Bluetooth: CAP: Implement unicast to broadcast handover

Implement the unicast to broadcast handover procedure,
as per the Bluetooth CAP specificiation.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>

Author: Thalley

include/zephyr/bluetooth/audio/cap.h

@@ -147,6 +147,22 @@ struct bt_cap_initiator_cb {
 	 */
 	void (*broadcast_stopped)(struct bt_cap_broadcast_source *source, uint8_t reason);
 #endif /* CONFIG_BT_BAP_BROADCAST_SOURCE */
+#if defined(CONFIG_BT_CAP_HANDOVER_SUPPORTED)
+	/**
+	 * @brief The unicast to broadcast handover procedure has finished
+	 *
+	 * @param err 0 if success else a negative errno value.
+	 * @param conn Pointer to the connection where the error
+	 *                       occurred or NULL local failure.
+	 * @param unicast_group NULL if the unicast group was deleted during the procedure, else
+	 *                      pointer to the unicast group provided in the parameters.
+	 * @param broadcast_source Pointer to newly created broadcast source, or NULL in case of an
+	 *                         error happening before it was created.
+	 */
+	void (*unicast_to_broadcast_complete)(int err, struct bt_conn *conn,
+					      struct bt_cap_unicast_group *unicast_group,
+					      struct bt_cap_broadcast_source *broadcast_source);
+#endif /* CONFIG_BT_CAP_HANDOVER_SUPPORTED */
 };
 
 /**
@@ -814,50 +830,47 @@ int bt_cap_initiator_broadcast_get_base(struct bt_cap_broadcast_source *broadcas
 
 /** Parameters for  bt_cap_initiator_unicast_to_broadcast() */
 struct bt_cap_unicast_to_broadcast_param {
+	/** The type of the set. */
+	enum bt_cap_set_type type;
+
 	/** The source unicast group with the streams. */
-	struct bt_bap_unicast_group *unicast_group;
+	struct bt_cap_unicast_group *unicast_group;
 
 	/**
-	 * @brief Whether or not to encrypt the streams.
+	 * @brief The advertising set to use for the broadcast source
 	 *
-	 * If set to true, then the broadcast code in @p broadcast_code
-	 * will be used to encrypt the streams.
+	 * This shall remain valid until the procedure has completed.
+	 * If the advertising set is not started at the time of calling
+	 * bt_cap_initiator_unicast_to_broadcast(),
+	 * the procedure will start the advertising set with @ref BT_LE_EXT_ADV_START_DEFAULT.
 	 */
-	bool encrypt;
+	struct bt_le_ext_adv *ext_adv;
+
+	uint8_t sid;
+	uint16_t pa_interval;
+	uint32_t broadcast_id;
 
 	/**
-	 * @brief 16-octet broadcast code.
-	 *
-	 * Only valid if @p encrypt is true.
+	 * @brief Broadcast source parameters
 	 *
-	 * If the value is a string or a the value is less than 16 octets,
-	 * the remaining octets shall be 0.
-	 *
-	 * Example:
-	 *   The string "Broadcast Code" shall be
-	 *   [42 72 6F 61 64 63 61 73 74 20 43 6F 64 65 00 00]
+	 * These parameters shall remain valid until the procedure has completed.
 	 */
-	uint8_t broadcast_code[BT_ISO_BROADCAST_CODE_SIZE];
+	struct bt_cap_initiator_broadcast_create_param *broadcast_create_param;
 };
 
 /**
  * @brief Hands over the data streams in a unicast group to a broadcast source.
  *
  * The streams in the unicast group will be stopped and the unicast group
- * will be deleted. This can only be done for source streams.
+ * will be deleted. This can only be done for sink streams.
  *
- * @note @kconfig{CONFIG_BT_CAP_INITIATOR},
- * @kconfig{CONFIG_BT_BAP_UNICAST_CLIENT} and
- * @kconfig{CONFIG_BT_BAP_BROADCAST_SOURCE} must be enabled for this function
- * to be enabled.
+ * @kconfig_dep{CONFIG_BT_CAP_HANDOVER_SUPPORTED}
  *
  * @param param         The parameters for the handover.
- * @param source        The resulting broadcast source.
  *
  * @return 0 on success or negative error value on failure.
  */
-int bt_cap_initiator_unicast_to_broadcast(const struct bt_cap_unicast_to_broadcast_param *param,
-					  struct bt_cap_broadcast_source **source);
+int bt_cap_initiator_unicast_to_broadcast(const struct bt_cap_unicast_to_broadcast_param *param);
 
 /** Parameters for  bt_cap_initiator_broadcast_to_unicast() */
 struct bt_cap_broadcast_to_unicast_param {
@@ -890,10 +903,7 @@ struct bt_cap_broadcast_to_unicast_param {
  * The streams in the broadcast source will be stopped and the broadcast source
  * will be deleted.
  *
- * @note @kconfig{CONFIG_BT_CAP_INITIATOR},
- * @kconfig{CONFIG_BT_BAP_UNICAST_CLIENT} and
- * @kconfig{CONFIG_BT_BAP_BROADCAST_SOURCE} must be enabled for this function
- * to be enabled.
+ * @kconfig_dep{CONFIG_BT_CAP_HANDOVER_SUPPORTED}
  *
  * @param[in]  param          The parameters for the handover.
  * @param[out] unicast_group  The resulting broadcast source.

subsys/bluetooth/audio/Kconfig.cap

@@ -48,3 +48,7 @@ config BT_CAP_COMMANDER
 		   BT_MCC
 	help
 	  Enabling this will enable the CAP Initiator role.
+
+config BT_CAP_HANDOVER_SUPPORTED
+	def_bool BT_CAP_COMMANDER && BT_CAP_INITIATOR && BT_BAP_BROADCAST_ASSISTANT && \
+		 BT_BAP_BROADCAST_SOURCE && BT_BAP_UNICAST_CLIENT

subsys/bluetooth/audio/cap_commander.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022-2023 Nordic Semiconductor ASA
+ * Copyright (c) 2022-2025 Nordic Semiconductor ASA
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -28,6 +28,7 @@
 #include <zephyr/sys/__assert.h>
 #include <zephyr/sys/check.h>
 #include <zephyr/sys/util.h>
+#include <zephyr/sys/util_macro.h>
 
 #include "audio_internal.h"
 #include "bap_endpoint.h"
@@ -338,7 +339,7 @@ int bt_cap_commander_broadcast_reception_start(
 		return -EINVAL;
 	}
 
-	if (bt_cap_common_test_and_set_proc_active()) {
+	if (bt_cap_common_test_and_set_proc_active() && !bt_cap_common_handover_is_active()) {
 		LOG_DBG("A CAP procedure is already in progress");
 
 		return -EBUSY;
@@ -798,7 +799,7 @@ int bt_cap_commander_distribute_broadcast_code(
 		return -EINVAL;
 	}
 
-	if (bt_cap_common_test_and_set_proc_active()) {
+	if (bt_cap_common_test_and_set_proc_active() && !bt_cap_common_handover_is_active()) {
 		LOG_DBG("A CAP procedure is already in progress");
 
 		return -EBUSY;
@@ -875,6 +876,18 @@ static void cap_commander_proc_complete(void)
 	failed_conn = active_proc->failed_conn;
 	err = active_proc->err;
 	proc_type = active_proc->proc_type;
+
+	if (IS_ENABLED(CONFIG_BT_CAP_HANDOVER_SUPPORTED) && bt_cap_common_handover_is_active()) {
+		/* Complete handover procedure. At this point we do not know if the remote
+		 * device will attempt to use PAST or scan for itself, so it's best to leave
+		 * this up to the application layer
+		 */
+		__ASSERT_NO_MSG(proc_type == BT_CAP_COMMON_PROC_TYPE_BROADCAST_RECEPTION_START);
+
+		bt_cap_handover_proc_complete();
+		return;
+	}
+
 	bt_cap_common_clear_active_proc();
 
 	if (cap_cb == NULL) {

subsys/bluetooth/audio/cap_common.c

@@ -21,6 +21,7 @@
 #include <zephyr/sys/atomic.h>
 #include <zephyr/sys/check.h>
 #include <zephyr/sys/util.h>
+#include <zephyr/sys/util_macro.h>
 
 #include "cap_internal.h"
 #include "csip_internal.h"
@@ -74,6 +75,23 @@ bool bt_cap_common_subproc_is_type(enum bt_cap_common_subproc_type subproc_type)
 }
 #endif /* CONFIG_BT_CAP_INITIATOR_UNICAST */
 
+void bt_cap_common_set_handover_active(void)
+{
+	if (IS_ENABLED(CONFIG_BT_CAP_HANDOVER_SUPPORTED)) {
+		atomic_set_bit(active_proc.proc_state_flags, BT_CAP_COMMON_PROC_STATE_HANDOVER);
+	}
+}
+
+bool bt_cap_common_handover_is_active(void)
+{
+	if (IS_ENABLED(CONFIG_BT_CAP_HANDOVER_SUPPORTED)) {
+		return atomic_test_bit(active_proc.proc_state_flags,
+				       BT_CAP_COMMON_PROC_STATE_HANDOVER);
+	} else {
+		return false;
+	}
+}
+
 struct bt_conn *bt_cap_common_get_member_conn(enum bt_cap_set_type type,
 					      const union bt_cap_set_member *member)
 {