ARM bare-metal programming in D (cont) - volatile

[Mike]

On Thursday, 24 October 2013 at 06:48:07 UTC, Walter Bright wrote:
> On 10/23/2013 11:19 PM, Mike wrote:
>> Thanks for the answer, Walter. I think this would be 
>> acceptable in many (most?)
>> cases, but not where high performance is needed I think these 
>> functions add too
>> much overhead if they are not inlined and in a critical path 
>> (bit-banging IO,
>> for example). Afterall, a read/write to a volatile address is 
>> a single atomic
>> instruction, if done properly.
>>
>> Is there a way to tell D to remove the function overhead, for 
>> example, like a
>> "naked" attribute, yet still retain the "volatile" behavior?
>
> You have to give up on volatile. Nobody agrees on what it 
> means. What does "don't optimize" mean? And that's not at all 
> the same thing as "atomic".
>
> I wouldn't worry about peek/poke being too slow unless you 
> actually benchmark it and prove it is. Then, your alternatives 
> are:
>
> 1. Write it in ordinary D, compile it, check the code 
> generated, and if it is what you want, you're golden (at least 
> for that compiler & switches).
>
> 2. Write it in inline asm. That's what it's for.
>
> 3. Write it in an external C function and link it in.

Well, I wasn't rooting for volatile, I just wanted a way to 
read/write my IO registers as fast as possible with D.

I think the last two methods you've given confirm my suspicions 
and will work.  But... I had my heart set on doing it all in D :-(

Thanks for the answers.