Re: [avr-gcc-list] generic queue library for AVR GCC?

[E. Weddington]

Dave Hansen wrote:

> [...]
>
> > The "critical" attribute doesn't hide anything more or less than a 
> > decent
> > set of macros or inline functions.  It makes it harder to get it wrong,
> > which is a good thing.  I suppose there is a danger of newbies 
> > mistakanly
> > using "critical" when they really mean "I want this function to run 
> > as fast
> > as possible".
>
>
> Such an attribute is useful if the critical section can be sensibly 
> encapsulated in a function.  I'm not completely convinced that is 
> always the case.  But in the project I'm currently working on, all the 
> critical sections are encapsulated within functions.
Any single statement or multiple statements can be encapsulated in a 
function. The question of whether it is efficient to do so is a design 
decision.

> It does invite abuse, however: it is harder to account the cost for 
> code you don't write.  To steal some of your code for an example:
>
>   void addToBuffer(uint8 b) {
>        CS_STATE_BUFFER csb;
>
>        csb = begin_critical_section();
>
>        if (length < bufferSize){
>           buffer[(start + length) % bufferSize] = b;
>           length++;
>        }
>
>        end_critical_section(csb);
>   }
>
> Given appropriate definitions of CS_STATE_BUFFER, 
> begin_critical_section(), and end_critical_section(), this would 
> generate code nearly identical to your original function.  But it's 
> easier to see the costs, and the implications of modifying the code.  
> IMHO, anyway.

Again, having a "critical" function attribute would be an *addition* to 
what is available. People are free to use it, or not. They could still 
"roll their own" and make it explicit as your example above. I think 
that it would depend upon the coding standards one would use.

Eric