The Real Time OS

You walk up to your ATM to get some cash. You insert your

card, and expect it to be recognized by the machine immediately. Within a minute,

you’re out of there with your money. You wouldn’t want to wait for, say, two

minutes or so just to get the system to boot, or reach the main menu, would you?

Or let’s say you’re on a flight, 30,000 feet

above sea level. The pilot reconfigures the onboard flight computer, warned of an

impending storm. What if the computer’s OS froze up, or responded after a few

minutes?

A real-time operating system (RTOS) is capable of handling

multiple events simultaneously and within a fixed-time frame. Computers running mission

critical embedded apps need an operating system that responds quickly or within "real

time" to requests. Let’s take another example. A computer program is controlling

an industrial motor. At a certain instant of time, it notices that the motor is running at

a speed higher than the considered safe limit. It immediately sends a signal to another

running program, telling it to shut the motor down. If the operating system running these

two processes doesn’t pass the signal between them fast enough, the motor can get

damaged.

There are two essential features that make an operating

system "real time". The operating system must support multi-tasking with

preemptive, priority-driven context switching with guaranteed interrupt handling. What it

means is that if the operating system receives an outside event, it should be able to

switch between the running process and the event handler process immediately. The OS must

also have a very efficient inter-process communication (IPC) subsystem. If a process

wishes to talk to another, it should be able to do so immediately and without fail.

A real-time operating system should have a very small

memory footprint. Most embedded apps are severely constrained by the amount of memory

available to them. If the OS were to take a large part of this memory, there would be

precious little left for apps. Networking capability is also essential to an RTOS. Most

real-time apps need to communicate with other such systems distributed over large

distances. To do this quickly and efficiently is critical.

Moreover, all subsystems of such an OS need to be highly

fault tolerant. If, for instance, a part of the network fails, the networking subsystem

should be capable of automatically re-routing network traffic through another part of the

network.

RTOSs are finding applications in almost all spheres of

modern life. From household electronics to the defense industry, from your wristwatch to

spacecraft, they are everywhere. Time critical apps depend on such highly responsive OS,

working in small amount of memory without failure. Everyone seems to be talking about an

Internet-enabled microwave or an Internet-enabled refrigerator. Even your watches will

soon be on the Net with their very own IP numbers. All these devices need RTOSs to do

their job. Interested in learning more? Read on about some real-life applications of these

exciting OSs.

The Philips MyWeb settop box for

the Internet

Internet television is now a reality. The Philips MyWeb is

a set-top box that provides access to the Internet through television sets. Just plug in

your telephone line and connect to the Web. This product is ideal for those who don’t

want to invest in a computer but still want access to the Net. Based on an AMD SC410

microprocessor, the device comes with 1 MB ROM, 2 MB flash read-write memory, and 4 MB

RAM.

It uses the QNX real-time operating system (refer the

article "QNX: GUI OS on a floppy") along with the Voyager Web browser. This OS

comes with a powerful graphical user interface called the Photon MicroGUI, which presents

a neat Windows-like environment to the user.

Hands-free driving on automated

highways

Within a few years, your computer could drive you to work.

That’s right, no more navigating through crazy traffic jams, or having to suddenly

slam your brakes because the bus in front of you decides to stop in the middle of the

road. Partners for Advanced Transit and Highways (PATH), CalTrans, GM, Hughes Aircraft,

and 30 other companies have formed a consortium for designing automated highways and

computer-driven vehicles.

Extensive research in this field is already underway, and

again the QNX RTOS is being used for the early prototypes. Real-time information including

distance, relative velocity, acceleration, throttle position are all monitored by apps

running on this OS. RTOSs play a crucial role here. Imagine what would happen if the RTOS

running your "future" car failed to respond in time to that bus right in front

of you? What if it gave an "illegal operation" and crashed?

Airborne warning and control system

AWACS aircraft provides crucial information about enemy

positions and movements to other friendly aircraft, monitoring deep inside enemy

territory. Fighters making deep penetration strikes into hostile territory rely on such

aircraft for up-to-date information on enemy locations, including positions of unfriendly

aircrafts.

The LynxOS, another RTOS, is Boeing’s step 1 mission

computer upgrade for the entire US Airforce’s AWACS fleet. Software running on this

OS will manage interfaces to on-board computers used for surveillance and C3 (command,

control and communication). According to Bill Hogan, president of Lynx, "AWACS is one

of the most technologically demanding systems in the world." As you would be well

aware, a fault tolerant and extremely efficient operating system is imperative for this

kind of an application. There can be no excuse for a failure on the operating

system’s part.

Transmission line monitoring system

Fujikura Corporation in Japan is implementing a system that

monitors ultra-high voltage transmission lines (20,000-50,000V). These power lines go

through the seabed or underground tunnels, and need to be observed constantly. Any faults

that occur need to be repaired immediately since these are the lifelines between the power

station and the cities.

Monitoring nodes are scattered all along the transmission

lines and any fault is immediately relayed to the central controlling units. A RTOS, OS-9,

is being used, mainly for the high reliability that is required. As is typical of an RTOS,

OS-9 is highly compact.

Advanced space vision system

A very high-technology application that an RTOS is being

put to, is the Advanced Space Vision System. The ASVS is a precision guidance system for

astronauts manipulating objects in space. Take the case of the space shuttle. Sometimes,

astronauts have to re-attach a payload to the space shuttle. Previously, all they had was

a few external TV cameras or the shuttle’s small windows to look through. This could

turn out to be a difficult, if not impossible proposition, especially if the cameras

didn’t catch the object of interest at the right angle.

Not any more. The Neptec Design Group has come out with a

system based on the QNX RTOS, which enables them to see exactly what they’re doing,

in real time. The system provides the astronauts exact location, orientation, and motion

information through a computer-generated view of the payload and any important reference

points.

RTOSs are here, and they are here to stay. With the growth

of the Internet and almost all previously mechanical applications now going electronic,

these operating systems will play a prominent part in the way we do things in the future.