The code below achieves what you are asking:
#include <avr/sleep.h>
#include <avr/power.h>
const byte AWAKE_LED = 8;
const byte GREEN_LED = 9;
const unsigned long WAIT_TIME = 5000;
ISR (PCINT2_vect)
{
// handle pin change interrupt for D0 to D7 here
} // end of PCINT2_vect
void setup()
{
pinMode (GREEN_LED, OUTPUT);
pinMode (AWAKE_LED, OUTPUT);
digitalWrite (AWAKE_LED, HIGH);
Serial.begin (9600);
} // end of setup
unsigned long lastSleep;
void loop()
{
if (millis () - lastSleep >= WAIT_TIME)
{
lastSleep = millis ();
noInterrupts ();
byte old_ADCSRA = ADCSRA;
// disable ADC
ADCSRA = 0;
// pin change interrupt (example for D0)
PCMSK2 |= bit (PCINT16); // want pin 0
PCIFR |= bit (PCIF2); // clear any outstanding interrupts
PCICR |= bit (PCIE2); // enable pin change interrupts for D0 to D7
set_sleep_mode (SLEEP_MODE_PWR_DOWN);
power_adc_disable();
power_spi_disable();
power_timer0_disable();
power_timer1_disable();
power_timer2_disable();
power_twi_disable();
UCSR0B &= ~bit (RXEN0); // disable receiver
UCSR0B &= ~bit (TXEN0); // disable transmitter
sleep_enable();
digitalWrite (AWAKE_LED, LOW);
interrupts ();
sleep_cpu ();
digitalWrite (AWAKE_LED, HIGH);
sleep_disable();
power_all_enable();
ADCSRA = old_ADCSRA;
PCICR &= ~bit (PCIE2); // disable pin change interrupts for D0 to D7
UCSR0B |= bit (RXEN0); // enable receiver
UCSR0B |= bit (TXEN0); // enable transmitter
} // end of time to sleep
if (Serial.available () > 0)
{
byte flashes = Serial.read () - '0';
if (flashes > 0 && flashes < 10)
{
// flash LED x times
for (byte i = 0; i < flashes; i++)
{
digitalWrite (GREEN_LED, HIGH);
delay (200);
digitalWrite (GREEN_LED, LOW);
delay (200);
}
}
} // end of if
} // end of loop
I used a pin-change interrupt on the Rx pin to notice when serial data arrives. In this test the board goes to sleep if there is no activity after 5 seconds (the "awake" LED goes out). Incoming serial data causes the pin-change interrupt to wake the board. It looks for a number and flashes the "green" LED that number of times.
Measured current
Running at 5 V, I measured about 120 nA of current when asleep (0.120 µA).
Awakening message
A problem however is that the first arriving byte is lost due to the fact that the serial hardware expects a falling level on Rx (the start bit) which has already arrived by the time it is fully awake.
I suggest (as in geometrikal's answer) that you first send an "awake" message, and then pause for a short time. The pause is to make sure the hardware does not interpret the next byte as part of the awake message. After that it should work fine.
Since this uses a pin-change interrupt no other hardware is required.
Amended version using SoftwareSerial
The version below successfully processes the first byte received on serial. It does this by:
Inspired by FarO in a comment, this lets the processor wake up in 6 clock cycles (750 ns). At 9600 baud each bit time is 1/9600 (104.2 µs) so the extra delay is insignificant.
#include <avr/sleep.h>
#include <avr/power.h>
#include <SoftwareSerial.h>
const byte AWAKE_LED = 8;
const byte GREEN_LED = 9;
const unsigned long WAIT_TIME = 5000;
const byte RX_PIN = 4;
const byte TX_PIN = 5;
SoftwareSerial mySerial(RX_PIN, TX_PIN); // RX, TX
void setup()
{
pinMode (GREEN_LED, OUTPUT);
pinMode (AWAKE_LED, OUTPUT);
digitalWrite (AWAKE_LED, HIGH);
mySerial.begin(9600);
} // end of setup
unsigned long lastSleep;
void loop()
{
if (millis () - lastSleep >= WAIT_TIME)
{
lastSleep = millis ();
noInterrupts ();
byte old_ADCSRA = ADCSRA;
// disable ADC
ADCSRA = 0;
set_sleep_mode (SLEEP_MODE_PWR_DOWN);
power_adc_disable();
power_spi_disable();
power_timer0_disable();
power_timer1_disable();
power_timer2_disable();
power_twi_disable();
sleep_enable();
digitalWrite (AWAKE_LED, LOW);
interrupts ();
sleep_cpu ();
digitalWrite (AWAKE_LED, HIGH);
sleep_disable();
power_all_enable();
ADCSRA = old_ADCSRA;
} // end of time to sleep
if (mySerial.available () > 0)
{
byte flashes = mySerial.read () - '0';
if (flashes > 0 && flashes < 10)
{
// flash LED x times
for (byte i = 0; i < flashes; i++)
{
digitalWrite (GREEN_LED, HIGH);
delay (200);
digitalWrite (GREEN_LED, LOW);
delay (200);
}
}
} // end of if
} // end of loop
Power consumption when asleep was measured as 260 nA (0.260 µA) so that is very low consumption when not needed.
Note that with the fuses set like that, the processor runs at 8 MHz. Thus you need to tell the IDE about that (eg. select "Lilypad" as the board type). That way the delays and SoftwareSerial will work at the correct speed.
