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Most Stable Raspberry Pi? Better NTP with Thermal Management

austinsnerdythings.com

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Re: Most Stable Raspberry Pi? Better NTP with Thermal Management

#61

Post by nottorp »

sceptic123 wrote: post #56
esskay wrote: post #35

Earlier quoted context omitted.

It's already there really. It's heat output on the 4 and more so the 5 benefits from active cooling. The good news is the pi is practically pointless as a product for most people these days, and vastly better options are available cheaper, so unless you genuinely need the gpio theres little reason to buy one - very much their own fault for focusing on commercial applications but the Pi 5 as a product is practically p…

What are the cheaper options for e.g. running a media centre?

Probably second hand intel/amd boxes.

Re: Most Stable Raspberry Pi? Better NTP with Thermal Management

#62

Post by geerlingguy »

throwaway81523 wrote: post #18

I wonder about using an RPI Pico for this instead, using the Pico's synchronous PIO gizmo to intercept the PPS pulses.

There was a discussion about this on the time-nuts mailing list that was enlightening; tldr was it's not going to get to the same accuracy as you'd expect compared to a dedicated timing circuit (like a good GPSDO), but it would be a fun learning exercise.

Re: Most Stable Raspberry Pi? Better NTP with Thermal Management

#63

Post by geerlingguy »

heresie-dabord wrote: post #60
echelon_musk wrote: post #59

Earlier quoted context omitted.

> I don't think Intel has any "efficient" CPU that can go passively cooled at load though. Maybe Apple can do it for the low end SoCs. Does the N100 not fit this criteria?

The N100 requires active cooling.

Technically it can work with passive cooling. Just, you need a pretty hefty heatsink in comparison to other SoCs.

Re: Most Stable Raspberry Pi? Better NTP with Thermal Management

#64

Post by sgarland »

nottorp wrote: post #24
mort96 wrote: post #22

Earlier quoted context omitted.

What is this even supposed to mean? What's "the Pentium 4 route"?

I'm an old fart :) Intel tried to scale frequency up with the Pentium 4 in the name of performance, and it ended up extremely hot and power hungry. Just like some high end CPUs now, but then it applied to every model from Intel. I suppose you don't remember when a Raspberry Pi could run fine even without a heatsink, let alone active cooling. That's more recent than the Pentium 4.

Thanks for giving me yet another reminder that I’m old. I caught the reference immediately and thought nothing of it, and then this shattered that.

The early ‘00s were a wild time. Intel boldly stating they expected to get the P4 up to 10 GHz, AMD having to assign clock speed equivalence ratings for their chips… I also remember thinking the P4EE was insanely priced ($1000, or about $1700 in 2025 USD), but now we have >$10K Threadrippers.

Re: Most Stable Raspberry Pi? Better NTP with Thermal Management

#65

Post by auspiv »

Austin from austinsnerdythings.com here! Posted this last night and went to sleep. Definitely didn't expect to wake up to it #1 on HN this morning!

Some notes that weren't included in this post:

I do have my LEA-M8T generating time pulses at 16 Hz, with a dpoll of -4 in the chrony config. The poll interval of 16 seconds means it gets 256 samples which also improved the stability.

I do also have that mentioned BH3SAP GPSDO sitting next to me on my desk. I had Claude update the firmware to allow "flywheel" behavior so it continues to generate pulses in the absence of GPS PPS. That's coming in another post. Also had Claude update the firmware to spit out TSIP (trimble proprietary protocol) info for lady heather.

Going to go through the comments and answer a couple other things I see.

Happy to answer any other questions!

Re: Most Stable Raspberry Pi? Better NTP with Thermal Management

#66

Post by auspiv »

jsolson wrote: post #5

You 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.

Worth a shot! I'll give it a go later today.

Re: Most Stable Raspberry Pi? Better NTP with Thermal Management

#67

Post by auspiv »

boricj wrote: post #52

Instead of dedicating an entire Raspberry Pi with fancy pinning and temperature management by burning CPU time, wouldn't a micro-controller and a precise external oscillator fare better for time-keeping stability? I would assume that a STM32 discovery kit running a NTP server on its Ethernet port could probably do better.

I do have that as well, but haven't done a write up on it yet. It was a $70 GPSDO from eBay (BH3SAP variant running Fredzo firmware with some changes to enable flywheel (generating pulse in absence of GPS PPS)). I have verified it can feed the Pi for NTP. Believe the STM32 driving the GPSDO can as well but it has no ethernet capability as-is

Re: Most Stable Raspberry Pi? Better NTP with Thermal Management

#68

Post by auspiv »

avidiax wrote: post #20

Why not put a resistor (for heating) and a bit of foam insulation on the crystal? This is way more direct than spacebar heating. You could also add a transistor attached to the resistor and a GPIO and use the clock drift as a proxy for temperature. PID is probably enough but since you have a 24 hour cycle you could calculate a baseline heating schedule.

I did this at one point, putting the pi directly on some packing foam. It for sure dampened the ambient effects but really I just need to stick the whole Pi in a temperature controlled chamber.

Re: Most Stable Raspberry Pi? Better NTP with Thermal Management

#69

Post by auspiv »

anonymousDan wrote: post #23

Couldn't you model the effect of temperature on clock drift and try to factor that in dynamically (e.g. using a temperature sensor) instead of burning CPU unnecessarily?

Chrony does have ability to do temperature compensation. I've done this and need to do a write up on it. It's not super easy to keep all the parts working together. Basically you feed chrony a table of temperatures and expected clock frequency and it subtracts it out.

Re: Most Stable Raspberry Pi? Better NTP with Thermal Management

#70

Post by esskay »

nottorp wrote: post #61
sceptic123 wrote: post #56

Earlier quoted context omitted.

What are the cheaper options for e.g. running a media centre?

Probably second hand intel/amd boxes.

yup bingo, you can pick up vastly better devices than a pi for quite literally half the price now.
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