Most Stable Raspberry Pi? Better NTP with Thermal Management

In 2025, there are extremely efficient CPUs from Intel and Apple. Under 5W idle!

The old Intel CPUs were grotesquely inefficient. Every single generation of Raspberry Pi has been well under 5W idle. And just so it's clear, the author is using an old Raspberry Pi 3.

From TFA:

> The RPi 3B’s 19.2 MHz oscillator is physically located near the CPU on the Raspberry Pi board, so by actively controlling CPU temperature, we’re indirectly controlling the oscillator’s temperature.

Also note that the R.Pi can even be further optimised by switching off HDMI.

https://www.pidramble.com/wiki/benchmarks/power-consumption

https://www.jeffgeerling.com/blogs/jeff-geerling/raspberry-p...

Sure, that's what the chrony closed loop is already doing (the estimated residual frequency is pretty linear with temperature), but no matter how robust your closed loop is, it's strictly better to not have disturbances in the first place.

some ideas -

1. using a second hand single frequency Ublox LEA-M8T GNSS receiver is not a good idea in 2025 when a dual frequency GNSS receiver chip can be purchased online for as little as $20-30. buy one of those ublox ZED-F9P receivers with the 2018/2019 firmware, they get you the exact same timing performance as ZED-F9T with QEerr support. PPS jitter is going to drop from 20ns to less than 2ns after qErr compensation.

2. you can replace that highly unstable crystal oscillator with a $10 used OCXO + $20 PLL board and save that PID temperature controller to be used as the secondary oven for that OCXO. people have been doing that for Raspberry Pi for ages.

3. or you can configure your GNSS receiver to output a 10Hz signal from the PPSOUT pin so chrony can get 10 updates per second, GNSS receiver's internal TCXO is going to be more stable than raspberry Pi's crystal oscillator.

4. for more fun - just keep measuring the frequency drift vs. temperature change. a sample set of 24-48 hours of such measurements should be enough to figure out the tempco of that unstable crystal oscillator so you can get chrony to do the drift compensation. from memory, chrony supports such a temperature compensation lookup table to be specified.

good luck and have fun

> In 2025, there are extremely efficient CPUs from Intel and Apple. Under 5W idle!

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.

The Pi 3 can go passively cooled and maybe even without a heatsink at load, but the newer Pis can't. Judging by the progression from 3 to 4 to 5, they will reach P4 levels of heat in the name of speed around ... 7?

> And just so it's clear, the author is using an old Raspberry Pi 3.

Yes, the author has harder problems to solve than what I'm whining about. But my concern is a bit related.

> The Pi 3 can go passively cooled and maybe even without a heatsink at load, but the newer Pis can't.

The Raspberry Pi 4 can be used without a fan. They are packaged inside keyboards, but both the Raspberry Pi 400 and the Raspberry Pi 500 are passively cooled.