XtratuM

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XtratuM

Universidad Politécnica de Valencia
Type	Hypervisor for safety-critical systems
License	GNU GPL-2.0
Website	www.xtratum.org

XtratuM is a bare-metal

It was initially developed by the

(GPL), version 2 or any later.

A new version of XtratuM from scratch (XtratuM New Generation XNG) is commercialized by fentISS under a proprietary license. It has been qualified for critical systems. ^[1]

XtratuM is a hypervisor designed for embedded systems to meet safety critical real-time requirements. It provides a framework to run several operating systems (or real-time executives) in a robust partitioned environment. XtratuM can be used to build a MILS (Multiple Independent Levels of Security) architecture.

History

The name XtratuM derives from the word stratum. In geology and related fields it means:

Layer of rock or soil with internally consistent characteristics that distinguishes it from contiguous layers.

In order to stress the tight relation with Linux and the open-source movements, the “S” was replaced by “X”. XtratuM would be the first layer of software (the one closest to the hardware), which provides a solid basis for the rest of the system.

XtratuM 1.0 was initially designed as a substitution of the

) to meet temporal and spatial partitioning requirements. The goal was to virtualize the essential hardware devices to execute several OSes concurrently, with at least one of these OSes being a RTOS. The other hardware devices (including booting) were left to a special domain, named root domain.

After this experience, it was redesigned to be independent of Linux and bootable. The result of this is XtratuM 2.0 which is type 1 hypervisor that uses para-virtualization. The para-virtualized operations are as close to the hardware as possible. Therefore, porting an operating system that already works on the native system is a simple task: replace some parts of the operating system HAL with the corresponding hypercalls.

Overview

The design of a hypervisor for critical real-time embedded systems follows these criteria:

• Strong temporal isolation: fixed cyclic scheduler.
• Strong spatial isolation: all partitions are executed in processor user mode, and do not share memory.
• Basic resource virtualization: clock and timers, interrupts, memory,
  CPU
  and special devices.
• Real-time scheduling policy for partition scheduling.
• Efficient context switch for partitions.
• Deterministic hypercalls (hypervisor system calls).
• Health monitoring support.
• Robust and efficient inter-partition communication mechanisms (sampling and queuing ports).
• Low overhead.
• Small size.
• Static system definition via configuration file (XML).

In the case of embedded systems, particularly avionics systems, the ARINC 653 standard defines a partitioning scheme. Although this standard was not designed to describe how a hypervisor must operate, some parts of the model are quite close to the functionality provided by a hypervisor.

The XtratuM API and internal operations resemble the ARINC 653 standard. XtratuM is not an ARINC 653 compliant system. The standard relies on the idea of a separation kernel defining both the API and operations of the partitions and also how the threads or processes are managed inside each partition.

XtratuM hypervisor supports the LEON 2/LEON 3/LEON 4 (SPARCv8) and Cortex R4/Cortex R5/Cortex A9 (ARMv7) architectures.^[1]

XtratuM support as execution environments:

• XAL (XtratuM Abstraction Layer) for bare-C applications
• POSIX PSE51 Partikle RTOS
• ARINC-653 P1 compliant LITHOS RTOS
• ARINC-653 P4 compliant uLITHOS runtime
• Ada Ravenscar profile ORK+^[2]
• RTEMS
• Linux

See also

• Kernel-based Virtual Machine
• L4 microkernels
• Xen
• Paravirtualization
• Nanokernel

References

External links

• XtratuM Official Page
• fentISS