pingpair_sleepy.pde

This is an example of how to use the RF24 class to create a battery- efficient system. It is just like the pingpair.pde example, but the ping node powers down the radio and sleeps the MCU after every ping/pong cycle.

/*
 Copyright (C) 2011 J. Coliz <maniacbug@ymail.com>

 This program is free software; you can redistribute it and/or
 modify it under the terms of the GNU General Public License
 version 2 as published by the Free Software Foundation.
 */

#include <SPI.h>
#include <avr/sleep.h>
#include <avr/power.h>
#include "nRF24L01.h"
#include "RF24.h"
#include "printf.h"

//
// Hardware configuration
//

// Set up nRF24L01 radio on SPI bus plus pins 9 & 10

RF24 radio(9,10);

// sets the role of this unit in hardware.  Connect to GND to be the 'pong' receiver
// Leave open to be the 'ping' transmitter
const int role_pin = 7;

//
// Topology
//

// Radio pipe addresses for the 2 nodes to communicate.
const uint64_t pipes[2] = { 0xF0F0F0F0E1LL, 0xF0F0F0F0D2LL };

//
// Role management
//
// Set up role.  This sketch uses the same software for all the nodes
// in this system.  Doing so greatly simplifies testing.  The hardware itself specifies
// which node it is.
//
// This is done through the role_pin
//

// The various roles supported by this sketch
typedef enum { role_ping_out = 1, role_pong_back } role_e;

// The debug-friendly names of those roles
const char* role_friendly_name[] = { "invalid", "Ping out", "Pong back"};

// The role of the current running sketch
role_e role;

//
// Sleep declarations
//

typedef enum { wdt_16ms = 0, wdt_32ms, wdt_64ms, wdt_128ms, wdt_250ms, wdt_500ms, wdt_1s, wdt_2s, wdt_4s, wdt_8s } wdt_prescalar_e;

void setup_watchdog(uint8_t prescalar);
void do_sleep(void);

const short sleep_cycles_per_transmission = 4;
volatile short sleep_cycles_remaining = sleep_cycles_per_transmission;

//
// Normal operation
//

void setup(void)
{
  //
  // Role
  //

  // set up the role pin
  pinMode(role_pin, INPUT);
  digitalWrite(role_pin,HIGH);
  delay(20); // Just to get a solid reading on the role pin

  // read the address pin, establish our role
  if ( digitalRead(role_pin) )
    role = role_ping_out;
  else
    role = role_pong_back;

  //
  // Print preamble
  //

  Serial.begin(57600);
  printf_begin();
  printf("\n\rRF24/examples/pingpair_sleepy/\n\r");
  printf("ROLE: %s\n\r",role_friendly_name[role]);

  //
  // Prepare sleep parameters
  //

  // Only the ping out role sleeps.  Wake up every 4s to send a ping
  if ( role == role_ping_out )
    setup_watchdog(wdt_1s);

  //
  // Setup and configure rf radio
  //

  radio.begin();

  //
  // Open pipes to other nodes for communication
  //

  // This simple sketch opens two pipes for these two nodes to communicate
  // back and forth.
  // Open 'our' pipe for writing
  // Open the 'other' pipe for reading, in position #1 (we can have up to 5 pipes open for reading)

  if ( role == role_ping_out )
  {
    radio.openWritingPipe(pipes[0]);
    radio.openReadingPipe(1,pipes[1]);
  }
  else
  {
    radio.openWritingPipe(pipes[1]);
    radio.openReadingPipe(1,pipes[0]);
  }

  //
  // Start listening
  //

  radio.startListening();

  //
  // Dump the configuration of the rf unit for debugging
  //

  radio.printDetails();
}

void loop(void)
{
  //
  // Ping out role.  Repeatedly send the current time
  //

  if (role == role_ping_out)
  {
    // First, stop listening so we can talk.
    radio.stopListening();

    // Take the time, and send it.  This will block until complete
    unsigned long time = millis();
    printf("Now sending %lu...",time);
    radio.write( &time, sizeof(unsigned long) );

    // Now, continue listening
    radio.startListening();

    // Wait here until we get a response, or timeout (250ms)
    unsigned long started_waiting_at = millis();
    bool timeout = false;
    while ( ! radio.available() && ! timeout )
      if (millis() - started_waiting_at > 250 )
        timeout = true;

    // Describe the results
    if ( timeout )
    {
      printf("Failed, response timed out.\n\r");
    }
    else
    {
      // Grab the response, compare, and send to debugging spew
      unsigned long got_time;
      radio.read( &got_time, sizeof(unsigned long) );

      // Spew it
      printf("Got response %lu, round-trip delay: %lu\n\r",got_time,millis()-got_time);
    }

    //
    // Shut down the system
    //

    // Experiment with some delay here to see if it has an effect
    delay(500);

    // Power down the radio.  Note that the radio will get powered back up
    // on the next write() call.
    radio.powerDown();

    // Sleep the MCU.  The watchdog timer will awaken in a short while, and
    // continue execution here.
    while( sleep_cycles_remaining )
      do_sleep();

    sleep_cycles_remaining = sleep_cycles_per_transmission;
  }

  //
  // Pong back role.  Receive each packet, dump it out, and send it back
  //
  // This is untouched from the pingpair example.
  //

  if ( role == role_pong_back )
  {
    // if there is data ready
    if ( radio.available() )
    {
      // Dump the payloads until we've gotten everything
      unsigned long got_time;
      bool done = false;
      while (!done)
      {
        // Fetch the payload, and see if this was the last one.
        done = radio.read( &got_time, sizeof(unsigned long) );

        // Spew it.  Include our time, because the ping_out millis counter is unreliable
        // due to it sleeping
        printf("Got payload %lu @ %lu...",got_time,millis());
      }

      // First, stop listening so we can talk
      radio.stopListening();

      // Send the final one back.
      radio.write( &got_time, sizeof(unsigned long) );
      printf("Sent response.\n\r");

      // Now, resume listening so we catch the next packets.
      radio.startListening();
    }
  }
}

//
// Sleep helpers
//

// 0=16ms, 1=32ms,2=64ms,3=125ms,4=250ms,5=500ms
// 6=1 sec,7=2 sec, 8=4 sec, 9= 8sec

void setup_watchdog(uint8_t prescalar)
{
  prescalar = min(9,prescalar);
  uint8_t wdtcsr = prescalar & 7;
  if ( prescalar & 8 )
    wdtcsr |= _BV(WDP3);

  MCUSR &= ~_BV(WDRF);
  WDTCSR = _BV(WDCE) | _BV(WDE);
  WDTCSR = _BV(WDCE) | wdtcsr | _BV(WDIE);
}

ISR(WDT_vect)
{
  --sleep_cycles_remaining;
}

void do_sleep(void)
{
  set_sleep_mode(SLEEP_MODE_PWR_DOWN); // sleep mode is set here
  sleep_enable();

  sleep_mode();                        // System sleeps here

  sleep_disable();                     // System continues execution here when watchdog timed out
}

// vim:ai:cin:sts=2 sw=2 ft=cpp