iMXRT1060 Watchdog resetting at wrong timing in custom board

[Abisheikv2]

We have made a custom board using iMXRT1060 for our product. The issue we are facing is around 10%(40 out of 440) of our products watchdog is not working properly. We set a timeout of 1.5 seconds but the device is resetting in less a second. For testing we modified the firmware with a timeout of 4 seconds but the device is resetting in less than one second. When we heat the microcontroller with a blower watchdog works fine for a while(around 10 to 15 mins) and then goes back to the old error state. We have other functionalities as well, we use USB and CSI which are working fine. Only watchdog is problematic. Could an assembly issue cause this problem? Can someone shed some light on what could be causing this issue.

Regards,

Abisheik S.

[Hui_Ma]

Hi,

First of all, sorry for the later reply.

If customer had tried with MCUXpresso SDK for RT1060 [wdog1] example? That example will shows system reset by WDOG timeout, which setting 8 seconds.

And there with below note:

Please notice that because WDOG control registers are write-once only. And for the field WDT, once software performs a write "1" operation to this bit, it can not be reset/cleared until the next POR, this bit does not get reset/cleared due to any system reset. So the WDOG_Init function can be called
only once after power reset when WDT set, and the WDOG_Disable function can be called only once after reset.

Thanks for the attention.

Mike

[Abisheikv2]

Hi Mike,
I think you've misunderstood the issue, The problem I face is 10% of the device we've made resets at wrong time. We have checked the firmware and it's fine. USB and CSI peripherals are working fine. Only watchdog is causing problem, Could a hardware issue cause this?

[Hui_Ma]

Hi,

Thank you for the info.

If mentioned WDOG issue always happen with those 10%(40 out of 440) boards? (Make sure reported issue could be regenerated at NXP quality analysis team Lab)

If yes, I would recommend customer to contact with  NXP Distributor to submit a quality failure analysis request.

Thanks for the attention.

Mike

[Abisheikv2]

Hello Mike,

      Thanks for the suggestion, Before contacting the supplier we would like to confirm somethings.
I compared the CCM registers of the working and non working boards and I could see that RTC_XTAL_SOURCE bit in XTALOSC24M_MISC0n register is set to 1 in the failure boards and we don't have an external crystal for 32768hz(The working boards have 0 which is right). I couldn't find any API's in the SDK to change it and couldn't change the register value manually as well. 

My queries are

1) Why is it different in boards which have the same firmware?

2)Is there a way to change it in software? or is it a read only kind of bit.

3) How to configure the RTC 32KHz clock to either internal ring oscillator or external RTC XTAL? 
Regards,
Abisheik.

[Hui_Ma]

Hi,

1. If customer does not using the external 32KHz crystal, please help to double check the circuit design: It is recommended to connect RTC_XTALI to GND and keep RTC_XTALO unconnected.

2. The RTC_XTAL_SOURCE bit in XTALOSC24M_MISC0n register is read only bit:

3. The on-chip ring oscillator with below switch condition:

Customer also could check the CCM_CCR register [COSC_EN] bit, which reset value is 1 means: enable on chip oscillator

Thanks for the attention.

Mike

[Abisheikv2]

Thanks for the information Mike,
My device detects that there's a external 32K crystal but we've not mounted any. Both the RTC_XTALI and RTC_XTALO are left floating. Is there any option to use the internal oscillator even if external crystal is detected/how to stop switching to external oscillator in software?
Regards,
Abisheik

[Hui_Ma]

Hi,

The RT1060 hardware design guide file shows below info:

I would recommend customer try to tie RTC_XTALI to GND and check again if related issued board would be fixed.

Wish it helps.

Mike

[Abisheikv2]

Hello Mike, I saw that but we've already assembled the boards and we don't have those pins exposed or connected to any trace. We'll take care of it in the next revision. My query here is, Is it possible to override this with software. Can we make the controller use internal oscillator even if external crystal is connected? Is there any register to configure it?

Regards,
Abisheik 

[Hui_Ma]

Hi,

There with no register bit to select using internal or external 32KHz clock source. There only has read only flag to show current using 32KHz clock source.

In another word, there with no software method to select 32KHz clock source.

Sorry for that may bring any inconvenience.

Mike