BLE_GATTS_EVT_HVN_TX_COMPLETE event does not works on NUS for multi-role device

[jinvers]

Hi,

In a multi-role central-peripheral code for a nRF52840-DK based device, I have to send a buffer acting as a peripheral. I use the ble_nus_data_send function sent as a trigger in the BLE_GAP_EVT_CONNECTED (into the ble_evt_handler function). So, I send the first data packet once the connection as peripheral has been established.

The rest of the buffer was expected to be sent using the BLE_GATTS_EVT_HVN_TX_COMPLETE event into the ble_evt_handler function. However, the event does not never occurs.

In fact, when I execute ble_nus_data_send the first time, it returns a NRF_ERROR_INVALID_STATE because it detects a condition ike !p_client->is_notification_enabled.

I have tried to clone the NUS configuration (as a peripheral) from the ble_app_uart example, working using the nRF5_SDK_17.1.0_ddde560. And including the sdk_config.h file configuration.

What should I setup to enable the BLE_GATTS_EVT_HVN_TX_COMPLETE event? Should I use another event?

Thank you very much in advance.

Best Regards,

Joel

[Einar Thorsrud]

Hi Joel,

I cannot think of any situation where you would not get a BLE_GATTS_EVT_HVN_TX_COMPLETE notification as long as the notification/indication is successfully sent. If it is, it should always arrive, though you might not get the same number of BLE_GATTS_EVT_HVN_TX_COMPLETE events as you send notifications, as the same event can cover more than one notification (in that case, the count field informs you how many notifications has been sent).

Could it be that you are for instance filtering on the wrong connection handle, and therefor do not see the events? This is just a guess, though.

If you don't make progress, perhaps you can share your event handling code here so that I can see if I spot anything?

[jinvers]

Hi Einar,

The definition is:

BLE_NUS_DEF(m_nus, NRF_SDH_BLE_TOTAL_LINK_COUNT);

The initialization is:

    ble_nus_init_t   nus_init;

    memset(&nus_init, 0, sizeof(nus_init));
    nus_init.data_handler = nus_data_handler;
    err_code = ble_nus_init(&m_nus, &nus_init);

In the ble_evt_handler. In the BLE_GAP_EVT_CONNECTED event it discriminates if it works a central device or like a peripheral. In this second case it executes the next:

                m_per_con_handle = p_gap_evt->conn_handle;
                NRF_LOG_INFO("Peripheral connection 0x%x established.", m_per_con_handle);    
                
                app_timer_start(m_post_message_delay_timer_id, APP_TIMER_TICKS(2000), 0);
                
                app_timer_stop(m_adv_led_blink_timer_id);
                
                bsp_board_led_on(PERIPHERAL_ADV_CON_LED);
                punter_buffer_accelerometre= 0;
                num_rebuts_buffer_accelerometre= 128003;
                send_data_ble_accel();

Into the function send_data_ble_accel function the code executes

               err_code = ble_nus_data_send(&m_nus, data_buf, &length, m_per_con_handle);

If I debug this function in this stage I can see that the notification is not enabled.

As a peer I'm using a second nRF52840-DK board running the ble_central_and_peripheral\experimental\ble_app_att_mtu_throughput example. Here I select the buttin 4. This board establish the connection as a central device and recognizes the other board.

Regards,

Joel

[Einar Thorsrud]

Hi Joel,

Ah, I misunderstood the question. I thought notifications actually were sent, but you did not see the BLE_GATTS_EVT_HVN_TX_COMPLETE  event. Based on what you write now I see that the notifications are not enabled and so they are not (and cannot be) sent.

So, the client (central in this case) needs to enable the notifications by writing to the CCCD. Once done, you can send notifications. So that is the first thing you must get working.

[jinvers]

Hi,

I'm trying to use Nordic examples as a entral device. AndI thought that in the ATT_MTU example working as central the client notification were enabled. Are they not? What should I do to enable them?

Or do you think should I use the ble_app_uart_c example? How should I enable the notifications there?

Thank you in advance.

Regards,

Joel

[Einar Thorsrud]

Hi Joel,

I am not exactly sure which changes you have done and how, but the way this works is that the Bluetooth connection is established, the GATT client (which is typically the central here) does service discovery, and after that it can enable notifications on characteristics that support it and it want notifications on. That seems to not be done here. If you refer to the NUS central example, you will see that it does enable notifications, and you must do the same (search for "ble_nus_c_tx_notif_enable" in examples/ble_central/ble_app_uart_c/main.c). 

[jinvers]

Hi Einar,

I will make a double check. I will come back tomorrow.

By the way, I will have to connect it to an iPhone app in the end. This app will work as the central that has to enable then the notifications. Do you see anything special should I do from the device side?

Regards,

Joel

[jinvers]

Hi Einar,

I attach the multi-role+multi-link code I'm using. It comes from the multi-link-multi-role example in github, adding the NUS service (I have modified it over SES environment).

ble_aggregator_NUS_6.zip

I have a problem. Acting as a peripheral I can see it the Aggregator device on the mobile app nRF Connect. However, it does not establish connection with a second nRF52840-DK board that has the ble_app_uart_c code running on it as a central. So, it's not clear that as an Aggregator multi-role could acting ok as a NUS peripheral. Please, may you suggest me something to get that this multi-role Aggregator can be linked also to a NUS Central?

Thank you in advance.

Regards,

Joel

[Einar Thorsrud]

Hi Joel,

jinvers said:

It comes from the multi-link-multi-role example in github

Which example is that? Can you link to it?

jinvers said:

However, it does not establish connection with a second nRF52840-DK board that has the ble_app_uart_c code running on it as a central.

In this case, the phone is also acting as a central I assume? And you want to connect with a second central (phone running ble_app_uart_c)? If so, that will not work. The project you have uploaded supports multiple central links but only a single peripheral link.

Is the intention to also support several peripheral links (links where the nRF acts as a peripheral role)? If so, the first thing you must do is adjust NRF_SDH_BLE_PERIPHERAL_LINK_COUNT and set it to the number of central links you want. This is among other things used when initializing the SoftDevice, so having this set to 1 more than 1 link will never work. You also need to do a bit of changes to the application code to support this (I see you have done some but I have not gone through your implementation in detail).

[jinvers]

Hi,

I have included the zip file with the example modified. The original link is

github.com/.../nrf52-ble-multi-link-multi-role

The example is a central and a peripheral device simultaneously. I have adjusted the parameters you have told me.

Regards,

Joel

[Einar Thorsrud]

HI Joel,

Ah, I was not aware of that repo.

I saw your project from your previous post. As mentioned, it clearly cannot support more than one connection in the peripheral role, particularly because you configure the SoftDevice handler library (and in turn the SoftDevice) to only support 1. So adjusting that needs to be the first thing you need to do (among several) for the problem you mentioned in your last post, which is that you cannot be connected to two centrals at the same time.

[jinvers]

Excuse me Einar, but I think èrhaps there is a misunderstanding. This device is a multi-role device. According to the aggregator multi-role and multi-link example it was possible to work simultaneously as a central and as a peripjheral.

When it works as a peripheral, it is only connected to one central and the configuration and the tests have all been done using one only central ever. I have never tried to connect it to two centrals.

However, this device is also a central for other peripherals.

Regards,

Joel

[Einar Thorsrud]

Hi joel,

jinvers said:

Excuse me Einar, but I think èrhaps there is a misunderstanding. This device is a multi-role device. According to the aggregator multi-role and multi-link example it was possible to work simultaneously as a central and as a peripjheral.

When it works as a peripheral, it is only connected to one central and the configuration and the tests have all been done using one only central ever. I have never tried to connect it to two centrals.

Aha, yes there could be a misunderstanding. I was reading this:

jinvers said:

I have a problem. Acting as a peripheral I can see it the Aggregator device on the mobile app nRF Connect. However, it does not establish connection with a second nRF52840-DK board that has the ble_app_uart_c code running on it as a central.

and interpreted it that you now tried to use both a phone and a second DK with ble_app_uart_c) at the same time, which would e two centrals, and that will not work with your application (which allows several links in the central role, but only one link in the peripheral role).  Perhaps we can back-track a bit, and you can explain in more detail how you test, describing all devices in use at the same time and which roles they have etc?

Assuming this is all from the misunderstanding, I guess the original issue remains, which seems to be that you (in the central role / as GATT client have not enabled notifications on the NUS characteristic, and therefor the NUS peripheral (GATT server) is not able to notify on it. This you just need to do as is doen in the NUS example (taking account that you have multiple connections).