Raspberry Pi 4

7c80, 7c81
store.mesanet.com/index.php?route=product/category&path=69_62

I downloaded the pricelist.

I think the cpu freq can be throttled without temperature rise.
so I think all users should fix thier cpu freq regardless of good coolers

because:

---

I've built the rpi4 system using JT's instructions.
I had a very nice cooler fan mounted. ( ice tower )
Then I ran it for 6 hours and got max 33uS with 4 glxgears.
No browser or video player on this build.
Then i checked randomly on the cpu freq and temp.
The temp remained 38-40 deg, but the freq occasionally went to 600mhz from the typical 1.5Ghz.
Even tho there is no terrible latency hit,
I imagine its not good for a realtime system to have the cpu frequency cut in half.

So, I wrote a bash script to log the freq and temp and let it run overnite.

#!/bin/bash
vcgencmd measure_clock arm >> report.txt
vcgencmd measure_temp >> report.txt

then i added it to crontab
*/5 * * * * /home/pi/report.sh

The next morning I saw infrequent freq throttling to 600 000 000 but never a high temp.
"""
frequency(48)=600117184
temp=38.0'C
"""

Then I checked some things
"""
$ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors
(NOTE I HAVE performance LISTED)
"""

then i checked max freq
"""
$ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
(NOTE MINE SAYS 1500000000)
"""

then to force that freq
pi@raspberrypi:~ $ sudo sh -c "cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq"

(afterthought: i see i might do similar for max_frew, but didnt do that yet )

then re-ran the logging cron job
and so far ( 30 entries) looks good
"""
temp=39.0'C
frequency(48)=1500398464
... snip
frequency(48)=1500345728
temp=41.0'C
frequency(48)=1500345728
temp=39.0'C
"""

i am now looking at how to make this pedal to the metal rule apply on next boot
as i think the cmd line fix above is not persistant

hth
tomp

You can set force_turbo = 1 in the [pi4] section of config.txt. this will stop the frequency changes and keep it at 1.5 GHz.

Another sample. I am running the latest kernel I've built and apparently have all governors present, currently ondemand, basicly at 600 with an occasional sortie to 700.

temps reported are a little higher as my fan is a 12 volt video card running on 5 volts. So while actually running linuxcnc and driveing the spindle at 100 rpms, its still at 600 with a 44C temp

I am only logging one latency overrun, the one that accompanies the linuxcnc startup. latency-test period= shows around 16 u-secs. I have set in config.txt a cpu_freq of 800 and force_turbo=1 but haven't rebooted to put it into effect. I thought I had the slower governors disabled but it appears I should recheck that and rebuild again. But I spent some time playing with the machine saturday an was pleasantly surprised, with this kernels lowered latency I was able to raise the rapids by around 40% z and 30% x. The pi4 has a lot more cajones than a pi3 ever displayed, and am well pleased with what I've seen. if a reboot puts it at 800, thats more than it needs to run this 2 axis lathe.
I have 2 threads, the basic 1 kliohertz servo, and one running at 200hz which is more than fast enough to handle the jog dials as I fitted 2 of them to replace the manual cranks that aren't there any more.

I'm pleased as can be.

tjtr33 please check your email, they are bouncing back.

JT