> - why do you want to avoid using PPS? > > I’m working on techniques for aligning the clocks on the X310's in > environments where a shared frequency reference and PPS distribution by > conventional means (cabled, or via GNSS) is not feasible. > > - are you using a common 10 MHz ref? > > For testing purposes I have a shared 10 MHz reference to keep the clocks from > drifting, so I only need to remove the initial timing bias. > > - what is the level of "synchronous" you are looking for? Are you hoping to > have simultaneous sampling across all channels? > > The goal is for the sampling to occur within +/-0.5 clock cycles between two > X310s while the shared frequency reference is present; the time bias > estimator has been verified to have sufficient accuracy to support this, thus > I’m limited by the accuracy with which I can set the clock. To achieve the > goal, the the clock set operation would need to be accurate to within one > clock cycle which I believe requires a method of setting the local time > offset (fetch, add, write-back) that occurs with a deterministic latency that > can be calibrated for. > In theory, this should be possible on the FPGA, but I’m wondering if this is > possible via existing means in the UHD API, or if it may be implemented using > custom RFNoC blocks somehow.
I don't see how it could work even on the FPGA. The FPGAs from USRPs 1 and 2 start off with different clocks. How is it helpful to have each FPGA read its own clock and add an offset? The problem is you have no way to know the delta between the clocks unless you could guarantee that each device reads its clock at the same time. Doesn't seem possible if the 'common denominator' is the PC sending get() commands over Linux/Ethernet. And, if the PC is not the common denominator, what is? Does your problem allow for the devices to be linked by fiber in a White Rabbit timing scenario? If so, this could be used to sync the devices. _______________________________________________ USRP-users mailing list -- usrp-users@lists.ettus.com To unsubscribe send an email to usrp-users-le...@lists.ettus.com
