feat(bus): implement Palette RAM and DISPSTAT

src/ppu.zig

@@ -4,10 +4,12 @@ const Allocator = std.mem.Allocator;
 
 pub const Ppu = struct {
     vram: Vram,
+    palette: Palette,
 
     pub fn init(alloc: Allocator) !@This() {
         return @This(){
             .vram = try Vram.init(alloc),
+            .palette = try Palette.init(alloc),
         };
     }
 
@@ -16,6 +18,44 @@ pub const Ppu = struct {
     }
 };
 
+const Palette = struct {
+    buf: []u8,
+    alloc: Allocator,
+
+    fn init(alloc: Allocator) !@This() {
+        return @This(){
+            .buf = try alloc.alloc(u8, 0x400),
+            .alloc = alloc,
+        };
+    }
+
+    fn deinit(self: *@This()) void {
+        self.alloc.free(self.buf);
+    }
+
+    pub inline fn get32(self: *const @This(), idx: usize) u32 {
+        return (@as(u32, self.get16(idx + 2)) << 16) | @as(u32, self.get16(idx));
+    }
+
+    pub inline fn set32(self: *@This(), idx: usize, word: u32) void {
+        self.set16(idx + 2, @truncate(u16, word >> 16));
+        self.set16(idx, @truncate(u16, word));
+    }
+
+    pub inline fn get16(self: *const @This(), idx: usize) u16 {
+        return (@as(u16, self.buf[idx + 1]) << 8) | @as(u16, self.buf[idx]);
+    }
+
+    pub inline fn set16(self: *@This(), idx: usize, halfword: u16) void {
+        self.buf[idx + 1] = @truncate(u8, halfword >> 8);
+        self.buf[idx] = @truncate(u8, halfword);
+    }
+
+    pub inline fn get8(self: *const @This(), idx: usize) u8 {
+        return self.buf[idx];
+    }
+};
+
 const Vram = struct {
     buf: []u8,
     alloc: Allocator,