[TriEmbed] 32u4 hardware interrupts and wake behaviors

[Pete Soper]

comments below

On 03/09/2018 08:37 AM, Alex Davis via TriEmbed wrote:
> Following on my sleep/wake issues with the Feather M0, I have switched 
> to the Feather 32u4. The 32u4 is less flexible with regards to 
> external pin change interrupts, so I have kept things simple and just 
> went with hardware interrupts INT2 and INT3.
>
> I’m using <avr/sleep.h> and have no trouble waking the micro on 
> external interrupt.
>
> The problem comes with polling the input used for the interrupt to 
> detect button presses. I would like to wake on pin LOW (button tied to 
> ground) and then time how long the button is pressed down. This way 
> accidental button presses will be less likely to turn the device on.
>
> The code looks like this - simplified with LEDs to show what it is 
> doing vs my actual code:
>
>   // red LED on until button is pressed
>   digitalWrite(RED_LED, HIGH);
>
>   // spin around until the button is pressed
>   while (digitalRead(BUTTON_0) == HIGH);
>
>   // red LED off
>   digitalWrite(RED_LED, LOW);
>   // blue LED on
>   digitalWrite(BLUE_LED, HIGH);
>   // wait a bit to settle bouncing
>   delay(50);
>   // start button timer
>   buttonTime = (unsigned long)millis();
>   // see if the button is held down long enough
>   while (digitalRead(BUTTON_0) == LOW)
>   {
>     // if the button is held down LONG_CLICK_MS or more
>     if (((unsigned long)millis() - buttonTime) > LONG_CLICK_MS)
>     {
>       digitalWrite(BLUE_LED, LOW);
>     }
>   }
>   digitalWrite(RED_LED, HIGH);
>
> This works as expected when it has not woke from an interrupt on 
> BUTTON_0 (INT2). However, if I wake from INT2 (detaching it as soon as 
> I wake) and run it, it will spin around forever in the second while 
> loop until the button is released. It is as though Arduino pin 0 
> (PD2/INT2) being
Wait, this is what the code is supposed to do: loop until the button is 
released. Is the bug that the blue LED never gets turned off? I confess 
I didn't look at this closely the other day. So the bug is that the 
counter in millis isn't incrementing while the pin is held low?

-Pete


> high somehow breaks millis(). It is not a case of millis() alone being 
> broken after waking, as I can use it as a delay loop right after 
> waking with no issue. I just can not combine it with polling the PD3 pin.
>
> My work around for the time being is to wake on INT2 (pin 0 or PD2) 
> and then look for a long press on pin 1 or PD3. It requires me to have 
> the second button, though.
>
> Interestingly enough, the exact same <avr/sleep.h> code and millis() 
> loop wake/long button press detect routine works fine on an ATTINY85 
> (as used in my UV meter business card).
>
> I NEED TO BUY A DEBUGGER!!!
>
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