BLE connection to iOS device disconnects consistently after 40 seconds

[erik_fw]

We are consistently seeing a BLE disconnection after being connected to an iOS device for 40 seconds. On the iOS side, the log output at the time of disconnection says: "[System]Error disconnect from peripheral <DeviceName> Unknown Error." We are handling the iOS data length updates successfully as well as MTU exchange. We are able to read/write/notify over the connection properly with no failures until we hit the 40-second point, upon which the connection drops immediately.

We have essentially breakpointed each instance of sd_ble_gap_disconnect() in our code, and verified that it is not being called from our code at the time of disconnection. We're not seeing any BLE events immediately before the disconnection that would lead us to believe that a request timeout or transmission failure occurred, and nothing in the iOS logs indicates any related failures either.

When testing this same code against a BLE connection with a PCA dev board thru the OSx NRF Connect app, connection is sustained indefinitely without any issues.

Any ideas as to what might be causing this?

iOS version: 11.3

Device: iPhone 7

SoftDevice: S132 5.1.0

SDK version: 14.2

Connection parameter configuration:

Min connection interval = 15ms

Max connection interval = 650ms

Slave latency = 0

Connection supervisory timeout = 4s

[Martin Lesund]

Hi Erik,

 

Could you try to provide a sniffer log to actually see what is happening over the air?

Could you also provide a snippet of the actual defines for the connection parameters?

Thanks.

 

//Martin L.

[erik_fw]

Having access to a BLE sniffer would be great, but it looks like there's no supported version for OSx as well as no hardware support for nRF52 dev boards (I'm seeing nRF51 but not 52).

Here are our connection parameter definitions:

/**< Minimum acceptable connection interval (0.015 seconds). */
#define MIN_CONN_INTERVAL MSEC_TO_UNITS(15, UNIT_1_25_MS)

/**< Maximum acceptable connection interval (0.65 second). */
#define MAX_CONN_INTERVAL MSEC_TO_UNITS(650, UNIT_1_25_MS)

/**< Slave latency. */
#define SLAVE_LATENCY 0

/**< Connection supervisory timeout (4 seconds). */
#define CONN_SUP_TIMEOUT MSEC_TO_UNITS(4000, UNIT_10_MS)

These parameters are being initialized with a call to sd_ble_gap_ppcp_set() with a pointer to a ble_gap_conn_params_t structure whose respective members are assigned to the constants defined above.

EDIT for additional info: the BLE_GAP_EVT_DISCONNECTED event gives a reason of 0x08 (BLE_HCI_CONNECTION_TIMEOUT)