Debouce Button Interrupt Routine

Kernel
1

gcgasson wrote on Monday, September 08, 2014:

Hi,

I am new with FREERTOS and require some assistance please.

I have a 5 button system with a 2 character LCD display. I am updating the display queue in the ISR as the button are pressed. This works great but I am getting a lot of bouncings on the switches and I am looking for away in which I can debounce the buttons in the FREERTOS.

I have decreased the size of the queue to 1 and this has helped but not 100%

Is there away in doing this?

For example what if I disable the port interrupt for 10ms and then re-enable them after the interrupt occurred?

What is the correct way of doing this in the FREERTOS?

Best Regards,

Gary

2

bowerymarc wrote on Monday, September 08, 2014:

I’d suggest to poll rather than use interrupts if those buttons are for human interaction only.
Create a thread, poll them and use a delay (wait). Debounce by looking for two consecutive readings of the same value, and adjust the delay until they are bounce free (best is to look with a 'scope to the switch lines, but you could just try some values like 20, 50mS etc).

Unless your product is very dependent on precise timing of the buttons this will probably give you the smallest code size.

On Sep 8, 2014, at 5:25 AM, “Gary” gcgasson@users.sf.net wrote:

Hi,

I am new with FREERTOS and require some assistance please.

I have a 5 button system with a 2 character LCD display. I am updating the display queue in the ISR as the button are pressed. This works great but I am getting a lot of bouncings on the switches and I am looking for away in which I can debounce the buttons in the FREERTOS.

I have decreased the size of the queue to 1 and this has helped but not 100%

Is there away in doing this?

For example what if I disable the port interrupt for 10ms and then re-enable them after the interrupt occurred?

What is the correct way of doing this in the FREERTOS?

Best Regards,

Gary

Debouce Button Interrupt Routine

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3

jdurand wrote on Monday, September 08, 2014:

On 09/08/2014 07:18 AM, Marc Lindahl wrote:

I’d suggest to poll rather than use interrupts if those buttons are
for human interaction only.
Create a thread, poll them and use a delay (wait). Debounce by looking
for two consecutive readings of the same value, and adjust the delay
until they are bounce free (best is to look with a 'scope to the
switch lines, but you could just try some values like 20, 50mS etc).

Unless your product is very dependent on precise timing of the buttons
this will probably give you the smallest code size.

Even though this isn’t a general programming list, I’ll give a freebie

#define mask (0b111) // make this any length you want for your debounce

uint i;

inside tick interrupt add:

i <<= 1;
if(Button_Down) {
i |= 1;
if(!(~i & mask)) {
set semaphore
}
}

–
Jerry Durand, Durand Interstellar, Inc. www.interstellar.com
tel: +1 408 356-3886, USA toll free: 1 866 356-3886
Skype: jerrydurand

4

heinbali01 wrote on Tuesday, September 09, 2014:

And if you like, here’s a routine if you do not want to use an interrupt: you can call vCheckKey() from a regular task as often as you like.

Both key-press as key-release events are being filtered for dender, not for noise.

#define DENDER_TIME 50 // Use 50 ticks anti dender time

TimeOut_t xTimeOut;
BaseType_t xWaitDender = pdFALSE;
BaseType_t xLastKey = 0;
BaseType_t xReportedKey = 0;
TickType_t xDenderTime;

BaseType_t xReadKey( void ) // Reports the current key status
{
    // Read some i/o pin
    return readPort(PORTA, 4);
}

void vHandleKey( BaseType_t xKeyPressed ) // Handle the key status
{
    printf ("Pressed %lu\n", xKeyPressed);
}

void vCheckKey( void )
{
    BaseType_t xKeyPressed = xReadKey( );

    if( xWaitDender == pdFALSE && xReportedKey != xKeyPressed )
    {
        // We were not waiting for dender,
        // so report the new key status
        xReportedKey = xKeyPressed;
        vHandleKey( xKeyPressed );
    }
    // Has the key value changed?
    if( xLastKey != xKeyPressed )
    {
        xLastKey = xKeyPressed;
        xDenderTime = DENDER_TIME;
        vTaskSetTimeOutState( &xTimeOut );
        xWaitDender = pdTRUE;
    }
    // Were we waiting for the dender?
    else if( xWaitDender == pdTRUE )
    {
        // See if the timer has expired
        if( xTaskCheckForTimeOut( &xTimeOut, &xDenderTime ) )
        {
            xWaitDender = pdFALSE;
        }
    }
}

Regards,
Hein