🛠 Surveiller température et fréquence CPU, piloter le ventilateur PWM

Objectives

Instrument the ROCK 3B (4× Cortex-A55 up to 2.0 GHz, RK3568 at 22 nm): read thermal zone temperatures, observe the actual frequency under load, and understand the 2-pin 1.25 mm fan connector (5 V PWM). Official temperature references: Community edition 0–60 °C, Industrial edition (RK3568J) −40–85 °C. >

Hardware

• Radxa ROCK 3B running Radxa OS, PD 12 V / 2 A power supply (a poor power supply simulates thermal throttling)
• Adhesive heatsink and/or 5 V fan on the 2-pin 1.25 mm connector
• sudo apt install stress-ng bc

Full code

# 1. Zones thermiques et températures (milli-°C)
paste <(for z in /sys/class/thermal/thermal_zone*/type; do cat $z; done) \
      <(for z in /sys/class/thermal/thermal_zone*/temp; do echo "scale=1;$(cat $z)/1000"|bc; done)

# 2. Fréquence réelle des cœurs sous charge
(stress-ng --cpu 4 --timeout 60s &) ; sleep 5
while sleep 2; do grep -H . /sys/devices/system/cpu/cpufreq/policy*/scaling_cur_freq; done

# 3. Politiques et seuils thermiques
grep . /sys/class/thermal/thermal_zone*/policy 2>/dev/null
sudo dmesg | grep -i -e thermal -e throttle

# 4. Ventilateur 2 broches : sous Radxa OS, vérifier rsetup (fan/thermal) ou
#    le contrôle PWM manuel du bus correspondant (pwmchip) — > 
#    l'exposition exacte du connecteur fan varie entre images constructeur.
ls /sys/class/pwm/

Expected verification

Under stress-ng --cpu 4, scaling_cur_freq rises towards 2.0 GHz and then stabilizes; without a heatsink, the frequency drops and dmesg may display throttling messages. With a heatsink/fan, the temperature caps lower and the frequency holds longer. Raw temp values are in milli-degrees (53000 = 53 °C).

Common errors

• Forgetting the division by 1000 on /sys/class/thermal/thermal_zone*/temp and panicking at "53000 °C".
• Sampling the frequency only once: it is an instantaneous value, so you must loop during the load.
• Blaming thermal issues when the power supply is too weak: re-test with the recommended 12 V / 2 A PD power supply.
• Reversing the polarity of the 1.25 mm fan or drawing more current than the 5 V connector can provide.
• Exceeding the Community edition range (max 60 °C ambient) in a closed cabinet: this is the use case for the Industrial edition rated at 85 °C.