Debounce in callbacks

Question

Hello! I currently have an external button and LED connected to the Icarus IoT dev board. For the time being, I just want to turn on the LED in the callback function when I press the button. However, the button (and the board) is highly sensitive and registers several interrupts with one push. I can even turn on the LED by touching the pin with my finger! So I was wondering if there is any easy way to add some kind of debounce code in the callback itself? I have seen some examples here and there, but none of them that is a really proper method nor being used inside the callback itself. 
 Looking forward to seeing your suggestions!

user102758 · Accepted Answer

Hi Baowz, 
 
 For debouncing a button, you can simply keep the uptime value at the moment of the button callback (eg k_uptime_get_32()) in a variable, let's call it last_button_press_time, and in your callback do something like the following: 
 
 #define BUTTON_DEBOUNCE_TIME 50
uint32_t last_button_press_time;

void button_pressed_callback(...) {
 uint32_t newPressTime = k_uptime_get_32();

 // debounce
 if (k_uptime_get_32() - last_button_press_time < BUTTON_DEBOUNCE_TIME) {
 return;
 }

 is_button_press_pending = true;
 // use (and re-set) the `is_button_press_pending` flag in your main loop
 // or submit work to queue at this point

 last_button_press_time = newPressTime;
}

Also, it sounds like you may not have the internal pull-up resistor active on your input, making your pin floating and triggering "too easily". Make sure to turn it on when you initialize your GPIO. 
 Let me know in case of any questions! 
 BR, 
 Mike

user102758 · Answer

Hello Baowz, 
 A device tree declaration will not initialize a pull-up resistor, you have to do it in the gpio_pin_configure(). If you want to use a similar way with what we do in the "leds & button" sample, then you should declare an extra button in your overlay (you can copy paste the button declaration from the icarus board files and change the gpio to pin 0 where you seem to have your external button connected) and just initialize the gpio the same way it is done for the on-board button in the sample, i.e. using the device tree flags in gpio_pin_configure(). 
 
 BR, 
 Mike

Debounce in callbacks

Top Replies