TIC-80 WebAssembly: pointers to fixed addresses

Pierce Ng pierce at samadhiweb.com
Sat Apr 16 14:29:09 UTC 2022


Hi all,

D newbie here. I'm building a D WebAssembly binding for 
[TIC-80](https://github.com/nesbox/TIC-80), a fantasy gaming 
console.

TIC-80 has a [fixed size 
RAM](https://github.com/nesbox/TIC-80/wiki/RAM) that is directly 
addressable by a running program using peek() and poke() 
functions. Basically, 16,384 bytes starting at address zero form 
the video RAM, next 8192 bytes are for storing tiles, next 8192 
bytes for sprites, etc.

Here's how Zig's TIC-80 binding describes the memory layout:

```
pub const FRAMEBUFFER: *allowzero volatile [16320]u8 = 
@intToPtr(*allowzero volatile [16320]u8, 0);
pub const TILES : *[8192]u8 = @intToPtr(*[8192]u8, 0x4000);
pub const SPRITES : *[8192]u8 = @intToPtr(*[8192]u8, 0x6000);
```

I believe the above is declaring that FRAMEBUFFER is a pointer to 
16320 (sic) bytes starting at address 0, TILES is a pointer to 
8192 bytes starting at address 0x4000, and SPRITES a pointer to 
8192 bytes starting at address 0x6000.

Currently for D I have the following, copying the D binding for 
Wasm4, another fantasy console:

```
const FRAMEBUFFER = cast(uint*)0;
const TILES = cast(uint*)0x4000;
const SPRITES = cast(uint*)0x6000;
```

How to express in D, similarly to Zig, that FRAMEBUFFER refers to 
a byte[16384] array starting from address zero, and so on?

Pierce


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