[USRP-users] FM Transmitter works well, Underruns after adding constant multiply block

Philip Balister philip at balister.org
Fri Feb 24 09:22:30 EST 2012


On 02/24/2012 08:56 AM, salingle wrote:
> Dear Knowledgeable People,
> 
> Just starting out with an E100 and UHD, have a basic FM transmitter that works nicely (transmitting a wav file, listening on dinosaur FM radio). 
> 
> 
> This works nicely:
> 
> Wavfile source (32ksps) -> blks2_wfm_tx(320ksps)->uhd_usrp_sink (interpolation of 400)
> 
> 
> However, adding a simple multiply by constant block results in repeated underruns:
> Wavfile source (32ksps) -> multiply_const->blks2_wfm_tx(320ksps)->uhd_usrp_sink
> 
> All of the above is done with python.  Is it as simple as the multiply block takes too long?  Would the same path work if coded in C?  Or, is some other principal being violated?

GNU Radio on the E100 very much needs blocks that take full advantage of
the NEON instructions (which does not happen by default).

Have you tried Tom's branch :

https://github.com/trondeau/gnuradio/tree/safe_align

This is supposed to use volk for more blocks.

Philip


> 
> Thanks!
> sal
> 
> 
> 
> 
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