[USRP-users] N210 Stops Transmitting

Liwei xieliwei+usrp at gmail.com
Sat Oct 18 06:06:45 EDT 2014

Hello list,
    Anyone with any suggestions? I understand that a "U" in the debug
output indicates an underflow, but am not sure why that should cause
gnuradio to stop sending samples.


On 9 October 2014 01:10, Liwei <xieliwei+usrp at gmail.com> wrote:
> Hello list,
>     This may have been asked before (I vaguely remember seeing an
> email with a similar issue some time back), but what causes UHD to
> stop sending transmission packets to an N210?
>     With a simple flowgraph [signal source] -> [uhd sink] at 200k
> sample rate over gigabit ethernet, I get up to about 3 seconds of
> transmission before everything suddenly goes silent.
>     Here's what I see logged:
> linux; GNU C++ version 4.8.2; Boost_105400; UHD_003.007.002-107-g0ca4b4f8
> -- Opening a USRP2/N-Series device...
> -- Current recv frame size: 1472 bytes
> -- Current send frame size: 1472 bytes
> SU
>     Nothing else after "SU".
>     Interestingly, if I add a receive + fft chain in the same
> flowgraph, the receive stream works fine even after the transmission
> has stopped. In fact, if I loop the TX and RX ports on the N210
> together (with an attenuator in between) I can see, in the received
> signal fft, the frequency peak for the few seconds the N210 is able to
> transmit.
>     Gqrx also works well receiving FM radio stations all the way up to
> about 10MHz sampling rate, after which samples start to get dropped.
>     I'm running on a fresh install of Ubuntu 14.04, with everything
> installed using pyBOMBS. I've tried switching to yesterday's 3.7.3
> maint branch but no difference. Firmware and FPGA image were updated
> after each version switch.
>     Attached is a screenshot in Wireshark showing the sudden
> transmission stop. Note that only packets originating from the
> computer is shown.
>     Also attached is the output from uhd_usrp_probe.
>     $ uname -a
> Linux Ubuntu 3.15.0-031500rc2-generic #201404201435 SMP Sun Apr 20
> 18:36:18 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
>     It may be due to a buggy ethernet adapter, but I've achieved over
> 900MBits/s for both TX and RX over iperf. I've also tried another Fast
> (instead of gigabit) ethernet adapter and even Wi-Fi, but no
> difference. There is currently a Dell managed switch in-between the
> computer and N210, but I've tried directly connecting both together
> with no difference in results either.
>     Also, the current setup works flawlessly with a B210 which I have on hand.
>     At this point, any hint would be great!
> Thanks
> Liwei

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