RPI4 clock speeds and serial port ( temperatures idle and -j4 buildworld buildkernel )

[Mark Millard]

On 2021-Mar-19, at 12:50, bob prohaska <fbsd at www.zefox.net> wrote:

> On Fri, Mar 19, 2021 at 08:07:36PM +0100, Klaus K??chemann wrote:
>> 
>> 
>>> Am 19.03.2021 um 18:43 schrieb bob prohaska <fbsd at www.zefox.net>:
>>> 
>>> 
>>> So my figures (~17 hours) seem reasonable for a default clocking.
>>> I thought maybe I'd done something wrong.
>> 
>> 
>> 17 hours sounds too long, you can simply enable ???powerd??? in rc.conf for automatically 
>> scaling from idle 600 to max. 1500 (non overclocked).
>> So, when you hit make -j4 xyz, you will see all cpus running @~100% and 
>> Powerd will then automatically set the clock speed  to 1500 on all 4. 
>> 
> 
> I've enabled powerd and rebooted, console messages report that powerd
> started with no explicit errors. A -j4 buildworld is running now.
> 
> Should I expect to see powerd mess up the default mini-uart serial console?
> So far, it hasn't with top reporting less than 1% idle. That's confusing....

Avoid confusing the arm_freq with the core_freq (core is
VPU, not arm). The two are independent (up to the RPi*
firmware's dynamic frequency clocking logic anyway).

I've already reported that the documentation indicates
that the core_freq is not supposed to be changed on the
RPi4's. (The use or not of 2 features controls the exact
value that it must be and the firmware appearently
already deals with tracking those: hdmi_enable_4kp60 and
enable_tvout .)

https://www.raspberrypi.org/documentation/configuration/uart.md

reports that the mini UART is tied to the core_freq, not
the arm_freq.

So on a RPi4B where hdmi_enable_4kp60 and enable_tvout are
not changing, the core_freq assignment should also not be
changing, no matter what arm_freq changes are being made.

That leaves core_freq_min for the RPi* firmware's dynamic
frequency clocking. The default is 250 or 275, apparently
depending on the status of hdmi_enable_4kp60, 275=550/2,
when hdmi_enable_4kp60 is enabled, otherwise 250 is used
(for the core_freq 500 and 360 cases). [The 360
(enable_tvout) case is not well documented for
core_freq_min .]

It is not clear when the dynamic frequency clocking
logic would adjust the actual core frequency but
it appears that the official way to avoid messing
up the mini UART is to assign: core_freq_min to
match the value of the core_freq setting so that
no other setting is available.

If the mini UART is working in your context and you
have not disabled Bluetooth or redirected the UART
Bluetooth is using, what I infer is that the RPi*
firmware's dynamic frequency clocking happens to
not be adjusting the live core_freq significantly
in your context.


Also of note . . .

QUOTE
Pi 4 - six UARTS

The Raspberry Pi 4 has four additional PL011s, which are disabled by default. The full list of UARTs on the Pi 4 is:

Name	Type
UART0	PL011
UART1	mini UART
UART2	PL011
UART3	PL011
UART4	PL011
UART5	PL011
END QUOTE



===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)