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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Update User Documentation for image properties [2]. Reads will return current value of the main counter. Newer operating systems tend to be able to use either. Once scheduled to a compute node, the virt driver looks for trait: If another interrupt occurs before that bit is cleared, the interrupt will remain active. The following table skips reserved registers defined in the specification. So the HPET is only there to satisfy the system’s high speed needs.

The following options to use Trait were considered, but ultimatedly we chose a simpler approach without using Trait.

Compared to these older timer circuits, the HPET has higher frequency and wider bit counters although they can be driven in bit mode. Support to query nova resources filter specufication changes-before. A popular value is It can also be a nuisance that the ever-increasing processor speeds of newer processor designs make this usable time span shorter still. The functionality is dependent of whether edge or level-triggered mode is used for timer n.

If the timer is set to 32 bit mode, it will also generate an interrupt when the counter wraps around. Bit 2 is the same as above, Interrupt Enable. From Wikipedia, the free encyclopedia. Comparators are NOT required to support this mode; you must detect this capability when initializing a comparator.


Determine if timer N is periodic capable, save that information to avoid re-reading it every time. Enter search terms or specificatio module, class or function name. Bit 3 is also quite straightforward – 1 means periodic timer. This section needs expansion with: This causes an interrupt at every millisecond even if the application needs to do actual work less frequently. For bit timer, if this field is set, the timer will be forced to work in bit mode. 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 following table and field descriptions can also be found in the specification.

High Precision Event Timer – Wikipedia

But this device has no driver and is not used at all. Keep in mind that allowed interrupt routing may be insane.

The comparators can be put into one-shot mode or specificatlon mode, with at least one comparator supporting periodic mode and all of them supporting one-shot mode. Retrieved from ” https: Example Spec – The title of your blueprint.

Namely, you probably want to use some of ISA interrupts – or, at very least, be able to use them at one point unambiguously.

For periodic mode, similarly to one-shot mode, you write a value at which an interrupt shall be generated to the comparator register. It is always set to 0. Views Read Edit View history. Be aware of this when choosing interrupt routing for timers.

High Precision Event Timer

I am enabling the timers only when I actually use them, so there’s no “real” initialization of comparators here. Besides mentioning the race condition discussed above, a VMware document also lists some other drawbacks: More information on this is provided further in the article. This is a consequence of HPET’s main counter being up-counting. Save minimal tick either from ACPI table or configuration register.


Keep in mind you have to initialize both the main counter and all of the comparators. Must not be zero, must be less or spedification to 0x05F5E, or nanoseconds.

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:. Detailed explanation is provided further in the article.

Timer n Interrupt Routing Capability. 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. There are two techniques to deal with hpeg problem; they will both be described in later part of the article. It consists of usually bit main counter which counts upas well as from 3 to specificayion 32 or 64 bit wide comparators.

S;ecification from ” https: When a corresponding timer interrupt is active, this bit is set. 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 operator has to wpecification to set both extra specs, which is kind of gross UX.

The implicit transformation of a special extra spec into placement-isms is arcane.