How do I use the iMX6 watchdog without a 32 kHz clock

[dougbailey]

I have an iMX6-DL based board where the iMX6 has been implemented without the 32 kHz clock source. (The clock pins are terminated.)

I am now trying to implement the watchdog timer but I noticed that the clock on the watchdog is dependent upon the ipg_clk_32k clock in order to drive the watchdog counter.

Does this mean that there is no clock to drive the watchdog timer?

Is there another clock source that can be used to drive the watchdog hardware?

Regards, 

Doug Bailey 

[igorpadykov]

Hi Doug

sect.70.3 Clocks i.MX6SDL Reference Manual shows clocks used by wdog,

according to sect.18.5.1.1 External Low Frequency Clock - CKIL  :

The chip can use a 32 kHz or 32.768 kHz crystal as the external low-frequency source
(XTALOSC). Throughout this chapter, the low-frequency crystal is referred to as the 32
kHz crystal.
This clock source should always be active when the chip is powered on.

http://www.nxp.com/assets/documents/data/en/reference-manuals/IMX6SDLRM.pdf 

 RTC_XTALI should be tied to GND and RTC_XTALO is left unconnected, for on-chip
oscillator is automatically engaged, as stated in Table 2-7. Oscillator and clock recommendations

i.MX6 System Development User’s Guide

https://www.nxp.com/docs/en/user-guide/IMX6DQ6SDLHDG.pdf 

Best regards
igor
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[emecc]

Igor,

Thank you for this post, we were seeing WDOG reset issues when we switched from a SD card to an eMMC chip. After much head scratching we figured out the 40 kHz clock feeding the watch dog counting would become unstable. We proved adding an external crystal would stabilize the watchdog timer clock, but this post mentioned the need to tie RTC_XTALI to GND if no crystal was needed.

I tried grounding the RTC_XTALI pin and this also stabilized the clock the feed the watchdog counter.

Thanks for the recommendation, 

Eric