PPS undersampling

Gary E. Miller gem at rellim.com
Wed Aug 31 06:33:09 UTC 2016

Yo Hal!

On Tue, 30 Aug 2016 23:24:26 -0700
Hal Murray <hmurray at megapathdsl.net> wrote:

> > Hm. I think I get it - and you've just added a pretty powerful
> > reason to eventually pull the refclocks into a separate daemon by
> > telling me I need to get ntpd itself out of the PPS-watching
> > business entirely in order to get rid of that timer.   
> The reason I want to get rid of the every-second timer is to save
> power when operating on battery with no refclocks.

Saving power is good, but I suspect the extra power is minimal.  I
hace USB power meters, so we can measure this.

> If you have a PPS, you have to take an interrupt every second.

No, every 500 millisecond.

>  I'm
> not a wizard on that area.  It would be interesting to know if you
> can get useful interrupt responses when starting from a power-save
> mode.  Similarly, can you wakeup in time to get data from a serial
> port without dropping any characters?  It may be that power-save just
> won't happen if you are using refclocks.

Easy to test, when we have a knob to twist.  It would depend a lot on the
mode the CPU is in.  I always set governor=performance, so I would see no
change in power.

> Moving the PPS processing out of ntpd doesn't change any of that.

True, whether it is on gpsd or ntpd it should be similar power.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588
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