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A new approach to building low-power, interrupt-driven, apps on Arduino:

• The processor mostly sleeps in a low-power mode, as low as possible giventhe currently-enabled devices.
• Devices wake the processor using interrupts, it services them before returning to sleep.
• State-machines are easily implemented: devices may be temporarily disabledwhen not needed in the current state.

• The master branch of this library is mostly compatible with the Arduino IDE;however it currently requiresuC-Makefile to build the examples.
• The ATtiny parts of this require Spence Konde's excellentATTinyCore. Only t84 and t85 are supported for now.
• This has been tested with Arduino 1.8.9 and Energia 1.8.7E21.

Seeblog articles.

#include <Interrupted.h>#define LED     13#define SER_OUT 99#define EXT0    2#define EXT1    3#define TIMER   1SerialOut output(SER_OUT, 115200);Watchdog timer(TIMER, 4);External int0(EXT0), int1(EXT1, RISING);Pin led(LED);Devices devices(timer, int0, int1, led, output);void setup(void){  devices.begin();   pinMode(LED, OUTPUT);  digitalWrite(LED, HIGH);}void loop(void){  switch (devices.select()) {  case EXT0:    digitalWrite(LED, HIGH);    break;  case TIMER:  case EXT1:    digitalWrite(LED, LOW);    break;  case LED:    int0.enable(!led.is_on());    int1.enable(led.is_on());    timer.enable(led.is_on());    break;  case SER_OUT:    output.enable(false);    return;  }  output.enable();  output.write("awake!\r\n");}

Remarks:

• This sketch manages a configuration with pins #2 and #3 connected to GND viapushbuttons:
  • when the button on pin #2 is pressed the LED on pin #13 is lit,
  • when that on pin #3 is pressed and released, the LED is turned off,
  • if the timer elapses when the LED is on, it is turned off again.
• Five devices:
  • awatchdog timer with id 1, interrupting every 4s,
  • twoexternal interrupts on ports 2 and 3,
  • a pin-change interrupt watching the LED on pin #13,
  • hardware serial output device running at 115200 baud.
• A device group ("devices") which manages them.
• Selecting on the device group sends the CPU to sleep if no device is ready.
• When a device is ready, select returns its id.
• Change of state of the LED pin triggers a state-machine change:
  • if the LED has come on, the timer and external interrupt #1 are enabled,
  • if the LED has been switched off, external interrupt #0 is enabled.
• Disabled interrupts don't wake the CPU and aren't "remembered".
• The serial port acts like any other device except that the processormust sleep in an IDLE mode when it is in use.
• The processor enters the deepest sleep allowed by the currently-enableddevices. When output is in progress, this is SLEEP_MODE_IDLE, when not,SLEEP_MODE_POWER_DOWN.

• Nick Gammon's excellentinterruptandpower-saving pages.
• TheConic and Regisprojects atImperial College London.
• Theselect system call.
• icaven for bugfixes and improvements.