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

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

Vidar Berg — Tue, 20 Aug 2019 09:13:24 GMT

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:

devzone.nordicsemi.com/.../service_5F00_changed_5F00_fix.diff devzone.nordicsemi.com/.../gatt_5F00_cache_5F00_manager.c

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

Bart Cerneels — Mon, 19 Aug 2019 06:45:03 GMT

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.

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

Vidar Berg — Mon, 19 Aug 2019 06:30:24 GMT

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

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

Bart Cerneels — Sat, 17 Aug 2019 07:10:20 GMT

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.

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

Vidar Berg — Tue, 07 May 2019 14:06:30 GMT

Thanks for confirming. I have reported this internally so it should be fixed for the next SDK release.

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

Karlis — Tue, 07 May 2019 12:19:13 GMT

Thanks, with new service_changed_cccd() all works!

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

Vidar Berg — Mon, 06 May 2019 13:20:24 GMT

Hi,

It appears that the service_changed_cccd() function is not implemented correctly, it returns not found even when the SC is present. I will report this internally. A temporary workaround is to add a break statement here in gatt_cache_manager.c (line ~382):

case NRF_ERROR_INVALID_STATE:
{
uint16_t cccd;
err_code = service_changed_cccd(conn_handle, &cccd);
NRF_LOG_INFO("err_code: 0x%x", err_code);
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.
break;
}
}

Edit 5/7-19

Please try to replace service_changed_cccd() with the one below instead of removing the fallthrough.

/**@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.
 */
static ret_code_t service_changed_cccd(uint16_t conn_handle, uint16_t * p_cccd)
{
    bool       sc_found = false;
    bool       generic_att_found = false;
    ble_gatts_attr_md_t attr_md;
    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};
        if (!generic_att_found)
        {
            err_code = sd_ble_gatts_value_get(conn_handle, handle, &value);
        }
        else
        {
            err_code = sd_ble_gatts_attr_get(handle, &uuid, NULL); 
        }

        if (err_code != NRF_SUCCESS)
        {
            return err_code;
        }
        else if (uuid.uuid == BLE_UUID_GATT)
        {
            generic_att_found = true;
        }
        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;
}

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

Karlis — Thu, 02 May 2019 09:39:29 GMT

Hi,

Yes, if there no MTU exchange, there are no errors. Characteristic is enabled.

And also if in gatt_cache_manager.c in function service_changed_send_in_evt remove "case NRF_ERROR_INVALID_STATE:" service changed indication works for iOS. Only problem is in fact that it never droped for Android or central witch not enabled service changed indication.

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

Vidar Berg — Thu, 02 May 2019 09:03:03 GMT

Hi,

Just to confirm, are you not getting this error when there's no MTU exchange? Also, have you enabled this characteristic in sdk_config.h. You can check if it's present with the nRF connect app on Android.

[quote user=""]Or handle associated with service changed cccd is allways the same and we can simply check if it exists?[/quote]

Correct, it does not change since there are no optional system attributes above this characteristic.