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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If an illegal value is written, then value read back from this field will not match the written value. HPET offers two operating modes: This field is used to allow software to directly set periodic timer’s accumulator.

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 hppet interrupts are generated at specified intervals.

Setting this bit to 1 enables triggering of interrupts. 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.

The following is the procedure you need to perform to initialize main counter and comparators in order to receive interrupts. Bit 2 is the same as above, Interrupt Enable. Common Devices Interrupts Time. Views Read View source View history. 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 Het using small message boxes All articles with unsourced statements Articles with unsourced statements from December Comparators can be driven by the operating system, e.

The following operating systems are known to be able to use HPET: As an end user looking to migrate specifivation 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.


Each comparator can generate an specificagion when the least significant bits are equal to the corresponding bits of the bit main counter value.

HPET – OSDev Wiki

In standard mapping, each timer has its own interrupt routing control. February Learn how and when to remove this template message. This page was last modified on 31 Octoberat These comparators are or specifiction.

If she forgets hw: This article needs additional citations for verification. Writes of 0 have no effect. Namely, you probably want to use some of ISA interrupts – or, at very least, be able to use them at one point unambiguously.

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. 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.

The implicit transformation of a special extra spec into placement-isms is arcane. The following table and field descriptions can also be found in the specification. Detailed explanation is provided further in the article. If it’s not, please analyze the meaning of specific fields in registers used above. But we’ve also set bit 6.

The following table skips reserved registers defined in the specification. The comparator register’s value is never written by the hardware, you are free to write to it and read from it at any time, therefore you can change at what value in the main counter the interrupt will spedification generated.

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. If we do get down to the virt driver and the trait is set, and the driver for whatever reason e.

Some hardware has specificqtion. Besides mentioning the race condition discussed above, a VMware document also lists some other drawbacks: Be aware of this specificatioon choosing interrupt routing for timers.


High Precision Event Timer

End users can indicate their desire to have HPET in the guest by uploading their own images zpecification the same trait. The operator has to remember to set both extra specs, which is kind of gross UX. Keep in mind you have to initialize both the main counter and all of the comparators. INI file to enforce its use.

More information on this procedure is provided further in the text. Enter search terms or a module, class or function name. HPET supports three interrupt mapping options: So the HPET is only there to satisfy the system’s high speed needs. Note 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. The following options to use Trait were considered, but ultimatedly we chose a simpler approach without using Trait.

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

But this device has no driver and is not used at all. Reads will return current value of the main counter. Must not be zero, must be less or equal to 0x05F5E, or nanoseconds. HPET is meant to supplement and replace the programmable interval timer and the RTC’s periodic interrupt function. There are two techniques to deal with this problem; they will both be described in later part of the article. Please help improve this article by adding citations to reliable sources. Operators can indicate their desire to have HPET in the guest by specifying a placement trait trait: More information on this is provided further in the article.

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