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.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 <patchvonbr...@gmail.com>
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
<patchvonbr...@gmail.com> 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
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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.
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