Interrupted

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 given the 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 disabled when not needed in the current state.

Note

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

See blog articles.

Example

#include <Interrupted.h>

#define LED     13
#define SER_OUT 99
#define EXT0    2
#define EXT1    3
#define TIMER   1

SerialOut 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 via pushbuttons:
  • 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:
  • a watchdog timer with id 1, interrupting every 4s,
  • two external 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 processor must sleep in an IDLE mode when it is in use.
• The processor enters the deepest sleep allowed by the currently-enabled devices. When output is in progress, this is SLEEP_MODE_IDLE, when not, SLEEP_MODE_POWER_DOWN.

Credits

• Nick Gammon's excellent interrupt and power-saving pages.
• The Conic and Regis projects at Imperial College London.
• The select system call.
• icaven for bugfixes and improvements.