Hello,
maybe someone has an idea or can share an similar experience. Since I'm currently in the evaluation phase for selecting an MCU for our new industrial embedded project. I want to inspect and analyze this problem, to be sure the used MCU is working fine and i can use it (STM32H735IGK6).
Issue:
Pushbuttons on different EXTI-Interrupt randomly fires twice or more times. Some GPIOs are effected, but not all, i have tested.
Setup:
Own PCB-Layout, 6 Pushbuttons, every one is debounced with 10kOhm and 10nF. Signal looks fine on scope, no bouncing can be seen with scope, absolutely clean signal.
Test 1:
apply a 200mHz sine-wave directly to the button pin. Expected behavior is: one interrupt on rising one interrupt on falling signal (due to the 200mV hysteresis on every input pin, as mentioned in datasheet). Behavior in RealLife: as soon as the voltage level on the pin reaches the switching thresholds of the input pin, i get lots of Interrupts (Rising and falling edge).
BUT now its getting freaky: if i turn off the running FMC access to an external RAM, instantly everything works as expected - only one single interrupt per transition.
Test 2:
same as above, but the FMC-access only bursts data every few seconds for approx. 250ms. Result: only, during FMC-access i get this accidential interrupts. (just to be sure: i checked the signal with the scope again: the waveform looks perfectly clean, without any noise, glitches, or something else)
I don't know if this can be an mcu-internal emc-issue or something like that, but fact is, if i enable the data transfer to the external RAM, the EXTI-Peripheral (or the schmitt trigger inside) gets extremely disturbed.
Of course, in this use case with buttons, a simple workaround is possible, but i also need a solution for other, more complex applications with combinations of FMC and EXTI (e.g. FPGA Communications, ...)
