What does each temperature zone mean: AO, PLL, Thermal

Autonomous Machines Jetson & Embedded Systems Jetson Nano
1

I get that CPU and GPU are the temps of the CPU and GPU - thats easy. But what are the AO, PLL and Thermal temps?

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3

What’s the “Thermal temps” from?

AO means always on thermal zone and PLL means PLL part thermal zone.

4

What does Always On mean? The other temps seem to be always “on” as well.
What does PLL stand for? My old electronics days would call that a Phase Locked Loop. A device used to lock into a certain frequency in comms equipment.

And what about the “thermal” temp?

5

Not all thermal zones are powered with always-on rail. PLL is as you said, the PLL thermal zone is located near to PLL part.

What do you mean the “Thermal temp”? Where is it from? In general it is the temperature threshold set for the thermal zone.

6

Here’s the values reported by tegrastats:

PLL@34C CPU@39C PMIC@100C GPU@33.5C AO@41C thermal@36C

So what is PMIC - 100 degrees - is that the cutoff temp - which sensor is it measured on?
What is the “thermal” temp? The actual zone is called “thermal-fan-est”.

AO always seems to be the highest value.

8

Hi,

Sorry for the late reply

  1. PMIC die temperature only tells the status whether die temp has crossed the 120degC or 140degC thresholds. There is no register to read the actual PMIC die temperature. So, if these two thresholds are not crossed then we just assume 100degC, as it is below the lower threshold temperature. Until the 120degC threshold is crossed, PMIC die is in safe temperature. Once any of the two thresholds is crossed, then accordingly we report the PMIC die temperature as 120degC or 140degC.

  2. Please refer to the document and you shall find the answer of what is “thermal” temp.

https://docs.nvidia.com/jetson/l4t/index.html#page/Tegra%2520Linux%2520Driver%2520Package%2520Development%2520Guide%2Fpower_management_jetson_xavier.html%23wwpID0E04L0HA

->thermal-fan-est
Weighted average of CPU-therm, GPU-therm, & AUX-therm (3:3:4)

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9

Thank you I think that explains it except for AO. I understand from your attached link that it means it’s always on and the other systems do not report temps in certain situations. Where is the AO sensor situated? Why is it always higher than the other values?

10

Hi,

I cannot tell why it is always higher than other zones. But I could point out the sensor location to you.

AOTAG THERMAL_ZONE_AO → Co-locate with TDIODE in pad-ring

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