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Support for Radio Clocks in OpenBSD

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and the drivers presented in this paper OpenBSD now. has complete support for precise time ... Several OpenBSD users donated radio clocks of any kind ...

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Support for Radio Clocks in OpenBSDPage 1Support for Radio Clocks in OpenBSDMarc Balmer <mbalmer@openbsd.org>The OpenBSD Project Micro Systems Marc BalmerAbstractEvery computer is equipped with at least a clock chipor a general purpose device to provide a timer function.While these timers are certainly precise enough for measuring relatively short periods of time they are not wellsuited for keeping the correct time and date over a longerperiod since almost every chip drifts by a few secondsper day. Even so called realtime clocks only approximately meet the real time.External time sources can be used to synchronize thelocal clock with a much preciser time information. Timesignals are disseminated over various systems the bestknown are the US american GPS (Global PositioningSystem) and Time Signal Stations. Time signal stations are available in many countries; while the codingschemes vary from time signal station to time signal station the decoding principles are similar.This paper outlines the general problems of setting acomputers time at runtime; it will then give an overviewabout time signal stations and the GPS system. In the lastsections the OpenBSD implementation is detailed.1 Introduction1.1 Adjusting the System TimeWhile receiving and decoding the time information iscomparatively simple introducing the current time intothe computer system may be a complex task. Generallyit is recommended to set the system time during the bootprocedure for example as part of the startup procedure.In this case everything is simple and no problems willarise. If it is however intended to update the systemtime while the computer is running and possibly executing programs that rely on absolute time or on time intervals serious problems may occur.There are two generally different concepts to changethe system time at runtime. The first concept gives maximum priority to the continuity of the time i.e. the timemay be compressed or streched but under no circumstances may a discret ...

Source: asiabsdcon.org

 

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