PPS undersampling

[Gary E. Miller]

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.

RGDS
GARY
---------------------------------------------------------------------------
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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