Example uses "volatile"; compiler says "undefined identifier volatile"

[Timo Sintonen]

On Thursday, 1 August 2019 at 03:04:27 UTC, Paul wrote:
> I'm trying to build a Bare Bones 'OS' via example.  Example 
> says to compile with
> "gdc -c kernel.main.d -o kernel.main.o -g"  I'm having trouble 
> getting GDC all set up..as I'm a rank amateur.  So, I tried 
> compiling the example below with DMD.  DMD spits out exceptions 
> to the use of 'volatile'. DIP62 on D wiki says status:REJECTED 
> for volatile.
> Whats my work around here?  This is what I'm trying to do-> 
> https:// wiki.osdev.org / D_Bare_Bones
>
> Thanks for any help.
>
> module kernel.main;
>
> extern(C) void main(uint magic, uint addr) {
>         int ypos = 0; //Starting points of the cursor
> 	int xpos = 0;
> 	const uint COLUMNS = 80; //Screensize
> 	const uint LINES = 25;
>
> 	ubyte* vidmem = cast(ubyte*)0xFFFF_8000_000B_8000; //Video 
> memory address
>
> 	for (int i = 0; i < COLUMNS * LINES * 2; i++) { //Loops 
> through the screen and clears it
> 			volatile *(vidmem + i) = 0;
> 	}
>
> 	volatile *(vidmem + (xpos + ypos * COLUMNS) * 2) = 'D' & 0xFF; 
> //Prints the letter D
> 	volatile *(vidmem + (xpos + ypos * COLUMNS) * 2 + 1) = 0x07; 
> //Sets the colour for D to be light grey (0x07)
>
> 	for (;;) { //Loop forever. You can add your kernel logic here
> 	}
> }

Accesses to peripheral regiters or memory need to be marked 
volatile. This tells the compiler that these operations have some 
other meaning than just store and load the data. Otherwise the 
compiler may reorder or remove operations.
Unfortunately the volatile feature was removed from the language 
some years ago. Instead, there are volatileLoad and volatileStore 
in core.bitop.

A simple program may work if all volatile words are just omitted 
and the program is compiled with all optimizations turned off. I 
made Volatile data type to access peripheral registers, you can 
see it here:
https://bitbucket.org/timosi/minlibd/src/default/tools/main/volatil3.d