I am trying to achieve two synchronized transmissions from two USRP2s.
Both USRPs are connected to each host PC and feed with 5PPS clocks, without
10Mhz reference clock.
But I cannot make it happen yet.
1. I have synchronized two USRP2s using clocks from GPS pps, and wait for 1
sec
* sdev->set_time_next_pps(uhd::time_spec_t(0.0));*
* boost::this_thread::sleep(boost::posix_time::seconds(1));*
2. Trigger the transmission of a stream of packets (10M samples = 500
packets) for both usrps
- with time delay 3 secs
for (size_t i = 0; i < num_packets; i++){
md.start_of_burst = true;
md.end_of_burst = (i == num_packets-1);
md.has_time_spec = (i == 0);
* md.time_spec = uhd::time_spec_t(uhd::time_spec_t(3.0));
* size_t samps_to_send = std::min(total_num_samps -
samps_per_packet*i, samps_per_packet);
size_t num_tx_samps = 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);
However, the two transmissions are not synchronized well. There is a
significant timing offset between the two transmissions, which
is hundreds of milliseconds.
I can hardly control the transmission timing, and the concept on the timing
control is pretty obscure to me yet.
- I used a shell scrip from another host to trigger the transmissions for 2
usrps. Timing delay between the two executions is < 0.2-0.3 sec
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