Software Developers Hpet Spec 1 0a – Download as PDF File .pdf), Text File .txt ) or read online. Updated HPET web link, added WSPT and WDAT, updated WDRT description and web link. Clarified that the endian-ness of data value. High Precision Event Timer Driver for Linux The High Precision Event Timer ( HPET) hardware follows a specification by Intel and Microsoft, revision 1.

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From Wikipedia, the free encyclopedia. HPET offers two operating modes: In standard mapping, each timer has its own interrupt routing control.

HPET is meant to supplement and replace the programmable interval timer and the RTC’s periodic interrupt function. When the interrupt is generated, however, the hardware will increase the value in comparator register by the last value written to it! Must not be zero, must be less or equal to 0x05F5E, or nanoseconds.

It can also be a nuisance that the ever-increasing processor speeds of newer processor designs make this usable time span shorter still.

Personal tools Log in. If she forgets hw: Compared to these older timer circuits, the HPET has higher frequency and wider bit counters although they can be driven in bit mode. Once scheduled to a compute node, the virt driver looks for trait: These comparators are or bit-wide.

High Precision Event Timer – Wikipedia

This causes an interrupt at every millisecond even if the application needs to do actual work less frequently. So, if the main counter’s value is when we set the timer up, and we write to sepcification i. If the timer is set to 32 bit mode, it will also generate an interrupt when the counter wraps around.


Save minimal tick either from ACPI table or configuration register.

In one-shot mode the comparator fires an interrupt once when the main counter reaches the value stored in the comparator’s register, while in the periodic mode the interrupts are generated at specified intervals.

Retrieved from ” https: A popular value is More information on this is provided further in the article.

Since HPET compares the actual timer value and the programmed target value on equality rather than “greater or equal”, interrupts can be missed if the target time has already passed when the comparator value is written into the chip’s register.

End users can indicate their desire to have HPET in the guest by uploading their own images with the same trait. Created using Sphinx 1.

Periodic mode is more tricky than non-periodic mode. Support to query nova resources filter by changes-before. There are two techniques to deal with this problem; they will both be described in later part of the article. If it’s not, please analyze the meaning of specific fields in registers used above.

High Precision Event Timer

So the HPET is only there to satisfy the system’s high speed needs. If we do get down to the virt driver and the trait is set, and the driver for whatever reason e. INI file to enforce its use. HPET is a continuously running timer that counts upward, not a one-shot device that counts down to zero, causes one interrupt and then stops. Work around hardware stupidity Archived at Archive.


Since the original specification for HPET in calls for a high resolution counter, which is then exposed by the QueryPerformanceFrequency and QueryPerformanceCounter API calls already available since Windowsit is the QueryPerformanceFrequency that can shed light on how this “high precision” counter is actually being provided.

This page was last modified on 31 Octoberat But this device has no driver and is not used at all. It was developed jointly by Intel and Microsoft and has been incorporated in PC chipsets since circa The following table and field descriptions can also be found in the specification.

Support High Precision Event Timer (HPET) on x86 guests — Nova Specs documentation

If you need any information not covered by this article, consult the HPET specification. HPET supports three interrupt mapping options: Views Read Edit View history.

Timer n Interrupt Routing Capability. Also, the routing as well as allowed specificatoin of comparator interrupts is independent, so you have to detect and set it up for each of them individually. A few options to use Traits were considered as described in the next section, but we end up choosing the hept approach due to the following reasons:.

Bit 3 is also quite straightforward – 1 means periodic timer. Example Spec – The title of your blueprint.