Bluetooth: Add option to configure peripheral connection parameters

This allows to configure desired parameters for peripheral. When set
PPCP characteristic is also added to GAP service. If disabled it is
up to application to controll connection parameters and stack will
only enforce 5 seconds delay before update.

Signed-off-by: Szymon Janc <szymon.janc@codecoup.pl>

subsys/bluetooth/host/Kconfig

@@ -349,6 +349,44 @@ config BT_MAX_PAIRED
 	  Maximum number of paired Bluetooth devices. The minimum (and
 	  default) number is 1.
 
+config BT_GAP_PERIPHERAL_PREF_PARAMS
+	bool "Configure peripheral preferred connection parameters"
+	default y
+	depends on BT_PERIPHERAL
+	help
+	  This allows to configure periphral preferred connection parameters.
+	  Enabling this option results in adding PPCP characteristic in GAP
+	  and sending request for connection parameters udpate after GAP
+	  recommended 5 seconds of connection as peripheral. If disabled it is
+	  up to application to set expected connection parameters.
+
+if BT_GAP_PERIPHERAL_PREF_PARAMS
+config BT_PERIPHERAL_PREF_MIN_INT
+	int "Peripheral preferred minimum connection interval in 1.25ms units"
+	default 24
+	range 6 3200
+
+config BT_PERIPHERAL_PREF_MAX_INT
+	int "Peripheral preferred maximum connection interval in 1.25ms units"
+	default 40
+	range 6 3200
+
+config BT_PERIPHERAL_PREF_SLAVE_LATENCY
+	int "Peripheral preferred slave latency in Connection Intervals"
+	default 0
+	range 0 499
+
+config BT_PERIPHERAL_PREF_TIMEOUT
+	int "Peripheral preferred supervision timeout in 10ms units"
+	default 42
+	range 10 3200
+	help
+	  It is up to user to provide valid timeout which pass required minimum
+	  value: in milliseconds it shall be larger than
+	  "(1+ Conn_Latency) * Conn_Interval_Max * 2"
+	  where Conn_Interval_Max is given in milliseconds.
+endif # BT_GAP_PERIPHERAL_PREF_PARAMS
+
 endif # BT_CONN
 
 config BT_SCAN_WITH_IDENTITY

subsys/bluetooth/host/conn.c

@@ -230,12 +230,32 @@ static void conn_le_update_timeout(struct k_work *work)
 		return;
 	}
 
-	param = BT_LE_CONN_PARAM(conn->le.interval_min,
+#if defined (CONFIG_BT_GAP_PERIPHERAL_PREF_PARAMS)
-				 conn->le.interval_max,
+	/* if application set own params use those, otherwise use defaults */
-				 conn->le.latency,
+	if (atomic_test_and_clear_bit(conn->flags, BT_CONN_SLAVE_PARAM_SET)) {
-				 conn->le.timeout);
+		param = BT_LE_CONN_PARAM(conn->le.interval_min,
+					 conn->le.interval_max,
+					 conn->le.latency,
+					 conn->le.timeout);
+	} else {
+		param = BT_LE_CONN_PARAM(CONFIG_BT_PERIPHERAL_PREF_MIN_INT,
+					 CONFIG_BT_PERIPHERAL_PREF_MAX_INT,
+					 CONFIG_BT_PERIPHERAL_PREF_SLAVE_LATENCY,
+					 CONFIG_BT_PERIPHERAL_PREF_TIMEOUT);
+	}
 
 	send_conn_le_param_update(conn, param);
+#else
+	/* update only if application set own params */
+	if (atomic_test_and_clear_bit(conn->flags, BT_CONN_SLAVE_PARAM_SET)) {
+		param = BT_LE_CONN_PARAM(conn->le.interval_min,
+					 conn->le.interval_max,
+					 conn->le.latency,
+					 conn->le.timeout);
+
+		send_conn_le_param_update(conn, param);
+	}
+#endif
 
 	atomic_set_bit(conn->flags, BT_CONN_SLAVE_PARAM_UPDATE);
 }
@@ -1796,6 +1816,7 @@ int bt_conn_le_param_update(struct bt_conn *conn,
 		conn->le.interval_max = param->interval_max;
 		conn->le.latency = param->latency;
 		conn->le.timeout = param->timeout;
+		atomic_set_bit(conn->flags, BT_CONN_SLAVE_PARAM_SET);
 	}
 
 	return 0;

subsys/bluetooth/host/conn_internal.h

@@ -28,6 +28,7 @@ enum {
 	BT_CONN_AUTO_PHY_UPDATE,        /* Auto-update PHY */
 	BT_CONN_AUTO_DATA_LEN,          /* Auto data len change in progress */
 	BT_CONN_SLAVE_PARAM_UPDATE,	/* If slave param update timer fired */
+	BT_CONN_SLAVE_PARAM_SET,	/* If slave param were set from app */
 
 	/* Total number of flags - must be at the end of the enum */
 	BT_CONN_NUM_FLAGS,

subsys/bluetooth/host/gatt.c

@@ -96,6 +96,27 @@ static ssize_t read_appearance(struct bt_conn *conn,
 				 sizeof(appearance));
 }
 
+#if defined (CONFIG_BT_GAP_PERIPHERAL_PREF_PARAMS)
+static ssize_t read_ppcp(struct bt_conn *conn, const struct bt_gatt_attr *attr,
+			 void *buf, u16_t len, u16_t offset)
+{
+	struct __packed {
+		uint16_t min_int;
+		uint16_t max_int;
+		uint16_t latency;
+		uint16_t timeout;
+	} ppcp;
+
+	ppcp.min_int = sys_cpu_to_le16(CONFIG_BT_PERIPHERAL_PREF_MIN_INT);
+	ppcp.max_int = sys_cpu_to_le16(CONFIG_BT_PERIPHERAL_PREF_MAX_INT);
+	ppcp.latency = sys_cpu_to_le16(CONFIG_BT_PERIPHERAL_PREF_SLAVE_LATENCY);
+	ppcp.timeout = sys_cpu_to_le16(CONFIG_BT_PERIPHERAL_PREF_TIMEOUT);
+
+	return bt_gatt_attr_read(conn, attr, buf, len, offset, &ppcp,
+				 sizeof(ppcp));
+}
+#endif
+
 #if defined(CONFIG_BT_CENTRAL) && defined(CONFIG_BT_PRIVACY)
 static ssize_t read_central_addr_res(struct bt_conn *conn,
 				     const struct bt_gatt_attr *attr, void *buf,
@@ -127,6 +148,10 @@ static struct bt_gatt_attr gap_attrs[] = {
 			       BT_GATT_CHRC_READ, BT_GATT_PERM_READ,
 			       read_central_addr_res, NULL, NULL),
 #endif /* CONFIG_BT_CENTRAL && CONFIG_BT_PRIVACY */
+#if defined(CONFIG_BT_GAP_PERIPHERAL_PREF_PARAMS)
+	BT_GATT_CHARACTERISTIC(BT_UUID_GAP_PPCP, BT_GATT_CHRC_READ,
+			       BT_GATT_PERM_READ, read_ppcp, NULL, NULL),
+#endif
 };
 
 static struct bt_gatt_service gap_svc = BT_GATT_SERVICE(gap_attrs);