Persistent data in SVNS LPGPR when rebooting

[elinbage]

Hello!

I want to store some data in the SVNS LPGPR2, that is persistent after a reboot. I am using the IMX8M Mini.

I can write to the register 

u-boot=> mw 0x30370098 0xDEADBEEF
u-boot=> md 0x30370098 4
30370098: deadbeef 00000000 00000000 00000000 ................

But after a reboot the register has gone back to the default value and I don't know why. I have read about non-volatile storage and from that I have understood that it should preserve the value even if there is a absents of power. I assume it would be the same for secure non-volatile storage, what am I missing?

[Harvey021]

For backward compatibility with earlier version of SNVS, LPGPR0...LPGPR3 are aliased at the earlier offset of 90h and LPGPR0 is also aliased at its original offset of 68h.New software should access the GPR register at the preferred offset of 100h.

The GPR will be automatically zeroized when an enabled security event occurs, unless GPR zeroization is disabled via the GPR_Z_DIS bit in the LP Control Register. 

Best regards

Harvey

[elinbage]

Okey, I have the reference manual "i.MX 8M Mini Applications Processor Reference Manual, Rev. 3, 11/2020", I guess this is outdated since I can't find anything about new preferred offset 100h or how to change GPR_Z_DIS in the SNVS_LP Control Register. Where can I find a newer Reference Manual? Or how do i disable the GPR_Z_DIS?

[Harvey021]

You have to sign an NDA to obtain security reference manual for more details. you can apply for it from (Support | NXP Semiconductors)  if there is no valid NDA.

Best regards

Harvey