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 >
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