AVR-Chat

Thomas Keller wrote:
> On Wed, 2005-10-26 at 22:46 -0500, Zack Widup wrote:
> 
>>I'm the same way.  I write mostly in assembler, for a couple reasons 
>>anyway: 1 - it makes me "think" like the microcontroller, and 2 - it
>>seems the little bits of C code I've written have redundundundant
>>lines in them that make the code longer than if I write it in
>>assembler.
> 
> 
>    Yes.  Assuming any degree of competence in assemblker at all, code
> written in assembler will be smaller and faster than code generated by a
> compiler.  This is because the compiler, in order to provide the very
> generalized programming environemnt necessary in high level languages,
> must use very generalized structures and flows.  Further, because the
> compiler has no way of "knowing" what your intentions as programmer are,
> it must manage resources on the target in fixed ways, which are often
> not efficient for the sopecific purpose your progarm is designed for.
> Vis all the ridiculous register swapping that compiled code often
> contains.
> 
> 
>>I'm not knocking the higher-level languages, it's just that I haven't 
>>really needed them myself.
> 
> 
>   Well, while I agree with you, I feel compelled to point out that the
> primary reasons most people who use high level languages to do embedded
> programming are 1) lack of knowledge and expoerience in assembly
> language programming, and 2)  in commercial development enviroinments,
> the time savings to develop working code can be significant, and time
> saved equates to development costs saved.
> 
>    Reason #2 is not going to ever go away, because it is almost always
> bean counters who make the important decisions in a business.  Reason #1
> probably won't ever go away either, because so many people are unwilling
> to learn new programming languages or methodologies.
> 
>    Personally, I plan to do most of my embedded programming in assem,bly
> language, because I find it challenegin and fun to, as you pointy out,
> "think like the processor," as well as because it affords me direct
> control over the hardware.  You just can't get any closer to the machine
> than assembly language (some might argue that programming in "machine
> language" (e.g., binary op codes directly entered into memory using a
> switch register) is closer, but I disagree.   With the exeception that
> most decent assemblers support macro processing and mnemonic labeling,
> assembly language translates directly into machine code, and is just as
> close to the hardware as the machine code is.
> 
> Tom

Good points there.  I personally like to model my programme 
in a high-level language on the PC mainly to get a feel for 
what it is that I am trying to do.  Then I refine that 
programme until I am satisfied with its performance.  When 
it works correctly on the PC, I then hand-translate it to 
assembler code.

Of course, there are limitations to that approach (like 
working with the on-chip peripherals which don't model 
easily), but it gives me a code base which I can then add 
stuff to.

The high-level is also useful in documentation where I am 
trying to explain just what it is that the programme does.

Things get even better if I have a compiler that excretes 
assembly code for whatever CPU I'm working with; then I can 
go in and hand-optimise the compiler's output.

erikc