On 3/19/2010 10:48 AM, David Evans wrote:
Hi,
I want to sync two USRP2s, and currently trying to modify the VRT
rx_timed_samples...
usrp2::clock_config_t cc;
cc.ref_source = usrp2::clock_config_t::REF_INT;
cc.pps_polarity = usrp2::clock_config_t::PPS_NEG;
cc.pps_source = usrp2::clock_config_t::PPS_SMA;
cc.provide_ref_to_mimo = false;
u2->config_clock(cc);
// u2->set_time(....); // replaced with...
u2->set_time_at_next_pps(...);
However, the code hangs at the start sampling, and manually applying a
pulse to the PPS SMA does nothing.
What is the correct voltage level and pulse shape required? Manually
toggling anything between 0-1.5v and 0-5v does nothing. I hope 5V
isn't too much!!!
When do you start_rx_streaming()? I've found that it works best to wait
until the next PPS (e.g. sleep(1) if the host PC doesn't have direct
access to the PPS signal), and then calling start_rx_streaming() with
the desired parameters (i.e. start streaming at current time + some
offset) works.
Ultimately, I want to capture coherent samples with both USRPs, maybe
with the MIMO cable, and a GPS reference + PPS. Would this be just a
case of...
For USRP A (with ref + PPS attached)...
cc.ref_source = usrp2::clock_config_t::REF_EXT;
cc.pps_polarity = usrp2::clock_config_t::PPS_NEG;
cc.pps_source = usrp2::clock_config_t::PPS_SMA;
cc.provide_ref_to_mimo = true;
For USRP B...
cc.ref_source = usrp2::clock_config_t::REF_EXT; ***MIMO???***
cc.pps_polarity = usrp2::clock_config_t::PPS_NEG;
cc.pps_source = usrp2::clock_config_t::PPS_SMA; ***MIMO???***
cc.provide_ref_to_mimo = false;
Kind Regards,
David
I haven't tried the MIMO cable at all, but sync'ing by providing the
same clock/PPS to both USRP2's works pretty well. You may also want to
review some of the recent discussions on mailing list about the possible
phase offsets you may get, even when all/both USRP2's are locked to the
same reference, and internal clocks are synchronized. This is due to the
implementation of the PLL on the individual daughterboards, and thus
will be dependent on what you're using.