Re: Clarifications about PPS SHM content

[Martin Boissonneault]

Hi all,

Just a quick update: My jitter wasn't caused by ntpheat.
For the past few days, I turned off ntpheat and this bad ~700ns jitter (had ~265ns before) is continuing. I've been hunting the cause, the clue I have is a negative clock offset spike every 45min.

So far, I think it's the timeout period of the ADS-B decoders (~3888s). My current hypothesis is that there are so few planes up there that the feeders/decoders restart because they haven't seen a plane in 45min. So, I've shut down the ADS-B decoders/feeders.

If I'm right, I'll know in a few hours! Then, if it's fixed, I'll be able to brag about my NTP server being affected by COVID-19 ;-)

Stay safe,
Martin

On 2020-03-30 09:05, David J Taylor wrote:

> Hi!
>       
>       
>       I ran a test with ntpheat for a day, and my jitter StdDev jumped
>       from
>       
>       ~275ns to ~700ns. For my setup, it's NOT better.
>       
>       
>       I'll see if my physical "mod" will help: I stuck two layers of
>       sticky
>       
>       thermal pads on top of each other, covering both the CPU footprint
>       and
>       
>       the crystal, on the underside of the CPU. My idea is to better
>       conduct
>       
>       heat from the CPU to the crystal while reducing heat transfer
>       transfer
>       
>       to air. The pads have better thermal conductivity than air, but
>       being on
>       
>       top of components like a blanket should provide some isolation to
>       air.
>       
>       Heat should spread a bit better between nearby components and the
>       PCB,
>       
>       but I have nothing on top to wick heat away. If I had thicker pads
>       (mine
>       
>       are pretty thin), I'd try to put a piece of metal to spread heat
>       across
>       
>       the whole area.
>       
>       
>       My CPU usage is already 25%x4 cores, there is some heat there. I
>       just
>       
>       have to stabilize it across the xtal and prevent too much air
>       movement.
>       
>       
>       I will report back later!
>       
>       
>       Martin
>       
>       =========================================
>       
>       
>       Thanks for your initial report, Martin!  I look forward to further
>       tests. In the light of your tests, I've updated my Web page to
>       indicate that it's not a cure-all, rather a try-it-and-see
>       solution.
>       
>       
>       Cheers,
>       
>       David
>       
>