Frank, Yes, you do have to open up the N2x0 and physically switch the jumper to change the clock reference. There is no way to switch it through software. The PPS reference is simply an XOR of the GPSDO and external PPS inputs, so only one may be connected at a time. If you want to use an external clock reference and the GPSDO PPS reference, you may do so by simply moving the jumper to the external source position, leaving the GPSDO connected, and connecting your external clock reference (leaving the external PPS disconnected). The software should be set to either "external" or "gpsdo" (either should work). If you are feeling more ambitious and understand Verilog and C, the PPS control can be controlled via software with changes to the FPGA and UHD driver code. The inputs to the FPGA are PPS_IN (for the external PPS) and PPS2_IN (for the GPSDO PPS) and the Verilog logic can be found at ( https://github.com/EttusResearch/uhd/blob/master/fpga/usrp2/top/N2x0/u2plus.v#L373 ). Best regards, Michael E. West Senior Software Engineer Ettus Research ---------- Forwarded message ---------- From: Wallace, Frank L CIV NSWCDD, Q41 <frank.l.wallace1@navy.mil> Date: Fri, Oct 11, 2013 at 10:10 AM Subject: [USRP-users] GPSDO and external 10 MHz reference To: usrp-users <usrp-users@lists.ettus.com> I have N2x0 radios and I have installed the GPSDO in several of them. Sometimes I want use the external reference and sometimes I want to use the GPS reference. Do I have to open them up and move the jumper when I want to switch or does it still honor the software command? There are also times when I want the 1 PPS to come from the GPSDO and the 10 MHz to come from an external source. Is this doable? Thanks, Frank _______________________________________________ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com