> Date: Tue, 13 Jan 2015 19:36:58 +0100
> From: Christian Weisgerber <na...@mips.inka.de>
>
> Here's a patch to switch the drift file from an unscaled frequency
> offset to ppm. The latter format is compatible with that of ntp.org.
> This allows easy switching between ntpd daemons. (I asked PHK and
> ntimed will probably not have a drift file at all.)
>
> Old drift files are handled automagically. All values greater than
> a threshold will be interpreted as ppm. I picked 5e-3 (== 5000 ppm)
> as the cut-off value, because that's the maximum adjtime() can
> handle and you are unlikely to find a higher frequency offset. In
> fact, the combination of ntp.org and ntp_adjtime() cannot correct
> offsets higher then 500 ppm. Conversely, offsets smaller than
> 0.005 ppm (== 5e-9) are improbable. This compatibility handling
> will be removed in a year.
Does this in any way force a write of the drift file or are you
relying on ntpd deciding that it has a better estimate of the drift somewhere
in the next year?
> Index: ntpd.c
> ===================================================================
> RCS file: /cvs/src/usr.sbin/ntpd/ntpd.c,v
> retrieving revision 1.84
> diff -u -p -r1.84 ntpd.c
> --- ntpd.c 13 Jan 2015 02:28:56 -0000 1.84
> +++ ntpd.c 13 Jan 2015 18:21:49 -0000
> @@ -474,6 +474,8 @@ ntpd_settime(double d)
> log_info("set local clock to %s (offset %fs)", buf, d);
> }
>
> +#define PPM_THRESHOLD 5e-3
> +
> void
> readfreq(void)
> {
> @@ -494,9 +496,15 @@ readfreq(void)
> if (adjfreq(NULL, ¤t) == -1)
> log_warn("adjfreq failed");
> else if (current == 0) {
> - if (fscanf(fp, "%le", &d) == 1)
> + if (fscanf(fp, "%lf", &d) == 1) {
> + if (d > PPM_THRESHOLD || d < -PPM_THRESHOLD)
> + /* drift file in ppm */
> + d /= 1e6;
> + else
> + log_debug("assuming unscaled frequency "
> + "offset in drift file");
> ntpd_adjfreq(d, 0);
> - else
> + } else
> log_warnx("can't read %s", DRIFTFILE);
> }
> fclose(fp);
> @@ -505,8 +513,9 @@ readfreq(void)
> int
> writefreq(double d)
> {
> - int r;
> FILE *fp;
> + double ppm;
> + int r;
> static int warnonce = 1;
>
> fp = fopen(DRIFTFILE, "w");
> @@ -518,7 +527,8 @@ writefreq(double d)
> return 0;
> }
>
> - fprintf(fp, "%e\n", d);
> + ppm = d * 1e6;
> + fprintf(fp, "%.3f\n", ppm);
> r = ferror(fp);
> if (fclose(fp) != 0 || r != 0) {
> if (warnonce) {
> --
> Christian "naddy" Weisgerber na...@mips.inka.de
>
>
