RPI4 clock speeds and serial port

[tech-lists]

On Thu, Mar 18, 2021 at 11:07:36AM -0700, bob prohaska wrote:
>
>72 C is rather toasty 8-)

it is, but it's been running like this fine for months. The machine also
builds some 500 ports with poudriere. It's never throttled down due to
heat; the ability to do this is I think outside of freebsd itself.
Importantly [1] for me, the speed isn't nailed up with a boost statement in
config.txt, so it can throttle back should the need arise.

>Maybe on FreeBSD it doesn't matter. Pi-related sites report that the
>mini-UART baudrate is tied to the clock of the GPU, if that changes
>the baudrate changes too. It wasn't clear to me if the speed-changes to
>config.txt affected the GPU clock. Apparently not, at least in FreeBSD.

The cable I used was a FTDI usb <> tty cable; it has endings 
that go over pins on the gpio. The FTDI chip in the usb end of the cable 
handles the speeds (i think/not sure) but would make sense because
there's no dtoverlay statement regarding uarts. I *do not* connect the
power wire. The connecting machine is also a freebsd machine (amd64)

I think connected in this way that this uart must be hardware and the
disable-bt statement has something to do with it.

[1] as fast as possible with 100% reliability, 24/7
[2] i'm sure you know, but bear in mind that not all silicon is equal, 
so some might not get to 2GHz without reliability issues

-- 
J.
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