SNVS/Tamper questions

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SNVS/Tamper questions

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algernonarbuthn
Contributor II

I have several questions about i.MX6UL SNVS and tamper:

* Processor is the G3 version.

* I am writing code in U-Boot, using SPL.

* I am running a secure setup, so SRK fuses are burned and U-Boot and U-Boot SPL are signed.

* In the U-Boot CSF scripts, I have unlocked the SNVS (LP SWR and ZMK WRITE).

* I need to implement active tamper.

My code works somewhat. The SNVS comes up as secure in trusted state. I can set ZMK, time etc. Setting the SW_LPSV generates a violation and ZMK is zeroed etc. However I have some issues & questions:

1. If I disconnect and reconnect the SNVS coin cell supply, an SNVS POR is forced, as expected. The SNVS PGD bit is set, also expected. However, I cannot clear the PGD bit - it always remains set. I can reset PGD by loading a signed image that does not unlock SNVS, so there is no problem with the battery circuit. The ROM code manages to reset PGD. How should I do this?

2. What SNVS initialisation does the ROM code carry out: a) if SNVS is not unlocked; b) if SNVS is unlocked.

3. If I read the LFSR parameter registers (LPATnCR), I always read zeros. If I write non-zero values to these registers, I always read back zeros. Is this expected?

4. Active tamper functionality appears in both the 'normal' SNVS registers and the LP_SNVS registers. For example routing control (LPATRC1R, LPATRC2R in SNVS vs ETRCTRL in LP_SNVS). If I leave DryIce disabled (DRYICE_EN=0), do the SNVS registers take precedence? Or do I have to enable DryIce and use the LP_SNVS registers?

5. The DryIce Trim Value Register documentation states that the trim values should be read from OCOTP. I assume these are set during manufacture? I can't find any reference to these fuse values in the documentation.

6. Do you have any SNVS sample code?

Any light you can throw on these questions would be appreciated.

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Yuri
NXP Employee
NXP Employee

Hello,

  Sorry, but the information you are requesting is treated as confidential info at this time and requires a signed NDA

(Non-Disclosure Agreement). Naturally, we cannot discuss this with you in public anyway, this requires to be handled as a Service Request (SR).

Have a great day,
Yuri

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Yuri
NXP Employee
NXP Employee

Hello,

  Sorry, but the information you are requesting is treated as confidential info at this time and requires a signed NDA

(Non-Disclosure Agreement). Naturally, we cannot discuss this with you in public anyway, this requires to be handled as a Service Request (SR).

Have a great day,
Yuri

-------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-------------------------------------------------------------------------------

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algernonarbuthn
Contributor II

Hi Yuri,

SNVS is documented in the RM, so I presumed public discussion would be fine.

How do I raise a Service Request (SR)?

Thanks,

Bill

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Yuri
NXP Employee
NXP Employee

Hello,

  There are several questions in Your request, in particular regarding boot ROM.

To create request (ticket) :

Support|NXP 

Regards,

Yuri.

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