[lkml]   [1998]   [Apr]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectProblem with kernel-pll in 2.0.3x (at least)
    I just found a problem with the kernel-pll in 2.0.34pre10 (well it
    hasn't changed since at least 2.0.33 as far as I can tell). It only
    affects Alpha hardware (though it would affect anything which has
    __KERNEL_HZ set to a value much larger than 100).

    On the alpha, asm-alpha/param.h defines __KERNEL_HZ to 1024 which is
    fine, so tick being the number of uS between clock updates is
    977. (well it should be ~977.5 but...).

    However, which means that a single unit change in tick alters the
    speed of the clock by 1024ppm. Again this isn't a real problem, but
    linux/timex.h defines MAXFREQ as

    #define MAXFREQ (200L << SHIFT_USEC) /* max frequency error (ppm) */

    so the kernel pll will not permit the frequence to be changed by more
    than +/- 200ppm. I think this should be (2 * HZ)ppm. If this is a
    really bad idea please let me know! Can this be added to 2.0.34 (and
    2.1.x if appropriate)?

    My poor little alpha clocks arn't within 200ppm so the clock adjust
    can't cope, and altering the tick doesn't help as it isn't that far

    As an aside can anyone tell me a good reason why ntp_adjtime() and
    ntp_gettime() are not implemented in glibc (2.0.7 and earlier don't
    have them). Not putting them in libc makes xntpd3 have to work much
    harder to use the kernel-pll (xntp3-5.93 won't detect it at all on my
    alphas without much hackery. I can provide trivial wrappers to
    __adjtimex() if anyone wants them. When I reported the problems to the
    xntpd maintainers they suggested I switch to FreeBSD!

    Jon Peatfield, DAMTP, Computer Officer, University of Cambridge
    Telephone: +44 1223 3 37852 Mail:

    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to

     \ /
      Last update: 2005-03-22 13:42    [W:0.021 / U:2.624 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site