Hi If you are after one of the AM modulated versions of IRIG, an MCU with a flash image of a 1 and a 0 as a sine wave to feed the DAC or PWM will get you a long way. If it’s an ARM with DMA to drive the PWM, there isn’t much overhead involved. You may be looking at a < $1 chip. At that point it’s not a real big decision. Syncing things up to a few microseconds isn’t all that hard in this case.
Bob > On Dec 1, 2016, at 1:09 PM, Chris Albertson <albertson.ch...@gmail.com> wrote: > > IIn theory it is pretty easy, first discipline the system clock using > something like NTP then interrupt on the system clock and the interrupt > handler runs a state machine. But if you need to output IRIG-B and when to > generate the sine wave carier in software you end up with latency in the > audio output because it buffers. Baseband output of a one bit output > could work under Linux but then you'd need external hardware modulate a > carrier. > > I think IRIG is best done on a small microcontroiller, perhaps tuning a > light weight RTOS where you can set up a hard 1KHz hardware interrupt. > > Either way I think yu have three threads > 1. Read the GPS PPS and use this to phase lock some kind of oscillator. > NTP does this. If will lock the system clock to GPS > 2, Generate interrupts at the IRIG frame rate from the above sync's > oscillator/clock > 3. output points on the carier that are modulated by the frames that are > computed in thread #2. > > You might be able to write loop that in effect implements three threads by > polling the system clock. You end up with one if statement per thread that > reads IF (time do do thread N) {run thread N} > or you let the POSIX thread system do the work or yu are running on a small > uP and set up hardware trimmer interrupts or let the RTOS do that for you. > > Thinking about this, IRIG-B generation would be best done inside the same > uP that runs a GPSDO. > > > On Thu, Dec 1, 2016 at 8:33 AM, Mark Sims <hol...@hotmail.com> wrote: > >> I played with trying to get Lady Heather to generate an IRIG audio >> signal. I never got it to work well... maybe someday... >> >> ------------------- >> >>> One other idea: Use a stereo audio format and record your audio to one >> track and a time code (like IRIG) on the other track. IRIG works even on >> analog multitrack tape recorders. Use it the same way on digital >> multitrack recordings. Google IRIG Time Code. >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/ >> mailman/listinfo/time-nuts >> and follow the instructions there. >> > > > > -- > > Chris Albertson > Redondo Beach, California > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.