Embedded Systems Design Europe - March 2008 - (Page 29)

linux structure of the operating system. But as Linus Torvalds commented recently, integrating it into Linux is not practical because there is no onesize-ﬁts-all “One True Virtualization” model appropriate to all the applications in which Linux is being used. It also wouldn’t help for those deploying devices without Linux (because they want to offer a choice of high-level operating systems, or maybe because they ship low-end devices in which a high-level operating systems makes no sense). A better place to implement an integrated para-virtualization mechanism is in the companion RTOS used to handle the hard real-time operations that Linux can’t. This approach requires more than a bare hypervisor: it needs a kernel that can provide basic operating-system mechanisms, such as a high-performance message-based microkernel, as Figure 4 shows. Unlike the classical monolithic operating system structure of Linux with a vertical structure of layers, each abstracting the layers below, a microkernel-based system, exhibits a horizontal structure. System components run beside application code and are invoked by sending messages. A notable property of a microkernel system is that as far as the kernel is concerned, there is no real difference between “system services” and “applications” – all are simply processes running in user mode. Each such userlevel process is encapsulated in its own hardware address space, set up by the kernel. ployed for years by VMWare and Xen from the University of Cambridge, both aimed at the enterprise market. Recently virtualization solutions aiming at embedded designs have emerged, such as L4/Wombat from the University of New South Wales, and the commercial systems Trango, VLX from VirtualLogix as well as OK4 from Open Kernel Labs. All have their advantages and disadvantages in different environments, but what most of these approaches all have in common is that they introduce another layer of software – and complexity – into the operating environment. And in many embedded applications, where code size frequently measures in the millions of lines of code, breaking this into two or three virtual machines is of limited help for improving overall system reliability and security. The isolation provided by current approaches to para-virtualization is by its nature coarse-grained – it provides the appearance of a complete machine for each subsystem. This means that each virtual machine is required to run its own operating system, making them relatively heavyweight. Consequently, increasing the number of virtual machines in order to reduce the granularity of the subsystems would create serious performance issues and signiﬁcantly increase the amount of code. This in turn not only requires increased memory size and thus power consumption, but also results in more points of failure. USING A MICROKERNEL AS A HYPERVISOR The most appropriate way to deploy para-virtualization in an embedded design is by integrating it into the 026-027-028-029-030_ESDE.indd 29 6/03/08 14:42:52 http://www.syslogic.com http://www.syslogic.com

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Embedded Systems Design Europe - March 2008 Distributors to Increase Embedded Focus Kontron and Quanta to Join Forces Coverity Raises $22m as European Business Booms Help is at Hand for Europe's Industrial Control Developers Milestones in Embedded Systems Microsoft is Recruiting for Embedded Center in Aachen European Designers to Win Cash for Green Designs Duo Work on Smaller Form Factor Europe Invests in Real-Time Java for Multicore Systems Curtiss-Wright Buys Pentland Systems Designing DSP-Based Motor Control Using Fuzzy Logic Lower the Cost of Intelligent Power Control with FPGAs Virtualizing Embedded Linux Back to the Future: Manchester Encoding Is Multicore Hype or Reality New Products Advertising Contacts

Embedded Systems Design Europe - March 2008

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