What is Prex?

Prex is an open source, royalty-free, real-time operating system for embedded systems. It is designed and implemented for resource-constrained systems that require predictable timing behavior. The highly portable code of Prex is written in 100% ANSI C based on traditional microkernel architecture.

The Prex microkernel provides only fundamental features for task, thread, memory, IPC, exception, and synchronization. The other basic OS functions - process, file system, application loading, and networking, are provided by the user mode servers. In addition, Prex provides a POSIX emulation layer in order to utilize existing *NIX applications. This design allows the system to perform both of the native real-time task and the generic POSIX process simultaneously without degrading real-time performance. It also helps platform designers to construct OS by choosing suitable system servers for their target requisition.

Project Goals

• To provide a small, portable, real-time, secure, and robust operating system.
• To provide simple and clean source codes for education and an experimental test-bed.
• To conform to open standards as much as possible.
• To enjoy our life with kernel hacking. ;-)

License

Prex is royalty-free software released under Revised BSD License.

Features

• Task & Thread Control: preemptive priority scheduling with 256 priority levels
• Memory Management: memory protection, virtual address mapping, shared memory, MMU or MMU-less configuration
• IPC: object name space, synchronous message passing between threads
• Exception: fault trapping, framework for POSIX signal emulation
• Synchronization: semaphores, condition variables, and mutexes with priority inheritance
• Timers: sleep timers, one-shot or periodic timers
• Interrupt: nested interrupt service routines, and prioritized interrupt service threads
• Device I/O: minimum synchronous I/O interface, DPC (Deferred Procedure Call)
• Security: task capability, pathname-based access control, I/O access permission.
• Real-time: low interrupt latency, high resolution timers and scheduling priority control
• Power Management: power policy, idle thread, DVS (Dynamic Voltage Scaling)
• Debugging Facility: event logging, kernel dump, GDB remote debug
• File Systems: multi-threaded, VFS framework, buffer cache, ramfs, fatfs, arfs, etc.
• POSIX Emulation: pid, fork, exec, file I/O, signal, pipe, tty, pthread, etc.
• Libc: C library fully optimized to generate a small executable file
• CmdBox: a small binary that includes tiny versions of many UNIX utilities.
• Networking: (plan) TCP/IP stack, BSD socket interface

Hardware Requirements

• Processor: 32-bit Processor (x86, ARM, PowerPC)
• Memory: 256KB of RAM (Kernel < 25k bytes)
• Timer: programmable interval timer

Note: RAM requirements may vary depending on the number of system servers being supported.