On Thursday 15 March 2001 16:14, jmartins wrote: > Hi > > We have to perform a hard real time project for ~2000 work hours. > For this project we have ~20 objects written in C++. > Approximately rewriting cost of these objects into plain C is ~200 work > hours. > > We have not make choice between RTLinux and RTAI yet > and hope to develop easy portable system from RTLinux to RTAI and vice > versa. > > Interesting - what is a more reasonable decision: > 1) to port our C++ objects into plain C > 2) acquire C++ for kernel programming > > We have some difficulties to make decision. It depends on a few things, such as which C++ features the existing code is relying on, what kind of real time programming model it's designed around, whether or not it does dynamic memory allocation, whether on not it instantiates objects in real time etc. I've done some kernel space C++ programing with RTL, and didn't run into any serious problems - but then I wrote the code directly for RTL, to run in a hard real time system, and considering determinism when designing the objects, avoiding excessive complexity. All you have to do is to implement new/delete (don't forget the array versions!), and keep in mind that you must call the global ctor/dtor hooks explicitly if you're using global instances of some classes. The most useful (IMHO) features of C++, such as virtual methods, class name spaces, inheritance and so on work just fine with RTL, provided you know what kind of code is generated. However, dynamic memory allocation - although possible to implement (done in RTAI, IIRC) - doesn't mix well with complex code and hard real time; actually not with hard real time at all in anything by the simplest programs. If you instantiate or destroy objects when responding to RT events, you're even deeper init, and have to keep track of which ctor/dtor functions are actually called, especially if there are heavy ones. Large inheritance trees can make that messy, but OTOH, there are tools that make that kind of work a lot easier. (After all, it's all in the code; you just have to make sure you don't miss the details.) In short, if the C++ code is properly designed for a hard real time system, you'd probably be wasting time converting it into C, but if it's "traditional" C++ code, you may actually save time that way. Then again, if the only real problem is too much dynamic (de)allocations, that can still be fixed without rewriting to C code - C++ is exactly what you make it, rather than inherently dynamic and indeterministic. Inheritance and object pools don't mix well, though. If objects are of reasonable and/or similar sizes, you can get away with a very simple LIFO stack memory manager with one or a few block sizes. Just keep in mind that if you don't have a strictly defined maximum memory use/object count *regardless of input values and timing*, it's easy to end up in the "Help! The pool is exhausted, and the deadline is in a few µs!!!" situation, which is not very nice in a system that's supposed to be deterministic. :-) //David .- M A I A -------------------------------------------------. | Multimedia Application Integration Architecture | | A Free/Open Source Plugin API for Professional Multimedia | `----------------------> http://www.linuxaudiodev.com/maia -' .- David Olofson -------------------------------------------. | Audio Hacker - Open Source Advocate - Singer - Songwriter | `--------------------------------------> [EMAIL PROTECTED] -' -- [rtl] --- To unsubscribe: echo "unsubscribe rtl" | mail [EMAIL PROTECTED] OR echo "unsubscribe rtl <Your_email>" | mail [EMAIL PROTECTED] -- For more information on Real-Time Linux see: http://www.rtlinux.org/rtlinux/
