Sending Hello World from a test node based on a Dragino LoRa Shield on a Mega2560, based on https://github.com/SensorsIot/LoRa/blob/master/Nodes/Dragino/HelloWorld/HelloWorld.ino

Mega2560DraginoLoRaHelloWorld.ino

// MIT License
// https://github.com/gonzalocasas/arduino-uno-dragino-lorawan/blob/master/LICENSE
// Based on examples from https://github.com/matthijskooijman/arduino-lmic
// Copyright (c) 2015 Thomas Telkamp and Matthijs Kooijman

// Adaptions: Andreas Spiess

#include <lmic.h>
#include <hal/hal.h>
//#include <credentials.h>

uint8_t NWKSKEY[] = { 0x0A, 0x50, 0x2A, 0x05, 0x2B, 0x05, 0x5D, 0x6E, 0x16, 0x76, 0x3B, 0xA8, 0x07, 0xC9, 0xEC, 0x5B };
uint8_t APPSKEY[] = { 0x14, 0x51, 0x6D, 0xA8, 0x09, 0x31, 0xC6, 0x2A, 0x44, 0x26, 0x28, 0x02, 0x1E, 0x4A, 0xDC, 0xC5 };
const long int DEVADDR = 0x2601103C;

// These callbacks are only used in over-the-air activation, so they are
// left empty here (we cannot leave them out completely unless
// DISABLE_JOIN is set in config.h, otherwise the linker will complain).
void os_getArtEui (u1_t* buf) { }
void os_getDevEui (u1_t* buf) { }
void os_getDevKey (u1_t* buf) { }

static osjob_t sendjob;

// Schedule TX every this many seconds (might become longer due to duty
// cycle limitations).
const unsigned TX_INTERVAL = 60;

// Pin mapping Dragino Shield
const lmic_pinmap lmic_pins = {
    .nss = 10,
    .rxtx = LMIC_UNUSED_PIN,
    .rst = 9,
    .dio = {2, 6, 7},
};
void onEvent (ev_t ev) {
    if (ev == EV_TXCOMPLETE) {
        Serial.println(F("EV_TXCOMPLETE (includes waiting for RX windows)"));
        // Schedule next transmission
        os_setTimedCallback(&sendjob, os_getTime()+sec2osticks(TX_INTERVAL), do_send);
    }
}

void do_send(osjob_t* j){
    // Payload to send (uplink)
    static uint8_t message[] = "hi";

    // Check if there is not a current TX/RX job running
    if (LMIC.opmode & OP_TXRXPEND) {
        Serial.println(F("OP_TXRXPEND, not sending"));
    } else {
        // Prepare upstream data transmission at the next possible time.
        LMIC_setTxData2(1, message, sizeof(message)-1, 0);
        Serial.println(F("Sending uplink packet..."));
    }
    // Next TX is scheduled after TX_COMPLETE event.
}

void setup() {
    Serial.begin(115200);
    Serial.println(F("Starting..."));

    // LMIC init
    os_init();

    // Reset the MAC state. Session and pending data transfers will be discarded.
    LMIC_reset();

    // Set static session parameters.
    LMIC_setSession (0x1, DEVADDR, NWKSKEY, APPSKEY);

    // Disable link check validation
    LMIC_setLinkCheckMode(0);

    // TTN uses SF9 for its RX2 window.
    LMIC.dn2Dr = DR_SF9;

    // Set data rate and transmit power for uplink (note: txpow seems to be ignored by the library)
    LMIC_setDrTxpow(DR_SF7,14);

    for (int i=1; i<=8; i++)
    { 
      LMIC_disableChannel(i); 
    }

    // Start job
    do_send(&sendjob);
}

void loop() {
    os_runloop_once();
}