What could cause the NMI interrupt to be ignored?

[javiercardona]

In our KL27-based design we have a button connected to the NMI line and the interrupt is triggered successfully when the button is pressed. After several successful triggers, the NMI handler will not be called anymore.  We have double checked that the PIN_Mux configuration for the NMI pin is sill valid.

That interrupt needs not be acknowledged, and by definition, cannot be masked...

Can anyone suggest how we can troubleshoot this?

Thanks,

kylemanna‌

[kerryzhou]

Hi Javier Cardona,

   Please check your NMI pin, did you add external 4.7K to 10K pull-up resistor in the NMI pin?

  Because the internal pull-up is weak, please add the external pull up.

   Besides, please also check your NMI wave when the problem happens, whether the button really pull down the NMI pin to ground.

Wish it helps you!

If you still have question, please let me know!

Have a great day,
Kerry

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[javiercardona]

Hi Kerry,

We ruled out any hardware problems because the button works very reliably until it stops working. Resetting the board makes the NMI interrupt to work again.  So it does not look like a problem that would be caused by insufficient pull-up.

Are there any (mis) configuration parameters in firmware that could cause the NMI interrupt to stop working entirely until the board is reset? My understanding is that thge NMI handler should be invoked even if the board is in the HardFault handler. 

Thanks!

Javier

[kerryzhou]

Hi Javier Cardona,

   1. KL27 reset can be masked in FOPT,  flash address is 0X40D.

2. Did you debug it? When the KL27 can't enter NMI interrupt, and you already click the NMI to low, where the code is stay?

  You can send me your test project, I will test it on my side.

Have a great day,

Kerry

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