We have recently been working on a project which involved implementing a Bluetooth stack on an ARM Cortex M3 micro, with only 48kB of memory and 256kB of flash. We chose to use the Light-weight Bluetooth library (lwBT), which is a small, cross platform, Bluetooth library designed for embedded environments.

The lwBT library provides basic functionality for the , L2CAP, SDP and Bluetooth layers. Additionaly, we implemented an OBEX layer with support for pushing files to remote devices and providing an OBEX push profile to allow files to be received from other Bluetooth devices. We also implemented a basic serial port profile (SPP) on top of the RFCOMM layer in lwBT which provides wireless serial communication. This can be used, for example, with the standard Linux BlueZ RFCOMM serial utilities. The entire lwBT stack fits in under 24kB of flash storage and uses between 5 and 10kB of memory depending on configuration options.

The lwBT stack provides a lot of the core Bluetooth functionality, but the interface to the library is very raw. Our Bluetooth API provides a set of simple access functions for common tasks such as sending and receiving data over an RFCOMM link and pushing files to other devices via OBEX. Our Bluetooth library was also designed to be as platform independent as possible. Only a thin platform specific layer must be written in order to move the Bluetooth library to a new device.

The following diagram shows the structure of the Bluetooth stack provided by our library: