Date: Wed, 1 May 1996 19:17:58 +1000 From: Bruce Evans <bde@zeta.org.au> To: bde@freefall.freebsd.org, current@freebsd.org Subject: Re: cvs commit: src/sys/i386/include clock.h src/sys/i386/isa clock.c src/sys/i386/i386 machdep.c Message-ID: <199605010917.TAA18171@godzilla.zeta.org.au>
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This change is supposed to make timekeeping more accurate when no external clocks are available. The RTC is probably more accurate than the i8254 clock so it is used as a reference. The nominal frequencies can be overridden using sysctl if desired. Please test it with the temporary options enabled: # If booted with -v, loop at boot time repeating the calibration and # printing the results until a key is hit. option CLK_CALIBRATION_LOOP # Use the result of the calibration of the i8254 clock relative to the # RTC instead of the default of 1193182. This option will probably be # the default unless the default is set using the TIMER_FREQ option. option CLK_USE_I8254_CALIBRATION # Use the result of the calibration of the i586 clock relative to the # RTC instead of the result of a sloppier calibration of the i586 clock # relative to the i8254 clock. This option will probably go away. option CLK_USE_I586_CALIBRATION Before trying these, you can look for the results of the calibrations in the boot messages and set them using sysctl. The sysctl variables are named machdep.i8254_freq and machdep.i586_freq. Bruce >bde 96/05/01 01:39:04 > Modified: sys/i386/i386 machdep.c > sys/i386/include clock.h > sys/i386/isa clock.c > Log: > Added calibration the i8254 and the i586 clocks agains the RTC at boot > time. The results are currently ignored unless certain temporary options > are used. > > Added sysctls to support reading and writing the clock frequency variables > (not the frequencies themselves). Writing is supposed to atomically > adjust all related variables. > > machdep.c: > Fixed spelling of a function name in a comment so that I can log this > message which should have been with the previous commit. > > Initialize `cpu_class' earlier so that it can be used in startrtclock() > instead of in calibrate_cyclecounter() (which no longer exists). > > Removed range checking of `cpu'. It is always initialized to CPU_XXX > so it is less likely to be out of bounds than most variables. > > clock.h: > Removed I586_CYCLECTR(). Use rdtsc() instead. > > clock.c: > TIMER_FREQ is now a variable timer_freq that defaults to the old value of > TIMER_FREQ. #define'ing TIMER_FREQ should still work and may be the best > way of setting the frequency. > > Calibration involves counting cycles while watching the RTC for one second. > This gives values correct to within (a few ppm) + (the innaccuracy of the > RTC) on my systems. > > Revision Changes Path > 1.186 +2 -2 src/sys/i386/i386/machdep.c > 1.13 +4 -9 src/sys/i386/include/clock.h > 1.58 +249 -43 src/sys/i386/isa/clock.c
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