bluetooth: BAS: add battery critical status char to bas service

Added the battery critical status char to bas service
as per bas_1.1 spec. Updated BSIM test for BAS service
to test the INDs of BAS critical characteristic.

Signed-off-by: Nithin Ramesh Myliattil <niym@demant.com>

include/zephyr/bluetooth/services/bas.h

@@ -26,6 +26,20 @@
 extern "C" {
 #endif
 
+/**
+ * @brief Battery Critical Status Characteristic flags.
+ *
+ * Enumeration for the flags indicating the presence
+ * of various fields in the Battery Critical Status characteristic.
+ */
+enum bt_bas_bcs_flags {
+	/**  Battery Critical Status Bit 0: Critical Power State */
+	BT_BAS_BCS_BATTERY_CRITICAL_STATE = BIT(0),
+
+	/**  Battery Critical Status Bit 1: Immediate Service Required */
+	BT_BAS_BCS_IMMEDIATE_SERVICE_REQUIRED = BIT(1),
+};
+
 /**
  * @brief Battery Level Status Characteristic flags.
  *

subsys/bluetooth/services/bas/CMakeLists.txt

@@ -1,3 +1,4 @@
 # SPDX-License-Identifier: Apache-2.0
 zephyr_sources_ifdef(CONFIG_BT_BAS bas.c)
 zephyr_sources_ifdef(CONFIG_BT_BAS_BLS bas_bls.c)
+zephyr_sources_ifdef(CONFIG_BT_BAS_BCS bas_bcs.c)

subsys/bluetooth/services/bas/Kconfig.bas

@@ -27,4 +27,9 @@ config BT_BAS_BLS_ADDITIONAL_STATUS_PRESENT
 	bool "Additional Battery Status Present"
 	help
 	  Enable this option if Additional Battery Status information is present.
+
+config BT_BAS_BCS
+	bool "Battery Critical Status"
+	help
+	  Enable this option to include Battery Critical Status Characteristic.
 endif

subsys/bluetooth/services/bas/bas.c

@@ -84,6 +84,12 @@ BT_GATT_SERVICE_DEFINE(
 			       BT_GATT_PERM_READ, bt_bas_bls_read_blvl_status, NULL, NULL),
 	BT_GATT_CCC(blvl_status_ccc_cfg_changed, BT_GATT_PERM_READ | BT_GATT_PERM_WRITE),
 #endif
+#if defined(CONFIG_BT_BAS_BCS)
+	BT_GATT_CHARACTERISTIC(BT_UUID_BAS_BATTERY_CRIT_STATUS,
+			       BT_GATT_CHRC_READ | BT_GATT_CHRC_INDICATE, BT_GATT_PERM_READ,
+			       bt_bas_bcs_read_critical_status, NULL, NULL),
+	BT_GATT_CCC(bt_bas_bcs_ccc_cfg_changed, BT_GATT_PERM_READ | BT_GATT_PERM_WRITE),
+#endif /* CONFIG_BT_BAS_BCS */
 );
 
 static int bas_init(void)

subsys/bluetooth/services/bas/bas_bcs.c

@@ -0,0 +1,98 @@
+/*
+ * Copyright (c) 2024 Demant A/S
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/bluetooth/services/bas.h>
+#include <zephyr/bluetooth/gatt.h>
+#include "bas_internal.h"
+
+#include <zephyr/logging/log.h>
+LOG_MODULE_DECLARE(bas, CONFIG_BT_BAS_LOG_LEVEL);
+
+#define BATTERY_CRITICAL_STATUS_CHAR_IDX 9
+
+static uint8_t battery_critical_status;
+
+void bt_bas_bcs_ccc_cfg_changed(const struct bt_gatt_attr *attr, uint16_t value)
+{
+	ARG_UNUSED(attr);
+
+	bool ind_enabled = (value == BT_GATT_CCC_INDICATE);
+
+	LOG_DBG("BAS Critical status Indication %s", ind_enabled ? "enabled" : "disabled");
+}
+
+ssize_t bt_bas_bcs_read_critical_status(struct bt_conn *conn, const struct bt_gatt_attr *attr,
+					void *buf, uint16_t len, uint16_t offset)
+{
+
+	return bt_gatt_attr_read(conn, attr, buf, len, offset, &battery_critical_status,
+				 sizeof(uint8_t));
+}
+
+static void bcs_indicate_cb(struct bt_conn *conn, struct bt_gatt_indicate_params *params,
+			    uint8_t err)
+{
+	if (err != 0) {
+		LOG_DBG("BCS Indication failed with error %u\n", err);
+	} else {
+		LOG_DBG("BCS Indication sent successfully\n");
+	}
+}
+
+static void bt_bas_bcs_update_battery_critical_status(void)
+{
+	/* Indicate all connections */
+	const struct bt_gatt_attr *attr = bt_bas_get_bas_attr(BATTERY_CRITICAL_STATUS_CHAR_IDX);
+
+	if (attr) {
+		uint8_t err;
+		/* Indicate battery critical status to all connections */
+		static struct bt_gatt_indicate_params bcs_ind_params;
+
+		bcs_ind_params.attr = attr;
+		bcs_ind_params.data = &battery_critical_status;
+		bcs_ind_params.len = sizeof(battery_critical_status);
+		bcs_ind_params.func = bcs_indicate_cb;
+		err = bt_gatt_indicate(NULL, &bcs_ind_params);
+		if (err && err != -ENOTCONN) {
+			LOG_DBG("Failed to send critical status ind to all conns (err %d)\n", err);
+		}
+	}
+}
+
+void bt_bas_bcs_set_battery_critical_state(bool critical_state)
+{
+	bool current_state = (battery_critical_status & BT_BAS_BCS_BATTERY_CRITICAL_STATE) != 0;
+
+	if (current_state == critical_state) {
+		LOG_DBG("Already battery_critical_state is %d\n", critical_state);
+		return;
+	}
+
+	if (critical_state) {
+		battery_critical_status |= BT_BAS_BCS_BATTERY_CRITICAL_STATE;
+	} else {
+		battery_critical_status &= ~BT_BAS_BCS_BATTERY_CRITICAL_STATE;
+	}
+	bt_bas_bcs_update_battery_critical_status();
+}
+
+void bt_bas_bcs_set_immediate_service_required(bool service_required)
+{
+	bool current_state = (battery_critical_status & BT_BAS_BCS_IMMEDIATE_SERVICE_REQUIRED) != 0;
+
+	if (current_state == service_required) {
+		LOG_DBG("Already immediate_service_required is %d\n", service_required);
+		return;
+	}
+
+	if (service_required) {
+		battery_critical_status |= BT_BAS_BCS_IMMEDIATE_SERVICE_REQUIRED;
+	} else {
+		battery_critical_status &= ~BT_BAS_BCS_IMMEDIATE_SERVICE_REQUIRED;
+	}
+	bt_bas_bcs_update_battery_critical_status();
+}

subsys/bluetooth/services/bas/bas_bls.c

@@ -194,6 +194,20 @@ void bt_bas_bls_set_battery_charge_level(enum bt_bas_bls_battery_charge_level le
 	bls.power_state &= ~BATTERY_CHARGE_LEVEL_MASK;
 	bls.power_state |= (level << BATTERY_CHARGE_LEVEL_SHIFT) & BATTERY_CHARGE_LEVEL_MASK;
 	bt_bas_bls_update_battery_level_status();
+
+	if (IS_ENABLED(CONFIG_BT_BAS_BCS)) {
+		/*
+		 * Set the BCS Critical Power State bit as per BAS 1.1 specification
+		 * section 3.4.1.1: The BCS Critical Power State bit should be set to true if the
+		 * Battery Charge Level is set to Critical in the Power State field.
+		 */
+		if (level == BT_BAS_BLS_CHARGE_LEVEL_CRITICAL) {
+			bt_bas_bcs_set_battery_critical_state(true);
+			return;
+		} else if (level != BT_BAS_BLS_CHARGE_LEVEL_UNKNOWN) {
+			bt_bas_bcs_set_battery_critical_state(false);
+		}
+	}
 }
 
 void bt_bas_bls_set_battery_charge_type(enum bt_bas_bls_battery_charge_type type)
@@ -232,6 +246,20 @@ void bt_bas_bls_set_service_required(enum bt_bas_bls_service_required value)
 	bls.additional_status &= ~SERVICE_REQUIRED_MASK;
 	bls.additional_status |= (value << SERVICE_REQUIRED_SHIFT) & SERVICE_REQUIRED_MASK;
 	bt_bas_bls_update_battery_level_status();
+
+	if (IS_ENABLED(CONFIG_BT_BAS_BCS)) {
+		/*
+		 * Set the BCS Immediate Service Required bit as per BAS 1.1 specification
+		 * section 3.4.1.1: The BCS Immediate Service Required bit should be set to true if
+		 * the service Required bit is set to true in the Additional Status field.
+		 */
+		if (value == BT_BAS_BLS_SERVICE_REQUIRED_TRUE) {
+			bt_bas_bcs_set_immediate_service_required(true);
+			return;
+		} else if (value != BT_BAS_BLS_SERVICE_REQUIRED_UNKNOWN) {
+			bt_bas_bcs_set_immediate_service_required(false);
+		}
+	}
 }
 
 void bt_bas_bls_set_battery_fault(enum bt_bas_bls_battery_fault value)

subsys/bluetooth/services/bas/bas_internal.h

@@ -111,13 +111,52 @@ struct bt_bas_bls {
  */
 void bt_bas_bls_init(void);
 
+/**
+ * @brief Read the Battery Critical Status characteristic.
+ *
+ * @param conn Pointer to the Bluetooth connection object representing the client requesting
+ *             the characteristic.
+ * @param attr Pointer to the GATT attribute of Battery Critical Status characteristic.
+ * @param buf Buffer to store the read value.
+ * @param len Length of the buffer.
+ * @param offset Offset within the characteristic value to start reading.
+ *
+ * @return The number of bytes read and sent to the client, or a negative error code on failure.
+ */
+ssize_t bt_bas_bcs_read_critical_status(struct bt_conn *conn, const struct bt_gatt_attr *attr,
+					void *buf, uint16_t len, uint16_t offset);
+
+/**
+ * @brief Callback function for BCS Client Characteristic Configuration changes.
+ *
+ *
+ * @param attr  Pointer to the GATT attribute of battery critical status char.
+ * @param value The new value of the CCC. This value indicates whether
+ *              notifications or indications are enabled or disabled.
+ */
+void bt_bas_bcs_ccc_cfg_changed(const struct bt_gatt_attr *attr, uint16_t value);
+
 /**
  * @brief Set the battery level characteristic value.
  *
  * @param battery_level The new battery level value in percent (0-100).
  */
 void bt_bas_bls_set_battery_level(uint8_t battery_level);
 
+/**
+ * @brief Set the battery critical state flag.
+ *
+ * @param critical_state The battery critical state to set (true for critical, false otherwise).
+ */
+void bt_bas_bcs_set_battery_critical_state(bool critical_state);
+
+/**
+ * @brief Set the immediate service required flag.
+ *
+ * @param service_required The immediate service required status to set.
+ */
+void bt_bas_bcs_set_immediate_service_required(bool service_required);
+
 /**
  * @brief Read the Battery Level Status characteristic.
  *

tests/bsim/bluetooth/samples/battery_service/prj.conf

@@ -6,9 +6,10 @@ CONFIG_BT_SMP=y
 CONFIG_BT_BAS=y
 CONFIG_BT_GATT_CLIENT=y
 CONFIG_BT_DEVICE_NAME="bsim_bas"
-CONFIG_BT_ATT_TX_COUNT=5
+CONFIG_BT_ATT_TX_COUNT=10
 
 CONFIG_BT_BAS_BLS=y
+CONFIG_BT_BAS_BCS=y
 CONFIG_BT_BAS_BLS_IDENTIFIER_PRESENT=y
 CONFIG_BT_BAS_BLS_BATTERY_LEVEL_PRESENT=y
 CONFIG_BT_BAS_BLS_ADDITIONAL_STATUS_PRESENT=y