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Re: [Discuss-gnuradio] FPGA time

From: Josh Blum
Subject: Re: [Discuss-gnuradio] FPGA time
Date: Tue, 28 Aug 2012 14:40:01 -0700
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On 08/28/2012 01:39 PM, Anisha Gorur wrote:
> Thats actually what we are using, however, when printing out the tick
> count, we randomly, and only sometimes, see a jump of about 30 ticks, and
> if each tick is 10ns, that is a huge 300ns jump. Do you know why this could
> be happening?

I'm very lost. Where are you getting the time_spec from? A receive
packet? usrp.get_time_now()? Or is this a time difference between devices?

get_time_now is completely asynchronous to the device, if thats what you
are calling in a loop, I would expect to see a lot of variation in time


> We are using gpsdo's as both a time and clock reference, though this
> problem seems to occur even if we set the clock and time reference to
> external. However, setting them to gpsdo seems to make it more stable, as
> we have seen the ~30 tick jump fewer times with those references. Another
> question is why would there be a big difference in what the reference is
> set as when either way, supposedly the internal GPSDO is being used.
> Thanks,
> On Tue, Aug 28, 2012 at 4:13 PM, Josh Blum <address@hidden> wrote:
>> On 08/28/2012 12:03 PM, Anisha Gorur wrote:
>>> Hello,
>>> We've been having some trouble with the synchronizing aspects of our
>>> project. What we want is the exact same time as the FPGA tick counter,
>> not
>>> a time_spec_t representation of time. Where can we get access to that?
>>> Thanks!
>>> -Anisha
>> call to_ticks with the clock rate of the device:
>> http://files.ettus.com/uhd_docs/doxygen/html/classuhd_1_1time__spec__t.html#ad75960ba4c788cd30a5d0c8904888da3
>> -josh
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