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Re: [avr-gcc-list] Simple but wrong code

From: dfx
Subject: Re: [avr-gcc-list] Simple but wrong code
Date: Tue, 14 Jan 2014 18:37:54 +0100
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Todd thank you very much for your contribution.

I added this line to the bottom of the ISR:

PCIFR | = (1 << PCIF3);

and I have also added a 10 uF capacitor to remove any possibility of bouncing (... and seeing the signals to the oscilloscope are very clean and exactly as expected).

The behavior remained absolutely identical. :-(

I can not use a polling technique for reasons of timing, and even a software debouncing (negate the advantages of the ISR).

To me it remains unclear why exactly does two flashes on press and on release the other two flashes (Why not sometime a single 1 or 3?) for a total of 4 flashes instead of just one.

Thanks again


Il 14/01/2014 18:02, Todd Batzler ha scritto:
You're in that isr a long time.  The isr bit that got set that resulted in the 
vector to your isr probably gets cleared upon entry to the isr, but could get 
set again due to switch bounce.  Try clearing the ISR pending flag for that ISR 
before returning.

Todd G. Batzler
Sr Staff Engineer
Technology Development

Miller Electric Mfg. Co.  An ITW Company
1635 West Spencer St.
P.O. Box 1079
Appleton, WI  54912-1079
920-735-4230 Office
920-735-4488 Fax
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-----Original Message-----
From: address@hidden [mailto:address@hidden On Behalf Of dfx
Sent: Tuesday, January 14, 2014 10:54 AM
To: address@hidden
Subject: [avr-gcc-list] Simple but wrong code

Please consider this code:

#define KEY_DDR DDRD
#define KEY_FUNC_SEL PIND4 // --> first key (Port D pin 4) ....
#define LED_PORT PORTB // Test led, to see action on keypress ....

#define FUNC_SEL_KEY 0x10 // First function --> first key (Port D pin 4) ....

int main() {

    while (1) {
      // waits indefinitely for keypress
    return (EXIT_SUCCESS); // Never reached }

void init() {
    LED_DDR |= (1 << DDB0); // Led out Port B pin 0

    KEY_PORT |= (1 << PORTD4) ; // pull-up resistor
    PCICR |= (1 << PCIE3); // Enable interrupts on PORTD (PCINT31:24)

    PCMSK0 = 0X00; // Disable unnecessary
    PCMSK1 = 0X00;
    PCMSK2 = 0X00;
    PCMSK3 |= (1 << PCINT28); // Enable  key

    uint8_t i;

    i = PORTD;
    if ((i & FUNC_SEL_KEY) > 0) { // Test a key
      LED_PORT |= (1 << PORTB0);
      LED_PORT &= ~(1 << PORTB0);

ISR(BADISR_vect) {
    LED_PORT |= (1 << PORTB0);
    LED_PORT &= ~(1 << PORTB0);
    LED_PORT |= (1 << PORTB0);
    LED_PORT &= ~(1 << PORTB0);
    LED_PORT |= (1 << PORTB0);
    LED_PORT &= ~(1 << PORTB0);

the button has a capacitor 1uF for debouncing (together with the pull-up from 
10 kohm)

The result is the following:

when I press the button,  are generated two flashes (instead of one),
   and when I release the button  are generated two more flashes.

Similarly, If I comment out the routine (ISR PCINT3_vect),
   the error routine (ISR BADISR_vect) generates double of the expected flashes.

Can anyone help me to understand the problem?

Thank you very much.


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