REAL-TIME OPERATING SYSTEMS AND STANDARDS - Hard Real-Time Computing Systems: Predictable Scheduling Algorithms and Applications - page 442

Ideally, to allow the designer to write partitioning-independent code, tasks partitioning
should be done at the end of the application design, without changing the application
source code. In practice, partitioning can be limited by the fact that some hardware
peripherals may not be available on all cores. The minimal partitioning item in a
system is the source file; hence the code of tasks allocated to different CPUs must be
on different files, to allow an easy partitioning in different CPU in a later stage of the
development.

In a heterogeneous system, each core usually has different peripherals and the memory
spaces shared between cores may vary. Cache coherency is often not present due to
cost reasons, and proper cache disabling techniques have to be used to avoid data
corruption. One of the CPUs usually works as the master CPU, which plays the role
of initializing the global data structures. That master CPU is also responsible for the
implementation of a startup barrier, which is used to synchronize all cores to have a
coherent operating system startup.

The current implementation of ERIKA Enterprise (available open source) supports
Altera Nios II multicore designs on FPGA, and Freescale PPC 5668G FADO, which
is a dual core hosting a PPC z6 and a PPC z0 (the second processor is typically used
to handle high-speed peripherals).

12.4.2 SHARK

SHARK 14 (Soft and HArd Real-time Kernel) is a dynamic configurable real-time op-
erating system developed at the Scuola Superiore S. Anna of Pisa [GAGB01] to sup-
port the development and testing of new scheduling algorithms, aperiodic servers, and
resource management protocols. The kernel is designed to be modular, so that ap-
plications can be developed independently of a particular system configuration, and
schedulers can be implemented independently of other kernel mechanisms.

The kernel is compliant with the POSIX 1003.13 PSE52 specifications and currently
runs on Intel x86 architectures. SHARK is currently used for education in several
real-time systems courses all over the world. It is available for free under GPL license
at http://shark.sssup.it .

14 SHARK: http://shark.sssup.it/