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? I guess there are large imprecise delay between gnuradio to USRP2 FPGA (gnuradio -> ethernet -> FPGA). 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? On Sun, Jan 2, 2011 at 2:36 PM, Josh Blum <j...@ettus.com> wrote: > > > On 01/02/2011 10:53 AM, Sangho Oh wrote: > > Hello, > > > > What I am trying to implement is a synchronized packet transmission from > > more than one USPRs. > > I wonder if there is a way to control the transmission timing under a > > microsecond level. > > > > If there is a way to control the transmission timing using external clock > > signal, then it will be really easy. Like making USRPs transmit packets > > triggered by the external clocks. This may request to change of code in > the > > firmware. > > > > I have tired to use UHD code to give backoff delays for each > > USRP transmission, but this method is quite not precise and cannot find a > > way to use it for a synchronized transmission. > > > > Any comments will be valuable to me. > > Thanks. > > > > With UHD (any USRP more recent than the USRP1 classic), you should be > able to precisely schedule transmit packets to the precision of a clock > cycle. Basically: send a packet with a timestamp that is less than the > time on the device (so that its not late). > > You can use a GPSDO to set an absolute time into the USRP device, or you > can use the time found on received packets to schedule transmit packets. > So it all depends on how deal with the time. > > I recommend looking at the timed tx example that comes with UHD. I think > to do this, you will need to code directly to the UHD api. To do this in > gnuradio will require tag-aware blocks that use the new gnuradio tagging > API. And we haven't crossed that bridge yet. :-) > > -josh > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio > -- *From: Sangho Oh * *Voice mail: (609) 759-1552*
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