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Re: [Discuss-gnuradio] 802.11 transceiver issue

From: Alexander Levedahl
Subject: Re: [Discuss-gnuradio] 802.11 transceiver issue
Date: Tue, 29 Mar 2016 15:57:19 -0400


I am not certain what to make of the asynch message buffer overflowing.

The __SSE2_MATH__, __SSE_MATH__, __SSE2__, __SSE__ defines are the SIMD preprocessor defines.  Can you run gcc --version and do cat /proc/cpuinfo | grep flags?  The former will indicate the gcc version number.  The latter will indicate what SIMD instructions the processor actually supports.  Also do you know what version of VOLK and gnuradio you have?

On Tue, Mar 29, 2016 at 3:50 PM, Abhinav Jadon <address@hidden> wrote:
Hi Alex ,
The output in the console was all 'U's before I disabled the WX/GUI blocks.
Now, it seems to run fine initially before throwing this message :

"WARN: asynchronous message buffer overflowing, dropping message"

The output of gcc -dM -E - < /dev/null | grep -e "SE" -e "AVX" was :
#define __SSE2_MATH__ 1
#define __ATOMIC_HLE_RELEASE 131072
#define __SSE_MATH__ 1
#define __SSE2__ 1
#define __SSE__ 1
#define __ATOMIC_SEQ_CST 5
#define __ATOMIC_RELEASE 3

I have an idea about what SIMD is, although I could not find any SIMD preprocessor defines.
Am I missing something here?

Abhinav PS  Jadon
Electronics and Communication Engineering Undergraduate
IIIT - Delhi
IASc Summer Research Fellow 2015
E: address@hidden

On Wed, Mar 30, 2016 at 12:42 AM, Alexander Levedahl <address@hidden> wrote:

When you run the flowgraph, can you look at system monitor?  This will give some indication whether the problem is that all the cores are pegged or if RAM is filling up. 
A couple of other things to look at:
1) Is there any text being printed to the console?
2) What happens if you disable the GUI blocks?  Simple method would be to open the flowgraph select the blocks that have GUIs associated with them, hit D (for disable) and then run the graph.
3) Would you happen to know which SIMD instructions it is using?  Run
gcc -dM -E - < /dev/null | grep -e "SE" -e "AVX"
The gcc -dM -E will print out the preprocessor defines. The - < /dev/null forces gcc to exit immediately.  The "SE" flag filters the preprocessor defines for any of the SSEE SIMD instructions; the "AVX" flag filters for the AVX SIMD instructions. 

Sometimes the processor supports SIMD instructions that the compiler (due to age) does not support.


On Tue, Mar 29, 2016 at 2:57 PM, Marcus Müller <address@hidden> wrote:
That's pretty much impossible to say.
My prime suspect would be the WX Gui visualization sink. Really, a couple of 64 FFTs aren't that terrible performance-wise.

On 29.03.2016 20:53, Abhinav Jadon wrote:
Thanks for all the help.
But Is my system underpowered ?
Also, I just observed that if I bunch few blocks in the tx flowgraph in a similar way as phy_hier block in the wifi_loopback flowgraph, I dont receive any more underruns.


Abhinav PS  Jadon
Electronics and Communication Engineering Undergraduate
IIIT - Delhi
IASc Summer Research Fellow 2015
E: address@hidden

On Wed, Mar 30, 2016 at 12:17 AM, Marcus Müller <address@hidden> wrote:
When you set the length tag field in the USRP sink, it starts looking for that stream tag, which contains number of samples in the starting burst.

Technically, that starts a uhd::tx_streamer for a finite number of samples, which means different things for different hardware.

Best regards,

On 29.03.2016 20:44, Abhinav Jadon wrote:
Hi Marcus,
I am working on a Core i7 8GB system, I dont know if its underpowered, if it is I have access to another Corei5 16 GB station. 
I know this is going to sound dumb but,
how does the USRP sink go into burst mode, I was under the impression that USRP could only transmit data continuously.  Do you toggle the RF frontend using a switch on receiving a message ?

Abhinav PS  Jadon

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