IBM LMIC library in TTGO Lora32 unable to send data to gateway

Hello All,
I am new to lorawan so I am having difficulties in sending data from end node to gateway. My configuration is TTGO Lora32 module to RAK7268 gateway connected to AWS IoT Core for Lorawan.
I am using IBM LMIC library for my Lora32 board. Here is the code -

#define CONFIG_SPIRAM_IGNORE_NOTFOUND
#include <lmic.h>
#include <hal/hal.h>
#include <SPI.h>

//#define hal_init LMICHAL_init

// This EUI must be in little-endian format, so least-significant-byte
// first. When copying an EUI from ttnctl output, this means to reverse
// the bytes. For TTN issued EUIs the last bytes should be 0xD5, 0xB3,
// 0x70.
static const u1_t PROGMEM APPEUI[8]={ 0x, 0x, 0x, 0x, 0x, 0x, 0x, 0x };
void os_getArtEui (u1_t* buf) { memcpy_P(buf, APPEUI, 8);}

// This should also be in little endian format, see above.
static const u1_t PROGMEM DEVEUI[8]={ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
void os_getDevEui (u1_t* buf) { memcpy_P(buf, DEVEUI, 8);}

// This key should be in big endian format (or, since it is not really a
// number but a block of memory, endianness does not really apply). In
// practice, a key taken from ttnctl can be copied as-is.
// The key shown here is the semtech default key.
static const u1_t PROGMEM APPKEY[16] = { 0x, 0x, 0x, 0x, 0x, 0x, 0x, 0x, 0x, 0x, 0x, 0x, 0x, 0x, 0x,0x };
void os_getDevKey (u1_t* buf) {  memcpy_P(buf, APPKEY, 16);}

static uint8_t mydata[] = "Hello, world!";
static osjob_t sendjob;

// Schedule TX every this many seconds (might become longer due to duty
// cycle limitations).
const unsigned TX_INTERVAL = 120;

// Pin mapping

const lmic_pinmap lmic_pins = {
    .nss = 18, 
    .rxtx = LMIC_UNUSED_PIN,
    .rst = 23,
    .dio = {/*dio0*/ 26, /*dio1*/ 33, /*dio2*/ 32} 
};
void onEvent (ev_t ev) {
    Serial.print(os_getTime());
    Serial.print(": ");
    switch(ev) {
        case EV_SCAN_TIMEOUT:
            Serial.println(F("EV_SCAN_TIMEOUT"));
            break;
        case EV_BEACON_FOUND:
            Serial.println(F("EV_BEACON_FOUND"));
            break;
        case EV_BEACON_MISSED:
            Serial.println(F("EV_BEACON_MISSED"));
            break;
        case EV_BEACON_TRACKED:
            Serial.println(F("EV_BEACON_TRACKED"));
            break;
        case EV_JOINING:
            Serial.println(F("EV_JOINING"));
            break;
        case EV_JOINED:
            Serial.println(F("EV_JOINED"));

            // Disable link check validation (automatically enabled
            // during join, but not supported by TTN at this time).
            LMIC_setLinkCheckMode(0);
            break;
        case EV_RFU1:
            Serial.println(F("EV_RFU1"));
            break;
        case EV_JOIN_FAILED:
            Serial.println(F("EV_JOIN_FAILED"));
            break;
        case EV_REJOIN_FAILED:
            Serial.println(F("EV_REJOIN_FAILED"));
            break;
            break;
        case EV_TXCOMPLETE:
            Serial.println(F("EV_TXCOMPLETE (includes waiting for RX windows)"));
            if (LMIC.txrxFlags & TXRX_ACK)
              Serial.println(F("Received ack"));
            if (LMIC.dataLen) {
              Serial.println(F("Received "));
              Serial.println(LMIC.dataLen);
              Serial.println(F(" bytes of payload"));
            }
            // Schedule next transmission
            os_setTimedCallback(&sendjob, os_getTime()+sec2osticks(TX_INTERVAL), do_send);
            break;
        case EV_LOST_TSYNC:
            Serial.println(F("EV_LOST_TSYNC"));
            break;
        case EV_RESET:
            Serial.println(F("EV_RESET"));
            break;
        case EV_RXCOMPLETE:
            // data received in ping slot
            Serial.println(F("EV_RXCOMPLETE"));
            break;
        case EV_LINK_DEAD:
            Serial.println(F("EV_LINK_DEAD"));
            break;
        case EV_LINK_ALIVE:
            Serial.println(F("EV_LINK_ALIVE"));
            break;
         default:
            Serial.println(F("Unknown event"));
            break;
    }
}

void do_send(osjob_t* j){
    // 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, mydata, sizeof(mydata)-1, 0);
        Serial.println(F("Packet queued"));
    }
    // Next TX is scheduled after TX_COMPLETE event.
}
void setup() {
    Serial.begin(115200);
    Serial.println(F("Starting"));

    #ifdef VCC_ENABLE
    // For Pinoccio Scout boards
    pinMode(VCC_ENABLE, OUTPUT);
    digitalWrite(VCC_ENABLE, HIGH);
    delay(1000);
    #endif

    // LMIC init
    os_init();
    Serial.println("os init() done");
    // Reset the MAC state. Session and pending data transfers will be discarded.
    LMIC_reset();
    Serial.println("reset done");


    // Start job (sending automatically starts OTAA too)
    do_send(&sendjob);
}

void loop() {
    os_runloop_once();
}

Serial Monitor -
entry 0x400805e4
Starting
os init() done
reset done
Packet queued
2716: EV_JOINING


It is the example code in the library itself for OTAA. The gateway is connected to AWS IoT Core, I can confirm this since it shows connected on AWS platform. The connection between the gateway and AWS uses LNS certs.
As you can see in the serial monitor, it says joining but it not going forward in sending the data. The keys are configured correctly I have only removed them for this post.
Can someone tell me what I am doing wrong or is missing? Thank you.

Hi @Sowmesh Let’s start confirming that the join request is received by the gateway. You can check this in the gateway WebUI:

  • For the v1 gateways, running the WisGateOS - Status → LoRa Packet Logger.
  • For the v2 gateways, running the WisGateOS2 - Dashboard → Overview → Packet capture.

Honestly, I am not so familiar with the TTGO, but where is your LoRa band defined?

Hi Todor,
Thank you for your reply. For further information, The lora band is AS923 and the device is in Hong Kong. I haven’t defined the band in the sketch but this is the example code for the LMIC library and doesn’t include that. The module however, only operates with on 923Mhz. The image below shows the packet capture on wisgate.


The device IDs of the devices that are sending the join request do not match with the device ID I have set in the sketch.

Not 100% sure (I am using AS923-3).
As far as I know AS923 devices uses for join request DR2, which is SF10 BW125.
But your device tries to join with SF8 BW125, which is DR4.

At least my devices are all joining with DR2 and then switching the DR to the required data rate for the payload size.

That might be the reason that the LNS doesn’t accept the Join Request.

Update on this topic. I was using the IBM LMIC library before for the TTGO lora32 board which I found out is not being maintained anymore. I am now using the MCCI Lorawan LMIC library which is modified for Arduino projects and the code (example sketch) works fine. Also just a heads up since you might end up spending sometime on this as a beginner, the APPEUI and DEVEUI should not be directly copy pasted from your network server instead you must reverse the bytes.