examples_linux/manualAcknowledgements.cpp

Written by 2bndy5 in 2020

A simple example of sending data from 1 nRF24L01 transceiver to another with manually transmitted (non-automatic) Acknowledgement (ACK) payloads. This example still uses ACK packets, but they have no payloads. Instead the acknowledging response is sent with write(). This tactic allows for more updated acknowledgement payload data, where actual ACK payloads' data are outdated by 1 transmission because they have to loaded before receiving a transmission.

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 & RX 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
    }
 
    // append a NULL terminating 0 for printing as a c-string
    payload.message[6] = 0;
 
    // Let these addresses be used for the pair of nodes used in this example
    uint8_t address[2][6] = {"1Node", "2Node"};
    //             the TX address^ ,  ^the RX address
    // 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;
 
    // 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.
 
    // save on transmission time by setting the radio to only transmit the
    // number of bytes we need to transmit a float
    radio.setPayloadSize(sizeof(payload)); // char[7] & uint8_t datatypes occupy 8 bytes
 
    // set the TX address of the RX node for use on the TX pipe (pipe 0)
    radio.stopListening(address[radioNumber]);
 
    // 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;
} // main

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 outgoing message
    radio.stopListening();                // put 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
 
        if (report) {
            // transmission successful; wait for response and print results
 
            radio.startListening();                 // put in RX mode
            unsigned long start_timeout = millis(); // timer to detect no response
            while (!radio.available()) {            // wait for response
                if (millis() - start_timeout > 200) // only wait 200 ms
                    break;
            }
            unsigned long elapsedTime = getMicros(); // end the timer
            radio.stopListening();                   // put back in TX mode
 
            // print summary of transactions
            uint8_t pipe;
            cout << "Transmission successful! ";
            if (radio.available(&pipe)) {               // is there a payload received? grab the pipe number that received it
                uint8_t bytes = radio.getPayloadSize(); // grab the incoming payload size
                cout << "Round trip delay = ";
                cout << elapsedTime;                      // print the timer result
                cout << " us. Sent: " << payload.message; // print outgoing message
                cout << (unsigned int)payload.counter;    // print outgoing counter
                PayloadStruct received;
                radio.read(&received, sizeof(received));     // get incoming payload
                cout << " Received " << (unsigned int)bytes; // print incoming payload size
                cout << " on pipe " << (unsigned int)pipe;   // print RX pipe number
                cout << ": " << received.message;            // print the incoming message
                cout << (unsigned int)received.counter;      // print the incoming counter
                cout << endl;
                payload.counter = received.counter; // save incoming counter for next outgoing counter
            }
            else {
                cout << "Received no response." << endl; // no response received
            }
        }
        else {
            cout << "Transmission failed or timed out"; // payload was not delivered
            cout << endl;
            failures++; // increment failure counter
        }               // report
 
        // 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 response message
    radio.startListening();               // put 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 received it
            uint8_t bytes = radio.getPayloadSize(); // get size of incoming payload
            PayloadStruct received;
            radio.read(&received, sizeof(received)); // get incoming payload
            payload.counter = received.counter + 1;  // increment payload for response
 
            // transmit response & save result to `report`
            radio.stopListening();                      // put in TX mode
            radio.writeFast(&payload, sizeof(payload)); // load response into TX FIFO
            bool report = radio.txStandBy(150);         // keep retrying for 150 ms
            radio.startListening();                     // put back in RX mode
 
            // print summary of transactions
            cout << "Received " << (unsigned int)bytes; // print the size of the payload
            cout << " bytes on pipe ";
            cout << (unsigned int)pipe;             // print the pipe number
            cout << ": " << received.message;       // print incoming message
            cout << (unsigned int)received.counter; // print incoming counter
 
            if (report) {
                cout << " Sent: " << payload.message;  // print outgoing message
                cout << (unsigned int)payload.counter; // print outgoing counter
                cout << endl;
            }
            else {
                cout << " Response failed to send." << endl; // failed to send response
            }
            startTimer = time(nullptr); // reset timer
        }                               // available
    }                                   // while
 
    cout << "Nothing received in 6 seconds. Leaving RX role." << endl;
    radio.stopListening(); // recommended idle mode 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;
}