am437x internal thermal sensor - bandgap not working, reading 0

Robert Woerle

I am trying to get the cpu temp via the bandgap module but it reads always 0

I basicly implemented this patch:

github.com/beagleboard/meta-beagleboard/blob/master/common-bsp/recipes-kernel/linux/linux-mainline-3.8/resources/0021-hwmon-add-driver-for-the-AM335x-bandgap-temperature-.patch

and added it to my dts.

So the bandgap module loads fine and access the regs as planned .. but nor the driver or even direct devmem access reads out anything else then 0

root@am437x-evm:~# devmem2 0x44e10448 w
b/dev/mem opened.
Memory mapped at address 0xb6fb0000.
Read at address 0x44E10448 (0xb6fb0448): 0x0000001E
root@am437x-evm:~# devmem2 0x44e10449 b
/dev/mem opened.
Memory mapped at address 0xb6f00000.
Read at address 0x44E10449 (0xb6f00449): 0x00

cat /sys/devices/44000000.ocp/44e10448.bandgap/temp1_input
0

Any hints ? There is nothing about this in the ERRATA or so

Regards Rob

over 8 years ago

0 Biser Gatchev-XID over 8 years ago

TI__Guru**** 393215 points

Hi Robert,

I will check with the factory team, but I think the bandgap is not available for user access.

0 Robert Woerle over 8 years ago in reply to Biser Gatchev-XID

Intellectual 380 points

Hi Biser

oh , if not , try to evaluate the possiblity to populate it. I would love to have that , knowing about a thermal shutdown and reading the core temp internally is priceless for many field applications of a industrial cpu range .

Thanks for your time

rob

0 Biser Gatchev-XID over 8 years ago in reply to Robert Woerle

TI__Guru**** 393215 points

Hi Rob,

I have confirmation from the factory that the bandgap is used internal test purposes and there is no plan to productize it at this point.

0 Robert Woerle over 8 years ago in reply to Biser Gatchev-XID

Intellectual 380 points

Dear Biser

I like to follow up on this topic. I see bandgap implementations in both am335x and dra7x in the ti kernel codes. Is this really true that am437x will miss that ?

0 Biser Gatchev-XID over 8 years ago in reply to Robert Woerle

TI__Guru**** 393215 points

The information I have from the factory team is that this sensor is not intended for end-user purposes.

0 Robert Woerle over 8 years ago in reply to Biser Gatchev-XID

Intellectual 380 points

Thanks Biser for the clarification. I will treat this a closed/answered then

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am437x internal thermal sensor - bandgap not working, reading 0