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--- en:edu:zmitac:s2:aih:lab:nrf52zephyrblecentral [2023/12/19 21:19] – [BLE Health Temperature peripheral] ktokarz
+++ en:edu:zmitac:s2:aih:lab:nrf52zephyrblecentral [2023/12/19 23:19] (current) – [Tasks to do during the laboratory] ktokarz
@@ Line 3: / Line 3: @@
 BLE client must be configured to connect to the peripheral which exposes some specific service and characteristic. To do the lab exercise there is a need to create the peripheral device first.
 ===== BLE Health Temperature peripheral =====
-The default Health Temperature example is sufficient to make the laboratory. How to import the project, flash, and execute is shown in ((en:edu:zmitac:s2:aih:lab:nrf52zephyrbleperipheral)).
+The default Health Temperature example is sufficient to make the laboratory. How to import the project, flash, and execute is shown in {{https://dokuwiki.zmitac.aei.polsl.pl/en:edu:zmitac:s2:aih:lab:nrf52zephyrbleperipheral|peripheral example}}.
+===== BLE central ====
+Among the examples provided with Zephyr OS, there is also one complementary to the Health Temperature peripheral. It is named central_ht ((..\.platformio\packages\framework-zephyr\samples\bluetooth\central_ht)). The program is quite complex, here we will explain the most important elements and the process of establishing the connection.\\
+The process of establishing and configuring a connection has a few steps:
+  - scanning the neighbourhood to find connectable devices
+  - comparing the advertising data to look for information on the required service
+  - establishing the connection to peripheral
+  - retrieving information on services and characteristics
+  - subscribing to the interesting data with a notification or indication mechanism (optional)
+  - reading data (by reading the characteristic value or automatically with notify/indicate)
+==== Scanning the neighbourhood ====
+In the main function, after the successful initialisation of the Bluetooth subsystem, scanning for nearby devices is started.
+<code>
+err = bt_enable(NULL);
+...
+err = scan_start();
+...
+</code>
+The "scan_start()" function calls "bt_le_scan_start(&scan_param, device_found)" function. The second parameter is the callback function which processes scan results.
+==== Searching advertising data for info on service ====
+The "device_found()" function parses received advertising data with the "bt_data_parse()" function to the function "eir_found()". The latter function searches advertising data for the UUID of the Health Thermometer (0x1809).
+==== Establishing the connection ====
+After a successful search establishes a connection with the remote device by calling the function "bt_conn_le_create()".\\
+Further processing is done by callback functions registered by the macro:
+<code>
+BT_CONN_CB_DEFINE(conn_callbacks) = {
+	.connected = connected,
+	.disconnected = disconnected,
+};
+</code>
+Zephyr OS keeps the "bt_conn_cb" structure that allows the programmer to attach callback functions to chosen events. "BT_CONN_CB_DEFINE" macro attaches "connected" and "disconnected" functions to appropriate events.
+The "connected()" function is executed after successfully establishing the connection to the peripheral device.
+==== Discovering the service ====
+This function registers the callback function "discover_func()", and starts the discovery process by searching for the Health Thermometer service (UUID = 0x1809).
+==== Searching for the characteristic ====
+After finding this service discovery_func() is executed which performs further searching. First, it looks for the Temperature Measurement characteristic (UUID = 0x2a1c).
+==== Subscribing to the data with indication ====
+This characteristic should have the descriptor Client Characteristic Configuration (UUID = 0x1902) which makes it possible to enable notifications or indications. The indication enabling and registering the "notify_func()" as the callback for incoming indications finishes the establishing connection process.\\
+==== Ready! ====
+Notice that after every successful discovery the function "discovery_func()" is called as the callback.\\
+While the peripheral device updates the thermometer sensor reading, our central device receives this data and calls the "notify_func()" callback which prints the data using the UART port.
+===== Tasks to do during the laboratory =====
+  - Create the Health Thermometer peripheral device and test if it operates properly
+  - Import central device program "central_ht" (main.c and prj.conf files must be imported)
+  - Compile and execute it observing its behaviour with and without peripheral running
+  - Modify the peripheral code and central code to enable LED control on the central board with a button press on the peripheral board
+<note>
+If you find problems with undefined BT_ATT_FIRST_ATTRIBUTE_HANDLE and BT_ATT_LAST_ATTRIBUTE_HANDLE define them as in the following code.
+</note>
+<code>
+#define BT_ATT_FIRST_ATTRIBUTE_HANDLE 0x0001
+#define BT_ATT_LAST_ATTRIBUTE_HANDLE 0xFFFF
+</code>
+<note>
+To send simple binary data you can use a binary sensor service (UUID = 0x183B) with a binary sensor response characteristic (UUID = 0x2B2C).
+</note>