Dynamic reading of BLE characteristic?

Just to add - there's no onRead at the moment, and while it may be possible to get notified after a characteristic is read, I don't think you can easily do something that returns the value you want to send as a response (and if you did, you'd probably be very time-limited).

What I normally see devices do is:

• host device subscribes to notifications on a characteristic
  
• host device writes anything to another characteristic
  
• when the reading/calculation is finished, the first characteristic is used to return the data