If I synchronize two USRPs using pps clock
uhd::time_spec_t time_spec = uhd::time_spec_t(0.0);
sdev->set_time_next_pps(time_spec);
boost::this_thread::sleep(boost::posix_time::seconds(1));
and give the metadata for the frame as following
md.time_spec = uhd::time_spec_t(seconds_in_future);
When is the packet is being transmitted?
I believe md.time_spec specify the delay of transmission, which is not an
absolute time of the transmission.
On Sun, Jan 2, 2011 at 4:08 PM, Josh Blum <j...@ettus.com> wrote:
>
>
> On 01/02/2011 12:59 PM, Sangho Oh wrote:
> > Hello Josh,
> >
> > I have used this command
> >
> > dev->send(&buff.front(), samps_to_send,
> > md, uhd::io_type_t::COMPLEX_FLOAT32,
> > uhd::device::SEND_MODE_FULL_BUFF, seconds_in_future + 0.1);
> >
> > The reference time for seconds_in_future is not clear to me. When does
> the
> > timer starts?
>
> that last parameter is a timeout. In the example, the samples are sent
> several seconds in the future, so the timeout should wait at least that
> long. See the docs for that call:
>
>
> http://www.ettus.com/uhd_docs/doxygen/html/classuhd_1_1device.html#a11cea7a2131f2764e9afa4eab34bd8d5
>
> The metadata specifies the timestamp of the packet:
>
>
> http://www.ettus.com/uhd_docs/doxygen/html/structuhd_1_1tx__metadata__t.html
>
> > I guess there are large imprecise delay between gnuradio to USRP2 FPGA
> > (gnuradio -> ethernet -> FPGA).
> >
>
> on the order of 10s of microseconds if the CPU is keeping up.
>
> > If I synchronize two USRPs using sync_to_pps(), just wondering how to
> > control the transmit timing from the reference timing stamp, which is
> reset
> > every second?
> >
>
> The time will be set at the next pps to the desired value, and increment
> forever after (its a 64 bit timer). So nothing is reset or rolls over
> every second.
>
>
> http://www.ettus.com/uhd_docs/doxygen/html/classuhd_1_1usrp_1_1single__usrp.html#a7fdb91ce9c7dd16a2c4cf210ebc8105f
>
> -josh
>
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>
--
*From: Sangho Oh
*
*Voice mail: (609) 759-1552*
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