    CHU(8)                                                     CHU(8)

    NAME
           chu - sets and disciplines the system clock

    SYNOPSIS
           /sbin/chu [-l:maxadj] [-d:propdelay] [file]

    DESCRIPTION
           chu sets and disciplines the system clock based on
           time broadcasts from radio station CHU.  You must have a
           shortwave receiver tuned to radio station CHU connected to
           the input of your sound card for this to work.

           With a good quality received signal, and reasonably stable
           system clock, chu can achive an accuracy of less
           than +/- 10 mS from UTC, and discipline the system clock
           frequency to within +/- 1 ppm.

           Theoretically, with a perfect received signal, chu
           should be able to yeild +/- 0.5 mS resolution.

           chu is usually run via crond(8) with a crontab entry
           that looks like this:

           5,35 * * * * /sbin/chu -l:120 -d:2000 >> /var/log/chu.log

           This will run chu at 5 and 35 minutes past each hour,
           and log the results to /var/log/chu.log  Also, it
           limits the maximum correction to 2 minutes (120 seconds).
           The -d option is used here to account for a delay of
           2 milliseconds.

    NOTES

           chu uses no ioctl() calls on the audio device.

           It assumes the audio format to be 8 KHz sample rate,
           8 bits per sample, each sample being an unsigned byte.
           This is the default for most audio devices in Linux.

           Reading from a file is really only useful for debugging
           since this will set the clock incorrectly.

           CHU broadcasts can be found on 3.330 MHz, 7.335 MHz,
           and 14.670 MHz.

    PARAMETERS
           file        -  PCM format file or sound device.
                          Default is /dev/dsp.

           -l:maxadj   -  Maximum time adjustment in seconds.
                          If not specified, adjustment is
                          not limited.

           -d:popdelay -  Propagation delay from CHU in microseconds.
                          Default is zero.

    FILES
           /etc/chu.last  Records the last time a correction was made
                          using the adjtimex(2) API.

    AUTHORS
           V0.1.29 William Rossi, bill@rossi.com, Feb 1999