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.
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