Peer Manager silently drop Service Changed indications if an ATT MTU exchange was happening

[Karlis]

Hello,

Using nRF5 SDK v15.3.0 Peer Manager drops Service Changed indications if an ATT MTU exchange is in progress, this hapens because function service_changed_cccd() in gatt_cache_manager.c allways returns NRF_ERROR_NOT_FOUND.

static ret_code_t service_changed_cccd(uint16_t conn_handle, uint16_t * p_cccd)
{
    bool       sc_found = false;
    uint16_t   end_handle;
    ret_code_t err_code = sd_ble_gatts_initial_user_handle_get(&end_handle);
    ASSERT(err_code == NRF_SUCCESS);

    for (uint16_t handle = 1; handle < end_handle; handle++)
    {
        uint16_t uuid;
        ble_gatts_value_t value = {.p_value = (uint8_t *)&uuid, .len = 2, .offset = 0};
        err_code = sd_ble_gatts_value_get(conn_handle, handle, &value);
        if (err_code != NRF_SUCCESS)
        {
            return err_code;
        }
        else if (!sc_found && (uuid == BLE_UUID_GATT_CHARACTERISTIC_SERVICE_CHANGED))
        {
            sc_found = true;
        }
        else if (sc_found && (uuid == BLE_UUID_DESCRIPTOR_CLIENT_CHAR_CONFIG))
        {
            value.p_value = (uint8_t *)p_cccd;
            return sd_ble_gatts_value_get(conn_handle, ++handle, &value);
        }
    }
    return NRF_ERROR_NOT_FOUND;
}

After some digging I found, as far as I understand, that sd_ble_gatts_value_get used in service_changed_cccd() returns handle value which is UUID only for service handles, but for characteristic handles UUID not stored as value.

Is there an other way how to find service changed cccd? 

Maybe it is allways last handle before user handles?

Or handle associated with service changed cccd is allways the same and we can simply check if it exists?

Thank You!

[Bart Cerneels]

I'm experiencing issues with SCI not being sent but I'm using SDK 15.2.0
Is this a known issue in that release? The code above does not match service_changed_send_in_evt() in gatt_cache_manager.c.

[Vidar Berg]

Yes, 15.2.0 had the same issue. The fix will be implemented in the next SDK release.

[Bart Cerneels]

How can we work around this in the meantime without upgrading to 15.3.0 as I need to solve this in a bugfix release.
The code snippet above does not apply.

[Vidar Berg]

You will need to modify the service_changed_send_in_evt() to handle the NRF_ERROR_INVALID_STATE case like in SDK 15.3.0. I.e., check if the invalid state error may have been caused by an ongoing MTU exchange and not assume it's because CCCD is not set. 

Update fix which I have quickly tested with SDK 15.2.0:

Fullscreen service_changed_fix.diff Download

diff --git a/components/ble/peer_manager/gatt_cache_manager.c b/components/ble/peer_manager/gatt_cache_manager.c
index 140b4dbd..79a808b6 100644
--- a/components/ble/peer_manager/gatt_cache_manager.c
+++ b/components/ble/peer_manager/gatt_cache_manager.c
@@ -284,6 +284,48 @@ static bool local_db_update_in_evt(uint16_t conn_handle)
 }
 
 #if PM_SERVICE_CHANGED_ENABLED
+
+
+/**@brief Function for getting the value of the CCCD for the service changed characteristic.
+ *
+ * @details This function will search all system handles consecutively.
+ *
+ * @param[in]  conn_handle  The connection to check.
+ * @param[out] p_cccd       The CCCD value of the service changed characteristic for this link.
+ *
+ * @return Any error from @ref sd_ble_gatts_value_get or @ref sd_ble_gatts_attr_get.
+ */
+static ret_code_t service_changed_cccd(uint16_t conn_handle, uint16_t * p_cccd)
+{
+    bool       sc_found = false;
+    uint16_t   end_handle;
+
+    ret_code_t err_code = sd_ble_gatts_initial_user_handle_get(&end_handle);
+    ASSERT(err_code == NRF_SUCCESS);
+
+    for (uint16_t handle = 1; handle < end_handle; handle++)
+    {
+        ble_uuid_t uuid;
+        ble_gatts_value_t value = {.p_value = (uint8_t *)&uuid.uuid, .len = 2, .offset = 0};
+
+        err_code = sd_ble_gatts_attr_get(handle, &uuid, NULL);
+        if (err_code != NRF_SUCCESS)
+        {
+            return err_code;
+        }
+        else if (!sc_found && (uuid.uuid == BLE_UUID_GATT_CHARACTERISTIC_SERVICE_CHANGED))
+        {
+            sc_found = true;
+        }
+        else if (sc_found && (uuid.uuid == BLE_UUID_DESCRIPTOR_CLIENT_CHAR_CONFIG))
+        {
+            value.p_value = (uint8_t *)p_cccd;
+            return sd_ble_gatts_value_get(conn_handle, handle, &value);
+        }
+    }
+    return NRF_ERROR_NOT_FOUND;
+}
+
 /**@brief Function for sending a service changed indication in an event context, where no return
  *        code can be given.
  *
@@ -319,8 +361,26 @@ static void service_changed_send_in_evt(uint16_t conn_handle)
             break;
 
         case NRF_ERROR_INVALID_STATE:
-            // CCCDs not enabled. Drop indication.
-            // Fallthrough.
+        {
+            uint16_t cccd;
+            err_code = service_changed_cccd(conn_handle, &cccd);
+            if ((err_code == NRF_SUCCESS) && cccd)
+            {
+                // Possible ATT_MTU exchange ongoing.
+                // Do nothing, treat as busy.
+                break;
+            }
+            else
+            {
+                if (err_code != NRF_SUCCESS)
+                {
+                    NRF_LOG_DEBUG("Unexpected error when looking for service changed CCCD: %s",
+                                  nrf_strerror_get(err_code));
+                }
+                // CCCDs not enabled or an error happened. Drop indication.
+                // Fallthrough.
+            }
+        }
 
         case NRF_ERROR_NOT_SUPPORTED:
             // Service changed not supported. Drop indication.

Fullscreen gatt_cache_manager.c Download

/**
 * Copyright (c) 2015 - 2018, Nordic Semiconductor ASA
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form, except as embedded into a Nordic
 *    Semiconductor ASA integrated circuit in a product or a software update for
 *    such product, must reproduce the above copyright notice, this list of
 *    conditions and the following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 *
 * 3. Neither the name of Nordic Semiconductor ASA nor the names of its
 *    contributors may be used to endorse or promote products derived from this
 *    software without specific prior written permission.
 *
 * 4. This software, with or without modification, must only be used with a
 *    Nordic Semiconductor ASA integrated circuit.
 *
 * 5. Any software provided in binary form under this license must not be reverse
 *    engineered, decompiled, modified and/or disassembled.
 *
 * THIS SOFTWARE IS PROVIDED BY NORDIC SEMICONDUCTOR ASA "AS IS" AND ANY EXPRESS
 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY, NONINFRINGEMENT, AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL NORDIC SEMICONDUCTOR ASA OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */
#include "sdk_common.h"
#if NRF_MODULE_ENABLED(PEER_MANAGER)
#include "gatt_cache_manager.h"

#include "ble_gap.h"
#include "ble_err.h"
#include "ble_conn_state.h"
#include "peer_manager_types.h"
#include "peer_manager_internal.h"
#include "id_manager.h"
#include "gatts_cache_manager.h"
#include "peer_data_storage.h"
#include "peer_database.h"
#include "nrf_mtx.h"

#define NRF_LOG_MODULE_NAME peer_manager_gcm
#if PM_LOG_ENABLED
    #define NRF_LOG_LEVEL       PM_LOG_LEVEL
    #define NRF_LOG_INFO_COLOR  PM_LOG_INFO_COLOR
    #define NRF_LOG_DEBUG_COLOR PM_LOG_DEBUG_COLOR
#else
    #define NRF_LOG_LEVEL       0
#endif // PM_LOG_ENABLED
#include "nrf_log.h"
#include "nrf_log_ctrl.h"
NRF_LOG_MODULE_REGISTER();
#include "nrf_strerror.h"

// The number of registered event handlers.
#define GCM_EVENT_HANDLERS_CNT      (sizeof(m_evt_handlers) / sizeof(m_evt_handlers[0]))

// GATT Cache Manager event handler in Peer Manager.
extern void pm_gcm_evt_handler(pm_evt_t * p_gcm_evt);

// GATT Cache Manager events' handlers.
// The number of elements in this array is GCM_EVENT_HANDLERS_CNT.
static pm_evt_handler_internal_t m_evt_handlers[] =
{
    pm_gcm_evt_handler
};

static bool                           m_module_initialized;
static nrf_mtx_t                      m_db_update_in_progress_mutex;  /**< Mutex indicating whether a local DB write operation is ongoing. */
static ble_conn_state_user_flag_id_t  m_flag_local_db_update_pending; /**< Flag ID for flag collection to keep track of which connections need a local DB update procedure. */
static ble_conn_state_user_flag_id_t  m_flag_local_db_apply_pending;  /**< Flag ID for flag collection to keep track of which connections need a local DB apply procedure. */
static ble_conn_state_user_flag_id_t  m_flag_service_changed_pending; /**< Flag ID for flag collection to keep track of which connections need to be sent a service changed indication. */
static ble_conn_state_user_flag_id_t  m_flag_service_changed_sent;    /**< Flag ID for flag collection to keep track of which connections have been sent a service changed indication and are waiting for a handle value confirmation. */
static ble_conn_state_user_flag_id_t  m_flag_car_update_pending;      /**< Flag ID for flag collection to keep track of which connections need to have their Central Address Resolution value stored. */

#ifdef PM_SERVICE_CHANGED_ENABLED
    STATIC_ASSERT(PM_SERVICE_CHANGED_ENABLED || !NRF_SDH_BLE_SERVICE_CHANGED,
                 "PM_SERVICE_CHANGED_ENABLED should be enabled if NRF_SDH_BLE_SERVICE_CHANGED is enabled.");
#else
    #define PM_SERVICE_CHANGED_ENABLED 1
#endif

/**@brief Function for resetting the module variable(s) of the GSCM module.
 *
 * @param[out]  The instance to reset.
 */
static void internal_state_reset()
{
    m_module_initialized = false;
}


static void evt_send(pm_evt_t * p_gcm_evt)
{
    p_gcm_evt->peer_id = im_peer_id_get_by_conn_handle(p_gcm_evt->conn_handle);

    for (uint32_t i = 0; i < GCM_EVENT_HANDLERS_CNT; i++)
    {
        m_evt_handlers[i](p_gcm_evt);
    }
}


/**@brief Function for checking a write event for whether a CCCD was written during the write
 *        operation.
 *
 * @param[in]  p_write_evt  The parameters of the write event.
 *
 * @return  Whether the write was on a CCCD.
 */
static bool cccd_written(ble_gatts_evt_write_t const * p_write_evt)
{
    return (    (p_write_evt->op        == BLE_GATTS_OP_WRITE_REQ)
             && (p_write_evt->uuid.type == BLE_UUID_TYPE_BLE)
             && (p_write_evt->uuid.uuid == BLE_UUID_DESCRIPTOR_CLIENT_CHAR_CONFIG)
           );
}


/**@brief Function for sending an PM_EVT_ERROR_UNEXPECTED event.
 *
 * @param[in]  conn_handle  The connection handle the event pertains to.
 * @param[in]  err_code     The unexpected error that occurred.
 */
static void send_unexpected_error(uint16_t conn_handle, ret_code_t err_code)
{
    pm_evt_t error_evt =
    {
        .evt_id = PM_EVT_ERROR_UNEXPECTED,
        .conn_handle = conn_handle,
        .params =
        {
            .error_unexpected =
            {
                .error     = err_code,
                .fds_error = false
            }
        }
    };
    evt_send(&error_evt);
}


/**@brief Function for performing the local DB update procedure in an event context, where no return
 *        code can be given.
 *
 * @details This function will do the procedure, and check the result, set a flag if needed, and
 *          send an event if needed.
 *
 * @param[in]  conn_handle  The connection to perform the procedure on.
 */
static void local_db_apply_in_evt(uint16_t conn_handle)
{
    bool set_procedure_as_pending = false;
    ret_code_t err_code;
    pm_evt_t event =
    {
        .conn_handle = conn_handle,
    };

    if (conn_handle == BLE_CONN_HANDLE_INVALID)
    {
        return;
    }

    err_code = gscm_local_db_cache_apply(conn_handle);

    switch (err_code)
    {
        case NRF_SUCCESS:
            event.evt_id = PM_EVT_LOCAL_DB_CACHE_APPLIED;

            evt_send(&event);
            break;

        case NRF_ERROR_BUSY:
            set_procedure_as_pending = true;
            break;

        case NRF_ERROR_INVALID_DATA:
            event.evt_id = PM_EVT_LOCAL_DB_CACHE_APPLY_FAILED;

            NRF_LOG_WARNING("The local database has changed, so some subscriptions to notifications "\
                            "and indications could not be restored for conn_handle %d",
                            conn_handle);
            evt_send(&event);
            break;

        case BLE_ERROR_INVALID_CONN_HANDLE:
            /* Do nothing */
            break;

        default:
            NRF_LOG_ERROR("gscm_local_db_cache_apply() returned %s which should not happen. "\
                          "conn_handle: %d",
                          nrf_strerror_get(err_code),
                          conn_handle);
            send_unexpected_error(conn_handle, err_code);
            break;
    }

    ble_conn_state_user_flag_set(conn_handle, m_flag_local_db_apply_pending, set_procedure_as_pending);
}


/**@brief Function for asynchronously starting a DB update procedure.
 *
 * @note This procedure can only be started asynchronously.
 *
 * @param[in]  conn_handle  The connection to perform the procedure on.
 * @param[in]  update       Whether to perform the procedure.
 */
static __INLINE void local_db_update(uint16_t conn_handle, bool update)
{
    ble_conn_state_user_flag_set(conn_handle, m_flag_local_db_update_pending, update);
}


/**@brief Function for performing the local DB update procedure in an event context, where no return
 *        code can be given.
 *
 * @details This function will do the procedure, and check the result, set a flag if needed, and
 *          send an event if needed.
 *
 * @param[in]  conn_handle  The connection to perform the procedure on.
 */
static bool local_db_update_in_evt(uint16_t conn_handle)
{
    bool set_procedure_as_pending = false;
    bool success = false;
    ret_code_t err_code = gscm_local_db_cache_update(conn_handle);

    switch (err_code)
    {
        case NRF_SUCCESS:
            success = true;
            break;

        case BLE_ERROR_INVALID_CONN_HANDLE:
            /* Do nothing */
            break;

        case NRF_ERROR_BUSY:
            set_procedure_as_pending = true;
            break;

        case NRF_ERROR_STORAGE_FULL:
        {
            pm_evt_t event =
            {
                .evt_id      = PM_EVT_STORAGE_FULL,
                .conn_handle = conn_handle,
            };

            NRF_LOG_WARNING("Flash full. Could not store data for conn_handle: %d", conn_handle);
            evt_send(&event);
            break;
        }

        default:
            NRF_LOG_ERROR("gscm_local_db_cache_update() returned %s for conn_handle: %d",
                          nrf_strerror_get(err_code),
                          conn_handle);
            send_unexpected_error(conn_handle, err_code);
            break;
    }

    local_db_update(conn_handle, set_procedure_as_pending);

    return success;
}

#if PM_SERVICE_CHANGED_ENABLED


/**@brief Function for getting the value of the CCCD for the service changed characteristic.
 *
 * @details This function will search all system handles consecutively.
 *
 * @param[in]  conn_handle  The connection to check.
 * @param[out] p_cccd       The CCCD value of the service changed characteristic for this link.
 *
 * @return Any error from @ref sd_ble_gatts_value_get or @ref sd_ble_gatts_attr_get.
 */
static ret_code_t service_changed_cccd(uint16_t conn_handle, uint16_t * p_cccd)
{
    bool       sc_found = false;
    uint16_t   end_handle;

    ret_code_t err_code = sd_ble_gatts_initial_user_handle_get(&end_handle);
    ASSERT(err_code == NRF_SUCCESS);

    for (uint16_t handle = 1; handle < end_handle; handle++)
    {
        ble_uuid_t uuid;
        ble_gatts_value_t value = {.p_value = (uint8_t *)&uuid.uuid, .len = 2, .offset = 0};

        err_code = sd_ble_gatts_attr_get(handle, &uuid, NULL);
        if (err_code != NRF_SUCCESS)
        {
            return err_code;
        }
        else if (!sc_found && (uuid.uuid == BLE_UUID_GATT_CHARACTERISTIC_SERVICE_CHANGED))
        {
            sc_found = true;
        }
        else if (sc_found && (uuid.uuid == BLE_UUID_DESCRIPTOR_CLIENT_CHAR_CONFIG))
        {
            value.p_value = (uint8_t *)p_cccd;
            return sd_ble_gatts_value_get(conn_handle, handle, &value);
        }
    }
    return NRF_ERROR_NOT_FOUND;
}

/**@brief Function for sending a service changed indication in an event context, where no return
 *        code can be given.
 *
 * @details This function will do the procedure, and check the result, set a flag if needed, and
 *          send an event if needed.
 *
 * @param[in]  conn_handle  The connection to perform the procedure on.
 */
static void service_changed_send_in_evt(uint16_t conn_handle)
{
    bool sc_pending_state = true;
    bool sc_sent_state = false;
    ret_code_t err_code = gscm_service_changed_ind_send(conn_handle);

    switch (err_code)
    {
        case NRF_SUCCESS:
        {
            pm_evt_t event =
            {
                .evt_id      = PM_EVT_SERVICE_CHANGED_IND_SENT,
                .conn_handle = conn_handle,
            };

            sc_sent_state = true;

            evt_send(&event);
            break;
        }

        case NRF_ERROR_BUSY:
            // Do nothing.
            break;

        case NRF_ERROR_INVALID_STATE:
        {
            uint16_t cccd;
            err_code = service_changed_cccd(conn_handle, &cccd);
            if ((err_code == NRF_SUCCESS) && cccd)
            {
                // Possible ATT_MTU exchange ongoing.
                // Do nothing, treat as busy.
                break;
            }
            else
            {
                if (err_code != NRF_SUCCESS)
                {
                    NRF_LOG_DEBUG("Unexpected error when looking for service changed CCCD: %s",
                                  nrf_strerror_get(err_code));
                }
                // CCCDs not enabled or an error happened. Drop indication.
                // Fallthrough.
            }
        }

        case NRF_ERROR_NOT_SUPPORTED:
            // Service changed not supported. Drop indication.
            sc_pending_state = false;
            gscm_db_change_notification_done(im_peer_id_get_by_conn_handle(conn_handle));
            break;

        case BLE_ERROR_GATTS_SYS_ATTR_MISSING:
            local_db_apply_in_evt(conn_handle);
            break;

        case BLE_ERROR_INVALID_CONN_HANDLE:
            // Do nothing.
            break;

        default:
            NRF_LOG_ERROR("gscm_service_changed_ind_send() returned %s for conn_handle: %d",
                          nrf_strerror_get(err_code),
                          conn_handle);
            send_unexpected_error(conn_handle, err_code);
            break;
    }

    ble_conn_state_user_flag_set(conn_handle, m_flag_service_changed_pending, sc_pending_state);
    ble_conn_state_user_flag_set(conn_handle, m_flag_service_changed_sent, sc_sent_state);
}
#endif

static void apply_pending_handle(uint16_t conn_handle, void * p_context)
{
    UNUSED_PARAMETER(p_context);
    local_db_apply_in_evt(conn_handle);
}


static __INLINE void apply_pending_flags_check(void)
{
    UNUSED_RETURN_VALUE(ble_conn_state_for_each_set_user_flag(m_flag_local_db_apply_pending,
                                                              apply_pending_handle,
                                                              NULL));
}


static void db_update_pending_handle(uint16_t conn_handle, void * p_context)
{
    UNUSED_PARAMETER(p_context);
    if (nrf_mtx_trylock(&m_db_update_in_progress_mutex))
    {
        if (local_db_update_in_evt(conn_handle))
        {
            // Successfully started writing to flash.
            return;
        }
        else
        {
            nrf_mtx_unlock(&m_db_update_in_progress_mutex);
        }
    }
}


#if PM_SERVICE_CHANGED_ENABLED
static void sc_send_pending_handle(uint16_t conn_handle, void * p_context)
{
    UNUSED_PARAMETER(p_context);
    if (!ble_conn_state_user_flag_get(conn_handle, m_flag_service_changed_sent))
    {
        service_changed_send_in_evt(conn_handle);
    }
}


static __INLINE void service_changed_pending_flags_check(void)
{
    UNUSED_RETURN_VALUE(ble_conn_state_for_each_set_user_flag(m_flag_service_changed_pending,
                                                              sc_send_pending_handle,
                                                              NULL));
}


static void service_changed_needed(uint16_t conn_handle)
{
    if (gscm_service_changed_ind_needed(conn_handle))
    {
        ble_conn_state_user_flag_set(conn_handle, m_flag_service_changed_pending, true);
    }
}
#endif


static void car_update_pending_handle(uint16_t conn_handle, void * p_context)
{
    UNUSED_PARAMETER(p_context);

    ble_uuid_t car_uuid;
    memset(&car_uuid, 0, sizeof(ble_uuid_t));
    car_uuid.uuid = BLE_UUID_GAP_CHARACTERISTIC_CAR;
    car_uuid.type = BLE_UUID_TYPE_BLE;

    ble_gattc_handle_range_t const car_handle_range = {1, 0xFFFF};

    ret_code_t err_code = sd_ble_gattc_char_value_by_uuid_read(conn_handle, &car_uuid, &car_handle_range);
    UNUSED_RETURN_VALUE(err_code);
}


static void car_update_needed(uint16_t conn_handle)
{
    pm_peer_data_t peer_data;
    if (pds_peer_data_read(im_peer_id_get_by_conn_handle(conn_handle),
                           PM_PEER_DATA_ID_CENTRAL_ADDR_RES,
                           &peer_data,
                           NULL) == NRF_ERROR_NOT_FOUND)
    {
        ble_conn_state_user_flag_set(conn_handle, m_flag_car_update_pending, true);
    }
}


static __INLINE void update_pending_flags_check(void)
{
    uint32_t count = ble_conn_state_for_each_set_user_flag(m_flag_local_db_update_pending,
                                                           db_update_pending_handle,
                                                           NULL);
    if (count == 0)
    {
        count = ble_conn_state_for_each_set_user_flag(m_flag_car_update_pending,
                                                      car_update_pending_handle,
                                                      NULL);
        UNUSED_RETURN_VALUE(count);
    }
}


/**@brief Callback function for events from the ID Manager module.
 *        This function is registered in the ID Manager module.
 *
 * @param[in]  p_event  The event from the ID Manager module.
 */
void gcm_im_evt_handler(pm_evt_t * p_event)
{
    switch (p_event->evt_id)
    {
        case PM_EVT_BONDED_PEER_CONNECTED:
            local_db_apply_in_evt(p_event->conn_handle);
#if (PM_SERVICE_CHANGED_ENABLED == 1)
            service_changed_needed(p_event->conn_handle);
#endif
            car_update_needed(p_event->conn_handle);
            update_pending_flags_check();
            break;
        default:
            break;
    }
}


/**@brief Callback function for events from the Peer Database module.
 *        This handler is extern in Peer Database.
 *
 * @param[in]  p_event  The event from the Security Dispatcher module.
 */
void gcm_pdb_evt_handler(pm_evt_t * p_event)
{
    if (   p_event->evt_id == PM_EVT_PEER_DATA_UPDATE_SUCCEEDED
        && p_event->params.peer_data_update_succeeded.action == PM_PEER_DATA_OP_UPDATE)
    {
        switch (p_event->params.peer_data_update_succeeded.data_id)
        {
            case PM_PEER_DATA_ID_BONDING:
            {
                uint16_t conn_handle = im_conn_handle_get(p_event->peer_id);

                if (conn_handle != BLE_CONN_HANDLE_INVALID)
                {
                    local_db_update(conn_handle, true);
                    car_update_needed(conn_handle);
                }
                break;
            }

#if PM_SERVICE_CHANGED_ENABLED
            case PM_PEER_DATA_ID_SERVICE_CHANGED_PENDING:
            {
                ret_code_t           err_code;
                pm_peer_data_flash_t peer_data;

                err_code = pdb_peer_data_ptr_get(p_event->peer_id,
                                                 PM_PEER_DATA_ID_SERVICE_CHANGED_PENDING,
                                                 &peer_data);

                if (err_code == NRF_SUCCESS)
                {
                    if (*peer_data.p_service_changed_pending)
                    {
                        uint16_t conn_handle = im_conn_handle_get(p_event->peer_id);
                        if (conn_handle != BLE_CONN_HANDLE_INVALID)
                        {
                            ble_conn_state_user_flag_set(conn_handle, m_flag_service_changed_pending, true);
                            service_changed_pending_flags_check();
                        }
                    }
                }
                break;
            }
#endif

            case PM_PEER_DATA_ID_GATT_LOCAL:
                if (m_db_update_in_progress_mutex == NRF_MTX_LOCKED)
                {
                    nrf_mtx_unlock(&m_db_update_in_progress_mutex);
                }

                // Expecting a call to update_pending_flags_check() immediately.
                break;

            default:
                /* No action */
                break;
        }
    }

    update_pending_flags_check();
}


ret_code_t gcm_init()
{
    NRF_PM_DEBUG_CHECK(!m_module_initialized);

    internal_state_reset();

    m_flag_local_db_update_pending = ble_conn_state_user_flag_acquire();
    m_flag_local_db_apply_pending  = ble_conn_state_user_flag_acquire();
    m_flag_service_changed_pending = ble_conn_state_user_flag_acquire();
    m_flag_service_changed_sent    = ble_conn_state_user_flag_acquire();
    m_flag_car_update_pending      = ble_conn_state_user_flag_acquire();

    if  ((m_flag_local_db_update_pending  == BLE_CONN_STATE_USER_FLAG_INVALID)
      || (m_flag_local_db_apply_pending   == BLE_CONN_STATE_USER_FLAG_INVALID)
      || (m_flag_service_changed_pending  == BLE_CONN_STATE_USER_FLAG_INVALID)
      || (m_flag_service_changed_sent     == BLE_CONN_STATE_USER_FLAG_INVALID)
      || (m_flag_car_update_pending       == BLE_CONN_STATE_USER_FLAG_INVALID)
      )
    {
        NRF_LOG_ERROR("Could not acquire conn_state user flags. Increase "\
                      "BLE_CONN_STATE_USER_FLAG_COUNT in the ble_conn_state module.");
        return NRF_ERROR_INTERNAL;
    }

    nrf_mtx_init(&m_db_update_in_progress_mutex);

    m_module_initialized = true;

    return NRF_SUCCESS;
}



void store_car_value(uint16_t conn_handle, bool car_value)
{
    // Use a uint32_t to enforce 4-byte alignment.
    static const uint32_t car_value_true  = true;
    static const uint32_t car_value_false = false;

    pm_peer_data_const_t peer_data =
    {
        .data_id      = PM_PEER_DATA_ID_CENTRAL_ADDR_RES,
        .length_words = 1,
    };
    peer_data.p_central_addr_res = car_value ? &car_value_true : &car_value_false;
    ret_code_t err_code = pds_peer_data_store(im_peer_id_get_by_conn_handle(conn_handle), &peer_data, NULL);
    if (err_code != NRF_SUCCESS)
    {
        NRF_LOG_WARNING("CAR char value couldn't be stored (error: %s). Reattempt will happen on the next connection.", nrf_strerror_get(err_code));
    }
}



/**@brief Callback function for BLE events from the SoftDevice.
 *
 * @param[in]  p_ble_evt  The BLE event from the SoftDevice.
 */
void gcm_ble_evt_handler(ble_evt_t const * p_ble_evt)
{
    uint16_t conn_handle = p_ble_evt->evt.gatts_evt.conn_handle;

    switch (p_ble_evt->header.evt_id)
    {
        case BLE_GATTS_EVT_SYS_ATTR_MISSING:
            local_db_apply_in_evt(conn_handle);
            break;

#if PM_SERVICE_CHANGED_ENABLED
        case BLE_GATTS_EVT_SC_CONFIRM:
        {
            pm_evt_t event =
            {
                .evt_id      = PM_EVT_SERVICE_CHANGED_IND_CONFIRMED,
                .peer_id     = im_peer_id_get_by_conn_handle(conn_handle),
                .conn_handle = conn_handle,
            };

            gscm_db_change_notification_done(event.peer_id);

            ble_conn_state_user_flag_set(conn_handle, m_flag_service_changed_sent, false);
            ble_conn_state_user_flag_set(conn_handle, m_flag_service_changed_pending, false);
            evt_send(&event);
            break;
        }
#endif

        case BLE_GATTS_EVT_WRITE:
            if (cccd_written(&p_ble_evt->evt.gatts_evt.params.write))
            {
                local_db_update(conn_handle, true);
                update_pending_flags_check();
            }
            break;

        case BLE_GATTC_EVT_CHAR_VAL_BY_UUID_READ_RSP:
        {
            bool car_value = false;
            conn_handle = p_ble_evt->evt.gattc_evt.conn_handle;

            ble_conn_state_user_flag_set(conn_handle, m_flag_car_update_pending, false);

            if (p_ble_evt->evt.gattc_evt.gatt_status == BLE_GATT_STATUS_ATTERR_ATTRIBUTE_NOT_FOUND)
            {
                // Store 0.
            }
            else if (p_ble_evt->evt.gattc_evt.gatt_status != BLE_GATT_STATUS_SUCCESS)
            {
                NRF_LOG_WARNING("Unexpected GATT status while getting CAR char value: 0x%x",
                                p_ble_evt->evt.gattc_evt.gatt_status);
                // Store 0.
            }
            else
            {
                if (p_ble_evt->evt.gattc_evt.params.char_val_by_uuid_read_rsp.count != 1)
                {
                    NRF_LOG_WARNING("Multiple (%d) CAR characteristics found, using the first.",
                                    p_ble_evt->evt.gattc_evt.params.char_val_by_uuid_read_rsp.count);
                }

                if (p_ble_evt->evt.gattc_evt.params.char_val_by_uuid_read_rsp.value_len != 1)
                {
                    NRF_LOG_WARNING("Unexpected CAR characteristic value length (%d), store 0.",
                                    p_ble_evt->evt.gattc_evt.params.char_val_by_uuid_read_rsp.value_len);
                    // Store 0.
                }
                else
                {
                    car_value = *p_ble_evt->evt.gattc_evt.params.char_val_by_uuid_read_rsp.handle_value;
                }
            }

            store_car_value(conn_handle, car_value);
            break;
        }
    }

    apply_pending_flags_check();
#if PM_SERVICE_CHANGED_ENABLED
    service_changed_pending_flags_check();
#endif
}


ret_code_t gcm_local_db_cache_update(uint16_t conn_handle)
{
    NRF_PM_DEBUG_CHECK(m_module_initialized);

    local_db_update(conn_handle, true);
    update_pending_flags_check();

    return NRF_SUCCESS;
}


#if PM_SERVICE_CHANGED_ENABLED
void gcm_local_database_has_changed(void)
{
    gscm_local_database_has_changed();

    ble_conn_state_conn_handle_list_t conn_handles = ble_conn_state_conn_handles();

    for (uint16_t i = 0; i < conn_handles.len; i++)
    {
        if (im_peer_id_get_by_conn_handle(conn_handles.conn_handles[i]) == PM_PEER_ID_INVALID)
        {
            ble_conn_state_user_flag_set(conn_handles.conn_handles[i], m_flag_service_changed_pending, true);
        }
    }

    service_changed_pending_flags_check();
}
#endif
#endif // NRF_MODULE_ENABLED(PEER_MANAGER)