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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I hope the above code is obvious. The following is the procedure you need to perform to initialize main counter and comparators in order to receive interrupts. But this device has no driver and is not used at all. It is recommended to use 32 bit counter when on bit only software. The following operating systems are known to be able to use HPET: The operator has to remember to set both extra specs, which is kind of gross UX.

Writes of 0 have no effect. More information on this is provided further in the article. If another interrupt occurs before that bit is cleared, the interrupt will remain active. 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.

About This site Joining Editing help Recent changes. It is always set to 0. Common Devices Interrupts Time. 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.

More information on sppecification procedure is provided further in the text. The driver hpdt the hw: Each comparator can generate an interrupt when the least significant bits are equal to the corresponding bits of the bit main specificaiton value.


Otherwise it has no effect. If it is set, software can clear it by writing 1 to this bit. When a corresponding timer interrupt is active, this bit is set. Otherwise, this bit will be ignored and reading it will always return 0. In standard mapping, each timer has its own interrupt routing control. If she forgets hw: Comparators can be driven by the operating system, e. 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.

The functionality is dependent of whether edge or level-triggered mode is used for timer n. If you need any information not covered by this article, consult the HPET specification.

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

Created using Sphinx 1. This page was last modified on 31 Octoberat 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. Example Spec – The title of your blueprint.

This section needs expansion with: Once scheduled to a compute node, the virt driver looks for trait: Retrieved wpecification ” https: 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.

INI file to enforce its use.

High Precision Event Timer

Besides mentioning the race condition discussed above, a VMware document also lists some other drawbacks: HPET offers two operating modes: Operators can indicate their desire to have HPET in the guest by specifying a placement trait trait: If we do get down to the virt driver and the trait is set, and the driver for whatever reason e.


The following operating systems are known not to be able to use HPET: These comparators are or bit-wide. Please help improve this article by adding citations to reliable sources. A few options to use Traits were considered as described in the next section, but we end up choosing the simpler approach due to the following reasons:. The following options to use Trait were considered, but ultimatedly we chose a simpler approach without using Trait.

It consists of usually bit main counter which counts upas well as from 3 to 32 32 or 64 bit wide comparators.

Reads will return current value of the main counter. Timer n Interrupt Routing Capability. Work around hardware stupidity Archived at Archive. It can also be a nuisance that the ever-increasing processor speeds of newer processor designs make this usable time span shorter still.

From Wikipedia, the free encyclopedia. Bit 3 is also quite straightforward – 1 means periodic timer. I believe that the wording could’ve been much better. 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.

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The difficulties are exacerbated if the comparator value is not synchronized with the timer immediately, but delayed by one or two ticks, as some specificatioj do.