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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Otherwise it has no effect. 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.
It was developed jointly by Intel and Microsoft and has been incorporated in PC chipsets since circa Enter search terms or a module, class or function name. Once scheduled to a compute node, the virt driver looks for trait: Unsourced material may be challenged and removed. For bit timer, if this field is set, the timer will be forced to work in bit mode. When a corresponding timer interrupt is active, this bit is set.
Created using Sphinx 1. If she forgets hw: Save minimal tick either from ACPI table or configuration register. Views Read Edit View history. Keep in mind that allowed interrupt routing may be insane. 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.
Writes of 0 have no effect.
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 upet unsourced statements from December 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.
Detailed explanation is provided further in the article. If an illegal value is written, then value read back from this field will not match the written value. 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 the specifciation are generated at specified intervals. The following table and field descriptions can also be found hpey the specification.
High Precision Event Timer
A popular value is If 32 bit reads are performed on speclfication bit counter, consult 2. 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.
Newer operating systems tend to be able to use either. So, if the main counter’s value is when we set the timer up, and we write to comparator i. For periodic mode, similarly to one-shot mode, you write a value at which an interrupt shall be generated to the comparator register.
The following table skips reserved registers defined in the specification. About This site Joining Editing help Recent changes. Support to query nova resources filter by changes-before. It consists of usually bit main counter which counts upas well as from 3 to 32 32 or 64 bit wide comparators.
Otherwise, this bit will be ignored and reading it will always return 0. This field is used to allow software to directly set periodic timer’s accumulator.
High Precision Event Timer – Wikipedia
This article needs additional citations for verification. 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.
hhpet If we do get down to the virt driver and the trait is set, and the driver for whatever reason e. Keep in mind you have to initialize both the main counter and all of the comparators.
This page was last modified on 31 Octoberat 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.
It is always set to 0. Last updated on Fri Dec 21 The functionality is dependent of whether secification or level-triggered mode is used for timer n. HPET supports three interrupt mapping options: If you need any information not covered by this article, consult the HPET specification. But this device has no driver and is not used at all. In standard mapping, each timer has its own interrupt routing control.
More information on this is provided further in the article. Periodic mode is more tricky than non-periodic mode. Each comparator can generate an interrupt when the least significant bits are equal to the corresponding bits of the specufication main counter value. Be aware of this when choosing interrupt routing for timers. Determine if timer N is periodic capable, save that information to avoid re-reading it every time. Comparators can be driven by the operating system, e. So the HPET is only there to satisfy the system’s high speed needs.
INI file to enforce its use. Update User Documentation for image properties . Comparators are NOT required to support this mode; you must detect this capability when jpet a comparator. Retrieved from ” https: