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| -rw-r--r-- | host/docs/usrp_n3xx.dox | 52 |
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diff --git a/host/docs/usrp_n3xx.dox b/host/docs/usrp_n3xx.dox index 194766d68..205f54328 100644 --- a/host/docs/usrp_n3xx.dox +++ b/host/docs/usrp_n3xx.dox @@ -8,6 +8,7 @@ - Dual SFP+ Transceivers (can be used with 1 GigE, 10 GigE, and Aurora) - External PPS input & output - External 10 MHz input & output (20 MHz and 25 MHz inputs also supported) + - External White Rabbit time/frequency reference input support - Internal 25 MHz reference clock - Internal GPSDO for timing, location, and 20 MHz reference clock + PPS - External GPIO Connector with UHD API control @@ -495,6 +496,57 @@ salt-minion): $ systemctl enable salt-minion +\section n3xx_synchronization Clock/Time Synchronization + +\subsection n3xx_synchronization_internal Internal references + +The N3xx series has an onboard GPSDO as well as a 25 MHz reference oscillator, +which can both be used as time- and clock references. The GPSDO will function +as a reference even when there is no GPS reception. + +Note that this does not enable the synchronization of multiple devices. +Using an internal reference is the default. + +\subsection n3xx_synchronization_external External references + +In order to synchronize multiple USRPs, an external reference, such as the +CDA-2990, is required. If only a clock reference is available, it is possible +to derive an internal PPS signal from the reference (which will allow devices +to share a frequency, but not a time reference). If both an external clock and +time source are provided, devices will be synchronized in frequency and time. + +```cpp +auto usrp = uhd::usrp::multi_usrp::make("type=n3xx,clock_source=external,time_source=external"); +``` + +\subsection n3xx_synchronization_whiterabbit White Rabbit + +White Rabbit is an Ethernet-based synchronization procedure; it is an extension +of the IEEE 1588 Precision Time Protocol (PTP). The N3xx device can be +configured as a White Rabbit slave. + +To use White Rabbit, it is necessary to provide an appropriate reference via +Ethernet. This reference must be connected to SFP0. Finally, a White Rabbit-compatible +FPGA must be loaded. SFP0 will not be available for data transport in this mode. + +The White Rabbit image is provided as a default image. To obtain the default +images, simply run: + + $ uhd_images_downloader + +Then, you can install the WX (or WA) image using `uhd_image_loader`: + + $ uhd_image_loader --args type=n3xx,addr=ni-n3xx-<DEVICE_SERIAL> --fpga-path=”<UHD_INSTALL_DIRECTORY>/share/uhd/images/usrp_n310_fpga_WX.bit + +Once the image is loaded, select `sfp0` as the clock and time source: + +```cpp +auto usrp = uhd::usrp::multi_usrp::make("type=n3xx,clock_source=sfp0,time_source=sfp0"); +``` + +For more information, refer to the [White Rabbit Homepage](https://www.ohwr.org/projects/white-rabbit), +or the [Ettus Research Knowledge Base](https://kb.ettus.com/Using_Ethernet-Based_Synchronization_on_the_USRP%E2%84%A2_N3xx_Devices). + \section n3xx_theory_of_ops Theory of Operation The N3xx-series are devices based on the MPM architecture (see |