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

Question

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 · Answer

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.

Emil Lenngren · Answer

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.