Programming on real-time system

My problem is understandi开发者_如何学Cng programming on real-time system. I'm confuse about this topic. What can I do and what I can not do in my source code? I know there are attensions to do during source code programming but I don't know exactly what. Some examples. Is possibile using dynamic memory allocation(new)? Is possible access to disk during real-time? What kind of IPC(Interprocess communication) can I use? Can I use standard interprocess locking? And what is with file locking? I have searched on internet but didn't find what I want. Where can I better understand this problems? I hope someone can help me. Sorry for my english!

You can do whatever your language/compiler of choice supports.

What you should do now, it really depends on what's the target system, what is your program (you could be writing an OS for all I know), etc...

Realtime system is all about determinacy - fixed timing for each . Check this out for some guidelines:

http://cs.brown.edu/~ugur/8rulesSigRec.pdf

What defines a real-time/near-real time system?

On the software side (your focus):

a. Avoid buffering or caching in your code. Caching are meant to speed up subsequent processing after the first, but then this result in indeterminacy of timing.

b. Minimize conditional branching, as it will generate different path resulting in different timing, this is especially important for the time-sensitive component.

c. Avoid asynchronous, or interrupt based design. Use polling whenever possible - that will increase the predictability of the timing.

d. Use a realtime OS (like LynxOS RTOS) whenever possible. It has high responsiveness and predictability in its processing. But if you look at its internals, you will see that it skips a lot of error processing, it has low threshold for maximum numbers of processes it can spawn etc. Ie, there is a lot of spare CPU computing power leftover always, to ensure that the responsiveness is there. Of course, the moment you pushed the numbers to its limits (eg, spawning lots of processes) the realtime behavior of LynxOS does not exhibit anymore.

Just lots of commonsense applied when you do coding.....