On 28/01/2023 20:00, jmalo...@umass.edu wrote:
Hello,
I am trying to develop an RFNoC application that starts collecting
samples when a trigger rises. However, I am unsure how to route the
TrigIn/PPS under the RFNoC utility. For example, I found the radio
RFNoC is used to interface with the TX/RX.
Thanks,
Joe
The PPS input isn't designed as a general-purpose trigger for sampling,
per se, but rather as a way of synchronizing of the
T.O.D. (Time-Of-Day) clocks across multiple USRP units. The
"set_time_next_pps()" and "set_time_unknown_pps()" methods
in the UHD API implement this. The basic idea is that each of the
USRP units receives one of these "set_time_next_pps()" calls,
when the the next 1PPS pulse arrives at the unit, the time-of-day
clock will be reset to whatever is specified. This provides
assurance that all the USRP units will agree on what time it is, so
that timestamping (and all the synchronized and
phase-coherent good that proceeds from that) can work.
Using it as a general-purpose sample trigger has been a fairly common
"thing" over the years, and it is possible, but with
some FPGA modifications. Some folks have also used one of the GPIO
inputs for this, rather than the 1 PPS input. Again,
with some FPGA modifications.
A general introduction to RFNoC is here:
https://kb.ettus.com/Getting_Started_with_RFNoC_in_UHD_4.0
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