Does anyone have some ideas on what else I can try right now? I'm out of ideas
on what is causing the underruns at the start of running the script that reads
the WAV file and outputs to the USRP LFTX.
Thank you, -Tom
________________________________
From: Tom Hendrick <sdtom...@yahoo.com>
To: Tom Hendrick <sdtom...@yahoo.com>; "discuss-gnuradio@gnu.org"
<discuss-gnuradio@gnu.org>
Sent: Wednesday, November 14, 2012 8:52 AM
Subject: Re: [Discuss-gnuradio] UHD Underrun with Wav File Source and USRP Sink
As an additional check, I reduced the signal amplitude further in the WAV file
to make sure there is no truncation. I still see the same two underruns at the
start of running the script.
Thanks, - Tom
________________________________
From: Tom Hendrick <sdtom...@yahoo.com>
To: "discuss-gnuradio@gnu.org" <discuss-gnuradio@gnu.org>
Sent: Wednesday, November 14, 2012 8:22 AM
Subject: Re: [Discuss-gnuradio] UHD Underrun with Wav File Source and USRP Sink
Hello Josh,
The wav file has float values in the -1 to 1 range. In the old GRC script I
had used a constant multiplier of (2**15-1) to get the correct amplitude.
In the newer GRC script I took that out since it was already in the correct
range.
When I check the output of the LFTX with an oscilloscope, they both look
identical except that I see the blip/noise (which I think is from underrun)
show up right at the start of the transmission. I have added zero padding to
the signal. This is for an audio recording project and the blip/noise causes
problems on the receive side because I am listening continuously for the
incoming signal and the blip causes unwanted effects.
Any other suggestions?
Thanks so much for your responses, - Tom
________________________________
From: Josh Blum <j...@ettus.com>
To: discuss-gnuradio@gnu.org
Sent: Tuesday, November 13, 2012 9:50 PM
Subject: Re: [Discuss-gnuradio] UHD Underrun with Wav File Source and USRP Sink
On 11/12/2012 02:10 PM, Tom Hendrick wrote:
>
>
> Hello Josh,
>
> Thanks for the suggestion. Yes I had zero padded the file with about 1
> second of zero signal prior to the signal I want to transmit. I had still
> seen the blip/noise when running the script even when there was 1 second of
> zero padded signal. Is there anything else I should try?
>
Well, then perhaps it not the result of an underflow.
What is your transmit amplitude? In the old libusrp1 floats were
+/-2**15, but now they are +/-1.0 fullscale. So you must have had to
adjust the amplitude of the baseband samples; but are they scaled small
enough to avoid truncation?
-josh
> Thanks, -Tom
>
>
> ________________________________
> From: Josh Blum <j...@ettus.com>
> To: discuss-gnuradio@gnu.org
> Sent: Monday, November 12, 2012 1:03 PM
> Subject: Re: [Discuss-gnuradio] UHD Underrun with Wav File Source and USRP
> Sink
>
>
>
> On 11/11/2012 01:21 PM, Tom Hendrick wrote:
>> Hello all,
>>
>> I am using a USRP1 and an LFTX daughtercard and Ubuntu 12.04.
>>
>> I am having an issue with a simple GRC script I made which has three
>> blocks. A WAV file source connects to a resampler block and then to
>> the UHD USRP sink.
>>
>> When I run the script I get a single underun right at the start of
>> running the script and no other underrun. When I run the script using
>> the sudo in front of it, I get two
underruns right at the start of
>> running the script and no other underrun. I monitored the
signal out
>> of the LFTX using an oscilloscope and noticed some blips/noise when
>> the script is run and I believe they correspond to the underruns. I
>> tried this with and without real-time scheduling enabled and didn't
>> see any difference.
>>
>>
>> I tried the same exact type of script with an older version of GRC on
>> a different laptop with Ubuntu 10.04. This uses the USRP sink block
>> not the UHD sink block. This script plays the file perfectly without
>> any underruns at all and I don't see the blips/noise at the beginning
>> of the signal.
>>
>> I am using the LFTX for an audio application and the blips/noise will
>> cause a problem for me. Does anyone know why I am seeing this
>> behavior with the newer UHD block? Is there anything I can do to
>> eliminate
it?
>>
>
> Hi Tom,
>
> If I am understanding correctly, you are getting some initial underflows
> when the flow graph begins processing. This is causing some
> discontinuous stream interruption over on the receiver side.
>
> If thats the case, I dont know of anything specifically to cause this,
> so it might just be the issue of interrupt coalescing. That is the host
> isnt initially ramped up to push out USB packets at full speed. So,
> driver wise, there may have been a subtle difference thats brining this
> out, USB 1.0 vs .1 for example.
>
> I'd like to replicate it over on end. But if I have a quick suggestion,
> it may be helpful to zero-pad the beginning of the wavefile so those
> initial discontinuities are only lost in the padding.
>
> -josh
>
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