TMS570LC4357: Push Button Debounce

Hi Dobby,

The instability you're experiencing is a common issue called "button bounce." When you press or release a mechanical button, the contacts don't make or break cleanly - they bounce multiple times over a period of 5-20ms, causing the GPIO register to change unpredictably.

Unfortunately, i don't have any ready example for this because most of this kind of requirements will be handled by customers themselves, so i never get this kind of issue before.

We have internal AI and it suggest couple of code flows like below, you can adopt to any of these methods.

Method-1:

// Debounce configuration
#define DEBOUNCE_TIME_MS    20    // Typical debounce time: 10-20ms
#define BUTTON_PRESSED      0     // Assuming active low with pull-up
#define BUTTON_RELEASED     1

// Global variables
static uint32_t lastButtonState = BUTTON_RELEASED;
static uint32_t buttonStateCounter = 0;
static uint32_t stableButtonState = BUTTON_RELEASED;

// Call this function periodically (e.g., every 1ms from a timer interrupt)
uint32_t debounceButton(uint32_t currentButtonState)
{
    if (currentButtonState != lastButtonState) {
        // Button state changed, reset counter
        buttonStateCounter = 0;
        lastButtonState = currentButtonState;
    } else {
        // Button state is stable, increment counter
        if (buttonStateCounter < DEBOUNCE_TIME_MS) {
            buttonStateCounter++;
        }
        
        // If stable for debounce time, update stable state
        if (buttonStateCounter >= DEBOUNCE_TIME_MS) {
            stableButtonState = currentButtonState;
        }
    }
    
    return stableButtonState;
}

// Usage in your main loop or timer ISR
void checkButton(void)
{
    uint32_t rawButtonState = gioGetBit(gioPORTA, BUTTON_PIN); // Read GPIO
    uint32_t debouncedState = debounceButton(rawButtonState);
    
    if (debouncedState == BUTTON_PRESSED) {
        // Button is pressed (stable)
        // Your action here
    }
}

Method-2:

typedef enum {
    BUTTON_STATE_RELEASED,
    BUTTON_STATE_PRESSED,
    BUTTON_STATE_DEBOUNCING_PRESS,
    BUTTON_STATE_DEBOUNCING_RELEASE
} ButtonState_t;

ButtonState_t buttonStateMachine(uint32_t rawInput)
{
    static ButtonState_t state = BUTTON_STATE_RELEASED;
    static uint32_t debounceCounter = 0;
    
    switch(state) {
        case BUTTON_STATE_RELEASED:
            if (rawInput == BUTTON_PRESSED) {
                state = BUTTON_STATE_DEBOUNCING_PRESS;
                debounceCounter = 0;
            }
            break;
            
        case BUTTON_STATE_DEBOUNCING_PRESS:
            if (rawInput == BUTTON_PRESSED) {
                debounceCounter++;
                if (debounceCounter >= DEBOUNCE_TIME_MS) {
                    state = BUTTON_STATE_PRESSED;
                    // Trigger button press event here
                }
            } else {
                state = BUTTON_STATE_RELEASED;
            }
            break;
            
        case BUTTON_STATE_PRESSED:
            if (rawInput == BUTTON_RELEASED) {
                state = BUTTON_STATE_DEBOUNCING_RELEASE;
                debounceCounter = 0;
            }
            break;
            
        case BUTTON_STATE_DEBOUNCING_RELEASE:
            if (rawInput == BUTTON_RELEASED) {
                debounceCounter++;
                if (debounceCounter >= DEBOUNCE_TIME_MS) {
                    state = BUTTON_STATE_RELEASED;
                    // Trigger button release event here
                }
            } else {
                state = BUTTON_STATE_PRESSED;
            }
            break;
    }
    
    return state;
}

Hardware Configuration Tips

1. Enable Internal Pull-up/Pull-down: Configure your GPIO with internal pull-up or pull-down resistors as appropriate for your button circuit

2. HALCoGen Configuration: Use HALCoGen to configure your GPIO properly:

   • Set the pin as input
   • Enable pull-up if button connects to ground when pressed
   • Enable pull-down if button connects to VCC when pressed

Timer Setup for Periodic Sampling

You'll need a timer to call your debounce function periodically (every 1ms is recommended):

// In HALCoGen, configure RTI (Real-Time Interrupt) for 1ms period
void rtiNotification(uint32 notification)
{
    if(notification == rtiNOTIFICATION_COMPARE0) {
        // Call your button check function here
        checkButton();
    }
}

--

Thanks & regards,
Jagadish.