Re: [Discuss-gnuradio] USRP-Overrun Problem

[Eric Blossom]

On Sun, May 09, 2010 at 08:57:28PM +0200, Eder Matthias wrote:
> Hello,
> 
> i'm newbe at Gnuradio and i started with a simple FM receiver project.
> I use a USRP1 interface with a TV Rx rev3 daugtherboard and gnuradio
> 3.3, installed on a Ubuntu 9.04 distribution.
> The CPU is a AMD X2 4800+, ramsize is 1GB.
> 
> The good news: The FM-receiver works very well.
> The bad news: "uOuOuOuO"-messages
> 
> 
> The USRP parameters are:
> freq: 102,4 MHz
> decimation: 256
> 
> Realtime scheduling is enabled too.
> 
> The decimation factor of 250 devides the full usb bandwith of 64MB/s
> to 256kB/s.
> In my point of view, this should be no problem for the pc to read
> this amount of data.
> Nevertheless i get many of the overrun messages ("uO").
> The effect of the lost messages is hearable to (of course!). I can
> hear a cyclic! click.
> 
> That means, that the pc isn't able to read the USB data fast enough.
> But why?
> The CPU load is about 15% of each core. But gnuradio isn't listed in
> the process-list. So i cannot say what load is produced by gnuradio
> itself.
> 
> Does anybody can give me any hint, where the problem could be?
> 
> Thank you for your help.
> Matthias

Could be that the clock in your audio card is slower than the clock in
the USRP, and thus the pipeline backs up.  (aka, "The two-clock problem")

Eric