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--- iothings:laboratoare:2025:lab2 [2025/10/06 13:31]
dan.tudose
+++ iothings:laboratoare:2025:lab2 [2025/10/07 13:44] (current)
dan.tudose [BLE Security and Pairing]
@@ Line 484: / Line 484: @@
 The Bluetooth Low Energy (BLE) Current Time Service (CTS) is a standardized GATT (Generic Attribute Profile) service defined by the Bluetooth SIG. It allows a BLE peripheral (like a smartwatch or a clock) to expose the current date and time to another device (like a smartphone or computer).
-Here’s a breakdown of what it is and how it works:
 ==== Overview ====
@@ Line 501: / Line 499: @@
 [[https://www.bluetooth.com/specifications/specs/cts-1-1/| here]]
+^ Field | Size (bytes) | Description | Range ^
+| Year | 2 | Year (e.g. 2025) | 1582–9999 |
+| Month | 1 | Month | 1–12 |
+| Day | 1 | Day of month | 1–31 |
+| Hours | 1 | Hours | 0–23 |
+| Minutes | 1 | Minutes | 0–59 |
+| Seconds | 1 | Seconds | 0–59 |
+| Day of Week | 1 | Monday = 1 … Sunday = 7 | 1–7 |
+| Fractions256 | 1 | 1/256th of a second (0–255) | — |
+| Adjust Reason | 1 | Why time was changed | Bitmask |
+Adjust Reason bitmask:
+^ Bit | Meaning ^
+| 0 | Manual time update |
+| 1 | External reference time update (e.g., via NTP or GNSS) |
+| 2 | Change of time zone |
+| 3 | Change of DST (Daylight Saving Time) |
+==== Operation Example ====
+  * A client (e.g., BLE thermometer) connects to a server (e.g., smartphone).
+  * The client reads the Current Time characteristic to get the date/time.
+  * The client may subscribe to notifications, so when the time updates (e.g., due to DST), it receives an update automatically.
+==== Set Up nRF Connect to Broadcast Current Time Service (CTS) ====
+<note warning>These steps are for Android. nRF Connect on iOS can advertise as a peripheral, but emulating CTS server behavior there is limited compared to Android.</note>
+=== Part 1 — Create a CTS GATT Server (Android) ===
+. **Open nRF Connect → Menu ☰ → “Configure GATT server”.**
+    * Tap **Add service**. From the list, pick **Current Time Service (0x1805)** (there’s a built-in preset).
+. **Verify characteristics.**
+    * Inside the service, you should see:
+      * **Current Time (0x2A2B)** — properties typically **Read**, **Notify**, and **Write (with response)**.
+      * (Optional) **Local Time Information (0x2A0F)** and **Reference Time Information (0x2A14)**.
+    * If something’s missing, add it manually with the correct 16-bit UUIDs.
+. **(Optional) Set an initial value manually** for testing:
+    The Current Time value is 10 bytes. Example for **2025-10-06 14:32:10**, **Monday**, fractions=0, **AdjustReason=External ref update**:
+    `E9 07 0A 06 0E 20 0A 01 00 02`
+    (Little-endian year 0x07E9, then month, day, hour, minute, second, day-of-week 1=Mon, fractions256, adjust-reason bitmask).
+=== Part 2 — Advertise it so Clients Can Find You ===
+. **Go to “Advertiser”** (tab at the bottom) and **create a new set**:
+    * Enable **Connectable** (so the client can connect).
+    * Add **Service UUID 0x1805** to the advertising data (helps clients filter).
+    * Start advertising.
+. **Start the server** (if your app version separates server start from advertising).
+    * Make sure your created CTS config is the active one.
+=== Part 3 — Connect from the Client and Sync Time ===
+. **Connect from your BLE client**.
+    * Many CTS clients will **read 0x2A2B** on connect and may **subscribe to notifications**.
+    * Some stacks require **bonding** before allowing CTS writes/reads; accept pairing if prompted.
+. **Confirm it works.**
+    * On the client, you should see **Service 0x1805** with **Characteristic 0x2A2B**.
+    * A read should return your current time payload; enabling notifications will push updates when you modify it.
+==== CTS Service on NimBLE ====
+Here is an example of a NimBLE client that discovers a peripheral advertising the Current Time Service, connects, reads characteristic 0x2A2B, and prints the decoded timestamp. Run it on your Sparrow node after setting up a CTS GATT Server.
+<code C main.cpp>
+#include <Arduino.h>
+#include <NimBLEDevice.h>
+#include <Wire.h>
+#include <Adafruit_SSD1306.h>
+namespace {
+const NimBLEUUID CTS_SERVICE_UUID((uint16_t)0x1805);
+const NimBLEUUID CTS_CHARACTERISTIC_UUID((uint16_t)0x2A2B);
+constexpr uint32_t CTS_READ_INTERVAL_MS = 10000; // 10 seconds
+const NimBLEAdvertisedDevice* g_targetDevice = nullptr;
+NimBLEClient* g_client = nullptr;
+NimBLERemoteCharacteristic* g_ctsChar = nullptr;
+bool g_doConnect = false;
+uint32_t g_lastReadMillis = 0;
+constexpr uint8_t OLED_WIDTH = 128;
+constexpr uint8_t OLED_HEIGHT = 64;
+constexpr uint8_t OLED_RESET_PIN = -1;
+constexpr uint8_t OLED_I2C_ADDR = 0x3C;
+constexpr uint8_t OLED_LINE_HEIGHT = 10;
+constexpr uint8_t OLED_TOP_MARGIN = 12;
+Adafruit_SSD1306 g_display(OLED_WIDTH, OLED_HEIGHT, &Wire, OLED_RESET_PIN);
+struct CurrentTime {
+  uint16_t year;
+  uint8_t month;
+  uint8_t day;
+  uint8_t hours;
+  uint8_t minutes;
+  uint8_t seconds;
+  uint8_t dayOfWeek;
+  uint8_t fractions256;
+  uint8_t adjustReason;
+};
+void printCurrentTime(const CurrentTime& time) {
+  static const char* kDays[] = {"Unknown", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"};
+  const char* dow = (time.dayOfWeek >= 1 && time.dayOfWeek <= 7) ? kDays[time.dayOfWeek] : kDays[0];
+  Serial.printf("[CTS] %04u-%02u-%02u %02u:%02u:%02u (%s) adj=0x%02X frac=%u\n",
+                time.year,
+                time.month,
+                time.day,
+                time.hours,
+                time.minutes,
+                time.seconds,
+                dow,
+                time.adjustReason,
+                time.fractions256);
+}
+bool parseCurrentTime(const uint8_t* buffer, size_t length, CurrentTime& out) {
+  if (length < 10) {
+    Serial.printf("[CTS] Expected 10 bytes, got %u\n", static_cast<unsigned>(length));
+    return false;
+  }
+  out.year = static_cast<uint16_t>(buffer[0] | (buffer[1] << 8));
+  out.month = buffer[2];
+  out.day = buffer[3];
+  out.hours = buffer[4];
+  out.minutes = buffer[5];
+  out.seconds = buffer[6];
+  out.dayOfWeek = buffer[7];
+  out.fractions256 = buffer[8];
+  out.adjustReason = buffer[9];
+  return true;
+}
+void displayStatusMessage(const char* message) {
+  g_display.clearDisplay();
+  g_display.setCursor(0, OLED_TOP_MARGIN);
+  g_display.println(message);
+  g_display.display();
+}
+void displayCurrentTime(const CurrentTime& time) {
+  g_display.clearDisplay();
+  g_display.setCursor(0, OLED_TOP_MARGIN);
+  char line[24];
+  snprintf(line, sizeof(line), "%04u-%02u-%02u", time.year, time.month, time.day);
+  g_display.println(line);
+  snprintf(line, sizeof(line), "%02u:%02u:%02u", time.hours, time.minutes, time.seconds);
+  g_display.println(line);
+  static const char* kDays[] = {"", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"};
+  const char* dow = (time.dayOfWeek >= 1 && time.dayOfWeek <= 7) ? kDays[time.dayOfWeek] : "";
+  g_display.println(dow);
+  g_display.display();
+}
+class ClientCallbacks : public NimBLEClientCallbacks {
+  void onConnect(NimBLEClient* client) override {
+    Serial.printf("[BLE] Connected to %s\n", client->getPeerAddress().toString().c_str());
+    displayStatusMessage("Connected");
+  }
+  void onDisconnect(NimBLEClient* client, int reason) override {
+    Serial.printf("[BLE] Disconnected (reason %d), restarting scan\n", reason);
+    g_ctsChar = nullptr;
+    g_lastReadMillis = 0;
+    NimBLEDevice::deleteClient(client);
+    g_client = nullptr;
+    displayStatusMessage("Disconnected");
+    NimBLEDevice::getScan()->start(0, false, true);
+  }
+};
+class ScanCallbacks : public NimBLEScanCallbacks {
+  void onResult(const NimBLEAdvertisedDevice* advertisedDevice) override {
+    if (!advertisedDevice->isAdvertisingService(CTS_SERVICE_UUID)) {
+      return;
+    }
+    Serial.printf("[BLE] Found CTS peripheral: %s\n", advertisedDevice->toString().c_str());
+    NimBLEDevice::getScan()->stop();
+    g_targetDevice = advertisedDevice;
+    g_doConnect = true;
+  }
+  void onScanEnd(const NimBLEScanResults& results, int reason) override {
+    Serial.printf("[BLE] Scan ended (reason %d, %d devices)\n", reason, results.getCount());
+    if (!g_doConnect && g_ctsChar == nullptr) {
+      NimBLEDevice::getScan()->start(0, false, true);
+    }
+  }
+};
+ClientCallbacks g_clientCallbacks;
+ScanCallbacks g_scanCallbacks;
+void startScan() {
+  NimBLEScan* scan = NimBLEDevice::getScan();
+  scan->setScanCallbacks(&g_scanCallbacks, false);
+  scan->setActiveScan(true);
+  scan->setInterval(160);
+  scan->setWindow(120);
+  scan->start(0, false, true);
+  Serial.println("[BLE] Scanning for Current Time Service peripherals...");
+  displayStatusMessage("Scanning...");
+}
+bool connectToCurrentTimeService() {
+  if (!g_doConnect || g_targetDevice == nullptr) {
+    return false;
+  }
+  g_doConnect = false;
+  if (g_client == nullptr) {
+    g_client = NimBLEDevice::createClient();
+    g_client->setClientCallbacks(&g_clientCallbacks, false);
+    g_client->setConnectionParams(12, 12, 0, 200);
+    g_client->setConnectTimeout(5000);
+  }
+  Serial.println("[BLE] Connecting to peripheral...");
+  if (!g_client->connect(g_targetDevice)) {
+    Serial.println("[BLE] Connection failed, restarting scan");
+    NimBLEDevice::deleteClient(g_client);
+    g_client = nullptr;
+    g_ctsChar = nullptr;
+    g_targetDevice = nullptr;
+    NimBLEDevice::getScan()->start(0, false, true);
+    return false;
+  }
+  NimBLERemoteService* service = g_client->getService(CTS_SERVICE_UUID);
+  if (service == nullptr) {
+    Serial.println("[BLE] Current Time Service not found on peripheral");
+    g_client->disconnect();
+    NimBLEDevice::deleteClient(g_client);
+    g_client = nullptr;
+    g_ctsChar = nullptr;
+    g_targetDevice = nullptr;
+    NimBLEDevice::getScan()->start(0, false, true);
+    return false;
+  }
+  NimBLERemoteCharacteristic* characteristic = service->getCharacteristic(CTS_CHARACTERISTIC_UUID);
+  if (characteristic == nullptr) {
+    Serial.println("[BLE] Current Time characteristic missing");
+    g_client->disconnect();
+    NimBLEDevice::deleteClient(g_client);
+    g_client = nullptr;
+    g_ctsChar = nullptr;
+    g_targetDevice = nullptr;
+    NimBLEDevice::getScan()->start(0, false, true);
+    return false;
+  }
+  if (!characteristic->canRead()) {
+    Serial.println("[BLE] Current Time characteristic is not readable");
+    g_client->disconnect();
+    NimBLEDevice::deleteClient(g_client);
+    g_client = nullptr;
+    g_ctsChar = nullptr;
+    g_targetDevice = nullptr;
+    NimBLEDevice::getScan()->start(0, false, true);
+    return false;
+  }
+  g_ctsChar = characteristic;
+  g_lastReadMillis = 0;
+  g_targetDevice = nullptr;
+  Serial.println("[BLE] Ready to read current time");
+  displayStatusMessage("CTS ready");
+  return true;
+}
+void readAndPrintCurrentTime() {
+  if (g_ctsChar == nullptr || g_client == nullptr) {
+    return;
+  }
+  if (!g_client->isConnected()) {
+    return;
+  }
+  const uint32_t now = millis();
+  if (now - g_lastReadMillis < CTS_READ_INTERVAL_MS) {
+    return;
+  }
+  g_lastReadMillis = now;
+  Serial.println("[CTS] Reading current time...");
+  NimBLEAttValue value = g_ctsChar->readValue();
+  if (value.length() == 0) {
+    Serial.println("[CTS] Read returned empty value");
+    return;
+  }
+  CurrentTime time{};
+  if (!parseCurrentTime(value.data(), value.length(), time)) {
+    return;
+  }
+  printCurrentTime(time);
+  displayCurrentTime(time);
+}
+} // namespace
+void setup() {
+  Serial.begin(115200);
+  while (!Serial) {
+    delay(10);
+  }
+  Serial.println();
+  Serial.println("[BOOT] BLE Current Time Service client");
+  NimBLEDevice::init("ESP32C6-CTS-Client");
+  NimBLEDevice::setPower(ESP_PWR_LVL_P9);
+  NimBLEDevice::setSecurityAuth(false, false, true);
+  Wire.begin(21, 22);
+  if (!g_display.begin(SSD1306_SWITCHCAPVCC, OLED_I2C_ADDR)) {
+    Serial.println("[OLED] SSD1306 allocation failed");
+    while (true) {
+      delay(1000);
+    }
+  }
+  g_display.clearDisplay();
+  g_display.setTextColor(SSD1306_WHITE);
+  g_display.setTextSize(2);
+  g_display.setCursor(0, OLED_TOP_MARGIN);
+  g_display.println("BLE CTS Client");
+  g_display.display();
+  startScan();
+}
+void loop() {
+  connectToCurrentTimeService();
+  readAndPrintCurrentTime();
+  delay(100);
+}
+</code>
+==== BLE Security and Pairing ====
+All BLE connections done so far in this lab have been without any authentication/encryption. For applications where this is necessary, BLE offers multiple security modes and a bonding scheme which establishes and encrypted connection between devices.
+^ Mode | Level | Description ^
+| **Mode 1, Level 1** | No security | No encryption or authentication |
+| **Mode 1, Level 2** | Unauthenticated pairing with encryption | "Just Works" — no MITM protection |
+| **Mode 1, Level 3** | Authenticated pairing with encryption | Uses Passkey/Numeric Comparison |
+| **Mode 1, Level 4** | Authenticated LE Secure Connections | Uses modern ECDH key exchange |
+A typical pairing scenarion over BLE goes through these steps:
+. **Pairing Request/Response:** Devices agree on IO capabilities (keyboard, display, none).
+. **Key Exchange:** Exchange temporary keys (STK, LTK, IRK, etc.).
+. **Encryption Setup:** Link is encrypted using generated keys.
+. **Bonding (optional):** Keys are stored persistently for future use.
+We can test pairing with the nRF Connect mobile app.
+  - Flash your ESP32-C6 firmware with the code below, which has security-enabled GATT characteristics.
+  - Open **nRF Connect → Scan → Connect** to your ESP32-C6.
+  - Try to **read** a protected characteristic — expect something like: <code>Error 0x05: Insufficient Authentication</code>
+  - Tap **⋮ → Bond** to start pairing.
+  - Depending on setup:
+    * **Just Works:** automatic pairing.
+    * **Passkey Entry:** app prompts for a 6-digit PIN.
+    * **Numeric Comparison:** both sides show a code for confirmation.
+  - After pairing, retry read — it should succeed.
+<code C main.cpp>
+#include <Arduino.h>
+#include <Wire.h>
+#include <cmath>
+#include <Adafruit_BME680.h>
+#include <NimBLEDevice.h>
+#include <NimBLEAdvertisementData.h>
+namespace {
+#define I2C_SDA_PIN 21
+#define I2C_SCL_PIN 22
+#define BME680_I2C_ADDR 0x77
+constexpr char kDeviceName[] = "ESP32C6 ESS";
+const NimBLEUUID kEnvironmentalServiceUUID((uint16_t)0x181A);
+const NimBLEUUID kTemperatureCharUUID((uint16_t)0x2A6E);
+const NimBLEUUID kHumidityCharUUID((uint16_t)0x2A6F);
+const NimBLEUUID kPressureCharUUID((uint16_t)0x2A6D);
+constexpr uint32_t kSecurityPasskey = 654321; // 6-digit static passkey for pairing
+constexpr uint32_t kNotifyIntervalMs = 5000;  // send notify every 5 seconds
+Adafruit_BME680 g_bme;
+bool g_bmeReady = false;
+NimBLECharacteristic* g_temperatureCharacteristic = nullptr;
+NimBLECharacteristic* g_humidityCharacteristic = nullptr;
+NimBLECharacteristic* g_pressureCharacteristic = nullptr;
+volatile bool g_isConnected = false;
+uint32_t g_lastNotify = 0;
+class ServerCallbacks : public NimBLEServerCallbacks {
+  void onConnect(NimBLEServer* server, NimBLEConnInfo& connInfo) override {
+    g_isConnected = true;
+    Serial.printf("[BLE] Central connected: %s\n", connInfo.getAddress().toString().c_str());
+  }
+  void onDisconnect(NimBLEServer* server, NimBLEConnInfo& connInfo, int reason) override {
+    g_isConnected = false;
+    Serial.printf("[BLE] Central disconnected (reason %d)\n", reason);
+    if (!NimBLEDevice::startAdvertising()) {
+      Serial.println("[BLE] Failed to restart advertising");
+    }
+  }
+  uint32_t onPassKeyDisplay() override {
+    Serial.printf("[BLE] Displaying passkey: %06u\n", kSecurityPasskey);
+    return kSecurityPasskey;
+  }
+  void onConfirmPassKey(NimBLEConnInfo& connInfo, uint32_t pin) override {
+    Serial.printf("[BLE] Confirm passkey %06u for %s\n", pin, connInfo.getAddress().toString().c_str());
+    NimBLEDevice::injectConfirmPasskey(connInfo, true);
+  }
+  void onAuthenticationComplete(NimBLEConnInfo& connInfo) override {
+    if (connInfo.isEncrypted()) {
+      Serial.printf("[BLE] Link encrypted; bonded=%s, authenticated=%s\n",
+                    connInfo.isBonded() ? "yes" : "no",
+                    connInfo.isAuthenticated() ? "yes" : "no");
+    } else {
+      Serial.printf("[BLE] Authentication failed; disconnecting %s\n", connInfo.getAddress().toString().c_str());
+      NimBLEDevice::getServer()->disconnect(connInfo.getConnHandle());
+    }
+  }
+};
+class ValueCallbacks : public NimBLECharacteristicCallbacks {
+  void onRead(NimBLECharacteristic* characteristic, NimBLEConnInfo& connInfo) override {
+    Serial.printf("[GATT] Read from %s on characteristic %s\n",
+                  connInfo.getAddress().toString().c_str(),
+                  characteristic->getUUID().toString().c_str());
+  }
+  void onWrite(NimBLECharacteristic* characteristic, NimBLEConnInfo& connInfo) override {
+    std::string value = characteristic->getValue();
+    Serial.printf("[GATT] Write to %s from %s, %zu bytes\n",
+                  characteristic->getUUID().toString().c_str(),
+                  connInfo.getAddress().toString().c_str(),
+                  value.size());
+  }
+};
+ServerCallbacks g_serverCallbacks;
+ValueCallbacks g_valueCallbacks;
+bool initBME680() {
+  if (!g_bme.begin(BME680_I2C_ADDR)) {
+    Serial.println("[BME680] Not found on 0x77, trying 0x76...");
+    if (!g_bme.begin(0x76)) {
+      Serial.println("[BME680] Sensor not found. Check wiring/power.");
+      return false;
+    }
+  }
+  g_bme.setTemperatureOversampling(BME680_OS_8X);
+  g_bme.setHumidityOversampling(BME680_OS_2X);
+  g_bme.setPressureOversampling(BME680_OS_4X);
+  g_bme.setIIRFilterSize(BME680_FILTER_SIZE_3);
+  g_bme.setGasHeater(0, 0); // Disable gas heater for periodic environmental sampling
+  Serial.println("[BME680] Sensor initialized");
+  return true;
+}
+bool readBME680(float& temperatureC, float& humidityPct, float& pressurePa) {
+  if (!g_bme.performReading()) {
+    Serial.println("[BME680] Failed to perform reading");
+    return false;
+  }
+  temperatureC = g_bme.temperature;
+  humidityPct = g_bme.humidity;
+  pressurePa = g_bme.pressure; // Library returns Pascals
+  return true;
+}
+void setupSecurity() {
+  NimBLEDevice::setSecurityAuth(true, true, true); // bonding, MITM, secure connections
+  NimBLEDevice::setSecurityIOCap(BLE_HS_IO_DISPLAY_YESNO);
+  NimBLEDevice::setSecurityPasskey(kSecurityPasskey);
+  NimBLEDevice::setPower(ESP_PWR_LVL_P9);
+}
+void setupGattServer() {
+  NimBLEServer* server = NimBLEDevice::createServer();
+  server->setCallbacks(&g_serverCallbacks, false);
+  NimBLEService* environmentalService = server->createService(kEnvironmentalServiceUUID);
+  g_temperatureCharacteristic = environmentalService->createCharacteristic(
+      kTemperatureCharUUID,
+      NIMBLE_PROPERTY::READ | NIMBLE_PROPERTY::READ_ENC |
+          NIMBLE_PROPERTY::READ_AUTHEN |
+          NIMBLE_PROPERTY::NOTIFY);
+  g_temperatureCharacteristic->setCallbacks(&g_valueCallbacks);
+  uint8_t tempPlaceholder[2] = {0xFF, 0x7F}; // NaN equivalent (0x7FFF)
+  g_temperatureCharacteristic->setValue(tempPlaceholder, sizeof(tempPlaceholder));
+  g_humidityCharacteristic = environmentalService->createCharacteristic(
+      kHumidityCharUUID,
+      NIMBLE_PROPERTY::READ | NIMBLE_PROPERTY::READ_ENC |
+          NIMBLE_PROPERTY::READ_AUTHEN |
+          NIMBLE_PROPERTY::NOTIFY);
+  g_humidityCharacteristic->setCallbacks(&g_valueCallbacks);
+  uint8_t humidityPlaceholder[2] = {0xFF, 0xFF};
+  g_humidityCharacteristic->setValue(humidityPlaceholder, sizeof(humidityPlaceholder));
+  g_pressureCharacteristic = environmentalService->createCharacteristic(
+      kPressureCharUUID,
+      NIMBLE_PROPERTY::READ | NIMBLE_PROPERTY::READ_ENC |
+          NIMBLE_PROPERTY::READ_AUTHEN |
+          NIMBLE_PROPERTY::NOTIFY);
+  g_pressureCharacteristic->setCallbacks(&g_valueCallbacks);
+  uint8_t pressurePlaceholder[4] = {0xFF, 0xFF, 0xFF, 0xFF};
+  g_pressureCharacteristic->setValue(pressurePlaceholder, sizeof(pressurePlaceholder));
+  environmentalService->start();
+  NimBLEAdvertising* advertising = NimBLEDevice::getAdvertising();
+  NimBLEAdvertisementData advData;
+  advData.setName(kDeviceName);
+  advData.addServiceUUID(kEnvironmentalServiceUUID);
+  advData.setAppearance(0x0341); // Thermometer
+  advertising->setAdvertisementData(advData);
+  NimBLEAdvertisementData scanData;
+  scanData.setName("Env Sensing", false);
+  advertising->setScanResponseData(scanData);
+  advertising->setConnectableMode(BLE_GAP_CONN_MODE_UND);
+  advertising->setDiscoverableMode(BLE_GAP_DISC_MODE_GEN);
+  if (advertising->start()) {
+    Serial.println("[BLE] Advertising environmental sensing service");
+  } else {
+    Serial.println("[BLE] Failed to start advertising");
+  }
+}
+void updateEnvironmentalMeasurements() {
+  if (!g_isConnected || !g_bmeReady ||
+      g_temperatureCharacteristic == nullptr ||
+      g_humidityCharacteristic == nullptr ||
+      g_pressureCharacteristic == nullptr) {
+    return;
+  }
+  const uint32_t now = millis();
+  if (now - g_lastNotify < kNotifyIntervalMs) {
+    return;
+  }
+  g_lastNotify = now;
+  float temperatureC = 0.0f;
+  float humidityPct = 0.0f;
+  float pressurePa = 0.0f;
+  if (!readBME680(temperatureC, humidityPct, pressurePa)) {
+    return;
+  }
+  const int16_t temperatureHundredths =
+      static_cast<int16_t>(std::lround(temperatureC * 100.0));
+  const uint16_t humidityHundredths =
+      static_cast<uint16_t>(std::lround(humidityPct * 100.0));
+  const uint32_t pressureValue = static_cast<uint32_t>(std::lround(pressurePa));
+  uint8_t temperaturePayload[2] = {
+      static_cast<uint8_t>(temperatureHundredths & 0xFF),
+      static_cast<uint8_t>((temperatureHundredths >> 8) & 0xFF),
+  };
+  g_temperatureCharacteristic->setValue(temperaturePayload, sizeof(temperaturePayload));
+  g_temperatureCharacteristic->notify();
+  uint8_t humidityPayload[2] = {
+      static_cast<uint8_t>(humidityHundredths & 0xFF),
+      static_cast<uint8_t>((humidityHundredths >> 8) & 0xFF),
+  };
+  g_humidityCharacteristic->setValue(humidityPayload, sizeof(humidityPayload));
+  g_humidityCharacteristic->notify();
+  uint8_t pressurePayload[4] = {
+      static_cast<uint8_t>(pressureValue & 0xFF),
+      static_cast<uint8_t>((pressureValue >> 8) & 0xFF),
+      static_cast<uint8_t>((pressureValue >> 16) & 0xFF),
+      static_cast<uint8_t>((pressureValue >> 24) & 0xFF),
+  };
+  g_pressureCharacteristic->setValue(pressurePayload, sizeof(pressurePayload));
+  g_pressureCharacteristic->notify();
+  Serial.printf("[ESS] Notified T=%.2fC H=%.2f%% P=%.2fhPa\n",
+                temperatureC,
+                humidityPct,
+                pressurePa / 100.0f);
+}
+} // namespace
+void setup() {
+  Serial.begin(115200);
+  while (!Serial) {
+    delay(10);
+  }
+  delay(1000);
+  Serial.println();
+  Serial.println("[BOOT] ESP32-C6 Environmental Sensing Server");
+  Wire.begin(I2C_SDA_PIN, I2C_SCL_PIN);
+  g_bmeReady = initBME680();
+  if (!g_bmeReady) {
+    Serial.println("[BOOT] BME680 not ready; characteristics will remain invalid");
+  }
+  NimBLEDevice::init(kDeviceName);
+  setupSecurity();
+  setupGattServer();
+}
+void loop() {
+  updateEnvironmentalMeasurements();
+  delay(100);
+}
+</code>
 ===== Web BLE Application =====
@@ Line 509: / Line 1165: @@
 Build the application in the tutorial and deploy the web page in your GitHub account.
-=== Assignment ===
+===== Assignment =====
 <note> Modify the web page and the BLE app to display the BME680 sensor data (temperature, pressure and humidity). </note>