When is NUS ready?

[kat829]

Hi!

We have two similar nRF52840 boards and want them to talk via nus_client and nus_server.

At the moment, we consider connection established after client receives the generic bluetooth connected callback and setups nus (below code).

static void connected(struct bt_conn *conn, uint8_t err) {
    // setup NUS
    static struct bt_gatt_exchange_params exchange_params;
    exchange_params.func = exchange_func;
    bt_gatt_exchange_mtu(conn, &exchange_params);
    bt_conn_set_security(conn, BT_SECURITY_L2);
    gatt_discover(conn);
    bt_scan_stop();


    <send first NUS data>
}

Of course, NUS is not ready at that moment, so the message is lost (without any error being reported), just as any messages sent within the next ~1 second.

Is there a way to register a callback that will notify us when NUS is actually ready?

We are using NCS_VERSION=v2.6.1

(I should note that I came across https://devzone.nordicsemi.com/f/nordic-q-a/28208/when-is-nus-ready, but it seems no longer relevant. If I am mistaken, then how can the mentioned handler registered?)

[kat829]

Bump?

Tl;dr: current state of affairs is that NUS server reports send_enabled before the client even starts gatt discovery.

[Sigurd]

kat829 said:

NUS server reports send_enabled before the client even starts gatt discovery.

Hva you paired and bonded to the client? If yes, then this might explain why this happens.

[kat829]

Yes, we have.

Any ideas what to do about it?

(I.e., to find out when the client is actually ready.)

[Sigurd]

In the bonded use-case, try waiting for the security_changed callback as well.

If that does not work either, then a sniffer trace might be useful here: https://www.nordicsemi.com/Products/Development-tools/nrf-sniffer-for-bluetooth-le