Hi Gabs, everyone, On 2016-10-21 1:53:55, Gabs Ricalde wrote:
The events can be timestamped by polling the PPS and event pins and using the cycle counter. A better approach would be to use the 100 MHz eCAP timers. The Beaglebone has two accessible eCAP pins, the PPS goes to one and the event goes to the other. The counters can be synchronized so the event timestamps can be referenced to the PPS timestamps.
This is a great idea, actually. At the moment, I'm using a BBB which I feed 24 MHz to tclkin, generated from a rubidium oscillator. The tclkin is used on run one of the dmtimers in capture mode for GPS PPS, so that gives about 42ns resolution. Using Dan Drown's Hardware Capture Driver (on Github) this 24MHz is set as the system clocksource. Works really well, but the 42ns resolution is a bit poor (or maybe I'm a time nut).
The eCAP runs from sysclk which I think is 200MHz on the BBB, and would provide 5ns resolution. Unfortunately the eCAP counter seems to only get input signals from the master clock, so it's not easy to provide them with a better input clock. But using them as a start/stop setup with the PPS from GPS as one input, and another PPS derived from a Rb would work quite nicely. In fact, that division by 24e6 from the Rubidium could probably be done by a second dmtimer also clocked from tclkin, keeping the parts count low.
Does that sound feasible? Regards, Paul Boven. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
