What are the basic features of a RTOS?

[asymbian]

What is a RTOS?

Hi all!
There have been many posts earlier about what an RTOS is and which RTOS is better... But I am not able to get the basic features of any OS that make it an RTOS. Are there any quantitative measures? Please give me some specific properties.
How should one evaluate an OS and find out its capability to work as an RTOS? If I were to compare a few RTOSs what would be the points of comparison? Moreover, if I were to write the basic features of an RTOS, what features would define the RTOS?

Regards,
asymbian.

 

[SkyHigh]

Re: What is a RTOS?

Dear asymbian,

RTOS should exhibit only event-triggered operations and it is usually used in Embedded Systems where power consumption, memory size, processor speed, bus bandwidth are main limiting factors.

Unlike OS, RTOS is usually designed to achieve several aims:
1. Real-Time Operations i.e. Perform immediate operations when needed
2. Low Power Consumption, i.e. no power consumption when not doing any work
3. RTOS usually has the basic and common features of OS to eliminate complexity.
4. Simple device interface.

Try to compare the following OS:

1. Embedded Linux
2. Embedded XP
3. WinCE
4. Nucleus Plus
5. Clie
6. Palm OS
7. Symbian 40/60/70/80/90/UIQ

What do you see in them?

1. Some are designed for powerful ARM Processors such as ARM 9 and 11. Certainly Microsoft targets a market for powerful portable/mobile/handheld consumer electronics with capabilities comparable to a notebook or a laptop, but they never clearly understood what is the meaning of Embedded Systems after so many years of experiences in Computing. RTOS in the concept of Microsoft, Symbian and Linuz is trying to make RTOS an OS, thus making their software re-use in "RTOS".

2. Some are designed for less powerful ARM 7, such ATI Nucleus Plus, Palm OS and Sony Clie. They were designed for Embedded Systems limited by slower processor speed, memory size, average performance bus, low voltage electronics, short battery lifespan, and truly handheld or palm-size gizmos.

A true RTOS is found in automobiles today. These RTOS cannot tolerate bullshits and cumbersome features found in most handheld consumer electronics.

Look at BMW, Mercedes-Benz and Renault cars. They have RTOS and Embedded Systems in control of critical actions such as car crash, security, ABS, engine performance stats and GPS. They have customised RTOS specifically for cars only unlike the ones seen in consumer electronics.


PhD (Imperial College London)
Analog Devices Plc (Ireland)

 

[asymbian]

Re: What is a RTOS?

Thanks SkyHigh!
As you said, RTOS is an OS that considers the constraints of time, memory and power. But then, are then any quantitative measures that would help me evaluate any RTOS? An introduction to any RTOS says that it shoud support preemption, should have a less footprint etc. But none specifies any values as a typical datasheet would. Perhaps it would be too abstract.
Could I have a list of features of an RTOS which would be common to all RTOSes but maybe with different values...

Regards,
asymbian.

 

[tlp71@hotmail.com]

Re: What is a RTOS?

do you now whic kind of embedded micro you have to target?
Is the first step to chose the right RTOS:

 

[banh]

What is a RTOS?

i think choosing may depend on your system requirements :rom, ram, scheduling method (preemptive, nonpreemptive...), specific microcontroller...which rtos supports that kind of microcontroller..etc.

 

[SkyHigh]

Re: What is a RTOS?

Dear asymbian,

Any powerful OS should offer preemptive context switching, i.e preemptive multitasking is possible. This forms the basis for any form of scheduling.

32-bit and higher processors are usually designed and optimised to work any commerical operating systems. Conversely operating systems are designed to cope with pipelining in high-end processors. Some 32-bit processors such as those in ARM are also designed to handle 16-bit operations. Hence it is very much a bi-lateral design considerations on both parties.

However, with respect to current trends in the industry and today's market share, ARM as a very favourable processor core has set the design trends for operating systems to be optimised for ARM processors rather than the other way round.

It is thus not difficult to find an operating system that suits an ARM processor, especially true if you intend to use ARM 9 and ARM 11. ARM 7 has a limited option now.

The otherwise is not true, i.e. it is difficult to find a microprocessor that suits an operating system. Some microprocessors are not designed to use an operating system at all. Such are meant for very simple embedded system applications, which usually do not require dedicated Man-Machine Interface such as GUI, i.e. stand-alone to operate on a remote or autonomous control.

Would you need an OS for an embedded system using 68HC11, PIC18F452, Z8 and 8751?

As already discussed in previous post, unlike OS, RTOS aims to perform task on triggered events, which makes it suitable for real-time controls in automobile, military vehicles and other time-critical systems.

Unlike interrupts which can only be serviced based on priorities, RTOS aims to resolve multiple time-critical tasks. Imagine you are driving on the road, slippery on snow, and a jeep banged your car from behind, and other van banged your sidedoor. All these trigger multiple yet simultaneous events to your system. All critical tasks iniated by the ABS, rear sensor and sidedoor sensor.

I hope all these information could satisfy your curiosity.