Ralph Aichinger <[email protected]> wrote: > As the Raspberry Pi I am currently using as a NTP box has > an audio output available, I am wondering if this otherwise > unused output (on a dedicated NTP box) could be used to > generate BBC style pips or other audible time signals? > > http://en.wikipedia.org/wiki/Greenwich_Time_Signal > > As I am probably not the first one to have that idea: > Is there software for Linux that does this? Playing > a sound file is easy. Playing it in sync with ntpd > is a lot harder. > > /ralph
It would actually be quite easy to output tones through the soundcard driver. I wrote a program for Linux some time ago to output an "on hold" signal for a PBX that had only support for external "music on hold", which is quite a hassle to use legally here. You just put a sine burst as a series of sound samples in an array and write that to /dev/dsp when you like. A couple of ioctl()s set the sample rate etc. I actually used a bit of ramp-up and ramp-down on the sine amplitude to avoid the nasty clicks that can be heard on that wikipedia page, which result from sudden switch to full amplitude. To start at the right time you can use a usleep() call to wait (after inquiring the time and calculating how long to wait). Of course first you wait a second or so too short and then get the time again and re-calculate, in case the clock has drifted a bit. _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
