[USRP-users] Using 4 USRP with a Gigabit switch

Josh Blum josh at ettus.com
Wed Feb 6 23:59:34 EST 2013



On 02/06/2013 03:14 PM, Damien Serant wrote:
> Hi list,
> 
> I am experiencing some issue with my configuration using an Ethernet switch
> even if i read on the list that it should work seamlessly . Here is the
> situation:
>  - I use 2 pairs of USRPN200. In each pair, the 2 USRP are connected
> together with a MIMO cable, and the master USRP of each pair has the
> internal GPSDO from Ettus.
>  - The master USRP of each pair is connected to a Netgear 8 port Gigabit
> switch.
>  - My PC is also connected to this switch.
>  - I wrote a simple UHD program (based on multi_sample_to_file) to record
> the sample of each USRP. I use 1 multi_usrp object constructed with the 4
> IP address of my USRP2 (all different of course). 1 have 1 rx_stream mapped
> over my four channels so obtained.
> - I record 4 files as expected, but the program spends more than 30 seconds
> to record 5 seconds of signal as if there was some bottle-neck somewhere
> (the same without writing to the HDD). The problem is that the sampling
> frequency is 200 kHz so the Gigabit network should handle that without any
> issue, no ?
> 

That sounds like a few MB worth of data. Shouldnt take much time at all.

Are you requesting continuous or finite streaming? I would recommend to
first count the number of samples coming out of the recv() call and make
sure its what is expected.

I guess another good approach would be to add in one device at a time
and see where the application starts getting funny / breaking assumptions.

> So my conclusion is that i am doing wrong somewhere. Actually i'm not sure
> how to handle my 4 usrp with UHD:
>  - Treat each USRP pair in different USRP object ?
>  - Use one multi_usrp object, but one rx_stream per pair ?
>  - Execute multi_sample_to_file.exe for each pair ? -> i tried this
> solution but it does not work : the files of one of two pair remains empty.

All of those options should work. Usually ganging all 4 devices together
into one object is a just convenience for dealing w/ alignment.

-josh

> 
> Thanks in advance
> Damien
> 
> 
> 
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