Writes to SNVS_LPCR from either uboot or linux do not persist after a power cycle

[todd_hb]

I need to change the debounce and on time fields for the power on event.  I've tried

mw.l 20cc038 00300020

from uboot, which does update the register.  But when I power cycle and read the register again, it is back to its default value, 0x00000020.

I've also tried /sbin/devmem to write this register from linux, with the same result.

Is there something I need to do before or after this write to make it persist after a power cycle?

[todd_hb]

Some additional details, this is an imx6ulz. U-Boot 2018.03, and Linux 4.14

[igorpadykov]

Hi todd_hb

regarding "data persist after a power cycle" one can check if backup battery/coin

was attached to VDD_SNVS_IN and was within voltage range defined in

Table 9. Operating ranges i.MX 6ULZ Applications Processors for Consumer Products

check it with oscilloscope during power cycles.

Best regards
igor

[todd_hb]

I'm getting the sinking feeling that you're telling me that the Secure Non Volatile Storage peripheral isn't actually nonvolatile.  Are these registers only retained as long as the VDD_SNVS_IN is within the ranges in the table you pointed to? 

[igorpadykov]

>I'm getting the sinking feeling that you're telling me that the Secure Non Volatile

>Storage peripheral isn't actually nonvolatile.

right

>Are these registers only retained as long as the VDD_SNVS_IN is within the ranges

>in the table you pointed to?

yes

Best regards
igor