use c language get CPU Thermal Sensor temperature(TX1)

Autonomous Machines Jetson & Embedded Systems Jetson TX1
1

hello everyone：
I would like to use C language through the internal sensor to obtain the temperature of the cpu，rather than use “cat /sys/devices/virtual/thermal/thermal_zone*/temp ”。Can anyone give me a hint, what API interface can call?

2

You can use a pseudo file as a normal file.
Here is a quick attempt to do that :

#include <stdio.h>   /* for FILE, fopen, fread, fclose, printf and sprintf */
#include <stdlib.h>  /* for atof */

int main (int argc, char **argv) {
   FILE *filePtr;
   char therm_path[64];  /* 64 bytes buffer for building current pseudo file path */
   char readBuf[16];     /* 16 bytes buffer for reading ASCII encoded value from pseudo file */
   float temp;         
   for (unsigned int curZone = 0; curZone < 8; curZone++) {
      unsigned int readBytes = 0;
      sprintf(therm_path, "/sys/devices/virtual/thermal/thermal_zone%u/temp", curZone);
      printf ("Reading %s:   ", therm_path);
      filePtr = fopen(therm_path, "r");
      if (!filePtr) {
    	printf ("Error, failed to open file\n");
    	continue;
      }
      while (readBytes < 16) {
         int curRead = fread(readBuf + readBytes, 1, 16 - readBytes, filePtr);
          if (curRead > 0)
    	     readBytes += curRead;
          else 
             break; /* nothing more to be read */
      }
      fclose (filePtr);

      if (readBytes > 0)
         *(readBuf + readBytes - 1) = 0; /* Remove last char '\n' */
      printf("[%s]  ", readBuf);

      temp = atof(readBuf);
      temp /= 1000.f;
      printf("%.02f\n", temp);
   }

   exit(0);
}

[EDIT: Output below comes from a TX2]

gcc -o test_thermal test_thermal.cpp
./test_thermal 
Reading /sys/devices/virtual/thermal/thermal_zone0/temp:   [41000]  41.00
Reading /sys/devices/virtual/thermal/thermal_zone1/temp:   [41000]  41.00
Reading /sys/devices/virtual/thermal/thermal_zone2/temp:   [47000]  47.00
Reading /sys/devices/virtual/thermal/thermal_zone3/temp:   [41000]  41.00
Reading /sys/devices/virtual/thermal/thermal_zone4/temp:   [41000]  41.00
Reading /sys/devices/virtual/thermal/thermal_zone5/temp:   [41000]  41.00
Reading /sys/devices/virtual/thermal/thermal_zone6/temp:   [41250]  41.25
Reading /sys/devices/virtual/thermal/thermal_zone7/temp:   [100000]  100.00
3

Hi Honey_Patouceul:
can you explain this “100” ? thanks.
Reading /sys/devices/virtual/thermal/thermal_zone0/temp [38500] 38.50
Reading /sys/devices/virtual/thermal/thermal_zone1/temp [35500] 35.50
Reading /sys/devices/virtual/thermal/thermal_zone2/temp [31000] 31.00
Reading /sys/devices/virtual/thermal/thermal_zone3/temp [33000] 33.00
Reading /sys/devices/virtual/thermal/thermal_zone4/temp [100000] 100.00
Reading /sys/devices/virtual/thermal/thermal_zone5/temp [35750] 35.75
Reading /sys/devices/virtual/thermal/thermal_zone6/temp [34000] 34.00
Reading /sys/devices/virtual/thermal/thermal_zone7/temp [33250] 33.25
zone0
AO-therm
zone1
CPU-therm
zone2
GPU-therm
zone3
PLL-therm
zone4
PMIC-Die
zone5
Tdiode_tegra
zone6
Tboard_tegra
zone7
thermal-fan-est.38

4

Not really, but it looks normal for PMIC-Die.
You may check: [url]https://devtalk.nvidia.com/default/topic/957806/jetson-tx1/thermal_zone4-reports-100-degree-celcius-/[/url]

The output log I sent was in fact run on a TX2, sorry for the confusion.
On TX2, there are 9 thermal zones and their order is different:
0: BCPU-therm
1: MCPU-therm
2: GPU-therm
3: PLL-therm
4: AO-therm
5: Tboard_tegra
6: Tdiode_tegra
7: PMIC-Die
8: thermal-fan-est

5

thank you very much。
AO-therm？can you explain AO-therm ?I find many source，but not

6

Hi sgh, AO-therm means always-on thermal zone.

7

Could you please provide the recommended range of each zone?

8

I don’t really know what is recommended, but at first you may have a look into various trip points in sysfs :

find /sys/devices/virtual/thermal -name 'trip_point*'
9

i have to guess - the original returned temperature value is reported in units of “milli degrees Celsius”, aka: m°C.

10

thanks for the proposal. its doing a nice job for what it was written (up to 8 queries from 0 to 7, if existing).

now just for hinting other non-skilled readers and coding beginners:

  • i see the issue, that the used buffer might overrun in cases where the unexpected will happen and a “long” answer is received.
  • the codes are probably pure c, no c++/cpp needed. (but have not checked it on my own.)