characteristic size different between read and notification

[wim]

Hi

Is there any limitation to characteristic size for use in notifications? The reason for asking is the following: I have a service with a characteristic with size 24 bytes. When doing a normal read of that characteristic, I get 24 bytes all right. But when I turn on the notifications and get values into my iPhone, then I only get 20 bytes.

Any ideas on what could be the cause of this?

I am using nrf51822 with SDK7.2.0, soft device S110 version 7.3. On the iPhone side, I use lightblue to read and write characteristics.

Wim

[Petter Myhre]

The default (and maximum) MTU size of the S110 SoftDevice is 23 bytes. If you take away 3 bytes for the header you end up with maximum of 20 bytes of data. So you can have 20 bytes of data in each GATT operation.

I'm guessing that lightblue does two read operations, first the first 20 bytes, then the next 4 bytes.