Re: [avr-gcc-list] Problem with delay loop

[Klaus Rudolph]

I think we are discussing not the solution :-)

The compiler optimizes unused code away, that is OK!
If we use a volatile, the WRITE ACCESS could not longer be optimized and 
also a new READ ACCESS before subtraction must! be done. That is what 
the compiler do, that is also OK!
If there is a "local" volatile variable, the compiler build a new stack 
frame which results in a big prologue and epilogue for the function, 
which is OK!

The solution to have a time consumtion function is to use the library!
Sorry that the volatile hack is not what you need. But it burnes time as 
expected :-) and nothing else is requested. If you need a handcafted 
delay loop use inline assembler instead. The behaviour of the compiler 
can change from version to version. And I hope it will change a lot to 
get better code!

Bye
 Klaus


> Royce Pereira wrote:
> > So I have to write more 'C' code :) to get the same
> > stuff done, in the 'new & smarter' compiler!
>
> Not more code, just correct code.
>
> Have you tried returning the final value of your delay argument from the 
> function?  If the compiler optimizes only within the boundaries of 
> individual functions it won't be able to take advantage of the fact that 
> the result is not used.  Strictly, this isn't correct either as the 
> compiler could just assign zero and return.  But, it may not be smart 
> enough to do that and you may get closer to your original assembly 
> language.  Another way to go would be to write the function directly in 
> assembly language.
>
> Graham.
>
>
>
>
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