examples_linux/acknowledgementPayloads.cpp

Written by 2bndy5 in 2020

A simple example of sending data from 1 nRF24L01 transceiver to another with Acknowledgement (ACK) payloads attached to ACK packets.

This example was written to be used on 2 devices acting as "nodes". Use ctrl+c to quit at any time.

/*
 * See documentation at https://nRF24.github.io/RF24
 * See License information at root directory of this library
 * Author: Brendan Doherty (2bndy5)
 */
 
#include <ctime>       // time()
#include <iostream>    // cin, cout, endl
#include <string>      // string, getline()
#include <time.h>      // CLOCK_MONOTONIC_RAW, timespec, clock_gettime()
#include <RF24/RF24.h> // RF24, RF24_PA_LOW, delay()
 
using namespace std;
 
/****************** Linux ***********************/
// Radio CE Pin, CSN Pin, SPI Speed
// CE Pin uses GPIO number with BCM and SPIDEV drivers, other platforms use their own pin numbering
// CS Pin addresses the SPI bus number at /dev/spidev<a>.<b>
// ie: RF24 radio(<ce_pin>, <a>*10+<b>); spidev1.0 is 10, spidev1.1 is 11 etc..
#define CSN_PIN 0
#ifdef MRAA
    #define CE_PIN 15 // GPIO22
#elif defined(RF24_WIRINGPI)
    #define CE_PIN 3 // GPIO22
#else
    #define CE_PIN 22
#endif
// Generic:
RF24 radio(CE_PIN, CSN_PIN);
/****************** Linux (BBB,x86,etc) ***********************/
// See http://nRF24.github.io/RF24/pages.html for more information on usage
// See https://github.com/eclipse/mraa/ for more information on MRAA
// See https://www.kernel.org/doc/Documentation/spi/spidev for more information on SPIDEV
 
// For this example, we'll be using a payload containing
// a string & an integer number that will be incremented
// on every successful transmission.
// Make a data structure to store the entire payload of different datatypes
struct PayloadStruct
{
    char message[7]; // only using 6 characters for TX & ACK payloads
    uint8_t counter;
};
PayloadStruct payload;
 
void setRole(); // prototype to set the node's role
void master();  // prototype of the TX node's behavior
void slave();   // prototype of the RX node's behavior
 
// custom defined timer for evaluating transmission time in microseconds
struct timespec startTimer, endTimer;
uint32_t getMicros(); // prototype to get elapsed time in microseconds
 
int main(int argc, char** argv)
{
    // perform hardware check
    if (!radio.begin()) {
        cout << "radio hardware is not responding!!" << endl;
        return 0; // quit now
    }
 
    // Let these addresses be used for the pair
    uint8_t address[2][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
 
    // print example's name
    cout << argv[0] << endl;
 
    // Set the radioNumber via the terminal on startup
    cout << "Which radio is this? Enter '0' or '1'. Defaults to '0' ";
    string input;
    getline(cin, input);
    radioNumber = input.length() > 0 && (uint8_t)input[0] == 49;
 
    // 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 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.
 
    // set the TX address of the RX node into the TX pipe
    radio.openWritingPipe(address[radioNumber]); // always uses pipe 0
 
    // set the RX address of the TX node into a RX pipe
    radio.openReadingPipe(1, address[!radioNumber]); // using pipe 1
 
    // For debugging info
    // radio.printDetails();       // (smaller) function that prints raw register values
    // radio.printPrettyDetails(); // (larger) function that prints human readable data
 
    // ready to execute program now
    setRole(); // calls master() or slave() based on user input
    return 0;
}
 
void setRole()
{
    string input = "";
    while (!input.length()) {
        cout << "*** PRESS 'T' to begin transmitting to the other node\n";
        cout << "*** PRESS 'R' to begin receiving from the other node\n";
        cout << "*** PRESS 'Q' to exit" << endl;
        getline(cin, input);
        if (input.length() >= 1) {
            if (input[0] == 'T' || input[0] == 't')
                master();
            else if (input[0] == 'R' || input[0] == 'r')
                slave();
            else if (input[0] == 'Q' || input[0] == 'q')
                break;
            else
                cout << input[0] << " is an invalid input. Please try again." << endl;
        }
        input = ""; // stay in the while loop
    }               // while
} // setRole()
 
void master()
{
    memcpy(payload.message, "Hello ", 6); // set the payload message
    radio.stopListening();                // put radio in TX mode
 
    unsigned int failures = 0; // keep track of failures
    while (failures < 6) {
        clock_gettime(CLOCK_MONOTONIC_RAW, &startTimer);      // start the timer
        bool report = radio.write(&payload, sizeof(payload)); // transmit & save the report
        uint32_t timerElapsed = getMicros();                  // end the timer
 
        if (report) {
            // payload was delivered
            cout << "Transmission successful! Time to transmit = ";
            cout << timerElapsed; // print the timer result
            cout << " us. Sent: ";
            cout << payload.message;               // print outgoing message
            cout << (unsigned int)payload.counter; // print outgoing counter counter
 
            uint8_t pipe;
            if (radio.available(&pipe)) {
                PayloadStruct received;
                radio.read(&received, sizeof(received)); // get incoming ACK payload
                cout << " Received ";
                cout << (unsigned int)radio.getDynamicPayloadSize(); // print incoming payload size
                cout << " bytes on pipe " << (unsigned int)pipe;     // print pipe that received it
                cout << ": " << received.message;                    // print incoming message
                cout << (unsigned int)received.counter << endl;      // print incoming counter
                payload.counter = received.counter + 1;              // save incoming counter & increment for next outgoing
            }                                                        // if got an ACK payload
            else {
                cout << " Received an empty ACK packet." << endl; // ACK had no payload
            }
        } // if delivered
        else {
            cout << "Transmission failed or timed out" << endl; // payload was not delivered
            failures++;                                         // increment failures
        }
 
        // to make this example readable in the terminal
        delay(1000); // slow transmissions down by 1 second
    }                // while
    cout << failures << " failures detected. Leaving TX role." << endl;
} // master
 
void slave()
{
    memcpy(payload.message, "World ", 6); // set the payload message
 
    // load the payload for the first received transmission on pipe 0
    radio.writeAckPayload(1, &payload, sizeof(payload));
 
    radio.startListening();                  // put radio in RX mode
    time_t startTimer = time(nullptr);       // start a timer
    while (time(nullptr) - startTimer < 6) { // use 6 second timeout
        uint8_t pipe;
        if (radio.available(&pipe)) {                      // is there a payload? get the pipe number that recieved it
            uint8_t bytes = radio.getDynamicPayloadSize(); // get the size of the payload
            PayloadStruct received;
            radio.read(&received, sizeof(received));         // fetch payload from RX FIFO
            cout << "Received " << (unsigned int)bytes;      // print the size of the payload
            cout << " bytes on pipe " << (unsigned int)pipe; // print the pipe number
            cout << ": " << received.message;
            cout << (unsigned int)received.counter; // print received payload
            cout << " Sent: ";
            cout << payload.message;
            cout << (unsigned int)payload.counter << endl; // print ACK payload sent
            startTimer = time(nullptr);                    // reset timer
 
            // save incoming counter & increment for next outgoing
            payload.counter = received.counter + 1;
            // load the payload for the first received transmission on pipe 0
            radio.writeAckPayload(1, &payload, sizeof(payload));
        } // if received something
    }     // while
    cout << "Nothing received in 6 seconds. Leaving RX role." << endl;
    radio.stopListening(); // recommended idle behavior is TX mode
} // slave
 
uint32_t getMicros()
{
    // this function assumes that the timer was started using
    // `clock_gettime(CLOCK_MONOTONIC_RAW, &startTimer);`
 
    clock_gettime(CLOCK_MONOTONIC_RAW, &endTimer);
    uint32_t seconds = endTimer.tv_sec - startTimer.tv_sec;
    uint32_t useconds = (endTimer.tv_nsec - startTimer.tv_nsec) / 1000;
 
    return ((seconds)*1000 + useconds) + 0.5;
}