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

[Walter Bright]

On 10/23/2013 5:43 PM, Mike wrote:
> I'm interested in ARM bare-metal programming with D, and I'm trying to get my
> head wrapped around how to approach this.  I'm making progress, but I found
> something that was surprising to me: deprecation of the volatile keyword.
>
> In the bare-metal/hardware/driver world, this keyword is important to ensure the
> optimizer doesn't cache reads to memory-mapped IO, as some hardware peripheral
> may modify the value without involving the processor.
>
> I've read a few discussions on the D forums about the volatile keyword debate,
> but noone seemed to reconcile the need for volatile in memory-mapped IO.  Was
> this an oversight?
>
> What's D's answer to this?  If one were to use D to read from memory-mapped IO,
> how would one ensure the compiler doesn't cache the value?

volatile was never a reliable method for dealing with memory mapped I/O. The 
correct and guaranteed way to make this work is to write two "peek" and "poke" 
functions to read/write a particular memory address:

     int peek(int* p);
     void poke(int* p, int value);

Implement them in the obvious way, and compile them separately so the optimizer 
will not try to inline/optimize them.