Random delays(upto 6 minutes) after closed the board for secure boot.

[krishnanpv]

Hi,

I have enabled Secure boot on i.MX6 Dual Lite custom board. I have enabled RNG_TRIM fuse and closed for secure boot. However, I see a strange behavior like occasionally  the board is not able to boot up. TThis behavior observed in only on the boards which are closed for secure boot. The board has PMIC chip to  control the supply of various voltage levels.

I have gone through the datasheet  (Section 4.3.2.2 LDO_2P5 ( In i.MX6 Dual Lite datasheet)) that  mention about  the voltage requirement. Can anyone experienced similar  problems? I am particularly interested in the voltage levels and clocks needed for secure boot and OCOTP controller.

Thanks in Advance,

Krishnan.

[krishnanpv]

Hello Yuri,

In the application note, it says deferring the instantiation of RNG  is a recommended option. This can be achieved by adding below lines in CSF configuration.

[Unlock]

Engine = CAAM

Features = RNG

However the below line in the AN4581 made me little obscure.

"This does not affect HAB-signed or encrypted boot features. Until the device is closed, HAB does not instantiate the RNG at boot."

In my case, I have closed the device for secure boot. So will the deferring of  RNG instantiation will reduce the boot time in my case?

Thanks,

Krishnan.

[Yuri]

Hello,

  Since Your device is closed, HAB does  instantiate the RNG at boot and it

may take some time. For Linux it also will take some time, but we can hope

smaller.  

Regards,

Yuri.

[Yuri]

Hello,

  Please refer to section 3.3.2 (RNG Trim fuses) of app note AN4581,

Secure Boot on i.MX50, i.MX53, and i.MX 6 Series using HABv4, Rev. 1, 10/2015

https://www.nxp.com/docs/en/application-note/AN4581.pdf 

Have a great day,
Yuri

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