Real VMX if a VxWorks like operating system kernel. However VxWorks is proprietary, which means that you have to pay license money if you wish to use it. Because of that Linux RT, which free has have taken over where VxWorks would normally be a better choice.
Linux is based on Unix, which is an operating system intended to be used on high-end workstations, with hundreds om megabytes of memory. Even the smallest Linux kernel is about 1MB big. Which is very much for an embedded system. Usually the embedded kernels are a few hundreds of kilobytes.
Linux usually run different programs as processes. Which means that the have a separate memory pool, isolated from other processes. This leads to an expensive context switch has to be made every time the processor should work on another process. In vmx everything are threads, which means that every thread or task have a separate stack and a separate set of processor registers. However the memory and all the system resources are shared among all tasks. This also makes comminication between tasks faster than for processes. Since there is no need to send the information trough filesystem or shared memory.
Windows are not even competing is this league since it is based on an old single tasking system, intended for sigle user home computers in the early 80:s. Even though it has been extended to act as a multitasking system in the latest decade. It still suffers from slow context switches (mentioned earlier) and are no way near as fast as a realtime system must be. This is why Windows is considered a ‘non-realtime’ system.
Realtime means that the timing is based on real world time, like milliseconds, and on electrical signals. Windows is simply to slow to be able to do the required processing within the time limits according to the realtime specification. Linux suffered from this a long time too, but eventuallt there was an Linux extension called Linux RT. Which is a layer between process-space and task-space. Which does indeeed fall inside the realtime specifications. There is also an operating system called Open VMS that does have these two modes, process-space (non-realtime) and task-space (realtime), but this operating system is only avilable for ‘big compuer’ achitectures like the VAX, Aplha and Intel Itanium.
Typical applications for Real VMX would be:
- Steering systems in aircrafts, spacecrafts and cars.
- Industrial systems for automated production.
- Labratory equipment.
- Video game consoles, digital television boxes, video
decoding.
- Clustered computing.
- Switches, routers and telecom equipment.
The limits for Real VMX is that it is still under development, and there are not any applications for it yet. However this blogg will be dedicated to follow the development of Real VMX, and see how it will get closer and closer to a serious alternative for embedded realtime-systems. Of cource you can run Real VMX on a stationary or laptop PC too. This is actually how Real VMX is beeing developed, but in the end the final application would be stored on e-prom
Links
Real VMX
project
Test group
Tutorials
File archive
VMXUS
/Leif Zeppelin