Most Stable Raspberry Pi? Better NTP with Thermal Management
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Most Stable Raspberry Pi? Better NTP with Thermal Management
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Re: Most Stable Raspberry Pi? Better NTP with Thermal Management
#2It's the good old OCXO - Oven Controlled Crystal Oscillator. But the heating element is the CPU. Fucking hilarious.
Re: Most Stable Raspberry Pi? Better NTP with Thermal Management
#3It's an SBC-scale OXCO. I half wonder if adding a larger heatsink, or even putting thermal mass around the existing oscillator could also help, or if the heating is more localized in the PCB itself.
Always fun new things to learn when doing something "simple" like setting up an NTP server!
Re: Most Stable Raspberry Pi? Better NTP with Thermal Management
#4I love this. Chasing perfection for perfection alone.
Re: Most Stable Raspberry Pi? Better NTP with Thermal Management
#5You might have even better precision if you stay away from CPU0 and also set idle=poll in your kernel command line. Lots of things (including other interrupts) often land on CPU0. It would not be my first choice for something where I wanted high timing precision.
Re: Most Stable Raspberry Pi? Better NTP with Thermal Management
#6It's an SBC-scale OXCO. I half wonder if adding a larger heatsink, or even putting thermal mass around the existing oscillator could also help, or if the heating is more localized in the PCB itself. Always fun new things to learn when doing something "simple" like setting up an NTP server!
> I half wonder if adding a larger heatsink, or even putting thermal mass around the existing oscillator could also help, or if the heating is more localized in the PCB itself.
That would likely make it worse. The trick here is that the other cores are running at essentially their maximum temperature and and will dynamically reduce their clockspeed if required to keep from going above that limit. In essence, the environment becomes actively temperature controlled. If the ambient heat goes higher, the cores clock lower, if it gets colder the cores clock higher (up to a point).
If you add too much heat dissipation, the total power used by those cores might not be enough to keep well above ambient.
Re: Most Stable Raspberry Pi? Better NTP with Thermal Management
#7Amazing project, great write-up. Would love to see a temperature graph as well! I'm wondering how good the PID controller here is working.
For future improvements, a cheap but effective win might be to put a temperature sensor on the oscillator (or two or three in various places). And use that to drive the PID loop.
Even if just experimental & not long term, it would be nice to have data on how strong the correlation is between the cpu & oscillator temperatures. To see their difference and how much that changes over time. Another graph! CPU vs txco (vs ambient?) temperatures over time.
Re: Most Stable Raspberry Pi? Better NTP with Thermal Management
#8It's an SBC-scale OXCO. I half wonder if adding a larger heatsink, or even putting thermal mass around the existing oscillator could also help, or if the heating is more localized in the PCB itself. Always fun new things to learn when doing something "simple" like setting up an NTP server!
I was thinking it might be nice to add some insulation around some the pi's enclosure, to reduce its cooling significantly. A little bit to tamp down any potential rapid fluctuations in the room's temperature (if someone opens a window, steps out of the bath, whatever). But more so that it could save a watt or two of power, by having the time-burner cores working much less.
You're right that this is a over-controller oscillator. The goal generally with ovens is to keep heat! (To an extent of course.)
Re: Most Stable Raspberry Pi? Better NTP with Thermal Management
#9It's an SBC-scale OXCO. I half wonder if adding a larger heatsink, or even putting thermal mass around the existing oscillator could also help, or if the heating is more localized in the PCB itself. Always fun new things to learn when doing something "simple" like setting up an NTP server!
> I half wonder if adding a larger heatsink, or even putting thermal mass around the existing oscillator could also help, or if the heating is more localized in the PCB itself. That would likely make it worse. The trick here is that the other cores are running at essentially their maximum temperature and and will dynamically reduce their clockspeed if required to keep from going above that limit. In essence, the envi…
Extreme power dissipation would keep temperature stable so that this whole setup might not be needed, though.
Author should experiment with liquid nitrogen ;) [1]
[11] https://www.xda-developers.com/liquid-nitrogen-cooling-raspb...
Re: Most Stable Raspberry Pi? Better NTP with Thermal Management
#10The related question is:
Is the Pi going the Pentium 4 route?