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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A benchmark in that environment for 10 million event counts found that TSC took about 0. When a corresponding timer interrupt is active, this bit is set. This page is not meant as a full description of HPET, only as a lightweight introduction.

Formerly referred to by Intel as a Multimedia Timer[1] the term HPET was selected to avoid confusion with the multimedia timers as a software feature introduced in the MultiMedia Extensions to Windows 3. This section needs expansion with: Please help improve this article by adding citations to reliable sources.

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High Precision Event Timer

Save minimal tick either from ACPI table or configuration register. If it is set, software can clear it by writing 1 to this bit. Retrieved from ” https: Webarchive template archiveis links Articles needing additional references from February All articles needing additional references Articles to be expanded from February All articles to be expanded Articles using small message boxes All articles with unsourced statements Articles with unsourced statements from December HPET offers two operating modes: The operator has to remember to set both extra specs, which is kind of gross UX.


If the timer is set to 32 bit mode, it will also generate an interrupt when the counter wraps around. The difficulties are exacerbated if the comparator value is not synchronized with the timer immediately, but delayed by one or two ticks, as some chipsets do. INI file to enforce its use. But this device has no driver and is not used at all. These comparators are or bit-wide.

In standard mapping, each timer has its own interrupt routing control.

The implicit transformation of a special extra spec into placement-isms is arcane. Determine if timer N is periodic capable, save that information to avoid re-reading it every time. This means that next write to timer N comparator register will have the usual meaning, while second next write will write directly to the accumulator.

This page has been accessed 35, times. If she forgets hw: This page was last modified on 31 Octoberat Hoet n Interrupt Routing Capability.

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

Spcification you need any information not covered by this article, consult the HPET specification. Be aware of this when choosing interrupt routing for timers. A popular value is It is recommended to use 32 bit counter when on bit only software.

The following is the procedure you need to perform to initialize main counter and comparators in order to receive interrupts. Views Read Edit View history. A corresponding flavor extra spec will not be introduced since enabling HPET is really a per-image concern rather than a resource concern for capacity planning. If another interrupt occurs before that bit is cleared, the interrupt will remain active.

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. You can help by adding to it. This has the express advantage of being independent of specificatioh CPU frequency and still provides a very reasonable sub-microsecond resolution and accuracy. Operators can indicate their desire to have HPET in the guest by specifying a placement trait trait: It was developed jointly by Intel and Microsoft and has been incorporated in PC chipsets since circa This specificaion is used to allow software to directly set periodic timer’s accumulator.


More information on this is provided further in the article. Determine allowed interrupt routing for current timer and allocate an interrupt for it. But we’ve also set bit 6. End users can indicate their desire to have HPET in the guest by uploading their own images with ypet same trait.

Otherwise it has no effect. The comparators can be put into one-shot mode or periodic mode, with at least one comparator supporting periodic mode and all of them supporting one-shot mode. Bit 3 is also quite straightforward – 1 means periodic timer.

Writes of 0 have no effect. Example Spec – The title of your blueprint. This is a consequence of HPET’s main counter spscification up-counting. If 32 bit reads are performed on 64 bit hept, consult 2.

Comparators are NOT required to support this mode; you must detect this capability when initializing a comparator. Unsourced material may be challenged and removed.