What i.MX6ULL security functions need RTC_XTAL?

[m_c]

Customer would like to using external RTC instead of internal, therefore there will not having RTC_XTAL clock when power off. So what i.MX6ULL security functions need RTC_XTAL clock when power off?

[igorpadykov · Accepted solution]

Hi m.c.

> what i.MX6ULL security functions need RTC_XTAL clock when power off?

security functions will not be affected.  Also on-chip ring oscillator is automatically engaged

in absence of external crystal.

Best regards
igor
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[andysc_liu]

Hi igor

If our design without power to SNVS when power off, dose the on-chip ring oscillator still work?

[TomE]

This has been answered. Obviously when there's no power supplied to the chip it can't work. It isn't like the i.MX chips have internal (nuclear?) batteries. Maybe you're wanting to know what the SNVS pin has to be connected to in a design without a battery? It has to be connected and it has to be the first power rail up in the power on sequence. Refer to the documentation for correct power sequencing and voltage levels.

HOWEVER there's another point that might cause you problems. It is very likely that these i.MX chips won't work properly unless there's an external 32 kHz crystal installed. It doesn't matter that you don't need an RTC in your design as that's not all the 32 kHz is used for. It is the master clock for the DRAM Reset for instance. You would assume the "Ring Oscillator" should take over if it isn't installed, but that's not the case. Basically the Sabre boards are the "reference", they have that crystal installed, and so not many tests have been run on a design that doesn't have the crystal.

Here's a previous post that you should read on this subject.

https://community.nxp.com/message/1069787 

We're using a design that has TWO 32 kHz crystals on it. One is on the external RTC chip and the other is on the i.MX53 so its power sequencing and DRAM work properly.

Tom

[andysc_liu]

Hi igor

If our design without power to SNVS when power off, dose the on-chip ring oscillator still work?

[igorpadykov]

>If our design without power to SNVS when power off, dose the on-chip ring oscillator still work?

what do you mean by "without power to SNVS when power off" ?

Without any power nothing will work: nor crystal, nor ring oscillator.

Best regards
igor

[andysc_liu]

Hi igor

System power off; generally, coin cell will provide power to SNVS.In our design coin cell won't provide power to SNVS for saving power and increasing service life because we must use primary cell for some reason,so SNVS can't obtain power when system power off.

According to your reply, on-chip ring oscillator couldn't work in this case,am I right? So It means no RTC CLK generating.

We want to know what i.MX6ULL security functions need RTC_XTAL clock when power off.

[igorpadykov]

>We want to know what i.MX6ULL security functions need RTC_XTAL clock when power off.

when chip is completely powered off,  RTC_XTAL clock absence will not affect processor security functions.

Best regards
igor