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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 * * * * /usr/local/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 /usr/local/etc/chu.last Records the last time a correc- tion was made using the adjtimex(2) API. AUTHORS V0.1.29 William Rossi, bill@rossi.com, Feb 1999
NAME | SYNOPSIS | DESCRIPTION | NOTES | PARAMETERS | FILES | AUTHORS
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