nRF52 automatically disconnects with iOS phone after 90 seconds

[RO]

Hello,

I am using a custom nRF52840 ( SDK 14.2.0, SoftDevice S140) based board to connect with an iOS(v 13.3) phone. 

I am sending data continuously over BLE. However I notice that after around 90 seconds the connection automatically ends.

On the Segger Embedded Studio debug terminal, I see the following when the board disconnects:

<info> app: ble_adv_evt fast
<info> app: Disconnect Complete.
<info> app: Disconnected

Here are the connection parameters I have defined, I think I have followed the guidelines given here for connection with Apple devices. Please correct me if I'm wrong.

#define APP_ADV_INTERVAL                 244                                        
#define APP_ADV_TIMEOUT_IN_SECONDS       0                                          

#define MIN_CONN_INTERVAL                MSEC_TO_UNITS(25, UNIT_1_25_MS)           
#define MAX_CONN_INTERVAL                MSEC_TO_UNITS(1500, UNIT_1_25_MS)           
#define SLAVE_LATENCY                    0                                         
#define CONN_SUP_TIMEOUT                 MSEC_TO_UNITS(5000, UNIT_10_MS)            

#define FIRST_CONN_PARAMS_UPDATE_DELAY   APP_TIMER_TICKS(5000)                      /**< Time from initiating event (connect or start of notification) to first time sd_ble_gap_conn_param_update is called (5 seconds). */
#define NEXT_CONN_PARAMS_UPDATE_DELAY    APP_TIMER_TICKS(30000)                     /**< Time between each call to sd_ble_gap_conn_param_update after the first call (30 seconds). */
#define MAX_CONN_PARAMS_UPDATE_COUNT     3                          

Unfortunately I don't have a setup for a BLE sniffer.

Can somebody help?

Thanks 

[jacksong]

sounds like it is update connection parameter fail, you need to check the reason code of disconnect.

you can add log code at on_ble_evt() , and then check the meaning of reason at "ble_hci.h"  at line 56.

on_ble_evt((ble_evt_t * p_ble_evt))
{
...
    case BLE_GAP_EVT_DISCONNECTED:
    {
        ...
    
        NRF_LOG_RAW_INFO("disconnect reason:0x%X",p_ble_evt->evt.gap_evt.params.disconnected.reason);

        ...
    }
    break;

...

}

[Vidar Berg]

I agree with jacksong, a good  first step is to figure out what the disconnect reason is.  You can also check the callback from the connection parameter module (registered through ble_conn_params_init() to see if the connection param update requests are being rejected.  Also, note that SDK 14.2.0 should not be used with 52840 because we had limited support for it in this release. It's important that you migrate to SDK v15 or preferably v16 before going to production.

Apple recommandations:

https://developer.apple.com/accessories/Accessory-Design-Guidelines.pdf

[RO]

I added the log code and I get '0x16' , which means Local host terminated connection.

It does seem something to do with connection parameter updates.

When I change the MAX_CONN_PARAMS_UPDATE_COUNT from 3 to 2, now the disconnections happen in 60 seconds.

#define FIRST_CONN_PARAMS_UPDATE_DELAY   APP_TIMER_TICKS(5000)                      /**< Time from initiating event (connect or start of notification) to first time sd_ble_gap_conn_param_update is called (5 seconds). */
#define NEXT_CONN_PARAMS_UPDATE_DELAY    APP_TIMER_TICKS(30000)                     /**< Time between each call to sd_ble_gap_conn_param_update after the first call (30 seconds). */
#define MAX_CONN_PARAMS_UPDATE_COUNT     2  

So what is the solution?

Thanks

[Vidar Berg]

Ok, it sounds like the FW app is disconnecting because the iPhone rejected "MAX_CONN_PARAMS_UPDATE_COUNT" number of requests. You can either change the app so it doesn't disconnect even if the requested connection parameters are rejected, or you can change your connection parameters according to the recommendations given in the Apple document I linked in my previous response.

Connection Parameters Negotiation