Fix timing issue during pairing, add pairing control/status methods

examples/Peripheral/EncryptedBatteryMonitor/EncryptedBatteryMonitor.ino

@@ -18,6 +18,14 @@
 #include <ArduinoBLE.h>
 
 
+#define PAIR_BUTTON D3        // button for pairing
+#define PAIR_LED 24           // LED used to signal pairing
+#define PAIR_LED_ON LOW       // Blue LED on Nano BLE has inverted logic
+#define PAIR_INTERVAL 30000   // interval for pairing after button press in ms
+
+#define CTRL_LED LED_BUILTIN
+
+
  // BLE Battery Service
 BLEService batteryService("180F");
 
@@ -31,13 +39,17 @@ BLEStringCharacteristic stringcharacteristic("183E", BLERead | BLEWrite, 31);
 BLEUnsignedCharCharacteristic secretValue("2a3F", BLERead | BLEWrite | BLEEncryption);
 
 int oldBatteryLevel = 0;  // last battery level reading from analog input
-long previousMillis = 0;  // last time the battery level was checked, in ms
+unsigned long previousMillis = 0;  // last time the battery level was checked, in ms
+unsigned long pairingStarted = 0;  // pairing start time when button is pressed
+bool wasConnected = 0;
 
 void setup() {
   Serial.begin(9600);    // initialize serial communication
   while (!Serial);
 
-  pinMode(LED_BUILTIN, OUTPUT); // initialize the built-in LED pin to indicate when a central is connected
+  pinMode(CTRL_LED, OUTPUT); // initialize the built-in LED pin to indicate when a central is connected
+  pinMode(PAIR_LED, OUTPUT);
+  pinMode(PAIR_BUTTON, INPUT_PULLUP);
 
 
   Serial.println("Serial connected");
@@ -145,6 +157,9 @@ void setup() {
     secretValue.writeValue(0);
 
     delay(1000);
+
+    // prevent pairing until button is pressed (will show a pairing rejected message)
+    BLE.setPairable(false);
 
     /* Start advertising BLE.  It will start continuously transmitting BLE
        advertising packets and will be visible to remote BLE central devices
@@ -169,30 +184,44 @@ void loop() {
   // wait for a BLE central
   BLEDevice central = BLE.central();
 
+
+  // If button is pressed, allow pairing for 30 sec
+  if (!BLE.pairable() && digitalRead(PAIR_BUTTON) == LOW){
+    pairingStarted = millis();
+    BLE.setPairable(Pairable::ONCE);
+    Serial.println("Accepting pairing for 30s");
+  } else if (BLE.pairable() && millis() > pairingStarted + PAIR_INTERVAL){
+    BLE.setPairable(false);
+    Serial.println("No longer accepting pairing");
+  }
+  // Make LED blink while pairing is allowed
+  digitalWrite(PAIR_LED, (BLE.pairable() ? (millis()%400)<200 : BLE.paired()) ? PAIR_LED_ON : !PAIR_LED_ON); 
+
+
   // if a central is connected to the peripheral:
-  if (central) {
-    Serial.print("Connected to central: ");
-    // print the central's BT address:
-    Serial.println(central.address());
+  if (central && central.connected()) {
+    if (!wasConnected){
+      wasConnected = true;
+      Serial.print("Connected to central: ");
+      // print the central's BT address:
+      Serial.println(central.address());
+    }
 
     // check the battery level every 200ms
     // while the central is connected:
-    while (central.connected()) {
-      long currentMillis = millis();
-      // if 200ms have passed, check the battery level:
-      if (currentMillis - previousMillis >= 1000) {
-        previousMillis = currentMillis;
-        updateBatteryLevel();
-        if(secretValue.value()>0){
-          digitalWrite(13,HIGH);
-        }else{
-          digitalWrite(13,LOW);
-        }
-      }
+    long currentMillis = millis();
+    // if 200ms have passed, check the battery level:
+    if (currentMillis - previousMillis >= 1000) {
+      previousMillis = currentMillis;
+      updateBatteryLevel();
+      digitalWrite(CTRL_LED, secretValue.value()>0 ? HIGH : LOW);
     }
+  } else if (wasConnected){
+    wasConnected = false;
     Serial.print("Disconnected from central: ");
     Serial.println(central.address());
   }
+
 }
 
 void updateBatteryLevel() {
@@ -208,4 +237,4 @@ void updateBatteryLevel() {
     batteryLevelChar.writeValue(batteryLevel);  // and update the battery level characteristic
     oldBatteryLevel = batteryLevel;           // save the level for next comparison
   }
-}
+}

keywords.txt

@@ -77,9 +77,12 @@ setEventHandler	KEYWORD2
 setAdvertisingInterval	KEYWORD2
 setConnectionInterval	KEYWORD2
 setConnectable	KEYWORD2
+setPairable	KEYWORD2
 setTimeout	KEYWORD2
 debug	KEYWORD2
 noDebug	KEYWORD2
+pairable	KEYWORD2
+paired	KEYWORD2
 
 properties	KEYWORD2
 valueSize	KEYWORD2

src/local/BLELocalDevice.cpp

@@ -214,6 +214,16 @@ bool BLELocalDevice::connected() const
   return ATT.connected();
 }
 
+/*
+ * Whether there is at least one paired device
+ */
+bool BLELocalDevice::paired()
+{
+  HCI.poll();
+
+  return ATT.paired();
+}
+
 bool BLELocalDevice::disconnect()
 {
   return ATT.disconnect();
@@ -395,6 +405,22 @@ void BLELocalDevice::setTimeout(unsigned long timeout)
   ATT.setTimeout(timeout);
 }
 
+/*
+ * Control whether pairing is allowed or rejected
+ * Use true/false or the Pairable enum
+ */
+void BLELocalDevice::setPairable(uint8_t pairable)
+{
+  L2CAPSignaling.setPairingEnabled(pairable);
+}
+
+/*
+ * Whether pairing is currently allowed
+ */
+bool BLELocalDevice::pairable()
+{
+  return L2CAPSignaling.isPairingEnabled();
+}
 
 void BLELocalDevice::setGetIRKs(int (*getIRKs)(uint8_t* nIRKs, uint8_t** BADDR_type, uint8_t*** BADDRs, uint8_t*** IRKs)){
   HCI._getIRKs = getIRKs;

src/local/BLELocalDevice.h

@@ -24,6 +24,12 @@
 #include "BLEService.h"
 #include "BLEAdvertisingData.h"
 
+enum Pairable {
+  NO = 0,
+  YES = 1,
+  ONCE = 2,
+};
+
 class BLELocalDevice {
 public:
   BLELocalDevice();
@@ -80,6 +86,10 @@ class BLELocalDevice {
 
   virtual void debug(Stream& stream);
   virtual void noDebug();
+
+  virtual void setPairable(uint8_t pairable);
+  virtual bool pairable();
+  virtual bool paired();
 
 /// TODO: Put in actual variable names
   virtual void setStoreIRK(int (*storeIRK)(uint8_t*, uint8_t*));

src/utility/ATT.cpp

@@ -497,6 +497,32 @@ bool ATTClass::connected(uint16_t handle) const
   return false;
 }
 
+/*
+ * Return true if any of the known devices is paired (peer encrypted)
+ * Does not check if the paired device is also connected
+ */
+bool ATTClass::paired() const
+{
+  for(int i=0; i<ATT_MAX_PEERS; i++){
+    if((_peers[i].encryption & PEER_ENCRYPTION::ENCRYPTED_AES) > 0){
+      return true;
+    }
+  }
+  return false;
+}
+
+/*
+ * Return true if the specified device is paired (peer encrypted)
+ */
+bool ATTClass::paired(uint16_t handle) const
+{  
+  for(int i=0; i<ATT_MAX_PEERS; i++){
+    if(_peers[i].connectionHandle != handle){continue;}
+    return (_peers[i].encryption & PEER_ENCRYPTION::ENCRYPTED_AES) > 0;
+  }
+  return false; // unknown handle
+}
+
 uint16_t ATTClass::mtu(uint16_t handle) const
 {
   for (int i = 0; i < ATT_MAX_PEERS; i++) {

src/utility/ATT.h

@@ -75,6 +75,8 @@ class ATTClass {
   virtual bool connected() const;
   virtual bool connected(uint8_t addressType, const uint8_t address[6]) const;
   virtual bool connected(uint16_t handle) const;
+  virtual bool paired() const;
+  virtual bool paired(uint16_t handle) const;
   virtual uint16_t mtu(uint16_t handle) const;
 
   virtual bool disconnect();

src/utility/HCI.cpp

@@ -24,6 +24,8 @@
 #include "btct.h"
 #include "HCI.h"
 
+//#define _BLE_TRACE_
+
 #define HCI_COMMAND_PKT   0x01
 #define HCI_ACLDATA_PKT   0x02
 #define HCI_EVENT_PKT     0x04
@@ -1335,23 +1337,29 @@ void HCIClass::handleEventPkt(uint8_t /*plen*/, uint8_t pdata[])
             break;
           }
 
-          uint8_t encryption = ATT.getPeerEncryption(connectionHandle);
 
           for(int i=0; i<32; i++) DHKey[31-i] = evtLeDHKeyComplete->DHKey[i];
 
 #ifdef _BLE_TRACE_
           Serial.println("Stored our DHKey:");
           btct.printBytes(DHKey,32);
 #endif
-          encryption |= PEER_ENCRYPTION::DH_KEY_CALULATED;
+          uint8_t encryption = ATT.getPeerEncryption(connectionHandle) | PEER_ENCRYPTION::DH_KEY_CALULATED;
           ATT.setPeerEncryption(connectionHandle, encryption);
+
+          if((encryption & PEER_ENCRYPTION::RECEIVED_DH_CHECK) > 0){
 #ifdef _BLE_TRACE_
-          if(encryption | PEER_ENCRYPTION::RECEIVED_DH_CHECK){
-            Serial.println("Recieved DHKey check already so calculate f5, f6.");
+            Serial.println("Recieved DHKey check already so calculate f5, f6 now.");
+#endif
+            L2CAPSignaling.smCalculateLTKandConfirm(connectionHandle, HCI.remoteDHKeyCheckBuffer);
+
           }else{
+#ifdef _BLE_TRACE_
             Serial.println("Waiting on other DHKey check before calculating.");
+#endif
           }
         }else{
+#ifdef _BLE_TRACE_
           Serial.print("Key generation error: 0x");
           Serial.println(evtLeDHKeyComplete->status, HEX);
 #endif

src/utility/HCI.h

@@ -22,6 +22,8 @@
 
 #include <Arduino.h>
 
+#include "L2CAPSignaling.h"
+
 #define OGF_LINK_CTL           0x01
 #define OGF_HOST_CTL           0x03
 #define OGF_INFO_PARAM         0x04
@@ -111,6 +113,7 @@ class HCIClass {
   // TODO: Send command be private again & use ATT implementation within ATT.
   virtual int sendCommand(uint16_t opcode, uint8_t plen = 0, void* parameters = NULL);
   uint8_t remotePublicKeyBuffer[64];
+  uint8_t remoteDHKeyCheckBuffer[16];
   uint8_t Na[16];
   uint8_t Nb[16];
   uint8_t DHKey[32];