u-blox NINA-B1 Series Getting Started page 5

The serial port service is implemented on top of the Generic Attribute Profile (GATT). It contains the following
characteristics:
•
FIFO for reading and writing data
•
Credits to simulate the Bluetooth BR/EDR credit-based flow control
To connect, the central/client side sets up the ACL (Asynchronous Connection-Less) link and enables indications
for both the FIFO and credits characteristics. Then, the server side sends the number of credits to the client using
the credit indication, and the client writes the number of credits to the server. The credits correspond to the
number of packets the remote side may write before receiving new credits. The received credits are added to the
remaining ones (if any).
Once connected and credits have been received, data transmission starts. The client writes to the FIFO and the
server sends indications or notifications with the FIFO data.
Connections without credits are also supported. Connections without credits are faster to establish and ideal for
scenarios where a small amount of data shall be transferred.
For more information see u-blox Low Energy Serial Port Service Protocol Specification [10].
UBX-16009942 - R04
NINA-B1 series - Getting Started
Introduction
Page 5 of 19