Odd issue with handling a hardware interrupt

Using Arduino Microcontrollers
1

Hi All...

I have a board based on the ATMega 12846p. I have a chip connected to the INT2 pin, and when this device brings the INT2 pin low an interrupt is indeed generated. I also have the card detect line of an SD card connected to port PA7 (Arduino digital pin 24). When I plug the card in, it also triggers the interrupt. I have checked the hardware carefully, there is no short of any type between the pins.

This is on Arduino 1.0.

Below is the code.

Any ideas?

Thanks...

attachInterrupt(INT_2, isrInt2, CHANGE);


/* Further down the file... */



void isrInt2(void)
{
  sei(); // Put interrupts back up
  
  void closeLogFiles(void);

  pinMode(LED_INFO, OUTPUT);
  pinMode(LED_ERROR, OUTPUT);
  int state = LOW;

  for(;;)
  {
    state = !state;
    digitalWrite(LED_ERROR, state);
    digitalWrite(LED_INFO, !state);
    delay(100);
  }
}
2

Hi,

Is it possible the INT2 pin is floating? Is a pull-up or pull-down connected? Does the connected chip always hold the pin in a defined state?

3

Hm, maybe it is floating... I should probably enable the internal pullup???

The device that triggers the interrupt takes the INT2 pin to ground and does hold it until the interrupt is cleared.

Thanks very much for the suggestion, I'll try that right now.

4

No Joy :frowning: I changed it to this:

  // Set up interrupt handler for INT2
  pinMode(INT_2, INPUT);
  digitalWrite(INT_2, HIGH);
  attachInterrupt(INT_2, isrInt2, CHANGE);

Still did the same thing. And the funny thing is, triggering other pins, like my push button inputs, does not do this.

5

Are you certain that this...

// Set up interrupt handler for INT2
pinMode(INT_2, INPUT);
digitalWrite(INT_2, HIGH);

...and this...

attachInterrupt(INT_2, isrInt2, CHANGE);

...reference the same pin?

Bear in mind that you may have crossed paths with a bug in the core. Even if the core author intended INT_2 to reference the same pin it may not work.

6

Yeah, INT_2 is one of my own constants. Hm, maybe it duplicates a constant from inside the core. I'll try doing it by the number directly...

Thanks, great thought!

7

Nope, no joy there :frowning:

Time to dig into the cores code on that function I guess...

8

Just in case this is helpful ... I believe you can trigger an interrupt without any external hardware by configuring the pin as an output and then toggling it. You may be able to use the technique to determine if there is a bug and to ensure everything is working as expected.

9

Thanks! I'll give that a try!

10

Why do do you enable interrupts inside your ISR?
not normally necessary unless there's a compelling reason
Also, the interrupt number and pin number ARE different
Pin 2 generates INT0, not INT2

11

mmcp42:
Why do do you enable interrupts inside your ISR?
not normally necessary unless there's a compelling reason
Also, the interrupt number and pin number ARE different
Pin 2 generates INT0, not INT2

Oh I was just experimenting with putting interrupts back up. I originally had some code in there to flash LEDs on a delay as a visual indicator that the ISR had been entered, and of course delay needs interrupts up. Also, closing files with SDFat may need interrupts up, but a quick look at that code makes me think it does not.

This is a 1284p uC, and INT2 is physical pin 42 and Arduino D2. Trapping D2 does cause the ISR to be called. But so does PA7 (physical pin 30, Arduino pin D24). That's the mystery, why D24 calls it also.

12

ah I understand the question now!
(no help with the answer though, sorry)

13

I put a lot of test code into the ISR to read the registers of the device that is triggering the interrupt. Reading things like the register that reports what caused the interrupt seems to indicate that the device is not set up correctly. I think what is happening is that inserting the SD card causes a very brief current drop, and causes the device to reset.

I coded around it by establishing the handler after the card is known to be inserted. I don't need it before then anyhow.

Thanks for all the helpful suggestions!

14

heard you're looking for an EAGLE part
watcha want?

15

mmcp42:
heard you're looking for an EAGLE part
watcha want?

Hi Mike! Sorry, I thought Bob told you. Its a boost regulator:

Its a Linear Technologies LTC3525.

This is a very very cool gadget!

16

he mentioned that there was something
any hoo
give this a whirl
cheers
Mike

Linear.lbr (6.92 KB)

17

mmcp42:
he mentioned that there was something
any hoo
give this a whirl
cheers
Mike

Thank you!!!