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Re: [Discuss-gnuradio] external 1pps pulse

From: Hans Glitsch
Subject: Re: [Discuss-gnuradio] external 1pps pulse
Date: Fri, 16 Mar 2007 14:55:56 -0700

I currently have four complex input signals coming in through USB
and I have a 1pps timing pulse coming from a gps source that I need
to synchronize the 64MHz clock to and also pass on to the PC so that
I know exactly which sample it occurred on.  Can someone give me
some guidance as to how I might accomplish this?

Thank you,

Hi Hans,

In the good news / bad news department, the good news is that this
shouldn't be hard to do with the "inband signaling" work that's
currently underway.  The bad news is that this work probably won't
be ready for a couple of months.

In the interim, if you're willing to steal an LSB, you could modify
the verilog such that it reported the presence or absence of the 1pps
in the LSB of say, the I component of the first channel.


Hi Eric,

Thanks for the reply. I could use an LSB on one signal, although I hate to lose a whole bit when I only have 12 to start with. I was hoping there might be a way to interleave another signal in with the four complex ones I'm receiving in the PC. My data rate is fairly low, so another signal would not hurt much. I haven't looked at the Verilog code yet. Would a fifth interleaved signal even be implement in the context of the verilog code? Also, what method would you use to receive the 1pps signal so the verilog code could stick it into an LSB, or another signal?

The other issue is synchronizing the 64MHz clock to the 1pps. Is there any way to do this synch with the usrp's onboard clock, or will I have to make an external clock?


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