Debounce filter on a button

In this use case, a simple debounce filter on a button will be set up.

Setup steps

Prerequisites

For the setup code of this use case to work, the following must be added to the project:

1. System Clock Management
2. Programmable Multilevel Interrupt Controller
3. General Purpose Input/Output
4. Real Time Counter (RTC)
5. Configuration info for the timeout service must be added to the conf_timeout.h file (located in the config folder):

   #define TIMEOUT_CLOCK_SOURCE_HZ     1024
   #define TIMEOUT_COUNT               1
   #define TIMEOUT_TICK_HZ             100

6. Configuration info for the RTC driver must be added to the conf_rtc.h file (located in the config folder):

   #define CONFIG_RTC_PRESCALER          RTC_PRESCALER_DIV1_gc
   #define CONFIG_RTC_CLOCK_SOURCE       CLK_RTCSRC_ULP_gc

Example code

The following must be added to the project:

#define DEBOUNCE_TIMEOUT    0
#define DEBOUNCE_TICKS      (50 * TIMEOUT_TICK_HZ / 1000)

Add to application initialization:

sysclk_init();
pmic_init();
timeout_init();

Workflow

1. Initialize system clock:

   • sysclk_init(); 

2. Initialize the PMIC driver:

   • pmic_init(); 

3. Initialize timeout service:

   • timout_init(); 

Example code

Add to application C-file:

bool button_pressed;
bool button_previous_state_pressed = false;
while (1) {
   button_pressed = gpio_pin_is_low(GPIO_PUSH_BUTTON_0);
   if (button_previous_state_pressed != button_pressed) {
      timeout_start_singleshot(DEBOUNCE_TIMEOUT, DEBOUNCE_TICKS);
      button_previous_state_pressed = button_pressed;
   }

   if (timeout_test_and_clear_expired(DEBOUNCE_TIMEOUT)) {
      if (button_pressed) {
         gpio_toggle_pin(LED0_GPIO);
      }
   }
}

Workflow

1. Create a variable to hold state of push button:

   • bool button_pressed; 

2. Create a variable to hold previous state of push button:

   • bool button_previous_state_pressed; 

3. Get button state:

   • button_pressed = gpio_pin_is_low(GPIO_PUSH_BUTTON_0); 

4. Check if button state has changed since last iteration:

   • if (button_previous_state_pressed != button_pressed) 

5. Start debounce timeout:

   • timeout_start_singleshot(DEBOUNCE_TIMEOUT, DEBOUNCE_TICKS);

6. Set previous state of button:

   • button_previous_state_pressed = button_pressed; 

7. Check if debounce timeout has expired:

   • if (timeout_test_and_clear_expired(DEBOUNCE_TIMEOUT)) 

8. Check if button is pressed down:

   • if (button_pressed) 

9. Toggle led:

   • gpio_toggle_pin(LED0_GPIO);