[USRP-users] N210 Stops Transmitting

Marcus Müller marcus.mueller at ettus.com
Sat Oct 18 07:49:28 EDT 2014

Hi Liwei,
"SU" is bad, because
"U" stands for underflow, which means the USRP hasn't gotten enough
samples in time and ran out of things to transmit.
The "S" represents a sequence error, which can only happen if for some
reason network packets got lost or reordered.
I haven't seen these errors very often, and in the few cases, it was due
to either a heavily underpowered PC, being so busy with signal
processing that the kernel just had to drop network packets, or due to a
horribly buggy network card, but you seem to achieve reasonable
throughput, so I'm a bit out of ideas here. Nevertheless, could you
share what
"lscpi|grep -i ethernet"
tells you?


On 18.10.2014 12:06, Liwei via USRP-users wrote:
> 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.
> Thanks
> 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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