When designing an operating system, the operating system engineer always faces a trade-off decision between an efficient system implementation on a given hardware platform and portability to other platforms. This is because usually operating system kernels make use of a hardware abstraction layer internally, which hides platform specifics to a certain extent, facilitating the porting process.

Whereas sacrificing efficiency and memory footprint for portability might be feasible in desktop and server operating system kernels, it is difficult to argue this way when building embedded operating systems. On the one hand, those systems need to be configurable and tailorable to the application needs, which runs on top of the kernel. This is what our research in the CiAO and VAMOS projects is focused on. On the other hand, the kernel will always need some kind of hardware abstraction layer, which needs to be ported to the different hardware platforms. The Sloth project investigates how to move down that abstraction layer a little, making better use of the underlying hardware platform to implement the offered system services and abstractions, trading the better efficiency and footprint for slightly more porting effort and hardware dependency.

The first part of the Sloth project is to investigate how to better implement threads in embedded real-time kernels.

The second part of the Sloth project, named Sleepy Sloth, focuses on how to provide the application with more flexibility by providing a blocking thread abstraction while still executing efficiently using interrupt hardware scheduling and dispatching.

The third part of the Sloth project, entitled Sloth on Time, investigates how to efficiently implement time-triggered real-time operating systems by making extensive use of timer cell arrays to dispatch time-triggered tasks and to implement related kernel services.