Writing GBA games with D!

[Raimondo Mancino]

On Wednesday, 19 May 2021 at 13:52:58 UTC, Raimondo Mancino wrote:
> ## 4. Notice
> At the moment, the binary is built correctly, but it does not 
> seem to link correctly when using D.
>
> Using GCC (for the C example above) instead of GDC with same 
> options works so my guess is that the linker script needs to be 
> updated.
>
> I think I need help for this; do you have any suggestions?
> Thank you in advance.

# Edit: It works!

To make it work correctly, you need to use volatile reference to 
VRAM.

So the correct hello world program is:

```d
import core.volatile;

@nogc:

enum VRAM = cast(ushort*) 0x6000000;
enum SCREEN_WIDTH = 240;
enum SCREEN_HEIGHT = 160;

enum FRAME_SEL_BIT = 0x10;
enum BG2_ENABLE = 0x400;

enum REG_DISP_CTL = cast(ushort*) 0x4000000;

extern(C) int main() {
     int i;

     volatileStore(REG_DISP_CTL, 3 | BG2_ENABLE);
     volatileStore(REG_DISP_CTL, volatileLoad(REG_DISP_CTL) & 
~FRAME_SEL_BIT);

     for(i = 0; i < SCREEN_WIDTH * SCREEN_HEIGHT; i++) {
         VRAM[i] = 31;
     }

     for(;;) { }

     return 0;
}
```

Since we used -fno-druntime, core/volatile.d needs to be included 
in our project.