examples/InterruptConfigure/InterruptConfigure.ino

Written by 2bndy5 in 2020

This example uses Acknowledgement (ACK) payloads attached to ACK packets to demonstrate how the nRF24L01's IRQ (Interrupt Request) pin can be configured to detect when data is received, or when data has transmitted successfully, or when data has failed to transmit.

This example was written to be used on 2 devices acting as "nodes". Use the Serial Monitor to change each node's behavior.

/*
 * See documentation at https://nRF24.github.io/RF24
 * See License information at root directory of this library
 * Author: Brendan Doherty (2bndy5)
 */

#include <SPI.h>
#include "printf.h"
#include "RF24.h"
 
// We will be using the nRF24L01's IRQ pin for this example
#define IRQ_PIN 2                      // this needs to be a digital input capable pin
volatile bool got_interrupt = false;   // used to signal processing of interrupt
volatile bool wait_for_event = false;  // used to wait for an IRQ event to trigger
 
#define CE_PIN 7
#define CSN_PIN 8
// instantiate an object for the nRF24L01 transceiver
RF24 radio(CE_PIN, CSN_PIN);
 
// Let these addresses be used for the pair
uint8_t address[][6] = { "1Node", "2Node" };
// It is very helpful to think of an address as a path instead of as
// an identifying device destination
 
// to use different addresses on a pair of radios, we need a variable to
// uniquely identify which address this radio will use to transmit
bool radioNumber = 1;  // 0 uses address[0] to transmit, 1 uses address[1] to transmit
 
// Used to control whether this node is sending or receiving
bool role = false;  // true = TX node, false = RX node
 
// For this example, we'll be using a payload containing
// a string that changes on every transmission. (successful or not)
// Make a couple arrays of payloads & an iterator to traverse them
const uint8_t tx_pl_size = 5;
const uint8_t ack_pl_size = 4;
uint8_t pl_iterator = 0;
// The " + 1" compensates for the c-string's NULL terminating 0
char tx_payloads[][tx_pl_size + 1] = { "Ping ", "Pong ", "Radio", "1FAIL" };
char ack_payloads[][ack_pl_size + 1] = { "Yak ", "Back", " ACK" };
 
void interruptHandler();  // prototype to handle IRQ events
void printRxFifo();       // prototype to print RX FIFO with 1 buffer
 
 
void setup() {
  Serial.begin(115200);
  while (!Serial) {
    // some boards need to wait to ensure access to serial over USB
  }
 
  // initialize the transceiver on the SPI bus
  if (!radio.begin()) {
    Serial.println(F("radio hardware is not responding!!"));
    while (1) {}  // hold in infinite loop
  }
 
  // print example's introductory prompt
  Serial.println(F("RF24/examples/InterruptConfigure"));
 
  // To set the radioNumber via the Serial monitor on startup
  Serial.println(F("Which radio is this? Enter '0' or '1'. Defaults to '0'"));
  while (!Serial.available()) {
    // wait for user input
  }
  char input = Serial.parseInt();
  radioNumber = input == 1;
  Serial.print(F("radioNumber = "));
  Serial.println((int)radioNumber);
 
  // role variable is hardcoded to RX behavior, inform the user of this
  Serial.println(F("*** PRESS 'T' to begin transmitting to the other node"));
 
  // setup the IRQ_PIN
  pinMode(IRQ_PIN, INPUT);
  attachInterrupt(digitalPinToInterrupt(IRQ_PIN), interruptHandler, FALLING);
  // IMPORTANT: do not call radio.available() before calling
  // radio.whatHappened() when the interruptHandler() is triggered by the
  // IRQ pin FALLING event. According to the datasheet, the pipe information
  // is unreliable during the IRQ pin FALLING transition.
 
  // Set the PA Level low to try preventing power supply related problems
  // because these examples are likely run with nodes in close proximity to
  // each other.
  radio.setPALevel(RF24_PA_LOW);  // RF24_PA_MAX is default.
 
  // For this example we use acknowledgment (ACK) payloads to trigger the
  // IRQ pin when data is received on the TX node.
  // to use ACK payloads, we need to enable dynamic payload lengths
  radio.enableDynamicPayloads();  // ACK payloads are dynamically sized
 
  // Acknowledgement packets have no payloads by default. We need to enable
  // this feature for all nodes (TX & RX) to use ACK payloads.
  radio.enableAckPayload();
 
  // set the TX address of the RX node for use on the TX pipe (pipe 0)
  radio.stopListening(address[radioNumber]);  // put radio in TX mode
 
  // set the RX address of the TX node into a RX pipe
  radio.openReadingPipe(1, address[!radioNumber]);  // using pipe 1
 
  // additional setup specific to the node's RX role
  if (!role) {
    // setup for RX mode
 
    // let IRQ pin only trigger on "data_ready" event in RX mode
    radio.setStatusFlags(RF24_RX_DR);
 
    // Fill the TX FIFO with 3 ACK payloads for the first 3 received
    // transmissions on pipe 1
    radio.writeAckPayload(1, &ack_payloads[0], ack_pl_size);
    radio.writeAckPayload(1, &ack_payloads[1], ack_pl_size);
    radio.writeAckPayload(1, &ack_payloads[2], ack_pl_size);
 
    radio.startListening();  // put radio in RX mode
  }
 
  // For debugging info
  // printf_begin();             // needed only once for printing details
  // radio.printDetails();       // (smaller) function that prints raw register values
  // radio.printPrettyDetails(); // (larger) function that prints human readable data
}
 
void loop() {
  if (got_interrupt) {
    assessInterruptEvent();
  }
 
  if (role && !wait_for_event) {
 
    // This device is a TX node. This if block is only triggered when
    // NOT waiting for an IRQ event to happen
 
    if (pl_iterator == 0) {
      // Test the "data ready" event with the IRQ pin
 
      Serial.println(F("\nConfiguring IRQ pin to ignore the 'data sent' event"));
      radio.setStatusFlags(RF24_RX_DR | RF24_TX_DF);
      Serial.println(F("   Pinging RX node for 'data ready' event..."));
 
    } else if (pl_iterator == 1) {
      // Test the "data sent" event with the IRQ pin
 
      Serial.println(F("\nConfiguring IRQ pin to ignore the 'data ready' event"));
      radio.setStatusFlags(RF24_TX_DS | RF24_TX_DF);
      Serial.println(F("   Pinging RX node for 'data sent' event..."));
 
    } else if (pl_iterator == 2) {
      // Use this iteration to fill the RX node's FIFO which sets us up for the next test.
 
      // write() uses virtual interrupt flags that work despite the masking of the IRQ pin
      // disable IRQ pin for this step
      radio.setStatusFlags();
 
      Serial.println(F("\nSending 1 payload to fill RX node's FIFO. IRQ pin is neglected."));
      // write() will call flush_tx() on 'data fail' events
      if (radio.write(&tx_payloads[pl_iterator], tx_pl_size)) {
        if (radio.rxFifoFull()) {
          Serial.println(F("RX node's FIFO is full; it is not listening any more"));
        } else {
          Serial.println("Transmission successful, but the RX node might still be listening.");
        }
      } else {
        Serial.println(F("Transmission failed or timed out. Continuing anyway."));
        radio.flush_tx();  // discard payload(s) that failed to transmit
      }
 
    } else if (pl_iterator == 3) {
      // test the "data fail" event with the IRQ pin
 
      Serial.println(F("\nConfiguring IRQ pin to reflect all events"));
      radio.setStatusFlags(RF24_IRQ_ALL);
      Serial.println(F("   Pinging inactive RX node for 'data fail' event..."));
    }
 
    if (pl_iterator < 4 && pl_iterator != 2) {
 
      // IRQ pin is LOW when activated. Otherwise it is always HIGH
      // Wait until IRQ pin is activated.
      wait_for_event = true;
 
      // use the non-blocking call to write a payload and begin transmission
      // the "false" argument means we are expecting an ACK packet response
      radio.startFastWrite(tx_payloads[pl_iterator++], tx_pl_size, false);
 
      // In this example, the "data fail" event is always configured to
      // trigger the IRQ pin active. Because the auto-ACK feature is on by
      // default, we don't need a timeout check to prevent an infinite loop.
 
    } else if (pl_iterator == 4) {
      // all IRQ tests are done; flush_tx() and print the ACK payloads for fun
 
      // CE pin is still HIGH which consumes more power. Example is now idling so...
      radio.stopListening();  // ensure CE pin is LOW
      // stopListening() also calls flush_tx() when ACK payloads are enabled
 
      printRxFifo();
      pl_iterator++;
 
 
      // inform user what to do next
      Serial.println(F("\n*** PRESS 'T' to restart the transmissions"));
      Serial.println(F("*** PRESS 'R' to change to Receive role\n"));
 
 
    } else if (pl_iterator == 2) {
      pl_iterator++;  // proceed from step 3 to last step (stop at step 4 for readability)
    }
 
  } else if (!role && radio.rxFifoFull()) {
    // This device is a RX node:
    // wait until RX FIFO is full then stop listening
 
    delay(100);             // let ACK payload finish transmitting
    radio.stopListening();  // also discards unused ACK payloads
    printRxFifo();          // flush the RX FIFO
 
    // Fill the TX FIFO with 3 ACK payloads for the first 3 received
    // transmissions on pipe 1.
    radio.writeAckPayload(1, &ack_payloads[0], ack_pl_size);
    radio.writeAckPayload(1, &ack_payloads[1], ack_pl_size);
    radio.writeAckPayload(1, &ack_payloads[2], ack_pl_size);
 
    delay(100);              // let TX node finish its role
    radio.startListening();  // We're ready to start over. Begin listening.
 
  }  // role
 
  if (Serial.available()) {
    // change the role via the serial monitor
 
    char c = toupper(Serial.read());
    if (c == 'T') {
      // Become the TX node
      if (!role)
        Serial.println(F("*** CHANGING TO TRANSMIT ROLE -- PRESS 'R' TO SWITCH BACK"));
      else
        Serial.println(F("*** RESTARTING IRQ PIN TEST ***"));
 
      role = true;
      wait_for_event = false;
      pl_iterator = 0;   // reset the iterator
      radio.flush_tx();  // discard any payloads in the TX FIFO
 
      // startListening() clears the IRQ masks also. This is required for
      // continued TX operations when a transmission fails.
      radio.stopListening();  // this also discards any unused ACK payloads
 
    } else if (c == 'R' && role) {
      // Become the RX node
      Serial.println(F("*** CHANGING TO RECEIVE ROLE -- PRESS 'T' TO SWITCH BACK"));
 
      role = false;
 
      // let IRQ pin only trigger on "data_ready" event in RX mode
      radio.setStatusFlags(RF24_RX_DR);
 
      // Fill the TX FIFO with 3 ACK payloads for the first 3 received
      // transmissions on pipe 1
      radio.flush_tx();  // make sure there is room for 3 new ACK payloads
      radio.flush_rx();  // make sure there is room for 3 incoming payloads
      radio.writeAckPayload(1, &ack_payloads[0], ack_pl_size);
      radio.writeAckPayload(1, &ack_payloads[1], ack_pl_size);
      radio.writeAckPayload(1, &ack_payloads[2], ack_pl_size);
      radio.startListening();
    }
  }  // Serial.available()
}  // loop
 

void interruptHandler() {
  got_interrupt = true;  // forward event handling back to main loop()
}

void assessInterruptEvent() {
  // print IRQ status and all masking flags' states
 
  Serial.println(F("\tIRQ pin is actively LOW"));  // show that this function was called
  delayMicroseconds(250);
  uint8_t flags = radio.clearStatusFlags();
  // Resetting the tx_df flag is required for
  // continued TX operations when a transmission fails.
  // clearing the status flags resets the IRQ pin to its inactive state (HIGH)
 
  Serial.print(F("\tdata_sent: "));
  Serial.print((flags & RF24_TX_DS) > 0);  // print "data sent" flag state
  Serial.print(F(", data_fail: "));
  Serial.print((flags & RF24_TX_DF) > 0);  // print "data fail" flag state
  Serial.print(F(", data_ready: "));
  Serial.println((flags & RF24_RX_DR) > 0);  // print "data ready" flag state
 
  if (flags & RF24_TX_DF)  // if TX payload failed
    radio.flush_tx();      // clear all payloads from the TX FIFO
 
  // print if test passed or failed. Unintentional fails mean the RX node was not listening.
  // pl_iterator has already been incremented by now
  if (pl_iterator <= 1) {
    Serial.print(F("   'Data Ready' event test "));
    Serial.println(flags & RF24_RX_DR ? F("passed") : F("failed"));
  } else if (pl_iterator == 2) {
    Serial.print(F("   'Data Sent' event test "));
    Serial.println(flags & RF24_TX_DS ? F("passed") : F("failed"));
  } else if (pl_iterator == 4) {
    Serial.print(F("   'Data Fail' event test "));
    Serial.println(flags & RF24_TX_DF ? F("passed") : F("failed"));
  }
  got_interrupt = false;   // reset this flag to prevent calling this function from loop()
  wait_for_event = false;  // ready to continue with loop() operations
}

void printRxFifo() {
  if (radio.available()) {  // if there is data in the RX FIFO
    // to flush the data from the RX FIFO, we'll fetch it all using 1 buffer
 
    uint8_t pl_size = !role ? tx_pl_size : ack_pl_size;
    char rx_fifo[pl_size * 3 + 1];  // RX FIFO is full & we know ACK payloads' size
    if (radio.rxFifoFull()) {
      rx_fifo[pl_size * 3] = 0;           // add a NULL terminating char to use as a c-string
      radio.read(&rx_fifo, pl_size * 3);  // this clears the RX FIFO (for this example)
    } else {
      uint8_t i = 0;
      while (radio.available()) {
        radio.read(&rx_fifo + (i * pl_size), pl_size);
        i++;
      }
      rx_fifo[i * pl_size] = 0;  // add a NULL terminating char to use as a c-string
    }
    Serial.print(F("Complete RX FIFO: "));
    Serial.println(rx_fifo);  // print the entire RX FIFO with 1 buffer
  }
}