Date: Thu, 16 Jul 1998 16:53:55 +1000 From: Bruce Evans <bde@zeta.org.au> To: bde@zeta.org.au, jak@cetlink.net Cc: current@FreeBSD.ORG Subject: Re: tickadj -t not changing tick Message-ID: <199807160653.QAA24751@godzilla.zeta.org.au>
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>>machdep.i8254_freq: always exists, never hurts to set it right, but only >> essential for it to be right on systems using it for timekeeping >> (2.2., -current on sub-586's and 586+'s running SMP or APM. > >Sysctl shows my default value of machdep.i8254_freq = 1,193,182, the >same value one of my hardware books says is the "standard" oscillator >rate input to the 8254. But since my clock runs fast, my oscillator >seems to be at a slightly higher rate. So am I correct in assuming I >need to increase the i8254_freq value to match the true oscillator >rate, and the kernel will adjust accordingly? It wouldn't hurt, but I guess you have a Pentium not running SMP or APM, so it wouldn;t help much. >And besides trial and error, is there any way of determining what the >true frequency of my oscillator is? Boot with -v and note the frequency calibrated relative to the RTC and use that is input to sysctl, or use CLK_USE_I8254_CALIBRATION to set this frequency by default. The RTC is usually more accurate than the i8254. >>machdep.tsc_freq: -current only, must be right if it is used for timekeeping. >> It is used on 586+'s not running SMP or APM. > >I know what the 8254 is, but what is the TSC? The "Pentium" TimeStamp Counter. It runs at 300 MHz for a CPU frequency of 300 MHz, etc. It is initially calibrated relative to the i8254. You can boot with -v to see its frequency relative to the RTC, or use CLK_USE_TSC_CALIBRATION to use this frequency by default. Another sysctl, `sysctl kern.timecounter.frequency', gives the frequency of the counter being used for timekeeping. If it is about 1 MHz then the i8254 is being used; otherwise the TSC is being used. Bruce To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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