ATTiny85 Wake from Sleep on Pin State Change Code Example

I spent an inordinate amount of time trying to figure out how put my ATTiny85 to sleep and then wake it up when the state of a pin changes. So I’ll document my test code in case anyone else goes searching for a simple example.

The reference I ended up using is:

http://www.avrfreaks.net/index.php?name=PNphpBB2&file=printview&t=128982

Unfortunately, even after reading through the forum thread the final working code was evidently never posted. However, there was enough here for me to figure out the problem and get it running.

The following code is very simple. It flashes the LED quickly to let you know the program is started. It then sets up for sleep mode and goes to sleep. When the button is pushed, it awakes, flashes the LED once and goes back to sleep.

#include <avr/sleep.h>
#include <avr/interrupt.h>

const int switchPin                     = 3;
const int statusLED                     = 2;

void setup() {

    pinMode(switchPin, INPUT);
    digitalWrite(switchPin, HIGH);
    pinMode(statusLED, OUTPUT);

    // Flash quick sequence so we know setup has started
    for (int k = 0; k < 10; k = k + 1) {
        if (k % 2 == 0) {
            digitalWrite(statusLED, HIGH);
            }
        else {
            digitalWrite(statusLED, LOW);
            }
        delay(250);
        } // for
    } // setup

void sleep() {

    GIMSK |= _BV(PCIE);                     // Enable Pin Change Interrupts
    PCMSK |= _BV(PCINT3);                   // Use PB3 as interrupt pin
    ADCSRA &= ~_BV(ADEN);                   // ADC off
    set_sleep_mode(SLEEP_MODE_PWR_DOWN);    // replaces above statement

    sleep_enable();                         // Sets the Sleep Enable bit in the MCUCR Register (SE BIT)
    sei();                                  // Enable interrupts
    sleep_cpu();                            // sleep

    cli();                                  // Disable interrupts
    PCMSK &= ~_BV(PCINT3);                  // Turn off PB3 as interrupt pin
    sleep_disable();                        // Clear SE bit
    ADCSRA |= _BV(ADEN);                    // ADC on

    sei();                                  // Enable interrupts
    } // sleep

ISR(PCINT0_vect) {
    // This is called when the interrupt occurs, but I don't need to do anything in it
    }

void loop() {
    sleep();
    digitalWrite(statusLED, HIGH);
    delay(1000);
    digitalWrite(statusLED, LOW);
    }

One additional comment: in my actual program, I will need to awake if either of two buttons is pressed. To handle this, I simply add these additional statements below their near twins:

    PCMSK |= _BV(PCINT4);                   // Use PB4 as interrupt pin
    PCMSK &= ~_BV(PCINT4);                  // Turn off PB4 as interrupt pin