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?)

[Sigurd]

Hi!

You can add a callback like this. This will be called when the client have enabled notifications, and you can then start sending notifications.

static void send_enabled(enum bt_nus_send_status status)
{

	LOG_INF("Notifications %sabled", (status == BT_NUS_SEND_STATUS_ENABLED) ? "en" : "dis");
}

static struct bt_nus_cb nus_cb = {
	.received = bt_receive_cb,
	.send_enabled = send_enabled,
};

[kat829]

Allright, I can see this used in nus server initialization.

Is there a similar callback for nus client?

[Sigurd]

Hi,

When you get the discovery_complete() and after bt_nus_subscribe_receive() is called in that callback.

https://github.com/nrfconnect/sdk-nrf/blob/v2.6.1/samples/bluetooth/central_uart/src/main.c#L296

[kat829]

Ok, thanks!

[kat829]

Actually, we are still having problems when sending messages from nus server to nus client.

static void send_enabled(enum bt_nus_send_status status)
{
    if (status == BT_NUS_SEND_STATUS_ENABLED) {
        NusServerInitialized = true;
    }
}

static struct bt_nus_cb nus_cb = {
    .received = received,
    .sent = sent,
    .send_enabled = send_enabled,
};

    while (NusServerInitialized == false) {
        k_sleep(K_MSEC(1));
    }
    for (int i = 0; i < 30; i++) {
        LogBt("=== Ping %i\n", i);
        k_sleep(K_MSEC(50));
    }

From the very first message, `bt_nus_send(NULL, data, len);` succeeds, we receive the `static void sent(struct bt_conn *conn)` callback with correct address, yet first 8 messages don't arrive on the client.

[Sigurd]

Hi!

Do you see any difference with`bt_nus_send(current_conn , data, len);` instead?