On Fri, 01 Nov 2013, Greg Troxel wrote:
But if NetBSD enables PPS on ucom, there's going to be an expectation that it is good enough for stratum-1 timekeeping, like PPS on real serial ports.I don't think there's any such expectation created. [...]People who expect the same as serial PPS are confused, and we are not responsible for that.
I think that PPS on a device with very high "interrupt" latency is sufficiently similar to PPS on a device with low interrupt latency that it deserves to have the same API. I don't think it even needs a sysctl to enable it.
I think that it just needs careful documentation, in ucom(4) and wherever we document the PPS API. Maybe the documentation for applications like ntpd should also warn against using PPS on USB interfaces.
--apb (Alan Barrett)