[time-nuts] Raspberry Pi 4 oscillator replacement

[Poul-Henning Kamp]

--------
Hal Murray writes:
> 
> phk at phk.freebsd.dk said:
> > I dont know if the datasheet for the Rpi4 is available to check what the
> > requirements are, but you should probably expect to need some kind of PLL
> > chip to deliver a clean 54 MHz on the RPi4, locked to your external
> > frequency. 
>
> Plan B would be to avoid the 10=>54 PLL chip by reprogramming the software 
> that sets up the internal PLLs to run off 10 MHz rather than 54MHz.  That may 
> not be possible.  It depends on how the clocking inside the ARM chip is setup.

One of the big problems with the RPi family is that only a skeleton
datasheet has been made available - because: Qualcom magic sauce
recipe or similar verbiage..

I've heard a lot of gripes about precisely the clock circuits being
underdocumented, but I have deliberately stayed well clear of the
details.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.