Re: [Discuss-gnuradio] USRP Streaming Latency

[Tom Hendrick]

Josh..

Thanks, real time scheduling is enabled, and I run my python script with sudo and I do not see the typical failure message saying real-time was not enabled.

When I run the C++ program in one terminal and output the modulated signal to a normal file, I can read that file in with my python script and see the output on the USRP with no gaps like I was seeing before.  The problem is that this isn't real-time and I am  writing to a file with the C++ program that grows with time.  I did however not see any uU underruns with the USRP so I am pretty sure the laptop can handle running both the C++ and the python script at the same time.

I'm guessing its some type of buffer size issue.  The C++ program flushes packet by packet.  When I run the C++ program and output to a fifo file and do cat tempfifo.dat > check.dat, the check.dat shows none of that latency or zero signal when I open it afterwards.  Could it be that the USRP or GRC script has a much smaller buffer size than the packet generated by the C++ program?

Does anyone else have any ideas on what I should try?

Thanks-Tom



--- On Mon, 3/28/11, Josh Blum <address@hidden> wrote:

From: Josh Blum <address@hidden>
Subject: Re: [Discuss-gnuradio] USRP Streaming Latency
To: address@hidden
Date: Monday, March 28, 2011, 8:54 PM

> I also see uU from the GRC script output about every 5 or so seconds.
> Does anyone have any idea if this is a FIFO problem, or is it a
> USRP/GRC issue?  I am using a Duo core SU7300 laptop so I would think
> it should run OK real-time unless the C++ and GRC script demand much
> more processing power when used at the same time.  Does anyone know
> any tricks I can try?
>

The U printed means underflow, the host does not feed the USRP fast
enough. Sometimes enabling RT scheduling on the flow graph can help with
this.

-Josh

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