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,

jinvers said:

I have made all the setup tests of MTU value, data length and connection interval using the ble_app_att_mtu_throughput example. MUT of 247, data length of 244 bytes and a connection intervbal of 50ms or 100ms get the best results. However, there is a big difference using that example compared to my new application.

Have you adjusted the event length? Looking at the project you attached here NRF_SDH_BLE_GAP_EVENT_LENGTH is set to 12, which is 15 ms. For maximum throughput this should be as large as possible (up to the connection interval). There is also the important point that you need to fit all connections within this though, so if you have up to 8 connections with the same interval as a central role for instance, that means the event length can be only an eight of the connection interval. Please note the key point here, that number of connections is a very important factor for maximum throughput.

jinvers said:

I understand that to get the necessary throughtput I will have to close temporarily the services not used.

I am not sure what you mean by close the service, but if a service is not used (so no data is passed in any way on it's characteristics), it is not used and does not have any consequences (other than that the service discovery might take more time if you have a lot of services). Also, there is no support for disabling services in the SoftDevice BLE stack.

jinvers said:

Moreover, is there a way to dinamically change and adjust the number of peripheral links in execution mode?

You can control how many links you have, but not the links you configure the SoftDevice for. That is configured when you initialize the SoftDevice.

[jinvers]

Hi Einar,

I have increased the NRF_SDH_BLE_GAP_EVENT_LENGTH value. Considering that in the ble_app_att_mtu_throughput the value is 400 and that here I have a total of 8 connections, I have setup a value of 3200 (just to test a extrem value). The throughput has been increased and I have reduced the time for transmitting 125KBytes to around 5 seconds.

I have also tried to reduce the number of communications from 8 to 4. But the throughput has not increased.

Regatds,

Joel

[Einar Thorsrud]

Hi Joel,

125 kB in 5 seconds is about 200 kbps, which is actually quite a decent throughput. With a 1 Mbps PHY the maximum you can achieve in practice is about 700 kbps, but a normal application will typically see significantly less as this depends on several factors you typically cannot control, especially if you are communicating with a phone. If you want to try to squeeze out more you could make a sniffer trace to see what happens on the link. It could be that the nRF has more data (so the MD field set), but the phone has other things to do - like WiFi, other BT links, or something else. 

[jinvers]

Hi Einar,

I will try to run a sniffer.

Anyway, may it be that I could also be tricked by the LOG information. I mean that I display Log NRF_LOG_INFO lines in the debug window to see the 125Kbytes sent. But in some of the lastest tests done to compare with the ble_app_att_mut_throughput example, I would say that the packets have been sent but there is still a queue of Logs messages to be displayed. So, perhaps the queue of NRF_LOG_INFO lines is tricking me. I have to double check.

Regards,

Joel

[jinvers]

Hi Einar,

I'm using the nRF Sniffer with Wireshark and a nRF52840-DK board. I'm able to see the advertising paquets from the aggregator, but it cannot capture no one paquet of the 125kBytes sent by notifications.

I'm filtering for RSSI level. Any suggestion for any specific setup?

Regards,

Joel