Unable to Subscribe to More than 3 BLE Notifications in NCS v3.1.0

[Krishhh]

Hi,

I am trying to subscribe to notifications from a peripheral device on my central device. The peripheral has more than 3 characteristics, but I am only able to successfully subscribe to 3 handles in my central.

For the 4th handle, I get the following error:  Subscribe failed for gas[3] (err -12)

Could you please clarify:

• Is there a limit on the number of simultaneous subscriptions in the SDK?

• Is there any configuration or workaround to allow subscribing to more than 3 characteristics?

Your guidance would be greatly appreciated and I have attached my code snippet as well .

static struct bt_gatt_subscribe_params gas_subscribe_params[8];

void subscribe_to_gas_notifications(void)
{

    for (int i = 0; i < gas_alert_count-1; i++) {
        gas_subscribe_params[i].ccc_handle = gas_ch_alert_handle[i+1] + 1;
        gas_subscribe_params[i].value_handle = gas_ch_alert_handle[i+1];
        gas_subscribe_params[i].value = BT_GATT_CCC_NOTIFY;
        gas_subscribe_params[i].notify = x_am_notify_cb;

        int err = bt_gatt_subscribe(default_conn, &gas_subscribe_params[i]);
        if (err) {
            #if DEBUG
            printk("Subscribe failed for gas[%d] (err %d)\n", i, err);
            #endif
        } else {
            #if DEBUG
            printk("Subscribed to gas[%d] (handle 0x%04x)\n", i, gas_ch_alert_handle[i+1]);
            #endif
        }
    }
}

Thank you.

[Turbo J]

Default config settings only allocate 3 buffers to be sent to the connected device. Look at the throughput sample how to increase count.

If you don't want to deal with the increased RAM footprint, you could re-try the failed calls at a later time, i.e. when the buffers are empty again.

[Benjamin]

Hi Krishnan,
What is your CONFIG_BT_ATT_TX_COUNT set to? Try increasing it. As mentioned in this ticket already, you can also re-try failed calls when the ATT request queue is empty.

Best regards,
Benjamin