# "D" errors after flowgraph runs for some time

**URL:** <https://www.ruby-forum.com/t/d-errors-after-flowgraph-runs-for-some-time/242936>\
**Category:** GNU Radio\
**Created:** [August 8, 2015, 8:58pm UTC](https://www.ruby-forum.com/t/d-errors-after-flowgraph-runs-for-some-time/242936 "2015-08-08T20:58:41Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Rafa\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/958977/32.png) [@Rafa\_F](https://www.ruby-forum.com/u/Rafa_F)\
**Post date:** [August 8, 2015, 8:58pm UTC](https://www.ruby-forum.com/t/d-errors-after-flowgraph-runs-for-some-time/242936/1 "2015-08-08T20:58:41Z")

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I am playing with a slightly modified version of Chris K.'s  
channelizer example for NOAA radio stations (my version attached). I’m  
using 3.7.6.1.

The program runs just fine for the first 20-30 minutes on my I7-4710HQ  
laptop. System monitor shows typically one core running at about 50%  
with the others ranging from idling to 30%. Only a fraction of system  
memory is used. The laptop is wired to a USRP2/WBX via GigE switch, and  
is showing about 5MIB/s of incoming data when the flowgraph is running.

But after 20-30 minutes I start to get a string of "D"s on the console,  
and while the program keeps decoding audio, the signal strength drops by  
40dB or more.

When I first started playing with Chris’ example, I also had a string of  
"D"s immediately upon startup which I cured by turning on realtime  
scheduling. It appears that just moved the problem off into the future.

I am guessing this is some sort of buffer exhaustion or similar problem.  
Any suggestions on how to address is?

Thanks,  
John

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**Author:** ![John\_Ackermann\_N8UR](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/cdc98d/32.png) [@John\_Ackermann\_N8UR](https://www.ruby-forum.com/u/John_Ackermann_N8UR)\
**Post date:** [August 8, 2015, 9:17pm UTC](https://www.ruby-forum.com/t/d-errors-after-flowgraph-runs-for-some-time/242936/2 "2015-08-08T21:17:23Z")

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I think I may have found the problem. The NBFM output rate was 25ksps  
while the audio sink was 24ksps. So there was a slow accumulation of  
excess samples. That also explains some gaps I saw in the channel  
output waterfall.

Adding a rational resampler to the NBFM block output seems to have  
cleaned things up. Revised .grc file attached.

## John

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**Author:** ![John\_Ackermann\_N8UR](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/cdc98d/32.png) [@John\_Ackermann\_N8UR](https://www.ruby-forum.com/u/John_Ackermann_N8UR)\
**Post date:** [August 8, 2015, 9:19pm UTC](https://www.ruby-forum.com/t/d-errors-after-flowgraph-runs-for-some-time/242936/3 "2015-08-08T21:19:09Z")

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Hi John,  
sounds like excellent work! Just to point you at a nice tool: If you can  
build a recent GNU Radio with control port and performance counters  
enabled, you can introspect things like buffer fillage with a GUI, which  
can be extremely handy in such cases.

Best regards,  
Marcus