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Re: [Discuss-gnuradio] start_rx_streaming_at patch

From: Douglas Geiger
Subject: Re: [Discuss-gnuradio] start_rx_streaming_at patch
Date: Thu, 17 Sep 2009 15:52:20 -0400

 If you're referring to the internals of the USRP2, you'd have to look
through the firmware (txrx.c would be the place to start) and fpga
code to see how/when things get reset. If you just want to reset the
clock/counter according to an external input (e.g. 1PPS from a
GPSDO/etc.) you can call the sync_to_pps() command.
Start_rx_streaming_at() only addresses the need to begin streaming at
a specific time relative to the last clock reset (e.g. via
sync_to_pps(), or when the USRP2 got turned on, or when it last rolled
over). It takes an uint32 as argument, which corresponds to the fpga's
clock count - as that increments at 100MHz, each tick is 10ns. So
you're basically specifying the number of 10ns ticks since the last
clock reset (or rollover) to start at.
 For the VRT code - it's in development now, but I'd have to let
someone more involved comment on it's status. There's code in:
http://gnuradio.org/cgit/gnuradio.git/tree/vrt and
http://gnuradio.org/cgit/gnuradio.git/tree/gr-vrt. The last
announcement about it - apparently the plan was to get it working with
some development hardware, and then port it over to the USRP2. If
you're more concerned about the internals of the USRP2 though
(buffers, etc.) that may not affect you at all - the VRT is just about
the transport mechanism between the host pc and the usrp2.
 Hope that helps,

On Thu, Sep 17, 2009 at 3:30 PM, Bruce McGuffin <address@hidden> wrote:
> Doug
> What I really want most right now, is a usrp2 function that resets all the
> buffers, data storage, counters, etc at the start of a data collect. Does
> start_rx_streaming_at do that? (Later I'll also need it to allow me to set
> the start time.)
> And how is the start time specified? Is it just a 32 (64?) bit unsigned
> integer
> that gives an offset from the most recent sync to PPS?
> What is this VRT code? And when will it be available?
> Thanks
> Bruce

Doug Geiger

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