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| -rw-r--r-- | sfn.tex | 38 |
1 files changed, 37 insertions, 1 deletions
@@ -141,9 +141,45 @@ therefore rewrite the above equation as: \sidenote{Explain relationship with ZeroMQ max buffer size} -\subsection{Using Ettus GPSDO} \subsection{Using ODR LEA-M8F GPSDO board} +The ODR GPSDO board integrating a u-blox LEA-M8F module can be used as time and +frequency reference for the USRP B200. \sidenote{TODO: Add Picture} +The board design is available on the Opendigitalradio website, with +a bill of materials describing how to source the components. The PCB itself can +be manufactured in any PCB fab. + +The module includes the correct pin header so that it can be mounted directly +onto the USRP B200, but also includes footprints for SMA connectors for other +usages. Communication between the PC and the GPS is possible through USB or over +UART through the B200. + +The u-blox LEA-M8F module is a GPS disciplined TCXO module, with a one-pulse per +second and a reference clock output at a frequency of $30.72$ MHz. This is +different than what the normal USRP firmware expects. + +Because the UART communication protocol and the reference clock frequency are +different than for the GPSDO units Ettus supports, a modified version of UHD is +necessary. This version includes new UHD sensors, used by ODR-DabMod to verify +that the GPSDO is locked properly, and different configuration settings for the +clock management PLL inside the USRP, making the USRP compatible to the +$30.72$MHz reference clock frequency. + +The modified UHD version is available at +\url{http://www.github.com/Opendigitalradio/uhd.git} and replaces Ettus' UHD. + +ODR-DabMod can be configured as follows: +\begin{lstlisting} +[uhdoutput] +refclk_source=gpsdo +pps_source=gpsdo +behaviour_refclk_lock_lost=crash +max_gps_holdover_time=600 +\end{lstlisting} + + +\subsection{Using Ettus GPSDO} + \sidenote{Give example} % vim: spl=en spell tw=80 et |