Send text message to mestastic primary channel from Arduino MKR WAN 1310 LoRa using meshtastic-lite library

meshtastic-lite-send-text.ino

// AES from Crypto library (https://github.com/rweather/arduinolibs)
#include <AES.h>
// arduino-LoRa library (https://github.com/sandeepmistry/arduino-LoRa)
// Firmware must be written using MKRWANFWUpdate_standalone example in https://github.com/arduino-libraries/MKRWAN, not v2!)
#include <LoRa.h>
// meshtastic-lite library (https://github.com/jstockdale/meshtastic-lite)
// A fix may be required to send messages longer than 12B (https://github.com/jstockdale/meshtastic-lite/pull/1)
#include <meshtastic.h>
#include <string.h>

static AES128  g_aes;
static uint8_t g_cached_key[16];
static bool    g_key_set = false;

extern "C" void mesh_aes_block_encrypt(const uint8_t *key, int key_bits,
                                        const uint8_t in[16], uint8_t out[16])
{
    (void)key_bits;
    if (!g_key_set || memcmp(key, g_cached_key, 16) != 0) {
        g_aes.setKey(key, 16);
        memcpy(g_cached_key, key, 16);
        g_key_set = true;
    }
    g_aes.encryptBlock(out, in);
}

// ─── Configuration ──────────────────────────────────────────────────────────

static const char     TX_TEXT[]       = "Test message from Arduino MKR1310 (meshtastic-lite)";
static const uint32_t TX_INTERVAL_MS  = 30000UL;  // 30 s between transmissions

// ─── Globals ────────────────────────────────────────────────────────────────

static MeshSession   session;
static uint8_t       tx_frame[255];
static unsigned long last_tx_ms;

// ─── SAMD21 node number from unique serial ──────────────────────────────────
// SAMD21 has a 128-bit serial spread across four non-contiguous NVM words:
//   word 0 @ 0x0080A00C,  word 3 @ 0x0080A048
// XOR gives a stable 32-bit value suitable as a Meshtastic node number.

static uint32_t getNodeNum() {
    const uint32_t w0 = *reinterpret_cast<const volatile uint32_t *>(0x0080A00Cu);
    const uint32_t w3 = *reinterpret_cast<const volatile uint32_t *>(0x0080A048u);
    return w0 ^ w3;
}

// ─── Send one Meshtastic text broadcast ─────────────────────────────────────

static void sendMessage() {
    size_t len = session.buildTextTx(
        0, MESH_ADDR_BROADCAST, TX_TEXT, false, false, tx_frame);
    if (len == 0) { Serial.println("buildTextTx failed"); return; }
    if (!LoRa.beginPacket()) { Serial.println("beginPacket failed"); return; }
    LoRa.write(tx_frame, len);
    LoRa.endPacket();
    Serial.print("TX "); Serial.print(len); Serial.println(" bytes OK");
}

// ─── Setup ──────────────────────────────────────────────────────────────────

void setup() {
    Serial.begin(115200);
    while (!Serial && millis() < 3000);  // wait up to 3 s for USB console

    // Derive node number from SAMD21 hardware unique serial
    uint32_t node_num = getNodeNum();
    Serial.print("Node num : 0x"); Serial.println(node_num, HEX);

    // Seed packet-ID generator with hardware entropy
    srand(node_num ^ (uint32_t)analogRead(A0));

    // Initialise Meshtastic session — JP LongFast, default PSK channel (AES-128)
    session.init(REGION_JP, MODEM_LONG_FAST, ROLE_CLIENT, node_num);
    session.channels.addDefaultChannel();

    // Derive all radio parameters from the session (frequency, SF, BW, CR, …)
    MeshRadioConfig rc = session.radioConfig();
    Serial.print("Frequency : "); Serial.print(rc.frequency_mhz, 3); Serial.println(" MHz");
    Serial.print("SF / BW   : "); Serial.print(rc.spreading_factor);
    Serial.print(" / "); Serial.print((int)rc.bandwidth_khz); Serial.println(" kHz");
    Serial.print("TX power  : "); Serial.print(rc.tx_power_dbm); Serial.println(" dBm");

    // Initialise LoRa radio
    if (!LoRa.begin((long)(rc.frequency_mhz * 1.0e6f))) {
        Serial.println("LoRa init FAILED — check antenna/module");
        while (1);
    }
    LoRa.setSpreadingFactor(rc.spreading_factor);                // 11
    LoRa.setSignalBandwidth((long)(rc.bandwidth_khz * 1000.0f)); // 250 000 Hz
    LoRa.setCodingRate4(rc.coding_rate);                         // 5 → 4/5
    LoRa.setSyncWord(rc.sync_word);                              // 0x2B (Meshtastic private)
    LoRa.setPreambleLength(rc.preamble_length);                  // 16 symbols
    LoRa.setTxPower(rc.tx_power_dbm);                            // 13 dBm (JP limit)
    LoRa.enableCrc();

    Serial.println("LoRa ready — sending first packet now");
    sendMessage();
    last_tx_ms = millis();
}

// ─── Loop ───────────────────────────────────────────────────────────────────

void loop() {
    if (millis() - last_tx_ms >= TX_INTERVAL_MS) {
        last_tx_ms = millis();
        sendMessage();
    }
}