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Hello, I was browsing through older posts that deal with the painful issue of portability (http://www.keil.com/forum/docs/thread8109.asp). I was (and still am) a big advocate of programming as much as possible conforming to the C standard, and having a layered structure that allowed "plugging-in" other hardware. But I have come to change my mind recently. I am reading the "ARM system developer's guide" (excellent book by the way. I'm reading it because I want to port some C167 code to an ARM9 environment) in which chapter 5 discusses writing efficient C code for an ARM. The point is, and it is fairly demonstrated, that even common, innocent looking C code can either be efficient of very inefficient on an ARM depending on specific choices made, let alone another processor used! So, if we are talking about squeezing every clock cycle out of a microcontroller - I do not believe that portability without ultimately littering the code is possible!
Did you know that am ARM does not have divide instructions in hardware ?
No, I haven't read the manual.
If you try to port code that heavily relies on divisions into an ARM (without modifications, such as converting divides into multiples), you are destined to be forced to use many calls to the compiler's C library. And that is going to hurt, not?
That depends whether you design 'by experience' or by research.
Jack, you wrote: "That depends whether you design 'by experience' or by research."
I was talking about software that was designed on a platform that has a certain design philosophy, then ported to another platform that behaves very differently. I don't fully understand how the above comment can reconcile this difficulty, because "redesigning" the code, as correctly mentioned already would merely serve as rewriting it (I personally agree with this statement - is strictly my opinion, I don't claim it to be an ultimate truth of course), so why not begin (almost) from scratch? Please clarify if you like.
... will design by a combination of the two.
If you design purely by experience you will, probably, be caught in a 'trap' or two.
If you design purely by research you will not have your project completed in a timely manner.
Erik