Advertise fast for at least 30 secs then slow down

On power up, advertise aggressively for at least 30 seconds then switch
to a longer interval to conserve battery life. This fast/slow pattern
is designed to balance connection response time and battery life.

When a disconnect event is received restart the fast/slow pattern.

When a failed connect event is received, restart the fast/slow pattern.

When the screen is activated and ble is not connected, restart the fast/slow pattern.

This pattern is consistent with Apple's BLE developer standards (QA 1931).

src/components/ble/NimbleController.cpp

@@ -122,6 +122,15 @@ void NimbleController::StartAdvertising() {
 
   adv_params.conn_mode = BLE_GAP_CONN_MODE_UND;
   adv_params.disc_mode = BLE_GAP_DISC_MODE_GEN;
+  /* fast advertise for 30 sec */
+  if (fastAdvCount < 15) {
+    adv_params.itvl_min = 32;
+    adv_params.itvl_max = 47;
+    fastAdvCount++;
+  } else {
+    adv_params.itvl_min = 1636;
+    adv_params.itvl_max = 1651;
+  }
 
   fields.flags = BLE_HS_ADV_F_DISC_GEN | BLE_HS_ADV_F_BREDR_UNSUP;
   fields.uuids128 = &dfuServiceUuid;
@@ -139,7 +148,7 @@ void NimbleController::StartAdvertising() {
   rc = ble_gap_adv_rsp_set_fields(&rsp_fields);
   ASSERT(rc == 0);
 
-  rc = ble_gap_adv_start(addrType, NULL, 5000, &adv_params, GAPEventCallback, this);
+  rc = ble_gap_adv_start(addrType, NULL, 2000, &adv_params, GAPEventCallback, this);
   ASSERT(rc == 0);
 }
 
@@ -163,6 +172,7 @@ int NimbleController::OnGAPEvent(ble_gap_event* event) {
         alertNotificationClient.Reset();
         connectionHandle = BLE_HS_CONN_HANDLE_NONE;
         bleController.Disconnect();
+        fastAdvCount = 0;
         StartAdvertising();
       } else {
         connectionHandle = event->connect.conn_handle;
@@ -181,6 +191,7 @@ int NimbleController::OnGAPEvent(ble_gap_event* event) {
       alertNotificationClient.Reset();
       connectionHandle = BLE_HS_CONN_HANDLE_NONE;
       bleController.Disconnect();
+      fastAdvCount = 0;
       StartAdvertising();
       break;
 

src/components/ble/NimbleController.h

@@ -72,6 +72,10 @@ namespace Pinetime {
       uint16_t connHandle();
       void NotifyBatteryLevel(uint8_t level);
 
+      void RestartFastAdv() {
+        fastAdvCount = 0;
+      }
+
     private:
       static constexpr const char* deviceName = "InfiniTime";
       Pinetime::System::SystemTask& systemTask;
@@ -94,6 +98,7 @@ namespace Pinetime {
 
       uint8_t addrType; // 1 = Random, 0 = PUBLIC
       uint16_t connectionHandle = BLE_HS_CONN_HANDLE_NONE;
+      uint8_t fastAdvCount = 0;
 
       ble_uuid128_t dfuServiceUuid {
         .u {.type = BLE_UUID_TYPE_128},

src/systemtask/SystemTask.cpp

@@ -233,6 +233,9 @@ void SystemTask::Work() {
           displayApp.PushMessage(Pinetime::Applications::Display::Messages::UpdateBatteryLevel);
           heartRateApp.PushMessage(Pinetime::Applications::HeartRateTask::Messages::WakeUp);
 
+          if (!bleController.IsConnected())
+            nimbleController.RestartFastAdv();
+
           isSleeping = false;
           isWakingUp = false;
           isDimmed = false;