Add documentation about BLE connection and services.

README.md

@@ -34,7 +34,11 @@ I've tested this project on the actual PineTime hardware.
  * Rich user interface (using [LittleVGL](https://littlevgl.com/)) via display, touchpanel and push button.
  * Digital watch face and 4 demo applications (spinning meter, analog gauche, push button and message box);
  * Watchdog (automatic reset in case of firmware crash) and reset support (push and hold the button for 7 - 10s);
- * BLE Notification support (still Work-In-Progress, companion app needed). 
+ * BLE Notification support (still Work-In-Progress, [companion app](https://github.com/JF002/gobbledegook) needed). 
+
+## Documentation
+
+ * [BLE implementation and API](./doc/ble.md)
 
 ## Stub using NRF52-DK
 ![Pinetime stub](./images/pinetimestub1.jpg "PinetimeStub")

doc/ble.md

@@ -0,0 +1,27 @@
+# Bluetooth Low-Energy : 
+## Introduction
+This page describes the BLE implementation and API built in this firmware.
+
+**Note** : I'm a beginner in BLE related technologies and the information of this document reflect my current knowledge and understanding of the BLE stack. These informations might be erroneous or incomplete. Feel free to submit a PR if you think you can improve these.  
+
+## BLE Connection
+When starting the firmware start a BLE advertising : it send small messages that can be received by any *central* device in range. This allows the device to announce its presence to other devices.
+
+A companion application (running on a PC, RasberryPi, smartphone) which received this avertising packet can request a connection to the device. This connection procedure allows the 2 devices to negociate communication parameters, security keys,...
+
+When the connection is established, the pinetime will try to discover services running on the companion application. For now **CTS** (**C**urrent **T**ime **S**ervice) and **ANS** (**A**lert **N**otification **S**ervice) are supported.
+
+If **CTS** is detected, it'll request the current time to the companion application. If **ANS** is detected, it will listen to new notifications coming from the companion application.
+
+![BLE connection sequence diagram](ble/connection_sequence.png "BLE connection sequence diagram")
+
+## BLE services
+[List of standard BLE services](https://www.bluetooth.com/specifications/gatt/services/)
+
+### CTS
+[Current Time Service](https://www.bluetooth.com/wp-content/uploads/Sitecore-Media-Library/Gatt/Xml/Services/org.bluetooth.service.alert_notification.xml)
+
+### ANS
+[Alert Notification Service](https://www.bluetooth.com/wp-content/uploads/Sitecore-Media-Library/Gatt/Xml/Services/org.bluetooth.service.current_time.xml)
+
+![ANS sequence diagram](./ble/ans_sequence.png "ANS sequence diagram")

doc/ble/ans_sequence.puml

@@ -0,0 +1,29 @@
+@startuml
+group Get configuration from server
+Pinetime -> CompanionApp : Read request (Supported 'new' notification categories - 0x2A47)
+CompanionApp --> Pinetime: Response (0xff = all categories)
+
+Pinetime -> CompanionApp : Read request (Supported 'unread' notification categories - 0x2A48)
+CompanionApp --> Pinetime: Response (0xff = all categories)
+end
+
+group Configure the server
+Pinetime -> CompanionApp : Configure 'new' notifications categories : Accept all (Write [0, 0xFF] to Control Point - 0x2A44)
+activate CompanionApp
+deactivate CompanionApp
+Pinetime -> CompanionApp : Configure 'unread' notifications categories : Accept all (Write [1, 0xFF] to Control Point - 0x2A44)
+activate CompanionApp
+deactivate CompanionApp
+end
+
+group Server sends a notification
+CompanionApp -> Pinetime : Notify new_alert (0x2A46)
+activate Pinetime
+note over Pinetime
+    Pinetime FW handles the
+    notification (display on UI)
+end note
+deactivate Pinetime
+end
+
+@enduml

doc/ble/connection_sequence.puml

@@ -0,0 +1,14 @@
+@startuml
+Pinetime --> CompanionApp: Start advertising
+
+group BLE Connection
+CompanionApp -> Pinetime: Connection request
+CompanionApp <-> Pinetime: Connection parameters negociation, security procedure,...
+end
+
+group Service Discovery
+CompanionApp <-> Pinetime: Discover service 0x1805 (CTS)
+CompanionApp <-> Pinetime: Discover service 0x1811 (ANS)
+end
+
+@enduml