master oscillator crystal (14.31818 MHz is 4 $\cdot$ 3.579545 MHz; see 14.31818 MHz
A note by Andrey Akinshin14.31818 MHz). Consequently, ACPI PM also has a huge access time.