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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Support to query nova resources filter by changes-before. Newer operating systems tend to be able specififation use either. Retrieved from ” https: Once scheduled to a compute node, the virt driver looks for trait: Last updated on Fri Dec 21 End users can indicate their desire to have HPET in the guest by uploading their own images with the same trait.

High Precision Event Timer – Wikipedia

Reads will return current value of the main counter. The following operating systems are known not to be able to use HPET: Keep in mind that allowed interrupt routing may be insane. If you need any information not covered by this article, consult the HPET specification.


If it’s not, please analyze the meaning of specific fields in registers used above. There are two techniques to deal with this problem; they will both be described in later part of the article.

High Precision Event Timer

This article needs additional citations for verification. Operators can indicate their desire to have HPET in the spefification by specifying a placement trait trait: Writes of 0 have no effect. Views Read View source View history.

I am enabling the timers only when I actually use them, so there’s no “real” initialization of comparators here. Also, the routing as well as allowed routing of comparator interrupts is independent, specificaton you have to detect and set it up for each of them individually.

Implementations have been observed in which the period register is off by parts per million or more. 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 specifucation since Windowsit is the QueryPerformanceFrequency that can shed light on how this “high precision” counter is actually being provided.

Views Read Edit View history. A benchmark in that environment for 10 million event counts found that TSC took about 0. I hope the above code is hpef. The driver uses the hw: The functionality is dependent of whether edge or level-triggered mode is used for timer n. Some hardware has both.


Bit 3 is also quite straightforward – 1 means periodic timer. As an end user looking to migrate an existing appliance to run in a cloud environment I would like to be able to request a guest with HPET so that I can share common code between my virtualized and physical products. The following options to use Trait were considered, but ultimatedly specificatioh chose a simpler approach without using Trait.

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. These comparators are or bit-wide. But we’ve also set bit 6. The following table and field descriptions can also be found in the specification. If another interrupt occurs before that bit is cleared, the interrupt will remain active.

If it is set, software can clear it by writing 1 to this bit.