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

[eles]

On Thursday, 24 October 2013 at 17:02:51 UTC, Walter Bright wrote:
> On 10/24/2013 4:18 AM, eles wrote:
>> On Thursday, 24 October 2013 at 06:48:07 UTC, Walter Bright 
>> wrote:
>>> On 10/23/2013 11:19 PM, Mike wrote:
> Like I said, nobody (on the standards committees) could agree 
> on exactly what that meant.

The standard committees might not agree, but there is somebody 
out there that really knows very accurately what that should 
mean: that somebody is the hardware itself.

Just imagine the best hardware example that you have at hand: the 
microprocessor that you are programming for.

It writes on the bus, there is a short delay before the signals 
are guaranteed to reach the correct levels, then reads the memory 
data and so on.

You cannot read the data before the delay passes. You cannot say 
"well, I could postpone the writing on the address on the bus, 
let's read the memory location first" -- or you would read 
garbage. Or you cannot say: well, first I will execute the 
program without a processor then, when the user is already pissed 
off, I would finally execute all those instructions at once. Too 
bad that the computer is already flying through the window at 
that time.

You command that processor from the compiler. Now, the thing 
that's needed is to give a way to do the same (ie commanding a 
hardware) from the program compiled by the compiler.