🛠 Surveiller la température et l'alimentation du TDA4VM

Objectives

Learn how to read the on-die temperature sensors of the TDA4VM SoC, understand the order of magnitude of power consumption measured in the System Reference Manual (idle U-Boot 210 mA, kernel boot peak 460 mA, kernel idle 350 mA, which is approximately 1.75 W at 5 V), and size the power supply and heatsink before loading the board.

Hardware

• 1 BeagleBone AI-64 with heatsink (the board weighs 192 g with the heatsink mounted — it is there for a reason)
• 1 high-quality 5 V / 3 A power supply (the SRM explicitly requires this)
• Optional: USB power meter, ventilated case for comparison

Complete code

# Identité et capteurs thermiques (les capteurs sont on-die uniquement)
cat /proc/device-tree/model
for z in /sys/class/thermal/thermal_zone*; do
  echo "$z type=$(cat $z/type) temp=$(cat $z/temp) (milli-°C)"
done

# Montée en charge contrôlée : 5 minutes de stress sur les 2 Cortex-A72
sudo apt install stress-ng
sudo stress-ng --cpu 2 --timeout 300 &
watch -n 2 'cat /sys/class/thermal/thermal_zone*/temp'

# Journal thermique : throttling ou seuils atteints ?
sudo dmesg | grep -iE "thermal|trip|throttl"

Expected verification

Temperatures rise progressively during the stress test and then stabilize (plateau) with the heatsink in place; values are expressed in thousandths of a degree (45000 = 45 °C). No throttling messages in dmesg during normal usage. When the stress test stops, the temperature drops slowly.

Common errors

• Reading “45000” and panicking: this is the milli-°C unit, not millivolts.
• Running the board without a heatsink or in a closed case: the TDA4VM has no fan and no external sensor, only on-die sensors.
• Powering via a simple PC USB port: the boot peak already exceeds 460 mA before any application load; brownouts manifest as random lockups at boot (see issue #43 on the LPDDR4 bring-up).
• Believing in a published commercial threshold: the SRM does not provide a commercial temperature range; for industrial deployment, refer to the TI TDA4VM datasheet.
• Confusing thermal zones: several thermal_zone entries exist (A72, DSP...), identify the correct one using the type field.