x86 Architecture

In the x86 architecture, Stand-Alone RTLinux works in Protected Mode without page management although users will be able to enable the page managment facility turning on the Memory Protection support in the configuration menu. It uses a flat memory design looking for lower memory access overhead (no address translation) and also it enhances architecture portability. Linux boot code has been inserted in the RTLinux arch directory to provide system with a basic Real Mode initialization code.

init_tasks() function is called after the system initialization and can be used to create user threads and initializate IPC variables. This function takes the role of init_module() in the standard RTLinux.

We choose paging as the MMU facility to implement memory protection.

we will use a single page table where virtual addresses are the same than physical addresses (page tables are only used as the method to protect pages, not to implement real virtual memory), therefore the same code can be executed with paging activated or deactivated. When entering kernel code, paging is disabled and with returning to the application paging is enabled. The IA-32 architecture has a special feature that permits to control whether the protection bits of the pages are honoured by the processor or not without the burden (invalidating TLB) of disabling and re-enabling paging system. It is a single bit called WP in the CR0 register.

XtratuM Virtual Architecture

XtratuM is a nanokernel that goes beyond the classical ideas of the nanokernel.

The lower level layer that directly dels with hardware is commonly called HAL (Hardware Access Layer). The most real time kernels (MaRTE OS,ORK,S.Ha.R.K, RTLinux, etc) access the hardware in a similar way.The are two hardware resources that directly affect the real-time capabilities of the RTOS: interrupts and timers. Special care has to be taken to program and manage interrupts in order to archieve a low latency handling. XtratuM nanokernel provides a small and simple API to manage HAL in order to implement real time domains above Linux OS.

With XtratuM, developers doesn't need to manage harware directly insted they will use XtratuM API.

StandAlone RTLinux porting to XtratuM virtual architecture provide users the way to port easily sa-RTL to the architectures where XtratuM was ported previously (nowadays just x86 architecture).

It also provides developers interesting ways to get debug information like Linux core dump or in the future gdb agent implementation using inter-domain communication methods.(http://www.xtratum.org)

StrongArm Architecture

Developing...