topic NMI and PTA4 behaviour? in Kinetis Microcontrollers

NMI and PTA4 behaviour?

q1220200 — Wed, 10 Jul 2019 00:13:19 GMT

Hello,

I just ran into some unexpected behaviour from PTA4 on the FRDM-KL25Z, and hoping someone can help me understand it.

I was trying to use PTA4 as a GPIO input with an IRQ handler. I noticed that when PTA4 was triggered the board's processing came to a halt, turns out that PTA4 is hooked up to an NMI interrupt vector which is just looping infinitely (as per the boilerplate code).

I'm surprised because I had set the MUX bits for that pin to ALT1 yet it seems to have no effect and continues to operate as the NMI (Alt 7).

Firstly, I don't really understand what the NMI does (my guess is that it's just an interrupt that can't be masked by software) and secondly, I can't understand why setting the MUX bits to ALT1 seems to have no impact on this pin.

As an aside, it's somewhat problematic for me, as I've noticed that on this chip / board only Port A and D have interrupts, so I've a limited number of pins I can actually use as interrupt GPIO without disabling other functionality elsewhere.

Anyway, if you could help shed some light on my ignorance that'd be appreciated as always.

Thanks,

Paul Swanson

Re: NMI and PTA4 behaviour?

kerryzhou — Wed, 10 Jul 2019 08:49:19 GMT

Hi Paul Swanson ,

NMI pin is the special pin, if you don't want to use it, you need to disable it from the FOPT.

FOPT in the flash configuration field, the address is: 0X40D

If you want to disable the NMI pin function, please configure NMI_DIS bit to 0.

Please try it again on your side.

Have a great day,
Kerry

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Re: NMI and PTA4 behaviour?

q1220200 — Thu, 25 Jul 2019 00:14:14 GMT

Thanks for your detailed answer, Kerry.

Re: NMI and PTA4 behaviour?

kerryzhou — Thu, 25 Jul 2019 02:11:21 GMT

Hi Paul Swanson ,

You are welcome!

If you have any further questions about it, please let me know.

If your question is solved, please help me make the correct answer, just to close this case, thank you!

Have a great day,
Kerry

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