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

[Mark Millard]

On 2021-Mar-19, at 11:13, Mark Millard <marklmi at yahoo.com> wrote:
> 
> On 2021-Mar-19, at 10:43, bob prohaska <fbsd at www.zefox.net> wrote:
> 
>> On Thu, Mar 18, 2021 at 10:14:26PM -0700, Mark Millard wrote:
>>> 
>>> World build completed on Thu Mar 18 21:31:44 PDT 2021
>>> World built in 29705 seconds, ncpu: 4, make -j4
>>> . . .
>>> Kernel build for GENERIC-NODBG completed on Thu Mar 18 22:10:02 PDT 2021
>>> Kernel(s)  GENERIC-NODBG built in 2298 seconds, ncpu: 4, make -j4
>>> 
>>> So somewhat under 9 hours.
>>> 
>> 
>> So my figures (~17 hours) seem reasonable for a default clocking.
>> I thought maybe I'd done something wrong.
>> 
>> For now I'll leave the clocking alone. But some puzzles remain:
>> It appears that the CPU and the GPU have separate clocks. Can they
>> be set separately, and does the GPU have any practical effect on
>> FreeBSD's behavior once boot is complete? 
> 
> See:
> 
> https://www.raspberrypi.org/documentation/configuration/config-txt/overclocking.md
> 
> It says that setting gpu_freq sets core_freq and also says:
> 
> QUOTE
> Changing core_freq in config.txt is not supported on the Pi 4
> any change from the default will almost certainly cause a
> failure to boot.
> END QUOTE
> 
> and:
> 
> QUOTE
> It is recommended when overclocking to use the individual
> frequency settings (isp_freq, v3d_freq etc) rather than gpu_freq,
> as since it attempts to set core_freq (which cannot be changed on]
> the Pi 4), it is not likely to have the desired effect.
> END QUOTE
> 
> There is more about the relationships to hdmi_enable_4kp60 and
> enable_tvout.

Back to temperature. See:

https://www.raspberrypi.org/documentation/hardware/raspberrypi/frequency-management.md

It indicates that 85C is the maximum temperature,
though lower figures can be set. It also reports
that a form of throttling starts at 80C by default.

The RPi3B+ also has a soft limit that changes the 1.4GHz
to 1.2 Ghz and the operating voltage is slightly reduced:
configurable temp_soft_limit but by default 60C.

For the RPi4B, "there is currently no soft limit defined".


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