[USRP-users] 10us+ sample delay between daughterboards

Marcus Müller marcus.mueller at ettus.com
Thu Jul 23 06:03:34 EDT 2020


On 23.07.20 11:44, Johannes Demel via USRP-users wrote:
> Hi Marcus,
> I tried to improve the situation. I had another look at [0,1].
> From [1] (N310 manual)
> "[..] which can both be used as time- and clock references. The GPSDO
> will function as a reference even when there is no GPS reception."
> This helps. I set
> Sync: "Unknown PPS"
> Clock/Time source: "O/B GPSDO"
> and all streams are in sync. That's sort of a relief for N310s.
> Since I don't have a GPS signal in the lab, I assume there's no point in
> trying to receive a GPS timestamp and set the device time on next PPS
> [0]

yep, I'm afraid that's true.

>. I would prefer to work with timestamps "since epoch" instead of
> "since start of flowgraph".

> I need to figure out how to use GPSDO on those X310s though. Since the
> GPS LED does not light up, I don't think it detects a GPSDO at all. And
> I just hope it can use a GPSDO like an N310.

> Since I work remotely, I can't just manually generate a sync pulse. 

That's what Hiwis are for... just kidding.

> But if I can find a device that works reliably I may switch to that.

ah, if you're working remotely: maybe something like a raspberry Pi with
a GPIO? You could remotely trigger it, or you could just synchronize its
clock via NTP, and let it toggle a GPIO pin every 500 ms starting at a
full second. (and of course you can build the fanciest control loop that
makes sure the GPIO timers and NTP time don't diverge. That might
actually be what Hiwis are for...)

> Thanks for the explanation and ASCII schematic.

Always! Also, I've done better schematics; one day, when I have infinite
time, I'll make use of more unicode for better living and schematics.


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