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