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stm32interruptgpio
Harry
Harry

Reputation: 4936

STM32 seems to ignore GPIO mode and triggers the interrupt on both edges, instead of one

Here's my configuration:

GPIO_InitTypeDef GPIO_InitStruct = {0};
GPIO_InitStruct.Pin = 8;
GPIO_InitStruct.Mode = GPIO_MODE_IT_FALLING;
GPIO_InitStruct.Pull = GPIO_NOPULL;
HAL_GPIO_Init(GPIOJ, &GPIO_InitStruct);

When I put the signal on the input pin (square, 2Hz, 3.3Vp-p) I get an interrupt every 250ms, so - on every RISING and falling edge of the signal. I changed the test signal duty cycle to test if it's really what is happening and it confirmed it. I get the interrupt on both edges.

I even debugged the HAL driver to test if it does what I think it does. And yes, it seems to configure the EXTI correctly, only for the falling edge for my pin.

What may be the cause of such behavior? My device is STM32H747I-DISCO discovery board with TouchGFX software used for presentation. The software works correctly, I tested it on measuring the time between other timer interrupts.

I monitor the test signal on the oscilloscope to ensure the input signal on my pin is correct. I tried to use another pin on the same port, but I observe identical behavior. I get interrupts on both rising and falling edges of the signal, despite the pin is configured to trigger the interrupt only on the falling edge.

I also tested the case with the rising edge only. Also in this case I get the interrupt on both edges.

Upvotes: 0

Views: 1058

Answers (1)

Harry
Harry

Reputation: 4936

The problem turned out to be a hardware error, a voltage spike I overlooked. The STM32 EXTI input worked correctly all the time. There was indeed a spurious falling edge.

Switching

Simulated problem illustration, the 10n capacitor causes voltage spikes and spurious edge detection. In the real circuit, when a digital oscilloscope was used and the time base was too long to capture the spike - the signal looked like a proper square wave. After shortening the time base I noticed the spike. As it is shown on the illustration, this behavior can be easily simulated in a circuit simulator:

SIMULATION LINK

Removing the capacitor from the circuit solved the problem.

To avoid getting noise and other spurious signals on the input shielded wires can be used. The real world circuit was tested and it works properly without the capacitor.

The opto-coupler is just a simplified model of the optical sensor used in the real machine.

Upvotes: 0

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