1. Enhanced ATT feature
Enhanced ATT is a BLE 5.2 standard feature: it is implemented for STM32WB and STM32WBA.
Whereas the original unenhanced Attribute protocol operates in a sequential manner, the Enhanced Attribute Protocol provides a way to perform concurrent/parallel transactions between a BLE client and a server and potentially reduce the latency of operations in some applications.
For example, this is useful on a smartphone where multiple apps may be interfacing with a Bluetooth Low Energy device.
By utilizing EATT, an app’s Attribute transaction would not be blocked while another app’s ATT transaction is in progress, essentially allowing different apps to interact with a Bluetooth Low Energy device in parallel and potentially reducing latency.
1.1. New Enhanced Attribute Protocol (EATT) capabilities
• EATT modifies the sequential transaction model, making concurrent ATT
transactions possible when conducted over distinct enhanced ATT bearers.
• EATT uses the L2CAP Enhanced Connection-Oriented Channels mode. This
L2CAP mode provides flow control so that EATT can be regarded as reliable.
• MTU values at the ATT layer and L2CAP layer have been made independently
configurable, and this may reduce latency experienced by some applications that
share the BLE stack with other applications.
1.2. Flag configuration on STM32WB
1.3. how to implement on STM32WBA
• Issue: the Enhanced ATT feature “can provide an improved user experience on devices where there are multiple applications using the BLE stack”. • Solution: we have introduced a new static GATT mode: • BLE_OPTIONS_ENHANCED_ATT This mode along with new commands and events implements the Enhanced ATT feature (see next slides). • Implemented: in tag 111 only for “full extended” stack (included as “enabled” in WB cube release 1.15, and as “certified” in release 1.16)