What Is a Contraction Timer?

High-precision event timer (English: High Precision Event Timer , HPET for short), also known as high-precision event timer , it is a hardware timer used in personal computers. It was jointly developed by Intel and Microsoft. It has been included in PC chipsets since 2005. Intel previously had a Multimedia Timer , so HPET was chosen as the term to avoid confusion with the multimedia timer introduced as a software feature in the multimedia extension in Windows 3.0.

An HPET chip contains a 64-bit up count at at least 10 MHz Hertz

HPET can provide higher resolution than RTC to generate periodic interrupts, and is often used to synchronize multimedia streams, provide smooth playback, and reduce the use of other timestamp calculations (such as x86 CPU-based RDTSC instructions).

HPET is designed to complement and replace the 8254 programmable interval timer and the periodic interrupt function of RTC. Compared to these older timer circuits, HPET has a higher frequency (at least 10 MHz) and a wider 64-bit counter (which can also be driven in 32-bit mode).

Although 8254 and RTC can enter one-shot mode similar to HPET, the setup process is so slow that their one-shot mode will not be used for tasks that require precise scheduling in practical applications. In contrast, 8254 and RTC are usually used in periodic mode at very small intervals. Using HPET can avoid extra interruptions because HPET one-shot timers are much less expensive to set up.

Operating systems designed before the advent of HPET could not use HPET, so other timer devices would be used. Newer operating systems can often use newer and older timers. Some hardware has both newer and older timers. In fact, most of the current Southbridge chips also support traditional PIT, PIC, Advanced Programmable Interrupt Controller (APIC), and RTC devices, regardless of whether the operating system is used, thereby helping very modern PCs run older models. operating system.

HPET is not known to work with the following operating systems: Windows XP SP2, Windows Server 2003 and earlier versions of Windows, Linux kernels prior to 2.6.

HPET is known to work with the following operating systems: Windows XP SP3, Windows Server 2008, Windows Server 2008 R2, Windows Vista, Windows 7, x86-based OS X, Linux operating system with 2.6 or higher kernel, FreeBSD, and OpenSolaris.

The Linux kernel can also use HPET as its clock source. The documentation for the second edition of Red Hat MRG states that TSC is the preferred clock sourcebecause its overhead is much lower and HPET is the backup clock source. A benchmark test with 10 million event counts shows that TSC takes about 0.6 seconds, HPET takes slightly more than 12 seconds, and ACPI power management timers take about 24 seconds.