[ntp:questions] Why is my precision=-15? I'm using anano kernel.

Chuck Swiger cswiger at mac.com
Tue Jan 15 20:30:12 UTC 2013


Hi--

On Jan 15, 2013, at 12:08 PM, Edward T. Mischanko wrote:
> I double checked the modified kernel that I made and it matched the changes Poul-Henning Kamp recommended.  Could you tutor me on the command to see what kernel I am actually running?

What does your dmesg say?  The most relevant bits would be the beginning,
specifically the timecounter lines, the CPU ID, and whether the ELAN
timecounter appears.  From a random sample dmesg:

FreeBSD 5.4-RELEASE #0: Sat May 27 00:13:00 WST 2006
    root <at> FreeServer:/usr/obj/usr/src/sys/SOEKRIS3
Timecounter "i8254" frequency 1193182 Hz quality 0
CPU: AMD Enhanced Am486DX4/Am5x86 Write-Back (486-class CPU)
  Origin = "AuthenticAMD"  Id = 0x494  Stepping = 4
  Features=0x1<FPU>
real memory  = 67108864 (64 MB)
avail memory = 60358656 (57 MB)
npx0: <math processor> on motherboard
npx0: INT 16 interface
cpu0 on motherboard
sysctl machdep.i8254_freq=1189161 returns 0
Timecounter "ELAN" frequency 8333333 Hz quality 1000
Timecounters tick every 6.666 msec
Elan-mmcr driver: MMCR at 0xc5888000. PPS support.

Note that the i8254 timing was changed from 1193182 Hz to 1189161 Hz, for example.
Also note that the ELAN MMCR timer is found and enabled with PPS support.  That's
what allows this HW to potentially achieve ~125ns precision; see:

  http://fxr.watson.org/fxr/source/i386/i386/elan-mmcr.c?v=FREEBSD82

Regards,
-- 
-Chuck



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