Nordic Uart Service TX delay while Service Discovery

[MichaelMe]

Hi,

currently we are developing a firmware for 52840 based on the nRF5 v.16 SDK with Softdevice 7.0.1 on a custom board. We are able to connect and bond up to 5 devices ( with nrf Connect App for Android ) via BLE and send/receive Data.

When we connect and pair a new device, we wait for the TX Characteristic notification flag to be set before we start sending data to it. Thats all fine.

But when we connect an previously bonded device, the flag is already set and we start sending data with NUS (ble_nus_data_send). Due to the service discovery by the phone, the data is not received in nrf Connect App.When we send continuous messages every 100ms, the first message shown in nrf Connect App log is ca. the 10th. On NUS side we get no errors for the first 10 messages. They are just lost.

Is there a possibility to determine if the service discovery is done and the app is ready to receive data?

Thanks for the help.

Michael

[Susheel Nuguru]

I guess until we have the GATT Caching this is a known problem.

If your device is the one that initiates the disconnect, then you can disable the TX notification flag just before disconnecting (haven't tried it myself). That way the peer when they do the service discovery, have to re-enable the TX notification flag.which could be a signal to your application?

In BLE5.1, when we support Gatt Caching, this problem will be solved, but until then we need to find some workaround like the one I mentioned above.

[MichaelMe]

We can't be sure the connection is always terminated by the phone ( e.g. when it is out of range or something).

So i think we have to send one message repeatedly until we get an answer, or wait a few seconds.

Thank you anyway for the support.