On Thu, Feb 3, 2022 at 5:02 PM David Raeman <da...@synopticengineering.com> wrote:
> > I’m working with an N320 and UHD 4.1, and I plan to use an external > reference clock (a 10MHz OCXO for reasons of RF phase stability) and the > radio’s internal GPSDO for timing (to synchronize capture start times > across radios). I found that “clock_source=external,time_source=gpsdo” is > not a supported sync_source combination. Taking a quick glance at the N320 > schematics, I’m speculating that GPS-synced timing is also dependent on > FPGA-REFCLK being slaved to the GPSDO, and not just the PPS, is that right? > Is there any viable way to accomplish the setup I described? > > > > It’s also not ideal how the set_clock_source/set_time_source API calls > behave in the case. I had originally been calling > set_clock_source(“external”) followed by set_time_source(“gpsdo”), which > both succeed. It took a lot of digging to figure out that the second call > is silently coercing the ref clock to be gpsdo, without any indication even > a debug print statement (in the MPM periph_manager code). > > > If you could start out with both 10MHz and PPS using GPS signal, set all clocks to the same time (e.g., zero) at the common PPS, and then switch to using external ref, it might be possible. My understanding is that the only thing the PPS is needed for is setting the common time. In other words, it's basically a trigger. Rob > >
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