Nucleo F746ZG PC13 User Button Triggering Interrupt on Init

Forum|Forum|2 years ago
September 27, 2024
3 replies
2614 views

I have a Nucleo 144-pin F746ZG and I want to configure the user button (PC13, pulled to ground according to MB1137 schematic) to toggle an onboard LED on a falling edge via EXTI interrupt.

I am using this sequence to initialize the interrupt handling:

1) Initialize SYSCFG.

2) Initialize GPIOC Clock.

3) Initialize GPIO registers for PC13, Falling Edge Trigger and Unmask.

4) Initialize SYSCFG_EXTICR, followed by ISER.

An issue I am running into is that on a falling edge it always triggers an interrupt after the initialization is done, even when I pull the pin low via PUPDR. Upon unmasking EXTI_IMR, the EXTI_PR bit is set to 1. If I change the order of the steps the issue goes away, but I doubt I am supposed to do this. What am I overlooking?

STM32F7 series

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Best answer by waclawek.jan

By enabling the EXTI interrupt *before* selecting the particular pin/port in SYSCFG.EXTICR you've enabled that interrupt for PA13. That is a debug interface pin, so if you had debugger connected there is enough activity there to trigger the interrupt.

JW

jiangfan

ST Employee

3) Initialize GPIO registers for PC13, Falling Edge Trigger and Unmask.

4) Initialize SYSCFG_EXTICR, followed by ISER.

I suppose you may clear the interrupt pending bit EXTI_PR before enabling the Falling Edge interrupt to avoid the issue.

J

JS5Author

Associate

Hi jiangfan,

Thank you for getting back to me. I have tried to clear EXTI_PR by explicitly setting it to 1 in a few different places, however it does not take effect and remains at 1. The interrupt is triggered right after NVIC_ISER is set. Once I clear it in the interrupt handler, then it gets updated to 0 as expected.

The issue does not occur if I change the order of initialization to:

1) Initialize SYSCFG.

2) Initialize SYSCFG_EXTICR, followed by ISER.

3) Initialize GPIOC Clock.

4) Initialize GPIO registers for PC13, Falling Edge Trigger and Unmask.

But again, not sure if this is the right thing to do. I haven't seen definitive example of the sequence in Reference Manual or other STM documents.

waclawek.janBest answer

Super User

By enabling the EXTI interrupt *before* selecting the particular pin/port in SYSCFG.EXTICR you've enabled that interrupt for PA13. That is a debug interface pin, so if you had debugger connected there is enough activity there to trigger the interrupt.

JW

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