Data corruption in app side

[Thomasthomas]

Hi all, 

In my project am sending ecg values over ble to android app. During first connection, the values are received and seems to be no problem, but when i disconnect and connect again i got corrupted values in the app. In order to get the correct values, i need to close the app and start again. How to solve this issue?

[Hung Bui]

Hi Thomas, 

Could you give some more information about the corrupt data you received in your app ? 
Could you try using nRF Connect app and verify if you also see the issue with nRF Connect app ? 

[Thomasthomas]

hy, am plotting ecg values using our app, on first connection the graph is correct but when i  disconnect and connect again the graph is corrupted

[Thomasthomas]

ecg graph comes with noise

[Hung Bui]

I suspect that when you disconnected the data was cached somehow and was not cleared when you plot it to a graph. I would suggest to log the data and then study which data you receive and why it comes with noise. 

[hmolesworth]

If you happen to be using something like the NUS service to transmit the data, be aware of this:

"If there are untransmitted packets in the TX buffer where there is a disconnect, those packets will be lost. So, those packets will not be transmitted automatically upon a re-connect. Upon a re-connect, if needed, the packets will have to be put manually into the TX buffer."

Not a problem if you are using discrete packets with some form of CRCC, but a big problem if you happen to be just streaming raw data and are not handling unexpectedly missing "chunks" in the raw data. More info ble-disconnect-packet-loss