hw.cpufreq.sdram_freq displays as -1094000000 for RPi4B booted (via u-boot) with sdram_freq_min=3200

[Mark Millard]

https://www.raspberrypi.org/documentation/configuration/config-txt/overclocking.md

documents default values for the RPi4B as:

sdram_freq:    3200
sdram_freq_min: 400

(in MHz). (It documents not being able to increase (overclock)
sdram_freq as well.)

So I tried sdram_freq_min=3200 in config.txt and
it seemed to work nicely based on some benchmark
results.

But . . .

FreeBSD mishandles the display of the value that results
when it is this large:

hw.cpufreq.sdram_freq: -1094000000

which for 32-bits 2s complement looks to be: 0xBECAE280
and that, as unsigned, turns back into decimal as: 3,200,967,296

Prior to the sdram_freq_min=3200 use I saw only:

hw.cpufreq.sdram_freq: 400000000

So it seems to be a signed-interpretation problem for
sufficiently large values and otherwise seems okay
for value display.

(It is unclear why I never saw larger values other
than by adjusting sdram_freq_min in config.txt or
by direct sysctl hw.cpufreq.sdram_freq assignments.)


Somewhat related note:

One point that I'm unsure of is:

hw.cpufreq.voltage_sdram_p: 1100000
hw.cpufreq.voltage_sdram_i: 1100000
hw.cpufreq.voltage_sdram_c: 1100000

The config.txt versions of those are documented on:

https://www.raspberrypi.org/documentation/configuration/config-txt/overclocking.md

as having a default of 1.2v on all models, not 1.1v.
It is possible that these would need adjustment, not
that I've seen evidence of such yet. (Which is good:
I prefer to leave as much automatic as is reasonable
for my experiments.)

In the config.txt file these are over_voltage_sdram_c,
over_voltage_sdram_i, over_voltage_sdram_p and have the
-16..8 range specifying teh nubmer an ddirection of
0.025v steps from the default. 0 is listed as having
1.2v as its matching voltage. There is a
over_voltage_sdram that sets all 3 at once. But
hopefully I'll not have to fiddle with these.

Should FreeBSD have defaults of:

hw.cpufreq.voltage_sdram_p: 1200000
hw.cpufreq.voltage_sdram_i: 1200000
hw.cpufreq.voltage_sdram_c: 1200000

(so over_voltage_sdram=0 instead of over_voltage_sdram=-4
in config.txt terms)?

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