imx8mm TMU not working in uboot

[borysszefler]

I have imx8mm on custom SOM and I'm running nxp uboot_imx(lf_v2022.04). Internal temperature sensor is not working as expected on multiple tested devices.
It displays only this string without actual temperature value:

CPU: Industrial temperature grade (-40C to 105C)

Uboot debugging showed that probably temperature value is out of range. (sensor range is 10-125). Return code of thermal_get_temp function (cpu.c) is -22(EINVAL).

I tried to read registers and the output is:

TMU_TSCR register value: 2147483657
TRITSR register value: 0

TSCR suggests that value is beyond range.

What can cause this issue?

[borysszefler · Accepted solution]

It turned out that I had wrong resistor value on TSENSOR_RES_EXT line. Solution was found on this old thread https://community.nxp.com/t5/i-MX-Processors/thermal-zone0-Resource-temporarily-unavailable/td-p/108....

I tried to confirm this but could not find this information in hardware design guidelines nor other imx8mm documentation.