In smartBASIC, how can I increase the max message size above 20 bytes on a BL65x module?

One of the major additions in Bluetooth v4.2 is LE Data Packet Length Extension. This feature allows the BLE packet size to increase from 27 to 251 bytes in the link layer, therefore significantly increasing the capacity of the data channel.

In order to take full advantage of the improvements provided by the Packet Length Extension Feature, both devices should be configured to support a larger ATTribute Maximum Transmission Unit (ATT_MTU) and the GATT server characteristic should be configured to support larger Attribute data lengths. The ATTribute Maximum Transmission Unit (ATT_MTU) defines the amount of data a device can send/receive per GATT operation and the Attribute Data Length is the size of the data inside a GATT server as per the image below.

The Application Note: BL65x Data Length Extensions provides additional guidance on how to configure these settings in smartBASIC and references our smartBASIC sample applications which demonstrate the syntax.