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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. So, if the main counter’s speckfication is when we set the timer up, and specificafion write to comparator i. HPET is meant to supplement and replace the programmable interval timer and the RTC’s periodic interrupt function. It can also be a nuisance that the ever-increasing processor speeds of newer processor designs make this usable time span shorter still.

If 32 bit reads are performed on 64 bit counter, consult 2. End users can indicate their desire to have HPET in the guest by uploading their own images with the same trait. Setting this bit to 1 enables triggering of interrupts. If it’s not, please analyze the meaning of specific fields in registers used above. 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 hpett written into the chip’s register.

This is a consequence of HPET’s main counter being up-counting. Support to query nova resources filter by changes-before. I believe that specifiction wording could’ve been much better.

It is always set to 0.

HPET – OSDev Wiki

This article needs additional citations for verification. 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 Once scheduled to a compute node, the virt driver looks for trait: Each comparator can generate an interrupt when the least significant het are equal to the soecification bits of the specifiaction main counter value.


The operator has to remember to set both extra specs, which is kind of gross UX. The following operating systems are known not to be able to use HPET: In standard mapping, each timer has its own interrupt routing control.

Besides mentioning the race condition discussed above, a VMware document also lists some other drawbacks: 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. By using this site, you agree to the Terms of Use and Privacy Policy. Bit specificatiin is also psecification straightforward – 1 means periodic timer.

These comparators are or bit-wide. This causes an interrupt at every millisecond even if the application needs to do actual work less frequently.

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. Enter search terms or a module, class or function name.

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. The upet is dependent of whether edge or level-triggered mode is used for timer n.

Also, the routing as well as allowed routing of comparator interrupts is independent, so you have to detect and set it up for each of them individually. HPET offers two operating modes: From Wikipedia, the free encyclopedia.


Retrieved from ” https: Sspecification information on this is provided further in the article. The following table skips reserved registers defined in the specification.

High Precision Event Timer – Wikipedia

Be aware of this when choosing interrupt routing for timers. February Learn how and when to remove this template message. As speciflcation 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.

It is recommended to use 32 bit counter when on bit only software. Namely, you probably want to use some of ISA interrupts – or, at very least, be able to use them at one point unambiguously.

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.

More information on this procedure is provided further in the text.

High Precision Event Timer

In non-periodic mode, the OS programs one of timer’s comparator registers with value of main counter that is to trigger an interrupt. Periodic mode is more tricky than specifcation mode. The driver uses the hw: I am enabling the timers only when I actually use them, so there’s no “real” initialization of comparators here.

Comparators can be driven by the operating system, e.