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Re: [Discuss-gnuradio] USRP2 PPS and REF

From: Matt Ettus
Subject: Re: [Discuss-gnuradio] USRP2 PPS and REF
Date: Fri, 13 Feb 2009 11:51:39 -0800
User-agent: Thunderbird (X11/20090105)

Suprin, Charles E. wrote:

Working only on my single channel setup, what appears to happen is
that there is the time stamp for the first sample in the frame. The
frame alignment seems to remain a function of when the device was
turned on.

NO. Frame alignment is under explicit control from the host, as long as you do a "receive at" request. That will allow you to specify EXACTLY when you want your samples. If you do a "receive now" request, which is what you're doing, you'll get samples starting right away, which will be a function of host computer latency.

Now if sync_every_pps worked with the 31 December 2008 firmware.  I
think I need to wait for a newer FPGA/VHDL firmware release for that
to happen.

Honestly, sync_every_pps is a hack and I don't know why you would want it. It causes you to not know what second it is, since the clock is reset every second.

The normal "sync at next pps" makes more sense. Since all the oscillators are locked, you only need to sync once, and everyone will remain in sync forever.


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