[time-nuts] Raspberry Pi 4 oscillator replacement

[ASSI]

Avamander wrote:
> I was wondering if anyone here has replaced the 54 MHz oscillator on the
> Raspberry Pi 4 with a GNSS-disciplined rubidium standard?

The same things as replacing the XTAL on an RPi 1…3 I'd guess.  So, you need 
to remove the XTAL (hot air rework station), figure out which pin you need to 
feed the external clock into (the "return from XTAL" path), and actually 
create a rubidium stabilized 54MHz (using a clock synthesizer like the SiLabs 
SI53xx series, for which you can get breakout boards rather easily).

> An overkill
> upgrade, but is technically doable? What hardware would it take in addition
> to a GNSS-disciplined rubidium standard and a Pi 4?

Not much, see above.

However you'll probably find that it really is overkill and you can get much 
of the same end result more easily or much cheaper.  For instance a good OCXO 
or even TCXO would already get you the sort of stability that the other 
sources of timing uncertainty produced by the whole SoC / OS interaction start 
to dominate.  I haven't gotten myself a Pi4 yet, but I expect that self-
ovenization would still work more or less the same as with the earlier models, 
so you might not even need to touch the XTAL.


Regards,
Achim.
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