iMX6Q Internal oscillator frequency (for WDT)

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iMX6Q Internal oscillator frequency (for WDT)

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lukaszmajewski
Contributor III

Dear Support,

Problem:
========

When I do set WDT to fire after 60s, it actually fires after ~42s.


My current findings:
====================
1. Errata for iMX6Q [1]:

ERR007926:
"The internal ring oscillator is less accurate than a crystal oscillator and may be up to two times
faster than a 32 kHz external crystal oscillator"

So the internal frequency may be up to 64 kHz? Is this correct?

2. WDT uses "Low frequency clock" (ckil_sync_clk_root) as input clock for WDT counter.

3. My PCB:

RTC_XTALI connected to GND via 1K, RTC_XTALO N.C. (floating) -
Please correct me, but it seems to me that iMX6Q will be forced to use its internal oscillator.

Just to compare - Wandboard QUAD rev. C uses 32.768 kHz oscillator connected to
RTC_XTALI and RTC_XTALO [3].

4 Measurements on my system (the CLKO1 output)

The ckil_sync_clk_root = 42 kHz (not expected 32 kHz or 32.768 kHz).

5. From the Applications Processor Reference Manual [2]:

Chapter 71. Cristal Oscillator (XTALOSC)

"Supply another ~32 kHz clock source based off an independent internal oscillator if
there is no oscillation sensed on the RTC_XTAL bumps(contacts) (32 kHz specific
feature). The internal oscillator will provide clocks to the same on-chip modules as
the external 32 kHz oscillator."

"Automatically switch to the external oscillation source when sensed on the
RTC_XTAL bumps(contacts) (32 kHz specific feature)."


Conclusion:
===========
===========

Please correct if I'm wrong, but it seems to me like:

- My iMX6Q board is forced to use internal oscillator

- The internal oscillator can generate frequency up to 64 kHz.

- I shall connect the 32.768 kHz oscillator to RTC_XTAL contacts to
have proper WDT operation.

References:
[1] https://www.nxp.com/docs/en/errata/IMX6DQCE.pdf
[2] i.MX 6Dual/6Quad Applications Processor Reference Manual, Rev. 4, 09/2017
[3] http://download.wandboard.org/wandboard-imx6/documentation/wb-edm-imx6-rev-c1.pdf
page 5/8


Thanks in advance for help,
Łukasz Majewski

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igorpadykov
NXP TechSupport
NXP TechSupport

Hi Łukasz 

you are right, based on description iMX6Q board was forced to use internal oscillator,

which can generate frequency up to 64 kHz. If one connects the 32.768 kHz oscillator

to RTC_XTAL contacts one can expect proper WDT operation.

Best regards
igor
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179 Views
igorpadykov
NXP TechSupport
NXP TechSupport

Hi Łukasz 

you are right, based on description iMX6Q board was forced to use internal oscillator,

which can generate frequency up to 64 kHz. If one connects the 32.768 kHz oscillator

to RTC_XTAL contacts one can expect proper WDT operation.

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

View solution in original post

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