Vrtx

VRTX: VRTX has two multitasking kernels: VRTXsa and VRTXmc. VRTXsa is designed for performance. It has a POSIX-compliant library, provides priority inheritance, and supports multiprocessing. Its system calls are deterministic and preemptable. In particular, VRTXsa 5.0 is compliant to POSIX real-time extensions. It is for medium and large real-time applications. VRTXmc, on the other hand, is optimized for power consumption and ROM and RAM sizes. It provides only basic functions and is intended for applications such as cellular phones and other small handheld devices. For such applications, the kernel typically requires only 4-8 kilobytes of ROM and 1 kilobyte of RAM.

Most noteworthy about VRTX is that it is the first commercial real-time operating system certified by the Federal Aviation Agency (FAA) for mission- and life-critical systems, such as avionics. (VRTX is compliant to the FAA RTCS/DO-178B level A standard. This is a standard for software on board aircraft, and level A is for software whose failure would cause or contribute to a catastrophic failure of the aircraft. The process of compliance certification involves 100 percent code coverage in testing.) VRTX is used for the avionics on board Boeing MD-11 aircraft.

Rather than providing users with a variety of optional components, VRTX provides hooks for extensibility. For example, the TCB of a new task created by TCREATE( ) is extended to include application-specific information. An application can also add system calls.

Like the other operating systems described here, VRTX also has its own API functions. An example is mailboxes, which can be used to transfer one long word of data at a time (as opposed to queues for transferring multiple long words of data).

VRTX allocates memory in fixed-size blocks. For efficiency, free pool may be divided into noncontiguous partitions with different size blocks.