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RE: [Discuss-gnuradio] Syncronous data aquisition using multiple USRP2 b
From: |
Ulrika Uppman |
Subject: |
RE: [Discuss-gnuradio] Syncronous data aquisition using multiple USRP2 boards |
Date: |
Tue, 23 Feb 2010 09:08:05 +0100 |
Hi,
What do we see in your example? Have you divided the clock by 10?
Is the output stable or are the edges jittering anything?
When I look at our clock outputs (in a very quick measurement) they are all
approximately in phase but the edges are jittering quite a bit, and I would
assume that to different usrp2s could in a worst case be as far apart as half a
clock cycle...
Regards,
Ulrika
> -----Original Message-----
> From: address@hidden
> [mailto:address@hidden
> On Behalf Of MarcW
> Sent: Thursday, February 18, 2010 6:51 PM
> To: address@hidden
> Subject: [Discuss-gnuradio] Syncronous data aquisition using
> multiple USRP2 boards
>
>
> I am trying to syncronise data acquisition for 3 USRP2 boxes
> at 2.4GHz to aquire say 1M samples from each board and write
> to a text file. So far I have managed to modify the firmware
> to output the USRP2 clock to the debug pins and to call
> config_mimo(WE_LOCK_TO_SMA) and sync_to_pps(). When I connect
> a 10MHz 2v Pk-Pk sine wave to each board (No PPS signal) and
> look at the clock output pin for each there is no drift in
> waveforms with respect to one another and the external clock
> reference. However, there is a phase offset between the clock
> edges on each board which changes every time they are reset
> (sometimes of half a clock period).
>
> Please see the example which includes the external clock
> reference and 3 clock outputs.
>
> Wont this mean that I have unsyncronised sampling since the
> ADC is controlled by the position of the clock edge?
>
> Is there a way to overcome this problem?
>
> My current python script to read in parallel is derived from
> the example /gr-utils/src/python/usrp2_rx_cfile.py using
> gr.hier_block2 to create multiple flow graphs (usrp2 -> text
> file replicated four times). Do I need any special
> syncronisation functions in here or should the problem be
> fully handled on the firmware/FPGA?
>
> Best regards,
> Marc.
>
> http://old.nabble.com/file/p27642862/scope_plot.jpg
> --
> View this message in context:
> http://old.nabble.com/Syncronous-data-aquisition-using-multipl
> e-USRP2-boards-tp27642862p27642862.html
> Sent from the GnuRadio mailing list archive at Nabble.com.
>
>
>
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