is there any data length limitation on notification/read data on BLE?

[PingISTL]

Hi, All

I am developing a host software for central BLE.

Just try to create a buffer to receive notification data and/or read data after peer connection is established , not sure how big the buffer should be, any specifications on this please?

Regards!

Ping

[Tom Nowak]

The maximum if you enable these is 247 octets.

CONFIG_BT_DATA_LEN_UPDATE=y

CONFIG_BT_USER_DATA_LEN_UPDATE=y

CONFIG_BT_CTLR_DATA_LENGTH_MAX=251

 

There are a couple more I can't remember. Also, remember to negotiate the MTU from the other side.

[PingISTL]

Hi, Tom

Thank you for your reply, does this mean it is user configurable? could you send a link for the explanation of these settings please?

Regards!

Ping

[Emil Lenngren]

For notifications, the maximum value length is MTU-3 or 512, whichever is the smallest.

For a simple Read Request, the maximum value length is MTU-1. To read the whole value, in case it does not fit in a Read Response given the current MTU, use the Read Long Value operation, which will issue multiple Read Blob Requests and concatenate the parts. The maximum attribute value length is 512 bytes so you cannot retrieve a larger value than this.

Note that the LE Data Length Extension is at a lower layer (only affects performance) and does not affect the semantics of ATT/GATT.