So there is a some difference regarding the clock between b200 and b200mini. At first I thought they are pretty much alike. Anyway, now I understood. Thanks Aaron.
On Mon, 23 Nov 2020, 02:42 Aaron Holtzman via USRP-users, < [email protected]> wrote: > On the b200mini, the 1pps actually *does* steer the internal reference. > Which is different behaviour then the rest of the entire Ettus lineup I > believe. > > For details on how it works, see > uhd/fpga/usrp3/top/b2xxmini/b205_ref_pll.v. It autodetects the external > reference type and applies the appropriate dividers and gain schedule. > > cheers, > Aaron > > > On Fri, Nov 20, 2020 at 1:45 PM Marcus D. Leech via USRP-users < > [email protected]> wrote: > >> On 11/20/2020 08:38 AM, 翁偉吾 via USRP-users wrote: >> > Hi, >> > >> > I have a question about the PPS inputs on b200 and b200mini models. >> > >> > I want to synchronize time for two b200 units. I connected the PPS to >> > a external GPS module. The Ref port was left open(Not used). Then I >> > set the system time with set_time_next_pps command. On another b200, >> > the configuration was the same. The problem is, after both device time >> > has been set to PPS with the same time spec. Their system time start >> > to drift away after a while. In other words, the PPS signal seems not >> > regulating the system time on a second basis. >> > >> > BTW, I have measured the PPS timing between these gps devices and it >> > was only 10ns off. >> > >> > I've read somewhere in the usrp maling list that the b200mini with >> > only PPS input can be used to regulate internal PLL clock. Does this >> > mean for every PPS edge it is adjusting the internal clock and make >> > the system time stable between two units? Can we achieve the same >> > regulation effect on b200? >> > >> > I already knew that using a GPSDO with b200 is the way to go for the >> > best synchronization result. But I didn't go that way because 1.GPSDO >> > can break my budget and 2. I only require hardware time sync on every >> > PPS edge. >> > >> > I'm grateful for any suggestions. Thanks. >> > >> The PPS input is simply used as a trigger for doing >> "set_time_next_pps()". It DOES NOT provide any on-going clock >> synchronization--that is >> what the 10MHz reference clock input is for. >> >> >> >> _______________________________________________ >> USRP-users mailing list >> [email protected] >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> > _______________________________________________ > USRP-users mailing list > [email protected] > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >
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