Ocera (Open Components for Embedded Real-Time Applications, is an European project, based on Open Source, which provides an integrated execution environment for embedded real-time applications. Ocera combines the use of two kernels, Linux and RTLinux-GPL to provide support for critical tasks and soft real-time applications.
What is Stand-Alone RTLinux?
RTLinux is a executive developped to work jointly with Linux. RTLinux takes the control of the real-time critical hardware devices (timers, interrupt controller and interrupt management processor instructions) while leaving to Linux the control of the rest of the system (device drivers, memory management, etc.). RTLinux is implemented as a modification (patch) of the Linux kernel, which intercepts the low level devices, and a set of modules that provide the API. RTLinux code takes the control of the system once Linux has booted the system.
Stand-Alone RTLinux will be a Linux independent implementation of RTLinux. Stand-Alone RTLinux will be a bootable executive with the following main features:
Low memory overhead. The core systems contains only following modules: the code of RTLinux, the minimum code needed to boot the system and basic virtual memory management.
Scalability. Users will be able to customize RTLinux funcionalities to reduce kernel memory usage.
Porting will be possible to systems without hardware for virtual memory support. Therefore, Stand-Alone RTLinux could be ported to a wider range of architectures.
Less TLB and memory cache misses since only real-time applications are being executed.
One problem of RTLinux is the use kernel modules or applications that execute directly interrupt management processor instructions (cli and sti), for example, some xfree86 drivers disable interrupts or lock the PCI bus for long time periods. Stand-Alone RTLinux removes this problem since the target system will be compiled to a single static and bootable kernel.
We are not longer limited by the Linux memory manager. Standard RTLinux memory management relays completely on the Linux so it is not possible to implement custom virtual memory management algorithms. Stand-Alone RTLinux has full control of the MMU.
Original implementation and design idea: