feat(ppu): introduce concept of 2 graphics engines + refactor

src/core/Scheduler.zig

@@ -66,7 +66,7 @@ pub fn handle(self: *@This(), bus_ptr: ?*anyopaque, event: Event, late: u64) voi
                     bus.ppu.onHdrawEnd(self, late);
                 },
                 .hblank => bus.ppu.onHblankEnd(self, late),
-                .vblank => bus.ppu.onHblankEnd(self, late),
+                .vblank => bus.ppu.onVblankEnd(self, late),
                 .sqrt => bus.io.sqrt.onSqrtCalc(),
                 .div => bus.io.div.onDivCalc(),
             }

src/core/emu.zig

@@ -132,7 +132,7 @@ pub const SharedCtx = struct {
     const KiB = 0x400;
 
     pub const Io = @import("io.zig").Io;
-    const Vram = @import("ppu.zig").Vram;
+    const Vram = @import("ppu/Vram.zig");
 
     io: *Io,
     main: *[4 * MiB]u8,

src/core/nds7/Bus.zig

@@ -4,7 +4,7 @@ const io = @import("io.zig");
 const Scheduler = @import("../Scheduler.zig");
 const SharedCtx = @import("../emu.zig").SharedCtx;
 const Wram = @import("../emu.zig").Wram;
-const Vram = @import("../ppu.zig").Vram;
+const Vram = @import("../ppu/Vram.zig");
 const Bios = @import("Bios.zig");
 const forceAlign = @import("../emu.zig").forceAlign;
 

src/core/nds9/Cp15.zig

@@ -2,7 +2,7 @@ const std = @import("std");
 
 const log = std.log.scoped(.cp15);
 
-const panic_on_unimplemented: bool = true;
+const panic_on_unimplemented: bool = false;
 
 control: u32 = 0x0005_2078,
 dtcm_size_base: u32 = 0x0300_000A,

src/core/nds9/io.zig

@@ -34,10 +34,6 @@ pub const Io = struct {
     /// Caller must cast the `u32` to either `nds7.IntRequest` or `nds9.IntRequest`
     irq: IntRequest = .{ .raw = 0x0000_0000 },
 
-    /// POWCNT1 - Graphics Power Control
-    /// Read / Write
-    powcnt: PowCnt = .{ .raw = 0x0000_0000 },
-
     // Read Only
     keyinput: AtomicKeyInput = .{},
 
@@ -82,7 +78,7 @@ pub fn read(bus: *const Bus, comptime T: type, address: u32) T {
             // Timers
             0x0400_0100...0x0400_010E => warn("TODO: impl timer", .{}),
 
-            0x0400_0004 => bus.ppu.io.dispstat.raw,
+            0x0400_0004 => bus.ppu.engines[0].dispstat.raw,
             0x0400_0130 => bus.io.keyinput.load(.Monotonic),
 
             0x0400_0180 => @truncate(bus.io.shr.ipc._nds9.sync.raw),
@@ -120,7 +116,7 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
             // Timers
             0x0400_0100...0x0400_010C => log.warn("TODO: impl timer", .{}),
 
-            0x0400_0000 => bus.ppu.io.dispcnt_a.raw = value,
+            0x0400_0000 => bus.ppu.engines[0].dispcnt.raw = value,
             0x0400_0180 => bus.io.shr.ipc.setIpcSync(.nds9, value),
             0x0400_0184 => bus.io.shr.ipc.setIpcFifoCnt(.nds9, value),
             0x0400_0188 => bus.io.shr.ipc.send(.nds9, value),
@@ -151,7 +147,7 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
                 bus.io.sqrt.schedule(bus.scheduler);
             },
 
-            0x0400_0304 => bus.io.powcnt.raw = value,
+            0x0400_0304 => bus.ppu.io.powcnt.raw = value,
 
             else => log.warn("unexpected: write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8})", .{ T, address, value }),
         },
@@ -177,7 +173,7 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
                 bus.io.sqrt.schedule(bus.scheduler);
             },
 
-            0x0400_0304 => bus.io.powcnt.raw = value,
+            0x0400_0304 => bus.ppu.io.powcnt.raw = value,
 
             else => log.warn("unexpected: write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>4})", .{ T, address, value }),
         },
@@ -241,7 +237,7 @@ fn warn(comptime format: []const u8, args: anytype) u0 {
     return 0;
 }
 
-const PowCnt = extern union {
+pub const PowCnt = extern union {
     // Enable flag for both LCDs
     lcd: Bit(u32, 0),
     engine2d_a: Bit(u32, 1),
@@ -382,8 +378,7 @@ const SquareRootUnit = struct {
 };
 
 pub const DispcntA = extern union {
-    bg_mode: Bitfield(u32, 0, 2),
+    bg_mode: Bitfield(u32, 0, 3),
-
     /// toggle between 2D and 3D for BG0
     bg0_dimension: Bit(u32, 3),
     tile_obj_mapping: Bit(u32, 4),
@@ -400,7 +395,25 @@ pub const DispcntA = extern union {
     bitmap_obj_1d_boundary: Bit(u32, 22),
     obj_during_hblank: Bit(u32, 23),
     character_base: Bitfield(u32, 24, 3),
-    screen_base: Bitfield(u32, 27, 2),
+    screen_base: Bitfield(u32, 27, 3),
+    bg_ext_pal_enable: Bit(u32, 30),
+    obj_ext_pal_enable: Bit(u32, 31),
+    raw: u32,
+};
+
+pub const DispcntB = extern union {
+    bg_mode: Bitfield(u32, 0, 3),
+    tile_obj_mapping: Bit(u32, 4),
+    bitmap_obj_2d_dimension: Bit(u32, 5),
+    bitmap_obj_mapping: Bit(u32, 6),
+    forced_blank: Bit(u32, 7),
+    bg_enable: Bitfield(u32, 8, 4),
+    obj_enable: Bit(u32, 12),
+    win_enable: Bitfield(u32, 13, 2),
+    obj_win_enable: Bit(u32, 15),
+    display_mode: Bitfield(u32, 16, 2),
+    tile_obj_1d_boundary: Bitfield(u32, 20, 2),
+    obj_during_hblank: Bit(u32, 23),
     bg_ext_pal_enable: Bit(u32, 30),
     obj_ext_pal_enable: Bit(u32, 31),
     raw: u32,

src/core/ppu.zig

@@ -4,6 +4,10 @@ const Allocator = std.mem.Allocator;
 const Scheduler = @import("Scheduler.zig");
 const System = @import("emu.zig").System;
 
+const Vram = @import("ppu/Vram.zig");
+const EngineA = @import("ppu/engine.zig").EngineA;
+const EngineB = @import("ppu/engine.zig").EngineB;
+
 pub const screen_width = 256;
 pub const screen_height = 192;
 const KiB = 0x400;
@@ -15,18 +19,14 @@ pub const Ppu = struct {
 
     vram: *Vram,
 
+    engines: struct { EngineA, EngineB } = .{ .{}, .{} },
+
     io: Io = .{},
 
     const Io = struct {
-        const nds9 = @import("nds9/io.zig");
+        const types = @import("nds9/io.zig");
 
-        /// Read / Write
+        powcnt: types.PowCnt = .{ .raw = 0x0000_0000 },
-        dispcnt_a: nds9.DispcntA = .{ .raw = 0x0000_0000 },
-        /// Read / Write
-        dispstat: nds9.Dispstat = .{ .raw = 0x0000 },
-
-        /// Read-Only
-        vcount: nds9.Vcount = .{ .raw = 0x0000 },
     };
 
     pub fn init(allocator: Allocator, vram: *Vram) !@This() {
@@ -41,64 +41,69 @@ pub const Ppu = struct {
     }
 
     pub fn drawScanline(self: *@This(), bus: *System.Bus9) void {
-        const bg_mode = self.io.dispcnt_a.display_mode.read();
+        if (self.io.powcnt.engine2d_a.read())
-        const scanline = self.io.vcount.scanline.read();
+            self.engines[0].drawScanline(bus, &self.fb, &self.io.powcnt);
 
-        switch (bg_mode) {
+        if (self.io.powcnt.engine2d_b.read())
-            0x0 => {},
+            self.engines[1].drawScanline(bus, &self.fb, &self.io.powcnt);
-            0x1 => {},
-            0x2 => {
-                // Draw Top Screen
-                {
-                    const buf = self.fb.top(.back);
-
-                    const ptr: *[screen_width * screen_height]u32 = @ptrCast(@alignCast(buf.ptr));
-                    const scanline_ptr = ptr[screen_width * @as(u32, scanline) ..][0..screen_width];
-
-                    const base_addr: u32 = 0x0680_0000 + (screen_width * @sizeOf(u16)) * @as(u32, scanline);
-
-                    // FIXME: I don't think it's okay to be accessing the ARM9 Bus instead of just working with
-                    // memory directly. However, I do understand that VRAM-A, VRAM-B might change things
-
-                    for (scanline_ptr, 0..) |*rgba, i| {
-                        const addr = base_addr + @as(u32, @intCast(i)) * @sizeOf(u16);
-                        rgba.* = rgba888(bus.dbgRead(u16, addr));
-                    }
-                }
-            },
-            0x3 => {},
-        }
     }
 
     /// HDraw -> HBlank
     pub fn onHdrawEnd(self: *@This(), scheduler: *Scheduler, late: u64) void {
-        const dots_in_hblank = 99;
+        inline for (&self.engines) |*engine| {
-        std.debug.assert(self.io.dispstat.hblank.read() == false);
+            std.debug.assert(engine.dispstat.hblank.read() == false);
-        std.debug.assert(self.io.dispstat.vblank.read() == false);
+            std.debug.assert(engine.dispstat.vblank.read() == false);
 
             // TODO: Signal HBlank IRQ
 
-        self.io.dispstat.hblank.set();
+            engine.dispstat.hblank.set();
+        }
+
+        const dots_in_hblank = 99;
         scheduler.push(.{ .nds9 = .hblank }, dots_in_hblank * cycles_per_dot -| late);
     }
 
+    // VBlank -> HBlank (Still VBlank)
+    pub fn onVblankEnd(self: *@This(), scheduler: *Scheduler, late: u64) void {
+        inline for (&self.engines) |*engine| {
+            std.debug.assert(!engine.dispstat.hblank.read());
+            std.debug.assert(engine.vcount.scanline.read() == 262 or engine.dispstat.vblank.read());
+
+            // TODO: Signal HBlank IRQ
+
+            engine.dispstat.hblank.set();
+        }
+
+        const dots_in_hblank = 99;
+        scheduler.push(.{ .nds9 = .hblank }, dots_in_hblank * cycles_per_dot -| late);
+    }
+
+    /// HBlank -> HDraw / VBlank
     pub fn onHblankEnd(self: *@This(), scheduler: *Scheduler, late: u64) void {
-        const scanline_count = 192 + 71;
+        const scanline_total = 263; // 192 visible, 71 blanking
 
-        const prev_scanline = self.io.vcount.scanline.read();
+        std.debug.assert(self.engines[0].vcount.scanline.read() == self.engines[1].vcount.scanline.read());
-        const scanline = (prev_scanline + 1) % scanline_count;
 
-        self.io.vcount.scanline.write(scanline);
+        inline for (&self.engines) |*engine| {
-        self.io.dispstat.hblank.unset();
+            const prev_scanline = engine.vcount.scanline.read();
+            const scanline = (prev_scanline + 1) % scanline_total;
 
-        const coincidence = scanline == self.io.dispstat.lyc.read();
+            engine.vcount.scanline.write(scanline);
-        self.io.dispstat.coincidence.write(coincidence);
+            engine.dispstat.hblank.unset();
+
+            const coincidence = scanline == engine.dispstat.lyc.read();
+            engine.dispstat.coincidence.write(coincidence);
+        }
+
+        const scanline = self.engines[0].vcount.scanline.read();
 
         // TODO: LYC == LY IRQ
 
         if (scanline < 192) {
-            std.debug.assert(self.io.dispstat.vblank.read() == false);
+            inline for (&self.engines) |*engine| {
-            std.debug.assert(self.io.dispstat.hblank.read() == false);
+                std.debug.assert(engine.dispstat.vblank.read() == false);
+                std.debug.assert(engine.dispstat.hblank.read() == false);
+            }
 
             // Draw Another Scanline
             const dots_in_hdraw = 256;
@@ -108,16 +113,22 @@ pub const Ppu = struct {
         if (scanline == 192) {
             // Transition from Hblank to Vblank
             self.fb.swap();
-            self.io.dispstat.vblank.set();
+
+            inline for (&self.engines) |*engine|
+                engine.dispstat.vblank.set();
 
             // TODO: Signal VBlank IRQ
         }
 
-        if (scanline == 262) self.io.dispstat.vblank.unset();
+        if (scanline == 262) {
-        std.debug.assert(self.io.dispstat.vblank.read() == (scanline != 262));
+            inline for (&self.engines) |*engine| {
+                engine.dispstat.vblank.unset();
+                std.debug.assert(engine.dispstat.vblank.read() == (scanline != 262));
+            }
+        }
 
-        const dots_in_scanline = 256 + 99;
+        const dots_in_vblank = 256;
-        scheduler.push(.{ .nds9 = .hblank }, dots_in_scanline * cycles_per_dot -| late);
+        scheduler.push(.{ .nds9 = .vblank }, dots_in_vblank * cycles_per_dot -| late);
     }
 };
 
@@ -126,15 +137,15 @@ pub const FrameBuffer = struct {
 
     current: u1 = 0,
 
-    ptr: *[len * 4]u8,
+    ptr: *align(@sizeOf(u32)) [len * 4]u8,
 
     const Position = enum { top, bottom };
     const Layer = enum { front, back };
 
     pub fn init(allocator: Allocator) !@This() {
-        const ptr = try allocator.create([len * 4]u8);
+        const buf = try allocator.alignedAlloc(u8, @sizeOf(u32), len * 4);
 
-        return .{ .ptr = ptr };
+        return .{ .ptr = buf[0 .. len * 4] };
     }
 
     pub fn deinit(self: @This(), allocator: Allocator) void {
@@ -162,303 +173,3 @@ pub const FrameBuffer = struct {
         return self.get(.bottom, layer);
     }
 };
-
-inline fn rgba888(bgr555: u16) u32 {
-    const b: u32 = bgr555 >> 10 & 0x1F;
-    const g: u32 = bgr555 >> 5 & 0x1F;
-    const r: u32 = bgr555 & 0x1F;
-
-    // zig fmt: off
-    return (r << 3 | r >> 2) << 24
-        |  (g << 3 | g >> 2) << 16
-        |  (b << 3 | b >> 2) << 8
-        |  0xFF;
-    // zig fmt: on
-}
-
-pub const Vram = struct {
-    const page_size = 16 * KiB; // smallest allocation is 16 KiB
-    const addr_space_size = 0x0100_0000; // 0x0600_0000 -> 0x06FF_FFFF (inclusive)
-    const table_len = addr_space_size / page_size;
-    const buf_len = 656 * KiB;
-
-    const IntFittingRange = std.math.IntFittingRange;
-    const log = std.log.scoped(.vram);
-
-    io: Io = .{},
-
-    _buf: *[buf_len]u8,
-    nds9_table: *const [table_len]?[*]u8,
-    nds7_table: *const [table_len]?[*]u8,
-
-    const Io = struct {
-        const nds9 = @import("nds9/io.zig");
-        const nds7 = @import("nds7/io.zig");
-        pub const Vramstat = @import("nds7/io.zig").Vramstat;
-
-        stat: nds7.Vramstat = .{ .raw = 0x00 },
-
-        /// Write-Only (according to melonDS these are readable lol)
-        cnt_a: nds9.Vramcnt.A = .{ .raw = 0x00 },
-        cnt_b: nds9.Vramcnt.A = .{ .raw = 0x00 },
-        cnt_c: nds9.Vramcnt.C = .{ .raw = 0x00 },
-        cnt_d: nds9.Vramcnt.C = .{ .raw = 0x00 },
-        cnt_e: nds9.Vramcnt.E = .{ .raw = 0x00 },
-        cnt_f: nds9.Vramcnt.C = .{ .raw = 0x00 },
-        cnt_g: nds9.Vramcnt.C = .{ .raw = 0x00 },
-        cnt_h: nds9.Vramcnt.H = .{ .raw = 0x00 },
-        cnt_i: nds9.Vramcnt.H = .{ .raw = 0x00 },
-    };
-
-    pub fn init(self: *@This(), allocator: Allocator) !void {
-        const buf = try allocator.create([buf_len]u8);
-        errdefer allocator.destroy(buf);
-        @memset(buf, 0);
-
-        const tables = try allocator.alloc(?[*]u8, 2 * table_len);
-        @memset(tables, null);
-
-        self.* = .{
-            .nds9_table = tables[0..table_len],
-            .nds7_table = tables[table_len .. 2 * table_len],
-            ._buf = buf,
-        };
-
-        // ROMS like redpanda.nds won't write to VRAMCNT before trying to write to VRAM
-        // therefore we assume some default allocation (in this casee VRAMCNT_A -> VRAMCNT_I are 0x00)
-        self.update();
-    }
-
-    pub fn deinit(self: @This(), allocator: Allocator) void {
-        allocator.destroy(self._buf);
-
-        const ptr: [*]?[*]const u8 = @ptrCast(@constCast(self.nds9_table));
-        allocator.free(ptr[0 .. 2 * table_len]);
-    }
-
-    pub fn stat(self: *const @This()) Io.Vramstat {
-        const vram_c: u8 = @intFromBool(self.io.cnt_c.enable.read() and self.io.cnt_c.mst.read() == 2);
-        const vram_d: u8 = @intFromBool(self.io.cnt_d.enable.read() and self.io.cnt_d.mst.read() == 2);
-
-        return .{ .raw = (vram_d << 1) | vram_c };
-    }
-
-    const Kind = enum {
-        a,
-        b,
-        c,
-        d,
-        e,
-        f,
-        g,
-        h,
-        i,
-
-        /// In Bytes
-        inline fn size(self: @This()) u32 {
-            return switch (self) {
-                .a => 128 * KiB,
-                .b => 128 * KiB,
-                .c => 128 * KiB,
-                .d => 128 * KiB,
-                .e => 64 * KiB,
-                .f => 16 * KiB,
-                .g => 16 * KiB,
-                .h => 32 * KiB,
-                .i => 16 * KiB,
-            };
-        }
-    };
-
-    // TODO: Rename
-    fn range(comptime kind: Kind, mst: u3, offset: u2) u32 {
-        const ofs: u32 = offset;
-        // panic messages are from GBATEK
-
-        return switch (kind) {
-            .a => switch (mst) {
-                0 => 0x0680_0000,
-                1 => 0x0600_0000 + (0x0002_0000 * ofs),
-                2 => 0x0640_0000 + (0x0002_0000 * (ofs & 0b01)),
-                3 => @panic("VRAMCNT_A: Slot OFS(0-3)"),
-                else => std.debug.panic("Invalid MST for VRAMCNT_{s}", .{[_]u8{std.ascii.toUpper(@tagName(kind)[0])}}),
-            },
-            .b => switch (mst) {
-                0 => 0x0682_0000,
-                1 => 0x0600_0000 + (0x0002_0000 * ofs),
-                2 => 0x0640_0000 + (0x0002_0000 * (ofs & 0b01)),
-                3 => @panic("VRAMCNT_B: Slot OFS(0-3)"),
-                else => std.debug.panic("Invalid MST for VRAMCNT_{s}", .{[_]u8{std.ascii.toUpper(@tagName(kind)[0])}}),
-            },
-            .c => switch (mst) {
-                0 => 0x0684_0000,
-                1 => 0x0600_0000 + (0x0002_0000 * ofs),
-                2 => 0x0600_0000 + (0x0002_0000 * (ofs & 0b01)),
-                3 => @panic("VRAMCNT_C: Slot OFS(0-3)"),
-                4 => 0x0620_0000,
-                else => std.debug.panic("Invalid MST for VRAMCNT_{s}", .{[_]u8{std.ascii.toUpper(@tagName(kind)[0])}}),
-            },
-            .d => switch (mst) {
-                0 => 0x0686_0000,
-                1 => 0x0600_0000 + (0x0002_0000 * ofs),
-                2 => 0x0600_0000 + (0x0002_0000 * (ofs & 0b01)),
-                3 => @panic("VRAMCNT_D: Slot OFS(0-3)"),
-                4 => 0x0660_0000,
-                else => std.debug.panic("Invalid MST for VRAMCNT_{s}", .{[_]u8{std.ascii.toUpper(@tagName(kind)[0])}}),
-            },
-            .e => switch (mst) {
-                0 => 0x0688_0000,
-                1 => 0x0600_0000,
-                2 => 0x0640_0000,
-                3 => @panic("VRAMCNT_E: Slots 0-3"),
-                else => std.debug.panic("Invalid MST for VRAMCNT_{s}", .{[_]u8{std.ascii.toUpper(@tagName(kind)[0])}}),
-            },
-            .f => switch (mst) {
-                0 => 0x0689_0000,
-                1 => 0x0600_0000 + (0x0000_4000 * (ofs & 0b01)) + (0x0001_0000 * (ofs >> 1)),
-                2 => 0x0640_0000 + (0x0000_4000 * (ofs & 0b01)) + (0x0001_0000 * (ofs >> 1)),
-                3 => @panic("VRAMCNT_F: Slot (OFS.0*1)+(OFS.1*4)"),
-                4 => @panic("VRAMCNT_F: Slot 0-1 (OFS=0), Slot 2-3 (OFS=1)"),
-                5 => @panic("VRAMCNT_F: Slot 0"),
-                else => std.debug.panic("Invalid MST for VRAMCNT_{s}", .{[_]u8{std.ascii.toUpper(@tagName(kind)[0])}}),
-            },
-            .g => switch (mst) {
-                0 => 0x0689_4000,
-                1 => 0x0600_0000 + (0x0000_4000 * (ofs & 0b01)) + (0x0001_0000 * (ofs >> 1)),
-                2 => 0x0640_0000 + (0x0000_4000 * (ofs & 0b01)) + (0x0001_0000 * (ofs >> 1)),
-                3 => @panic("VRAMCNT_G: Slot (OFS.0*1)+(OFS.1*4)"),
-                4 => @panic("VRAMCNT_G: Slot 0-1 (OFS=0), Slot 2-3 (OFS=1)"),
-                5 => @panic("VRAMCNT_G: Slot 0"),
-                else => std.debug.panic("Invalid MST for VRAMCNT_{s}", .{[_]u8{std.ascii.toUpper(@tagName(kind)[0])}}),
-            },
-            .h => switch (mst) {
-                0 => 0x0689_8000,
-                1 => 0x0620_0000,
-                2 => @panic("VRAMCNT_H: Slot 0-3"),
-                else => std.debug.panic("Invalid MST for VRAMCNT_{s}", .{[_]u8{std.ascii.toUpper(@tagName(kind)[0])}}),
-            },
-            .i => switch (mst) {
-                0 => 0x068A_0000,
-                1 => 0x0620_8000,
-                2 => 0x0660_0000,
-                3 => @panic("Slot 0"),
-                else => std.debug.panic("Invalid MST for VRAMCNT_{s}", .{[_]u8{std.ascii.toUpper(@tagName(kind)[0])}}),
-            },
-        };
-    }
-
-    fn buf_offset(comptime kind: Kind) usize {
-        // zig fmt: off
-        return switch (kind) {
-            .a => 0,                                                            // 0x00000
-            .b => (128 * KiB) * 1,                                              // 0x20000 (+ 0x20000)
-            .c => (128 * KiB) * 2,                                              // 0x40000 (+ 0x20000)
-            .d => (128 * KiB) * 3,                                              // 0x60000 (+ 0x20000)
-            .e => (128 * KiB) * 4,                                              // 0x80000 (+ 0x20000)
-            .f => (128 * KiB) * 4 + (64 * KiB),                                 // 0x90000 (+ 0x10000)
-            .g => (128 * KiB) * 4 + (64 * KiB) + (16 * KiB) * 1,                // 0x94000 (+ 0x04000)
-            .h => (128 * KiB) * 4 + (64 * KiB) + (16 * KiB) * 2,                // 0x98000 (+ 0x04000)
-            .i => (128 * KiB) * 4 + (64 * KiB) + (16 * KiB) * 2 + (32 * KiB)    // 0xA0000 (+ 0x08000)
-        };
-        // zig fmt: on
-    }
-
-    fn CntType(comptime kind: Kind) type {
-        const io = @import("nds9/io.zig");
-
-        return switch (kind) {
-            .a => io.Vramcnt.A,
-            .b => io.Vramcnt.A,
-            .c => io.Vramcnt.C,
-            .d => io.Vramcnt.C,
-            .e => io.Vramcnt.E,
-            .f => io.Vramcnt.C,
-            .g => io.Vramcnt.C,
-            .h => io.Vramcnt.H,
-            .i => io.Vramcnt.H,
-        };
-    }
-
-    fn cntValue(self: *const @This(), comptime kind: Kind) CntType(kind) {
-        return switch (kind) {
-            .a => self.io.cnt_a,
-            .b => self.io.cnt_b,
-            .c => self.io.cnt_c,
-            .d => self.io.cnt_d,
-            .e => self.io.cnt_e,
-            .f => self.io.cnt_f,
-            .g => self.io.cnt_g,
-            .h => self.io.cnt_h,
-            .i => self.io.cnt_i,
-        };
-    }
-
-    // TODO: We always update the entirety of VRAM when that argubably isn't necessary
-    pub fn update(self: *@This()) void {
-        const nds9_tbl = @constCast(self.nds9_table);
-        const nds7_tbl = @constCast(self.nds7_table);
-
-        for (nds9_tbl, nds7_tbl, 0..) |*nds9_ptr, *nds7_ptr, i| {
-            const addr = 0x0600_0000 + (i * page_size);
-
-            inline for (std.meta.fields(Kind)) |f| {
-                const kind = @field(Kind, f.name);
-                const cnt = cntValue(self, kind);
-                const ofs = switch (kind) {
-                    .e, .h, .i => 0,
-                    else => cnt.offset.read(),
-                };
-
-                const min = range(kind, cnt.mst.read(), ofs);
-                const max = min + kind.size();
-                const offset = addr & (kind.size() - 1);
-
-                if (min <= addr and addr < max) {
-                    if ((kind == .c or kind == .d) and cnt.mst.read() == 2) {
-                        // Allocate to ARM7
-                        nds7_ptr.* = self._buf[buf_offset(kind) + offset ..].ptr;
-                    } else {
-                        nds9_ptr.* = self._buf[buf_offset(kind) + offset ..].ptr;
-                    }
-                }
-            }
-        }
-    }
-
-    // TODO: Rename
-    const Device = enum { nds9, nds7 };
-
-    pub fn read(self: @This(), comptime T: type, comptime dev: Device, address: u32) T {
-        const bits = @typeInfo(IntFittingRange(0, page_size - 1)).Int.bits;
-        const masked_addr = address & (addr_space_size - 1);
-        const page = masked_addr >> bits;
-        const offset = masked_addr & (page_size - 1);
-        const table = if (dev == .nds9) self.nds9_table else self.nds7_table;
-
-        if (table[page]) |some_ptr| {
-            const ptr: [*]const T = @ptrCast(@alignCast(some_ptr));
-
-            return ptr[offset / @sizeOf(T)];
-        }
-
-        log.err("{s}: read(T: {}, addr: 0x{X:0>8}) was in un-mapped VRAM space", .{ @tagName(dev), T, address });
-        return 0x00;
-    }
-
-    pub fn write(self: *@This(), comptime T: type, comptime dev: Device, address: u32, value: T) void {
-        const bits = @typeInfo(IntFittingRange(0, page_size - 1)).Int.bits;
-        const masked_addr = address & (addr_space_size - 1);
-        const page = masked_addr >> bits;
-        const offset = masked_addr & (page_size - 1);
-        const table = if (dev == .nds9) self.nds9_table else self.nds7_table;
-
-        if (table[page]) |some_ptr| {
-            const ptr: [*]T = @ptrCast(@alignCast(some_ptr));
-            ptr[offset / @sizeOf(T)] = value;
-
-            return;
-        }
-
-        log.err("{s}: write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8}) was in un-mapped VRA< space", .{ @tagName(dev), T, address, value });
-    }
-};

src/core/ppu/Vram.zig

@@ -0,0 +1,291 @@
+const std = @import("std");
+const KiB = 0x400;
+
+const Allocator = std.mem.Allocator;
+const IntFittingRange = std.math.IntFittingRange;
+
+const page_size = 16 * KiB; // smallest allocation is 16 KiB
+const addr_space_size = 0x0100_0000; // 0x0600_0000 -> 0x06FF_FFFF (inclusive)
+const table_len = addr_space_size / page_size;
+const buf_len = 656 * KiB;
+
+const log = std.log.scoped(.vram);
+
+io: Io = .{},
+
+_buf: *[buf_len]u8,
+nds9_table: *const [table_len]?[*]u8,
+nds7_table: *const [table_len]?[*]u8,
+
+const Io = struct {
+    pub const Vramstat = nds7.Vramstat;
+
+    const nds9 = @import("../nds9/io.zig");
+    const nds7 = @import("../nds7/io.zig");
+
+    stat: nds7.Vramstat = .{ .raw = 0x00 },
+
+    /// Write-Only (according to melonDS these are readable lol)
+    cnt_a: nds9.Vramcnt.A = .{ .raw = 0x00 },
+    cnt_b: nds9.Vramcnt.A = .{ .raw = 0x00 },
+    cnt_c: nds9.Vramcnt.C = .{ .raw = 0x00 },
+    cnt_d: nds9.Vramcnt.C = .{ .raw = 0x00 },
+    cnt_e: nds9.Vramcnt.E = .{ .raw = 0x00 },
+    cnt_f: nds9.Vramcnt.C = .{ .raw = 0x00 },
+    cnt_g: nds9.Vramcnt.C = .{ .raw = 0x00 },
+    cnt_h: nds9.Vramcnt.H = .{ .raw = 0x00 },
+    cnt_i: nds9.Vramcnt.H = .{ .raw = 0x00 },
+};
+
+pub fn init(self: *@This(), allocator: Allocator) !void {
+    const buf = try allocator.create([buf_len]u8);
+    errdefer allocator.destroy(buf);
+    @memset(buf, 0);
+
+    const tables = try allocator.alloc(?[*]u8, 2 * table_len);
+    @memset(tables, null);
+
+    self.* = .{
+        .nds9_table = tables[0..table_len],
+        .nds7_table = tables[table_len .. 2 * table_len],
+        ._buf = buf,
+    };
+
+    // ROMS like redpanda.nds won't write to VRAMCNT before trying to write to VRAM
+    // therefore we assume some default allocation (in this casee VRAMCNT_A -> VRAMCNT_I are 0x00)
+    self.update();
+}
+
+pub fn deinit(self: @This(), allocator: Allocator) void {
+    allocator.destroy(self._buf);
+
+    const ptr: [*]?[*]const u8 = @ptrCast(@constCast(self.nds9_table));
+    allocator.free(ptr[0 .. 2 * table_len]);
+}
+
+/// NDS7 VRAMSTAT
+pub fn stat(self: *const @This()) Io.Vramstat {
+    const vram_c: u8 = @intFromBool(self.io.cnt_c.enable.read() and self.io.cnt_c.mst.read() == 2);
+    const vram_d: u8 = @intFromBool(self.io.cnt_d.enable.read() and self.io.cnt_d.mst.read() == 2);
+
+    return .{ .raw = (vram_d << 1) | vram_c };
+}
+
+const Kind = enum {
+    a,
+    b,
+    c,
+    d,
+    e,
+    f,
+    g,
+    h,
+    i,
+
+    /// In Bytes
+    inline fn size(self: @This()) u32 {
+        return switch (self) {
+            .a => 128 * KiB,
+            .b => 128 * KiB,
+            .c => 128 * KiB,
+            .d => 128 * KiB,
+            .e => 64 * KiB,
+            .f => 16 * KiB,
+            .g => 16 * KiB,
+            .h => 32 * KiB,
+            .i => 16 * KiB,
+        };
+    }
+};
+
+// TODO: Rename
+fn range(comptime kind: Kind, mst: u3, offset: u2) u32 {
+    const ofs: u32 = offset;
+    // panic messages are from GBATEK
+
+    return switch (kind) {
+        .a => switch (mst) {
+            0 => 0x0680_0000,
+            1 => 0x0600_0000 + (0x0002_0000 * ofs),
+            2 => 0x0640_0000 + (0x0002_0000 * (ofs & 0b01)),
+            3 => @panic("VRAMCNT_A: Slot OFS(0-3)"),
+            else => std.debug.panic("Invalid MST for VRAMCNT_{s}", .{[_]u8{std.ascii.toUpper(@tagName(kind)[0])}}),
+        },
+        .b => switch (mst) {
+            0 => 0x0682_0000,
+            1 => 0x0600_0000 + (0x0002_0000 * ofs),
+            2 => 0x0640_0000 + (0x0002_0000 * (ofs & 0b01)),
+            3 => @panic("VRAMCNT_B: Slot OFS(0-3)"),
+            else => std.debug.panic("Invalid MST for VRAMCNT_{s}", .{[_]u8{std.ascii.toUpper(@tagName(kind)[0])}}),
+        },
+        .c => switch (mst) {
+            0 => 0x0684_0000,
+            1 => 0x0600_0000 + (0x0002_0000 * ofs),
+            2 => 0x0600_0000 + (0x0002_0000 * (ofs & 0b01)),
+            3 => @panic("VRAMCNT_C: Slot OFS(0-3)"),
+            4 => 0x0620_0000,
+            else => std.debug.panic("Invalid MST for VRAMCNT_{s}", .{[_]u8{std.ascii.toUpper(@tagName(kind)[0])}}),
+        },
+        .d => switch (mst) {
+            0 => 0x0686_0000,
+            1 => 0x0600_0000 + (0x0002_0000 * ofs),
+            2 => 0x0600_0000 + (0x0002_0000 * (ofs & 0b01)),
+            3 => @panic("VRAMCNT_D: Slot OFS(0-3)"),
+            4 => 0x0660_0000,
+            else => std.debug.panic("Invalid MST for VRAMCNT_{s}", .{[_]u8{std.ascii.toUpper(@tagName(kind)[0])}}),
+        },
+        .e => switch (mst) {
+            0 => 0x0688_0000,
+            1 => 0x0600_0000,
+            2 => 0x0640_0000,
+            3 => @panic("VRAMCNT_E: Slots 0-3"),
+            else => std.debug.panic("Invalid MST for VRAMCNT_{s}", .{[_]u8{std.ascii.toUpper(@tagName(kind)[0])}}),
+        },
+        .f => switch (mst) {
+            0 => 0x0689_0000,
+            1 => 0x0600_0000 + (0x0000_4000 * (ofs & 0b01)) + (0x0001_0000 * (ofs >> 1)),
+            2 => 0x0640_0000 + (0x0000_4000 * (ofs & 0b01)) + (0x0001_0000 * (ofs >> 1)),
+            3 => @panic("VRAMCNT_F: Slot (OFS.0*1)+(OFS.1*4)"),
+            4 => @panic("VRAMCNT_F: Slot 0-1 (OFS=0), Slot 2-3 (OFS=1)"),
+            5 => @panic("VRAMCNT_F: Slot 0"),
+            else => std.debug.panic("Invalid MST for VRAMCNT_{s}", .{[_]u8{std.ascii.toUpper(@tagName(kind)[0])}}),
+        },
+        .g => switch (mst) {
+            0 => 0x0689_4000,
+            1 => 0x0600_0000 + (0x0000_4000 * (ofs & 0b01)) + (0x0001_0000 * (ofs >> 1)),
+            2 => 0x0640_0000 + (0x0000_4000 * (ofs & 0b01)) + (0x0001_0000 * (ofs >> 1)),
+            3 => @panic("VRAMCNT_G: Slot (OFS.0*1)+(OFS.1*4)"),
+            4 => @panic("VRAMCNT_G: Slot 0-1 (OFS=0), Slot 2-3 (OFS=1)"),
+            5 => @panic("VRAMCNT_G: Slot 0"),
+            else => std.debug.panic("Invalid MST for VRAMCNT_{s}", .{[_]u8{std.ascii.toUpper(@tagName(kind)[0])}}),
+        },
+        .h => switch (mst) {
+            0 => 0x0689_8000,
+            1 => 0x0620_0000,
+            2 => @panic("VRAMCNT_H: Slot 0-3"),
+            else => std.debug.panic("Invalid MST for VRAMCNT_{s}", .{[_]u8{std.ascii.toUpper(@tagName(kind)[0])}}),
+        },
+        .i => switch (mst) {
+            0 => 0x068A_0000,
+            1 => 0x0620_8000,
+            2 => 0x0660_0000,
+            3 => @panic("Slot 0"),
+            else => std.debug.panic("Invalid MST for VRAMCNT_{s}", .{[_]u8{std.ascii.toUpper(@tagName(kind)[0])}}),
+        },
+    };
+}
+
+fn buf_offset(comptime kind: Kind) usize {
+    // zig fmt: off
+        return switch (kind) {
+            .a => 0,                                                            // 0x00000
+            .b => (128 * KiB) * 1,                                              // 0x20000 (+ 0x20000)
+            .c => (128 * KiB) * 2,                                              // 0x40000 (+ 0x20000)
+            .d => (128 * KiB) * 3,                                              // 0x60000 (+ 0x20000)
+            .e => (128 * KiB) * 4,                                              // 0x80000 (+ 0x20000)
+            .f => (128 * KiB) * 4 + (64 * KiB),                                 // 0x90000 (+ 0x10000)
+            .g => (128 * KiB) * 4 + (64 * KiB) + (16 * KiB) * 1,                // 0x94000 (+ 0x04000)
+            .h => (128 * KiB) * 4 + (64 * KiB) + (16 * KiB) * 2,                // 0x98000 (+ 0x04000)
+            .i => (128 * KiB) * 4 + (64 * KiB) + (16 * KiB) * 2 + (32 * KiB)    // 0xA0000 (+ 0x08000)
+        };
+        // zig fmt: on
+}
+
+fn CntType(comptime kind: Kind) type {
+    const Vramcnt = @import("../nds9/io.zig").Vramcnt;
+
+    return switch (kind) {
+        .a => Vramcnt.A,
+        .b => Vramcnt.A,
+        .c => Vramcnt.C,
+        .d => Vramcnt.C,
+        .e => Vramcnt.E,
+        .f => Vramcnt.C,
+        .g => Vramcnt.C,
+        .h => Vramcnt.H,
+        .i => Vramcnt.H,
+    };
+}
+
+fn cntValue(self: *const @This(), comptime kind: Kind) CntType(kind) {
+    return switch (kind) {
+        .a => self.io.cnt_a,
+        .b => self.io.cnt_b,
+        .c => self.io.cnt_c,
+        .d => self.io.cnt_d,
+        .e => self.io.cnt_e,
+        .f => self.io.cnt_f,
+        .g => self.io.cnt_g,
+        .h => self.io.cnt_h,
+        .i => self.io.cnt_i,
+    };
+}
+
+// TODO: We always update the entirety of VRAM when that argubably isn't necessary
+pub fn update(self: *@This()) void {
+    const nds9_tbl = @constCast(self.nds9_table);
+    const nds7_tbl = @constCast(self.nds7_table);
+
+    for (nds9_tbl, nds7_tbl, 0..) |*nds9_ptr, *nds7_ptr, i| {
+        const addr = 0x0600_0000 + (i * page_size);
+
+        inline for (std.meta.fields(Kind)) |f| {
+            const kind = @field(Kind, f.name);
+            const cnt = cntValue(self, kind);
+            const ofs = switch (kind) {
+                .e, .h, .i => 0,
+                else => cnt.offset.read(),
+            };
+
+            const min = range(kind, cnt.mst.read(), ofs);
+            const max = min + kind.size();
+            const offset = addr & (kind.size() - 1);
+
+            if (min <= addr and addr < max) {
+                if ((kind == .c or kind == .d) and cnt.mst.read() == 2) {
+                    // Allocate to ARM7
+                    nds7_ptr.* = self._buf[buf_offset(kind) + offset ..].ptr;
+                } else {
+                    nds9_ptr.* = self._buf[buf_offset(kind) + offset ..].ptr;
+                }
+            }
+        }
+    }
+}
+
+// TODO: Rename
+const Device = enum { nds9, nds7 };
+
+pub fn read(self: @This(), comptime T: type, comptime dev: Device, address: u32) T {
+    const bits = @typeInfo(IntFittingRange(0, page_size - 1)).Int.bits;
+    const masked_addr = address & (addr_space_size - 1);
+    const page = masked_addr >> bits;
+    const offset = masked_addr & (page_size - 1);
+    const table = if (dev == .nds9) self.nds9_table else self.nds7_table;
+
+    if (table[page]) |some_ptr| {
+        const ptr: [*]const T = @ptrCast(@alignCast(some_ptr));
+
+        return ptr[offset / @sizeOf(T)];
+    }
+
+    log.err("{s}: read(T: {}, addr: 0x{X:0>8}) was in un-mapped VRAM space", .{ @tagName(dev), T, address });
+    return 0x00;
+}
+
+pub fn write(self: *@This(), comptime T: type, comptime dev: Device, address: u32, value: T) void {
+    const bits = @typeInfo(IntFittingRange(0, page_size - 1)).Int.bits;
+    const masked_addr = address & (addr_space_size - 1);
+    const page = masked_addr >> bits;
+    const offset = masked_addr & (page_size - 1);
+    const table = if (dev == .nds9) self.nds9_table else self.nds7_table;
+
+    if (table[page]) |some_ptr| {
+        const ptr: [*]T = @ptrCast(@alignCast(some_ptr));
+        ptr[offset / @sizeOf(T)] = value;
+
+        return;
+    }
+
+    log.err("{s}: write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8}) was in un-mapped VRA< space", .{ @tagName(dev), T, address, value });
+}

src/core/ppu/engine.zig

@@ -0,0 +1,91 @@
+const std = @import("std");
+const Bus = @import("../nds9/Bus.zig");
+
+const FrameBuffer = @import("../ppu.zig").FrameBuffer;
+
+const DispcntA = @import("../nds9/io.zig").DispcntA;
+const DispcntB = @import("../nds9/io.zig").DispcntB;
+
+const Dispstat = @import("../nds9/io.zig").Dispstat;
+const Vcount = @import("../nds9/io.zig").Vcount;
+
+const PowCnt = @import("../nds9/io.zig").PowCnt;
+
+const width = @import("../ppu.zig").screen_width;
+const height = @import("../ppu.zig").screen_height;
+
+const EngineKind = enum { a, b };
+
+pub const EngineA = Engine(.a);
+pub const EngineB = Engine(.b);
+
+fn Engine(comptime kind: EngineKind) type {
+    const log = std.log.scoped(.engine2d);
+    _ = log; // TODO: specify between 2D-A and 2D-B
+
+    // FIXME: don't commit zig crimes
+    const Type = struct {
+        fn inner(comptime TypeA: type, comptime TypeB: type) type {
+            return if (kind == .a) TypeA else TypeB;
+        }
+    }.inner;
+
+    return struct {
+        dispcnt: Type(DispcntA, DispcntB) = .{ .raw = 0x0000_0000 },
+        dispstat: Dispstat = .{ .raw = 0x0000_0000 },
+        vcount: Vcount = .{ .raw = 0x0000_0000 },
+
+        pub fn drawScanline(self: *@This(), bus: *Bus, fb: *FrameBuffer, powcnt: *PowCnt) void {
+            const disp_mode = self.dispcnt.display_mode.read();
+
+            switch (disp_mode) {
+                0 => { // Display Off
+                    const buf = switch (kind) {
+                        .a => if (powcnt.display_swap.read()) fb.top(.back) else fb.btm(.back),
+                        .b => if (powcnt.display_swap.read()) fb.btm(.back) else fb.top(.back),
+                    };
+
+                    @memset(buf, 0xFF); // set everything to white
+                },
+                1 => @panic("TODO: standard graphics display (text mode, etc)"),
+                2 => { // VRAM display
+                    if (kind == .b) return;
+                    // TODO: Master Brightness can still affect this mode
+
+                    const scanline: u32 = self.vcount.scanline.read();
+                    const buf = if (powcnt.display_swap.read()) fb.top(.back) else fb.btm(.back);
+
+                    const scanline_buf = blk: {
+                        const rgba_ptr: *[width * height]u32 = @ptrCast(@alignCast(buf));
+                        break :blk rgba_ptr[width * scanline ..][0..width];
+                    };
+
+                    const base_addr: u32 = 0x0680_0000 + (width * @sizeOf(u16)) * @as(u32, scanline);
+
+                    for (scanline_buf, 0..) |*rgba, i| {
+                        const addr = base_addr + @as(u32, @intCast(i)) * @sizeOf(u16);
+                        rgba.* = rgba888(bus.dbgRead(u16, addr));
+                    }
+                },
+                3 => {
+                    if (kind == .b) return;
+
+                    @panic("TODO: main memory display");
+                },
+            }
+        }
+    };
+}
+
+inline fn rgba888(bgr555: u16) u32 {
+    const b: u32 = bgr555 >> 10 & 0x1F;
+    const g: u32 = bgr555 >> 5 & 0x1F;
+    const r: u32 = bgr555 & 0x1F;
+
+    // zig fmt: off
+    return (r << 3 | r >> 2) << 24
+        |  (g << 3 | g >> 2) << 16
+        |  (b << 3 | b >> 2) << 8
+        |  0xFF;
+    // zig fmt: on
+}