But you know what I observed and what is weird? When I ask for an external source and I intentionally turn off the external generator providing a 10 MHz signal, USRP behaves as if it was still seeing a 10 MHz reference signal at its input. Doesn't matter if the generator is switched on or off - USRP behaves the same way. Because of that I am not sure if USRP is being clocked from an internal or external clock source. Is it the bug in the GNU radio or UHD or am I doing something wrong? How can I get the feedback from the USRP hardware that it was locked to the external clock? Is it even possible?
śr., 11 maj 2022 o 16:14 Marcus D. Leech <[email protected]> napisał(a): > On 2022-05-11 09:51, Marcin Puchlik wrote: > > Will it be enough to clock USRP from the external 10 MHz signal generator? > When I run the flowgraph I cannot see the information that is using the > external clock. Here is the output from GNU Radio: > [INFO] [UHD] linux; GNU C++ version 9.4.0; Boost_107100; > UHD_3.15.0.HEAD-0-gaea0e2de > [INFO] [B200] Detected Device: B200 > [INFO] [B200] Operating over USB 2. > [INFO] [B200] Initialize CODEC control... > [INFO] [B200] Initialize Radio control... > [INFO] [B200] Performing register loopback test... > [INFO] [B200] Register loopback test passed > [INFO] [B200] Setting master clock rate selection to 'automatic'. > [INFO] [B200] Asking for clock rate 16.000000 MHz... > [INFO] [B200] Actually got clock rate 16.000000 MHz. > [INFO] [B200] Asking for clock rate 51.200000 MHz... > [INFO] [B200] Actually got clock rate 51.200000 MHz. > [INFO] [MULTI_USRP] 1) catch time transition at pps edge > [INFO] [MULTI_USRP] 2) set times next pps (synchronously) > [INFO] [B200] Asking for clock rate 51.200000 MHz... > [INFO] [B200] OK > [INFO] [B200] Asking for clock rate 51.200000 MHz... > [INFO] [B200] OK > [WARNING] [AD936X] Selected Tx sample rate (0.2 MHz) is less than > analog frontend filter bandwidth (0.2 MHz). > > > [image: image.png] > > Yeah, I don't think it puts out an "i'm locked to the external reference" > message. > > But you've asked for "external" clock source, so you should be good to go, > assuming your external generator meets the requirements. > > > śr., 11 maj 2022 o 15:24 Marcus D. Leech <[email protected]> > napisał(a): > >> On 2022-05-11 09:18, Marcin Puchlik wrote: >> >> Marcus, >> Thank you very much for the answer. Does it mean that 1 PPS signal is >> optional? Can I only provide an external 10 MHz clock without 1 PPS? >> *Z poważaniem * >> *Marcin Puchlik* >> >> >> >> >> >> >> >> >> >> *Yes, absolutely. If timestamp synchronization is not important to you, >> then you can just provide a 10MHz reference when you want better >> frequency accuracy and drift characteristics than are offered by the >> on-board clock and/or you want some type of phase-synchronization but >> don't care much about mutual phase offsets.... * >> >> >> >> śr., 11 maj 2022 o 14:24 Marcus D. Leech <[email protected]> >> napisał(a): >> >>> On 2022-05-11 06:17, Marcin Puchlik wrote: >>> >>> Hello Community, >>> Like in the topic, I know that a stable 10 MHz source is needed as a >>> clock signal but why do we need 1 PPS signal? How is it used by the USRP >>> hardware? Can someone explain that to me? >>> Thanks >>> Marcin >>> >>> _______________________________________________ >>> USRP-users mailing list -- [email protected] >>> To unsubscribe send an email to [email protected] >>> >>> 1PPS is used to provide timestamp-clock synchronization across multiple >>> devices, typically. This is important when your application requires this, >>> such as in MIMO or >>> multi-receiver TDOA schemes, etc. >>> >>> Basically, when you have multiple devices you use set_time_unknown_pps() >>> or set_time_next_pps() to signal to all devices in your multi_usrp object >>> that at the next >>> 1PPS, to set the timestamp clock to the value given in the the API >>> call. >>> >>> This turns out to be useful even in single devices that are "bicameral", >>> such as B210 and X310, where there are (for historic and architectural >>> reasons) >>> TWO timestamp clocks. Use the 1PPS synchronization primitives causes >>> the internal timestamp clocks to become synchronized. >>> >>> >>> _______________________________________________ >>> USRP-users mailing list -- [email protected] >>> To unsubscribe send an email to [email protected] >>> >> >> >
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