fix: create and draw ui even when running in gdb mode

TODO: deduplicate please

.gitignore

@@ -3,3 +3,6 @@ zig-out/
 bin/
 doc/
 imgui.ini
+.build_config/
+
+**/*.log

.gitmodules

@@ -4,6 +4,3 @@
 [submodule "lib/zgui"]
 	path = lib/zgui
 	url = https://git.musuka.dev/paoda/zgui
-[submodule "lib/arm32"]
-	path = lib/arm32
-	url = https://git.musuka.dev/paoda/arm32.git

build.zig

@@ -1,8 +1,7 @@
 const std = @import("std");
 
-const Sdk = @import("lib/SDL.zig/Sdk.zig");
+const Sdk = @import("lib/SDL.zig/build.zig");
 const zgui = @import("lib/zgui/build.zig");
-const arm32 = @import("lib/arm32/build.zig");
 
 // Although this function looks imperative, note that its job is to
 // declaratively construct a build graph that will be executed by an external
@@ -28,21 +27,23 @@ pub fn build(b: *std.Build) void {
         .optimize = optimize,
     });
 
-    exe.addModule("arm32", arm32.module(b));
+    exe.root_module.addImport("arm32", b.dependency("arm32", .{}).module("arm32"));
-    exe.addModule("zig-clap", b.dependency("zig-clap", .{}).module("clap"));
+    exe.root_module.addImport("gdbstub", b.dependency("zba-gdbstub", .{}).module("gdbstub"));
+    exe.root_module.addImport("zig-clap", b.dependency("zig-clap", .{}).module("clap"));
 
-    exe.addAnonymousModule("bitfield", .{ .source_file = .{ .path = "lib/bitfield.zig" } }); // https://github.com/FlorenceOS/
+    exe.root_module.addAnonymousImport("bitfield", .{ .root_source_file = .{ .path = "lib/bitfield.zig" } }); // https://github.com/FlorenceOS/
-    exe.addAnonymousModule("gl", .{ .source_file = .{ .path = "lib/gl.zig" } }); // https://github.com/MasterQ32/zig-opengl
+    exe.root_module.addAnonymousImport("gl", .{ .root_source_file = .{ .path = "lib/gl.zig" } }); // https://github.com/MasterQ32/zig-opengl
 
     // https://github.com/MasterQ32/SDL.zig
     const sdk = Sdk.init(b, null);
-    sdk.link(exe, .dynamic);
+    sdk.link(exe, .static);
-    exe.addModule("sdl2", sdk.getNativeModule());
+    exe.root_module.addImport("sdl2", sdk.getNativeModule());
 
     // https://git.musuka.dev/paoda/zgui
-    // .shared option should stay in sync with SDL.zig call above where true == .dynamic, and false == .static
+
-    const zgui_pkg = zgui.package(b, target, optimize, .{ .options = .{ .backend = .sdl2_opengl3, .shared = true } });
+    const zgui_pkg = zgui.package(b, target, optimize, .{ .options = .{ .backend = .sdl2_opengl3 } });
     zgui_pkg.link(exe);
+    sdk.link(zgui_pkg.zgui_c_cpp, .static);
 
     // This declares intent for the executable to be installed into the
     // standard location when the user invokes the "install" step (the default

build.zig.zon

@@ -1,15 +1,25 @@
 .{
     .name = "turbo",
     .version = "0.1.0",
+    .paths = .{
+        "lib/bitfield.zig",
+        "lib/gl.zig",
+        "src",
+        "build.zig",
+        "build.zig.zon",
+    },
     .dependencies = .{
         .@"zig-clap" = .{
-            .url = "https://github.com/Hejsil/zig-clap/archive/f49b94700e0761b7514abdca0e4f0e7f3f938a93.tar.gz",
+            .url = "https://github.com/Hejsil/zig-clap/archive/4267b0b60ef6f87cccf3ee6ed481e6d0759180c6.tar.gz",
-            .hash = "1220f48518ce22882e102255ed3bcdb7aeeb4891f50b2cdd3bd74b5b2e24d3149ba2",
+            .hash = "12202fa30d679d821292bcd953458b9e76097a5d16999489125a206db63a53392833",
         },
-        .@"zba-util" = .{
+        .@"zba-gdbstub" = .{
-            // Necessary to use paoda/arm32 as a git submodule
+            .url = "https://git.musuka.dev/paoda/zba-gdbstub/archive/7ae72ed5a892d2fc6cc3f5511e2b96134d928b59.tar.gz",
-            .url = "https://git.musuka.dev/paoda/zba-util/archive/322c798e384a0d24cc84ffcfa2e4a3ca807798a0.tar.gz",
+            .hash = "1220823e961f369e22b62edc1b4da3742af0a7cb420ae9a52ec33216ff5a8ef270c8",
-            .hash = "12209ce0e729460b997706e47a53a32f1842672cd120189e612f4871731780a30ed0",
+        },
+        .arm32 = .{
+            .url = "https://git.musuka.dev/paoda/arm32/archive/6f0e27136072610e6dba97ff8aaf5e2ec86e2c09.tar.gz",
+            .hash = "122047d0affe12b9e9e9c655a7ba6d51b311f02d688e9f1c9a91394a03103f1c0cd5",
         },
     },
 }

dl_sdl2.ps1

@@ -0,0 +1,32 @@
+$SDL2Version = "2.30.0"
+$ArchiveFile = ".\SDL2-devel-mingw.zip"
+$Json = @"
+{
+	"x86_64-windows-gnu": {
+		"include": "SDL2\\include",
+		"libs": "SDL2\\lib",
+		"bin": "SDL2\\bin"
+	}
+}	
+"@
+
+New-Item -Force -ItemType Directory -Path .\.build_config
+Set-Location -Path .build_config -PassThru
+
+if (!(Test-Path -PathType Leaf $ArchiveFile)) {
+	Invoke-WebRequest "https://github.com/libsdl-org/SDL/releases/download/release-$SDL2Version/SDL2-devel-$SDL2Version-mingw.zip" -OutFile $ArchiveFile
+}
+
+Expand-Archive $ArchiveFile
+
+if (Test-Path -PathType Leaf .\SDL2) {
+	Remove-Item -Recurse .\SDL2
+}
+
+New-Item -Force -ItemType Directory -Path .\SDL2 
+Get-ChildItem -Path ".\SDL2-devel-mingw\SDL2-$SDL2Version\x86_64-w64-mingw32" | Move-Item -Destination .\SDL2
+
+New-Item -Force .\sdl.json -Value $Json
+
+Remove-Item -Recurse .\SDL2-devel-mingw
+Set-Location -Path .. -PassThru

src/core/emu.zig

@@ -2,9 +2,13 @@ const std = @import("std");
 
 const Header = @import("cartridge.zig").Header;
 const Scheduler = @import("Scheduler.zig");
+const Ui = @import("../platform.zig").Ui;
 
 const Allocator = std.mem.Allocator;
 
+const dma7 = @import("nds7/dma.zig");
+const dma9 = @import("nds9/dma.zig");
+
 /// Load a NDS Cartridge
 ///
 /// intended to be used immediately after Emulator initialization
@@ -110,27 +114,19 @@ pub fn runFrame(scheduler: *Scheduler, system: System) void {
         switch (isHalted(system)) {
             .both => scheduler.tick = scheduler.peekTimestamp(),
             inline else => |halt| {
-                if (comptime halt != .arm9) {
+                if (!dma9.step(system.arm946es) and comptime halt != .arm9) {
                     system.arm946es.step();
                     system.arm946es.step();
                 }
 
-                if (comptime halt != .arm7)
+                if (!dma7.step(system.arm7tdmi) and comptime halt != .arm7) {
                     system.arm7tdmi.step();
+                }
             },
         }
 
         if (scheduler.check()) |ev| {
             const late = scheduler.tick - ev.tick;
-
-            // this is kinda really jank lol
-            const bus_ptr: ?*anyopaque = switch (ev.kind) {
-                .heat_death => null,
-                .nds7 => system.bus7,
-                .nds9 => system.bus9,
-            };
-            _ = bus_ptr;
-
             scheduler.handle(system, ev, late);
         }
     }
@@ -270,15 +266,12 @@ pub const Wram = struct {
         }
     }
 
-    // TODO: Rename
+    pub fn read(self: @This(), comptime T: type, comptime proc: System.Process, address: u32) T {
-    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;
+        const table = if (proc == .nds9) self.nds9_table else self.nds7_table;
 
         if (table[page]) |some_ptr| {
             const ptr: [*]const T = @ptrCast(@alignCast(some_ptr));
@@ -286,16 +279,16 @@ pub const Wram = struct {
             return ptr[offset / @sizeOf(T)];
         }
 
-        log.err("{s}: read(T: {}, addr: 0x{X:0>8}) was in un-mapped WRAM space", .{ @tagName(dev), T, 0x0300_0000 + address });
+        log.err("{s}: read(T: {}, addr: 0x{X:0>8}) was in un-mapped WRAM space", .{ @tagName(proc), T, 0x0300_0000 + address });
         return 0x00;
     }
 
-    pub fn write(self: *@This(), comptime T: type, comptime dev: Device, address: u32, value: T) void {
+    pub fn write(self: *@This(), comptime T: type, comptime proc: System.Process, 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;
+        const table = if (proc == .nds9) self.nds9_table else self.nds7_table;
 
         if (table[page]) |some_ptr| {
             const ptr: [*]T = @ptrCast(@alignCast(some_ptr));
@@ -304,7 +297,7 @@ pub const Wram = struct {
             return;
         }
 
-        log.err("{s}: write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8}) was in un-mapped WRAM space", .{ @tagName(dev), T, 0x0300_0000 + address, value });
+        log.err("{s}: write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8}) was in un-mapped WRAM space", .{ @tagName(proc), T, 0x0300_0000 + address, value });
     }
 };
 
@@ -320,6 +313,8 @@ pub const System = struct {
     pub const Arm7tdmi = @import("arm32").Arm7tdmi;
     pub const Arm946es = @import("arm32").Arm946es;
 
+    pub const Process = enum { nds7, nds9 };
+
     arm7tdmi: *Arm7tdmi,
     arm946es: *Arm946es,
 
@@ -332,17 +327,29 @@ pub const System = struct {
         self.bus7.deinit(allocator);
         self.bus9.deinit(allocator);
     }
+
+    fn Cpu(comptime proc: Process) type {
+        return switch (proc) {
+            .nds7 => Arm7tdmi,
+            .nds9 => Arm946es,
+        };
+    }
+
+    fn Bus(comptime proc: Process) type {
+        return switch (proc) {
+            .nds7 => Bus7,
+            .nds9 => Bus9,
+        };
+    }
 };
 
-// FIXME: Using Wram.Device here is jank. System should probably carry an Enum + some Generic Type Fns
+pub fn handleInterrupt(comptime proc: System.Process, cpu: *System.Cpu(proc)) void {
-pub fn handleInterrupt(comptime dev: Wram.Device, cpu: if (dev == .nds9) *System.Arm946es else *System.Arm7tdmi) void {
+    const bus_ptr: *System.Bus(proc) = @ptrCast(@alignCast(cpu.bus.ptr));
-    const Bus = if (dev == .nds9) System.Bus9 else System.Bus7;
-    const bus_ptr: *Bus = @ptrCast(@alignCast(cpu.bus.ptr));
 
     if (!bus_ptr.io.ime or cpu.cpsr.i.read()) return; // ensure irqs are enabled
     if ((bus_ptr.io.ie.raw & bus_ptr.io.irq.raw) == 0) return; // ensure there is an irq to handle
 
-    switch (dev) {
+    switch (proc) {
         .nds9 => {
             const cp15: *System.Cp15 = @ptrCast(@alignCast(cpu.cp15.ptr));
             cp15.wait_for_interrupt = false;
@@ -359,6 +366,208 @@ pub fn handleInterrupt(comptime dev: Wram.Device, cpu: if (dev == .nds9) *System
 
     cpu.r[14] = ret_addr;
     cpu.spsr.raw = spsr.raw;
-    cpu.r[15] = if (dev == .nds9) 0xFFFF_0018 else 0x0000_0018;
+    cpu.r[15] = if (proc == .nds9) 0xFFFF_0018 else 0x0000_0018;
     cpu.pipe.reload(cpu);
 }
+
+pub fn fastBoot(system: System) void {
+    {
+        const Bank = System.Arm946es.Bank;
+
+        const cpu = system.arm946es;
+
+        // from advanDS
+        cpu.spsr = .{ .raw = 0x0000_000DF };
+
+        @memset(cpu.r[0..12], 0x0000_0000); // r0 -> r11 are zeroed
+        // TODO: r12, r14, and r15 are set to the entrypoint?
+        cpu.r[13] = 0x0300_2F7C; // FIXME: Why is there (!) in GBATEK?
+        cpu.bank.r[Bank.regIdx(.Irq, .R13)] = 0x0300_3F80;
+        cpu.bank.r[Bank.regIdx(.Supervisor, .R13)] = 0x0300_3FC0;
+        cpu.bank.spsr[Bank.spsrIdx(.Irq)] = .{ .raw = 0x0000_0000 };
+        cpu.bank.spsr[Bank.spsrIdx(.Supervisor)] = .{ .raw = 0x0000_0000 };
+    }
+    {
+        const Bank = System.Arm7tdmi.Bank;
+
+        const cpu = system.arm7tdmi;
+
+        // from advanDS
+        cpu.spsr = .{ .raw = 0x0000_000D3 };
+
+        @memset(cpu.r[0..12], 0x0000_0000); // r0 -> r11 are zeroed
+        // TODO: r12, r14, and r15 are set to the entrypoint?
+        cpu.r[13] = 0x0380_FD80;
+        cpu.bank.r[Bank.regIdx(.Irq, .R13)] = 0x0380_FF80;
+        cpu.bank.r[Bank.regIdx(.Supervisor, .R13)] = 0x0380_FFC0;
+        cpu.bank.spsr[Bank.spsrIdx(.Irq)] = .{ .raw = 0x0000_0000 };
+        cpu.bank.spsr[Bank.spsrIdx(.Supervisor)] = .{ .raw = 0x0000_0000 };
+    }
+}
+
+pub const Sync = struct {
+    const Atomic = std.atomic.Value;
+
+    should_quit: Atomic(bool) = Atomic(bool).init(false),
+
+    pub fn init(self: *Sync) void {
+        self.* = .{};
+    }
+};
+
+pub const debug = struct {
+    const Interface = @import("gdbstub").Emulator;
+    const Server = @import("gdbstub").Server;
+    const AtomicBool = std.atomic.Value(bool);
+    const log = std.log.scoped(.gdbstub);
+
+    const nds7 = struct {
+        const target: []const u8 =
+            \\<target version="1.0">
+            \\    <architecture>armv4t</architecture>
+            \\    <feature name="org.gnu.gdb.arm.core">
+            \\        <reg name="r0" bitsize="32" type="uint32"/>
+            \\        <reg name="r1" bitsize="32" type="uint32"/>
+            \\        <reg name="r2" bitsize="32" type="uint32"/>
+            \\        <reg name="r3" bitsize="32" type="uint32"/>
+            \\        <reg name="r4" bitsize="32" type="uint32"/>
+            \\        <reg name="r5" bitsize="32" type="uint32"/>
+            \\        <reg name="r6" bitsize="32" type="uint32"/>
+            \\        <reg name="r7" bitsize="32" type="uint32"/>
+            \\        <reg name="r8" bitsize="32" type="uint32"/>
+            \\        <reg name="r9" bitsize="32" type="uint32"/>
+            \\        <reg name="r10" bitsize="32" type="uint32"/>
+            \\        <reg name="r11" bitsize="32" type="uint32"/>
+            \\        <reg name="r12" bitsize="32" type="uint32"/>
+            \\        <reg name="sp" bitsize="32" type="data_ptr"/>
+            \\        <reg name="lr" bitsize="32"/>
+            \\        <reg name="pc" bitsize="32" type="code_ptr"/>
+            \\
+            \\        <reg name="cpsr" bitsize="32" regnum="25"/>
+            \\    </feature>
+            \\</target>
+        ;
+
+        // Remember that a lot of memory regions are mirrored
+        const memory_map: []const u8 =
+            \\ <memory-map version="1.0">
+            \\     <memory type="rom" start="0x00000000" length="0x00004000"/>
+            \\     <memory type="ram" start="0x02000000" length="0x01000000"/>
+            \\     <memory type="ram" start="0x03000000" length="0x00800000"/>
+            \\     <memory type="ram" start="0x03800000" length="0x00800000"/>
+            \\     <memory type="ram" start="0x04000000" length="0x00100010"/>
+            \\     <memory type="ram" start="0x06000000" length="0x01000000"/>
+            \\     <memory type="rom" start="0x08000000" length="0x02000000"/>
+            \\     <memory type="rom" start="0x0A000000" length="0x01000000"/>
+            \\ </memory-map>
+        ;
+    };
+
+    pub fn Wrapper(comptime proc: System.Process) type {
+        return struct {
+            system: System,
+            scheduler: *Scheduler,
+
+            tick: u64 = 0,
+
+            pub fn init(system: System, scheduler: *Scheduler) @This() {
+                return .{ .system = system, .scheduler = scheduler };
+            }
+
+            pub fn interface(self: *@This(), allocator: Allocator) Interface {
+                return Interface.init(allocator, self);
+            }
+
+            pub fn read(self: *const @This(), addr: u32) u8 {
+                const arm = switch (proc) {
+                    .nds7 => self.system.arm7tdmi,
+                    .nds9 => self.system.arm946es,
+                };
+
+                return arm.dbgRead(u8, addr);
+            }
+
+            pub fn write(self: *@This(), addr: u32, value: u8) void {
+                const arm = switch (proc) {
+                    .nds7 => self.system.arm7tdmi,
+                    .nds9 => self.system.arm946es,
+                };
+
+                return arm.dbgWrite(u8, addr, value);
+            }
+
+            pub fn registers(self: *const @This()) *[16]u32 {
+                const arm = switch (proc) {
+                    .nds7 => self.system.arm7tdmi,
+                    .nds9 => self.system.arm946es,
+                };
+
+                return &arm.r;
+            }
+
+            pub fn cpsr(self: *const @This()) u32 {
+                const arm = switch (proc) {
+                    .nds7 => self.system.arm7tdmi,
+                    .nds9 => self.system.arm946es,
+                };
+
+                return arm.cpsr.raw;
+            }
+
+            pub fn step(self: *@This()) void {
+                const scheduler = self.scheduler;
+                const system = self.system;
+
+                var did_step: bool = false;
+
+                // TODO: keep in lockstep with runFrame
+                while (true) {
+                    if (did_step) break;
+
+                    switch (isHalted(system)) {
+                        .both => scheduler.tick = scheduler.peekTimestamp(),
+                        inline else => |halt| {
+                            if (!dma9.step(system.arm946es) and comptime halt != .arm9) {
+                                system.arm946es.step();
+
+                                switch (proc) {
+                                    .nds9 => did_step = true,
+                                    .nds7 => system.arm946es.step(),
+                                }
+                            }
+
+                            if (!dma7.step(system.arm7tdmi) and comptime halt != .arm7) {
+                                if (proc == .nds7 or self.tick % 2 == 0) system.arm7tdmi.step();
+
+                                if (proc == .nds7) {
+                                    did_step = true;
+                                    self.tick += 1;
+                                }
+                            }
+                        },
+                    }
+
+                    if (scheduler.check()) |ev| {
+                        const late = scheduler.tick - ev.tick;
+                        scheduler.handle(system, ev, late);
+                    }
+                }
+            }
+        };
+    }
+
+    pub fn run(allocator: Allocator, ui: *Ui, scheduler: *Scheduler, system: System, sync: *Sync) !void {
+        var wrapper = Wrapper(.nds9).init(system, scheduler);
+
+        var emu_interface = wrapper.interface(allocator);
+        defer emu_interface.deinit();
+
+        var server = try Server.init(emu_interface, .{ .target = nds7.target, .memory_map = nds7.memory_map });
+        defer server.deinit(allocator);
+
+        const thread = try std.Thread.spawn(.{}, Server.run, .{ &server, allocator, &sync.should_quit });
+        defer thread.join();
+
+        try ui.debug_run(scheduler, system, sync);
+    }
+};

src/core/io.zig

@@ -14,7 +14,7 @@ pub const Io = struct {
     wramcnt: WramCnt = .{ .raw = 0x00 },
 
     // Read Only
-    keyinput: AtomicKeyInput = .{},
+    input: Input = .{},
 };
 
 fn warn(comptime format: []const u8, args: anytype) u0 {
@@ -36,8 +36,6 @@ const Ipc = struct {
 
     // TODO: DS Cartridge I/O Ports
 
-    const Source = enum { nds7, nds9 };
-
     const Impl = struct {
         /// IPC Synchronize
         /// Read/Write
@@ -60,8 +58,8 @@ const Ipc = struct {
 
     /// IPCSYNC
     /// Read/Write
-    pub fn setIpcSync(self: *@This(), comptime src: Source, value: anytype) void {
+    pub fn setIpcSync(self: *@This(), comptime proc: System.Process, value: anytype) void {
-        switch (src) {
+        switch (proc) {
             .nds7 => {
                 self._nds7.sync.raw = masks.ipcFifoSync(self._nds7.sync.raw, value);
                 self._nds9.sync.raw = masks.mask(self._nds9.sync.raw, (self._nds7.sync.raw >> 8) & 0xF, 0xF);
@@ -109,8 +107,8 @@ const Ipc = struct {
 
     /// IPCFIFOCNT
     /// Read/Write
-    pub fn setIpcFifoCnt(self: *@This(), comptime src: Source, value: anytype) void {
+    pub fn setIpcFifoCnt(self: *@This(), comptime proc: System.Process, value: anytype) void {
-        switch (src) {
+        switch (proc) {
             .nds7 => self._nds7.cnt.raw = masks.ipcFifoCnt(self._nds7.cnt.raw, value),
             .nds9 => self._nds9.cnt.raw = masks.ipcFifoCnt(self._nds9.cnt.raw, value),
         }
@@ -118,8 +116,8 @@ const Ipc = struct {
 
     /// IPC Send FIFO
     /// Write-Only
-    pub fn send(self: *@This(), comptime src: Source, value: u32) void {
+    pub fn send(self: *@This(), comptime proc: System.Process, value: u32) void {
-        switch (src) {
+        switch (proc) {
             .nds7 => {
                 if (!self._nds7.cnt.enable_fifos.read()) return;
                 self._nds7.fifo.push(value) catch unreachable; // see early return above
@@ -173,8 +171,8 @@ const Ipc = struct {
 
     /// IPC Receive FIFO
     /// Read-Only
-    pub fn recv(self: *@This(), comptime src: Source) u32 {
+    pub fn recv(self: *@This(), comptime proc: System.Process) u32 {
-        switch (src) {
+        switch (proc) {
             .nds7 => {
                 const enabled = self._nds7.cnt.enable_fifos.read();
                 const val_opt = if (enabled) self._nds9.fifo.pop() else self._nds9.fifo.peek();
@@ -327,6 +325,11 @@ pub const IntEnable = extern union {
     hblank: Bit(u32, 1),
     coincidence: Bit(u32, 2),
 
+    dma0: Bit(u32, 8),
+    dma1: Bit(u32, 9),
+    dma2: Bit(u32, 10),
+    dma3: Bit(u32, 11),
+
     ipcsync: Bit(u32, 16),
     ipc_send_empty: Bit(u32, 17),
     ipc_recv_not_empty: Bit(u32, 18),
@@ -410,24 +413,54 @@ pub const KeyInput = extern union {
     raw: u16,
 };
 
-const AtomicKeyInput = struct {
+pub const ExtKeyIn = extern union {
-    const Self = @This();
+    x: Bit(u16, 0),
-    const Ordering = std.atomic.Ordering;
+    y: Bit(u16, 1),
-
+    debug: Bit(u16, 3),
-    inner: KeyInput = .{ .raw = 0x03FF },
+    stylus: Bit(u16, 6),
-
+    hinge: Bit(u16, 7),
-    pub inline fn load(self: *const Self, comptime ordering: Ordering) u16 {
+    raw: u16,
-        return switch (ordering) {
-            .AcqRel, .Release => @compileError("not supported for atomic loads"),
-            else => @atomicLoad(u16, &self.inner.raw, ordering),
 };
+
+const Input = struct {
+    const AtomicOrder = std.builtin.AtomicOrder;
+    const AtomicRmwOp = std.builtin.AtomicRmwOp;
+
+    inner: u32 = 0x007F_03FF,
+
+    pub inline fn keyinput(self: *const Input) KeyInput {
+        const value = @atomicLoad(u32, &self.inner, .Monotonic);
+        return .{ .raw = @truncate(value) };
     }
 
-    pub inline fn fetchOr(self: *Self, value: u16, comptime ordering: Ordering) void {
+    pub inline fn set_keyinput(self: *Input, comptime op: AtomicRmwOp, input: KeyInput) void {
-        _ = @atomicRmw(u16, &self.inner.raw, .Or, value, ordering);
+        const msked = switch (op) {
+            .And => 0xFFFF_FFFF & @as(u32, input.raw),
+            .Or => 0x0000_0000 | @as(u32, input.raw),
+            else => @compileError("not supported"),
+        };
+
+        _ = @atomicRmw(u32, &self.inner, op, msked, .Monotonic);
     }
 
-    pub inline fn fetchAnd(self: *Self, value: u16, comptime ordering: Ordering) void {
+    pub inline fn extkeyin(self: *const Input) ExtKeyIn {
-        _ = @atomicRmw(u16, &self.inner.raw, .And, value, ordering);
+        const value = @atomicLoad(u32, &self.inner, .Monotonic);
+        const shifted: u16 = @truncate(value >> 16);
+
+        return .{ .raw = shifted | 0b00110100 }; // bits 2, 4, 5 are always set
+    }
+
+    pub inline fn set_extkeyin(self: *Input, comptime op: AtomicRmwOp, input: ExtKeyIn) void {
+        const msked = switch (op) {
+            .And => 0xFFFF_FFFF & (@as(u32, ~input.raw) << 16),
+            .Or => 0x0000_0000 | (@as(u32, input.raw) << 16),
+            else => @compileError("not supported"),
+        };
+
+        _ = @atomicRmw(u32, &self.inner, op, msked, .Monotonic);
+    }
+
+    pub inline fn set(self: *Input, comptime op: AtomicRmwOp, value: u32) void {
+        _ = @atomicRmw(u32, &self.inner, op, value, .Monotonic);
     }
 };

src/core/nds7/Bios.zig

@@ -29,7 +29,6 @@ pub fn deinit(self: @This(), allocator: Allocator) void {
 
 // Note: Parts of 16MiB addrspace that aren't mapped to BIOS are typically undefined
 pub fn read(self: *const @This(), comptime T: type, address: u32) T {
-    const readInt = std.mem.readIntLittle;
     const byte_count = @divExact(@typeInfo(T).Int.bits, 8);
 
     // if (address >= len) return 0x0000_0000; // TODO: What is undefined actually?
@@ -39,7 +38,7 @@ pub fn read(self: *const @This(), comptime T: type, address: u32) T {
         @panic("TODO: ability to load in NDS7 BIOS just-in-time");
     };
 
-    return readInt(T, ptr[address & (len - 1) ..][0..byte_count]);
+    return std.mem.readInt(T, ptr[address & (len - 1) ..][0..byte_count], .little);
 }
 
 pub fn write(_: *const @This(), comptime T: type, address: u32, value: T) void {

src/core/nds7/Bus.zig

@@ -8,6 +8,8 @@ const Vram = @import("../ppu/Vram.zig");
 const Bios = @import("Bios.zig");
 const forceAlign = @import("../emu.zig").forceAlign;
 
+const Controllers = @import("dma.zig").Controllers;
+
 const Allocator = std.mem.Allocator;
 
 const Mode = enum { normal, debug };
@@ -22,6 +24,8 @@ shr_wram: *Wram,
 wram: *[64 * KiB]u8,
 vram: *Vram,
 
+dma: Controllers = .{},
+
 io: io.Io,
 bios: Bios,
 
@@ -58,8 +62,6 @@ pub fn dbgRead(self: *@This(), comptime T: type, address: u32) T {
 
 fn _read(self: *@This(), comptime T: type, comptime mode: Mode, address: u32) T {
     const byte_count = @divExact(@typeInfo(T).Int.bits, 8);
-    const readInt = std.mem.readIntLittle;
-
     const aligned_addr = forceAlign(T, address);
 
     switch (mode) {
@@ -69,13 +71,13 @@ fn _read(self: *@This(), comptime T: type, comptime mode: Mode, address: u32) T
     }
 
     return switch (aligned_addr) {
-        0x0000_0000...0x01FF_FFFF => self.bios.read(T, address),
+        0x0000_0000...0x01FF_FFFF => self.bios.read(T, aligned_addr),
-        0x0200_0000...0x02FF_FFFF => readInt(T, self.main[aligned_addr & 0x003F_FFFF ..][0..byte_count]),
+        0x0200_0000...0x02FF_FFFF => std.mem.readInt(T, self.main[aligned_addr & 0x003F_FFFF ..][0..byte_count], .little),
         0x0300_0000...0x037F_FFFF => switch (self.io.shr.wramcnt.mode.read()) {
-            0b00 => readInt(T, self.wram[aligned_addr & 0x0000_FFFF ..][0..byte_count]),
+            0b00 => std.mem.readInt(T, self.wram[aligned_addr & 0x0000_FFFF ..][0..byte_count], .little),
             else => self.shr_wram.read(T, .nds7, aligned_addr),
         },
-        0x0380_0000...0x03FF_FFFF => readInt(T, self.wram[aligned_addr & 0x0000_FFFF ..][0..byte_count]),
+        0x0380_0000...0x03FF_FFFF => std.mem.readInt(T, self.wram[aligned_addr & 0x0000_FFFF ..][0..byte_count], .little),
         0x0400_0000...0x04FF_FFFF => io.read(self, T, aligned_addr),
         0x0600_0000...0x06FF_FFFF => self.vram.read(T, .nds7, aligned_addr),
 
@@ -93,7 +95,6 @@ pub fn dbgWrite(self: *@This(), comptime T: type, address: u32, value: T) void {
 
 fn _write(self: *@This(), comptime T: type, comptime mode: Mode, address: u32, value: T) void {
     const byte_count = @divExact(@typeInfo(T).Int.bits, 8);
-    const writeInt = std.mem.writeIntLittle;
 
     const aligned_addr = forceAlign(T, address);
 
@@ -104,13 +105,13 @@ fn _write(self: *@This(), comptime T: type, comptime mode: Mode, address: u32, v
     }
 
     switch (aligned_addr) {
-        0x0000_0000...0x01FF_FFFF => self.bios.write(T, address, value),
+        0x0000_0000...0x01FF_FFFF => self.bios.write(T, aligned_addr, value),
-        0x0200_0000...0x02FF_FFFF => writeInt(T, self.main[aligned_addr & 0x003F_FFFF ..][0..byte_count], value),
+        0x0200_0000...0x02FF_FFFF => std.mem.writeInt(T, self.main[aligned_addr & 0x003F_FFFF ..][0..byte_count], value, .little),
         0x0300_0000...0x037F_FFFF => switch (self.io.shr.wramcnt.mode.read()) {
-            0b00 => writeInt(T, self.wram[aligned_addr & 0x0000_FFFF ..][0..byte_count], value),
+            0b00 => std.mem.writeInt(T, self.wram[aligned_addr & 0x0000_FFFF ..][0..byte_count], value, .little),
             else => self.shr_wram.write(T, .nds7, aligned_addr, value),
         },
-        0x0380_0000...0x0380_FFFF => writeInt(T, self.wram[aligned_addr & 0x0000_FFFF ..][0..byte_count], value),
+        0x0380_0000...0x03FF_FFFF => std.mem.writeInt(T, self.wram[aligned_addr & 0x0000_FFFF ..][0..byte_count], value, .little),
         0x0400_0000...0x04FF_FFFF => io.write(self, T, aligned_addr, value),
         0x0600_0000...0x06FF_FFFF => self.vram.write(T, .nds7, aligned_addr, value),
         else => log.warn("unexpected: write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8})", .{ T, address, value }),

src/core/nds7/dma.zig

@@ -0,0 +1,401 @@
+const std = @import("std");
+
+const System = @import("../emu.zig").System;
+const DmaCnt = @import("io.zig").DmaCnt;
+
+const rotr = std.math.rotr;
+const shift = @import("../../util.zig").shift;
+const subset = @import("../../util.zig").subset;
+
+const handleInterrupt = @import("../emu.zig").handleInterrupt;
+
+const log = std.log.scoped(.nds7_dma_transfer);
+
+pub const Controllers = struct {
+    Controller(0) = Controller(0){},
+    Controller(1) = Controller(1){},
+    Controller(2) = Controller(2){},
+    Controller(3) = Controller(3){},
+};
+
+pub fn read(comptime T: type, dma: *const Controllers, addr: u32) ?T {
+    const byte_addr: u8 = @truncate(addr);
+
+    return switch (T) {
+        u32 => switch (byte_addr) {
+            0xB0, 0xB4 => null, // DMA0SAD, DMA0DAD,
+            0xB8 => @as(T, dma.*[0].dmacntH()) << 16, // DMA0CNT_L is write-only
+            0xBC, 0xC0 => null, // DMA1SAD, DMA1DAD
+            0xC4 => @as(T, dma.*[1].dmacntH()) << 16, // DMA1CNT_L is write-only
+            0xC8, 0xCC => null, // DMA2SAD, DMA2DAD
+            0xD0 => @as(T, dma.*[2].dmacntH()) << 16, // DMA2CNT_L is write-only
+            0xD4, 0xD8 => null, // DMA3SAD, DMA3DAD
+            0xDC => @as(T, dma.*[3].dmacntH()) << 16, // DMA3CNT_L is write-only
+            else => warn("unaligned {} read from 0x{X:0>8}", .{ T, addr }),
+        },
+        u16 => switch (byte_addr) {
+            0xB0, 0xB2, 0xB4, 0xB6 => null, // DMA0SAD, DMA0DAD
+            0xB8 => 0x0000, // DMA0CNT_L, suite.gba expects 0x0000 instead of 0xDEAD
+            0xBA => dma.*[0].dmacntH(),
+
+            0xBC, 0xBE, 0xC0, 0xC2 => null, // DMA1SAD, DMA1DAD
+            0xC4 => 0x0000, // DMA1CNT_L
+            0xC6 => dma.*[1].dmacntH(),
+
+            0xC8, 0xCA, 0xCC, 0xCE => null, // DMA2SAD, DMA2DAD
+            0xD0 => 0x0000, // DMA2CNT_L
+            0xD2 => dma.*[2].dmacntH(),
+
+            0xD4, 0xD6, 0xD8, 0xDA => null, // DMA3SAD, DMA3DAD
+            0xDC => 0x0000, // DMA3CNT_L
+            0xDE => dma.*[3].dmacntH(),
+            else => warn("unaligned {} read from 0x{X:0>8}", .{ T, addr }),
+        },
+        u8 => switch (byte_addr) {
+            0xB0...0xB7 => null, // DMA0SAD, DMA0DAD
+            0xB8, 0xB9 => 0x00, // DMA0CNT_L
+            0xBA, 0xBB => @truncate(dma.*[0].dmacntH() >> shift(u16, byte_addr)),
+
+            0xBC...0xC3 => null, // DMA1SAD, DMA1DAD
+            0xC4, 0xC5 => 0x00, // DMA1CNT_L
+            0xC6, 0xC7 => @truncate(dma.*[1].dmacntH() >> shift(u16, byte_addr)),
+
+            0xC8...0xCF => null, // DMA2SAD, DMA2DAD
+            0xD0, 0xD1 => 0x00, // DMA2CNT_L
+            0xD2, 0xD3 => @truncate(dma.*[2].dmacntH() >> shift(u16, byte_addr)),
+
+            0xD4...0xDB => null, // DMA3SAD, DMA3DAD
+            0xDC, 0xDD => 0x00, // DMA3CNT_L
+            0xDE, 0xDF => @truncate(dma.*[3].dmacntH() >> shift(u16, byte_addr)),
+            else => warn("unexpected {} read from 0x{X:0>8}", .{ T, addr }),
+        },
+        else => @compileError("DMA: Unsupported read width"),
+    };
+}
+
+pub fn write(comptime T: type, dma: *Controllers, addr: u32, value: T) void {
+    const byte_addr: u8 = @truncate(addr);
+
+    switch (T) {
+        u32 => switch (byte_addr) {
+            0xB0 => dma.*[0].setDmasad(value),
+            0xB4 => dma.*[0].setDmadad(value),
+            0xB8 => dma.*[0].setDmacnt(value),
+
+            0xBC => dma.*[1].setDmasad(value),
+            0xC0 => dma.*[1].setDmadad(value),
+            0xC4 => dma.*[1].setDmacnt(value),
+
+            0xC8 => dma.*[2].setDmasad(value),
+            0xCC => dma.*[2].setDmadad(value),
+            0xD0 => dma.*[2].setDmacnt(value),
+
+            0xD4 => dma.*[3].setDmasad(value),
+            0xD8 => dma.*[3].setDmadad(value),
+            0xDC => dma.*[3].setDmacnt(value),
+            else => log.warn("Tried to write 0x{X:0>8}{} to 0x{X:0>8}", .{ value, T, addr }),
+        },
+        u16 => switch (byte_addr) {
+            0xB0, 0xB2 => dma.*[0].setDmasad(subset(u32, u16, byte_addr, dma.*[0].sad, value)),
+            0xB4, 0xB6 => dma.*[0].setDmadad(subset(u32, u16, byte_addr, dma.*[0].dad, value)),
+            0xB8 => dma.*[0].setDmacntL(value),
+            0xBA => dma.*[0].setDmacntH(value),
+
+            0xBC, 0xBE => dma.*[1].setDmasad(subset(u32, u16, byte_addr, dma.*[1].sad, value)),
+            0xC0, 0xC2 => dma.*[1].setDmadad(subset(u32, u16, byte_addr, dma.*[1].dad, value)),
+            0xC4 => dma.*[1].setDmacntL(value),
+            0xC6 => dma.*[1].setDmacntH(value),
+
+            0xC8, 0xCA => dma.*[2].setDmasad(subset(u32, u16, byte_addr, dma.*[2].sad, value)),
+            0xCC, 0xCE => dma.*[2].setDmadad(subset(u32, u16, byte_addr, dma.*[2].dad, value)),
+            0xD0 => dma.*[2].setDmacntL(value),
+            0xD2 => dma.*[2].setDmacntH(value),
+
+            0xD4, 0xD6 => dma.*[3].setDmasad(subset(u32, u16, byte_addr, dma.*[3].sad, value)),
+            0xD8, 0xDA => dma.*[3].setDmadad(subset(u32, u16, byte_addr, dma.*[3].dad, value)),
+            0xDC => dma.*[3].setDmacntL(value),
+            0xDE => dma.*[3].setDmacntH(value),
+            else => log.warn("Tried to write 0x{X:0>4}{} to 0x{X:0>8}", .{ value, T, addr }),
+        },
+        u8 => switch (byte_addr) {
+            0xB0, 0xB1, 0xB2, 0xB3 => dma.*[0].setDmasad(subset(u32, u8, byte_addr, dma.*[0].sad, value)),
+            0xB4, 0xB5, 0xB6, 0xB7 => dma.*[0].setDmadad(subset(u32, u8, byte_addr, dma.*[0].dad, value)),
+            0xB8, 0xB9 => dma.*[0].setDmacntL(subset(u16, u8, byte_addr, dma.*[0].word_count, value)),
+            0xBA, 0xBB => dma.*[0].setDmacntH(subset(u16, u8, byte_addr, dma.*[0].cnt.raw, value)),
+
+            0xBC, 0xBD, 0xBE, 0xBF => dma.*[1].setDmasad(subset(u32, u8, byte_addr, dma.*[1].sad, value)),
+            0xC0, 0xC1, 0xC2, 0xC3 => dma.*[1].setDmadad(subset(u32, u8, byte_addr, dma.*[1].dad, value)),
+            0xC4, 0xC5 => dma.*[1].setDmacntL(subset(u16, u8, byte_addr, dma.*[1].word_count, value)),
+            0xC6, 0xC7 => dma.*[1].setDmacntH(subset(u16, u8, byte_addr, dma.*[1].cnt.raw, value)),
+
+            0xC8, 0xC9, 0xCA, 0xCB => dma.*[2].setDmasad(subset(u32, u8, byte_addr, dma.*[2].sad, value)),
+            0xCC, 0xCD, 0xCE, 0xCF => dma.*[2].setDmadad(subset(u32, u8, byte_addr, dma.*[2].dad, value)),
+            0xD0, 0xD1 => dma.*[2].setDmacntL(subset(u16, u8, byte_addr, dma.*[2].word_count, value)),
+            0xD2, 0xD3 => dma.*[2].setDmacntH(subset(u16, u8, byte_addr, dma.*[2].cnt.raw, value)),
+
+            0xD4, 0xD5, 0xD6, 0xD7 => dma.*[3].setDmasad(subset(u32, u8, byte_addr, dma.*[3].sad, value)),
+            0xD8, 0xD9, 0xDA, 0xDB => dma.*[3].setDmadad(subset(u32, u8, byte_addr, dma.*[3].dad, value)),
+            0xDC, 0xDD => dma.*[3].setDmacntL(subset(u16, u8, byte_addr, dma.*[3].word_count, value)),
+            0xDE, 0xDF => dma.*[3].setDmacntH(subset(u16, u8, byte_addr, dma.*[3].cnt.raw, value)),
+            else => log.warn("Tried to write 0x{X:0>2}{} to 0x{X:0>8}", .{ value, T, addr }),
+        },
+        else => @compileError("DMA: Unsupported write width"),
+    }
+}
+
+fn warn(comptime format: []const u8, args: anytype) u0 {
+    log.warn(format, args);
+    return 0;
+}
+
+/// Function that creates a DMAController. Determines unique DMA Controller behaiour at compile-time
+fn Controller(comptime id: u2) type {
+    return struct {
+        const Self = @This();
+
+        const sad_mask: u32 = if (id == 0) 0x07FF_FFFF else 0x0FFF_FFFF;
+        const dad_mask: u32 = if (id != 3) 0x07FF_FFFF else 0x0FFF_FFFF;
+        const WordCount = if (id == 3) u16 else u14;
+
+        /// Write-only. The first address in a DMA transfer. (DMASAD)
+        /// Note: use writeSrc instead of manipulating src_addr directly
+        sad: u32 = 0x0000_0000,
+        /// Write-only. The final address in a DMA transffer. (DMADAD)
+        /// Note: Use writeDst instead of manipulatig dst_addr directly
+        dad: u32 = 0x0000_0000,
+        /// Write-only. The Word Count for the DMA Transfer (DMACNT_L)
+        word_count: WordCount = 0,
+        /// Read / Write. DMACNT_H
+        /// Note: Use writeControl instead of manipulating cnt directly.
+        cnt: DmaCnt = .{ .raw = 0x0000 },
+
+        /// Internal. The last successfully read value
+        data_latch: u32 = 0x0000_0000,
+        /// Internal. Currrent Source Address
+        sad_latch: u32 = 0x0000_0000,
+        /// Internal. Current Destination Address
+        dad_latch: u32 = 0x0000_0000,
+        /// Internal. Word Count
+        _word_count: WordCount = 0,
+
+        /// Some DMA Transfers are enabled during Hblank / VBlank and / or
+        /// have delays. Thefore bit 15 of DMACNT isn't actually something
+        /// we can use to control when we do or do not execute a step in a DMA Transfer
+        in_progress: bool = false,
+
+        pub fn reset(self: *Self) void {
+            self.* = Self.init();
+        }
+
+        pub fn setDmasad(self: *Self, addr: u32) void {
+            self.sad = addr & sad_mask;
+        }
+
+        pub fn setDmadad(self: *Self, addr: u32) void {
+            self.dad = addr & dad_mask;
+        }
+
+        pub fn setDmacntL(self: *Self, halfword: u16) void {
+            self.word_count = @truncate(halfword);
+        }
+
+        pub fn dmacntH(self: *const Self) u16 {
+            return self.cnt.raw & if (id == 3) 0xFFE0 else 0xF7E0;
+        }
+
+        pub fn setDmacntH(self: *Self, halfword: u16) void {
+            const new = DmaCnt{ .raw = halfword };
+
+            if (!self.cnt.enabled.read() and new.enabled.read()) {
+                // Reload Internals on Rising Edge.
+                self.sad_latch = self.sad;
+                self.dad_latch = self.dad;
+                self._word_count = if (self.word_count == 0) std.math.maxInt(WordCount) else self.word_count;
+
+                // Only a Start Timing of 00 has a DMA Transfer immediately begin
+                self.in_progress = new.start_timing.read() == 0b00;
+
+                // this is just for debug purposes
+                const start_timing: Kind = @enumFromInt(new.start_timing.read());
+
+                switch (start_timing) {
+                    .immediate, .vblank => {},
+                    else => log.err("TODO: Implement DMA({}) {s} mode", .{ id, @tagName(start_timing) }),
+                }
+
+                // Debug stuff
+                {
+                    const sad_adj: Adjustment = @enumFromInt(new.sad_adj.read());
+                    const dad_adj: Adjustment = @enumFromInt(new.dad_adj.read());
+                    const byte_count = @as(u32, @sizeOf(u16)) << @intFromBool(new.transfer_type.read());
+
+                    const sad_final = switch (sad_adj) {
+                        .Increment, .IncrementReload => self.sad_latch +% self._word_count * byte_count,
+                        .Decrement => self.sad_latch -% self._word_count * byte_count,
+                        .Fixed => self.sad_latch,
+                    };
+
+                    const dad_final = switch (dad_adj) {
+                        .Increment, .IncrementReload => self.dad_latch +% self._word_count * byte_count,
+                        .Decrement => self.dad_latch -% self._word_count * byte_count,
+                        .Fixed => self.dad_latch,
+                    };
+
+                    log.debug("configured {s} transfer from 0x{X:0>8} -> 0x{X:0>8} to 0x{X:0>8} -> 0x{X:0>8} ({} words) for DMA{}", .{
+                        @tagName(start_timing),
+                        self.sad_latch,
+                        sad_final,
+                        self.dad_latch,
+                        dad_final,
+                        self._word_count,
+                        id,
+                    });
+                }
+            }
+
+            self.cnt.raw = halfword;
+        }
+
+        pub fn setDmacnt(self: *Self, word: u32) void {
+            self.setDmacntL(@truncate(word));
+            self.setDmacntH(@truncate(word >> 16));
+        }
+
+        pub fn step(self: *Self, cpu: *System.Arm7tdmi) void {
+            const bus_ptr: *System.Bus7 = @ptrCast(@alignCast(cpu.bus.ptr));
+
+            const is_fifo = (id == 1 or id == 2) and self.cnt.start_timing.read() == 0b11;
+            const sad_adj: Adjustment = @enumFromInt(self.cnt.sad_adj.read());
+            const dad_adj: Adjustment = if (is_fifo) .Fixed else @enumFromInt(self.cnt.dad_adj.read());
+
+            const transfer_type = is_fifo or self.cnt.transfer_type.read();
+            const offset: u32 = if (transfer_type) @sizeOf(u32) else @sizeOf(u16);
+
+            const mask = if (transfer_type) ~@as(u32, 3) else ~@as(u32, 1);
+            const sad_addr = self.sad_latch & mask;
+            const dad_addr = self.dad_latch & mask;
+
+            if (transfer_type) {
+                if (sad_addr >= 0x0200_0000) self.data_latch = cpu.bus.read(u32, sad_addr);
+                cpu.bus.write(u32, dad_addr, self.data_latch);
+            } else {
+                if (sad_addr >= 0x0200_0000) {
+                    const value: u32 = cpu.bus.read(u16, sad_addr);
+                    self.data_latch = value << 16 | value;
+                }
+
+                cpu.bus.write(u16, dad_addr, @as(u16, @truncate(rotr(u32, self.data_latch, 8 * (dad_addr & 3)))));
+            }
+
+            switch (@as(u8, @truncate(sad_addr >> 24))) {
+                // according to fleroviux, DMAs with a source address in ROM misbehave
+                // the resultant behaviour is that the source address will increment despite what DMAXCNT says
+                0x08...0x0D => self.sad_latch +%= offset, // obscure behaviour
+                else => switch (sad_adj) {
+                    .Increment => self.sad_latch +%= offset,
+                    .Decrement => self.sad_latch -%= offset,
+                    .IncrementReload => log.err("{} is a prohibited adjustment on SAD", .{sad_adj}),
+                    .Fixed => {},
+                },
+            }
+
+            switch (dad_adj) {
+                .Increment, .IncrementReload => self.dad_latch +%= offset,
+                .Decrement => self.dad_latch -%= offset,
+                .Fixed => {},
+            }
+
+            self._word_count -= 1;
+
+            if (self._word_count == 0) {
+                if (self.cnt.irq.read()) {
+                    switch (id) {
+                        0 => bus_ptr.io.irq.dma0.set(),
+                        1 => bus_ptr.io.irq.dma1.set(),
+                        2 => bus_ptr.io.irq.dma2.set(),
+                        3 => bus_ptr.io.irq.dma3.set(),
+                    }
+
+                    handleInterrupt(.nds7, cpu);
+                }
+
+                // If we're not repeating, Fire the IRQs and disable the DMA
+                if (!self.cnt.repeat.read()) self.cnt.enabled.unset();
+
+                // We want to disable our internal enabled flag regardless of repeat
+                // because we only want to step A DMA that repeats during it's specific
+                // timing window
+                self.in_progress = false;
+            }
+        }
+
+        fn poll(self: *Self, comptime kind: Kind) void {
+            if (self.in_progress) return; // If there's an ongoing DMA Transfer, exit early
+
+            // No ongoing DMA Transfer, We want to check if we should repeat an existing one
+            // Determined by the repeat bit and whether the DMA is in the right start_timing
+
+            switch (kind) {
+                .vblank => self.in_progress = self.cnt.enabled.read() and self.cnt.start_timing.read() == 0b01,
+                .cartridge_slot, .immediate, .special => {},
+            }
+
+            // If we determined that the repeat bit is set (and now the Hblank / Vblank DMA is now in progress)
+            // Reload internal word count latch
+            // Reload internal DAD latch if we are in IncrementRelaod
+            if (self.in_progress) {
+                self._word_count = if (self.word_count == 0) std.math.maxInt(@TypeOf(self._word_count)) else self.word_count;
+                if (@as(Adjustment, @enumFromInt(self.cnt.dad_adj.read())) == .IncrementReload) self.dad_latch = self.dad;
+            }
+        }
+
+        pub fn requestAudio(self: *Self, _: u32) void {
+            comptime std.debug.assert(id == 1 or id == 2);
+            if (self.in_progress) return; // APU must wait their turn
+
+            // DMA May not be configured for handling DMAs
+            if (self.cnt.start_timing.read() != 0b11) return;
+
+            // We Assume the Repeat Bit is Set
+            // We Assume that DAD is set to 0x0400_00A0 or 0x0400_00A4 (fifo_addr)
+            // We Assume DMACNT_L is set to 4
+
+            // FIXME: Safe to just assume whatever DAD is set to is the FIFO Address?
+            // self.dad_latch = fifo_addr;
+            self.cnt.repeat.set();
+            self._word_count = 4;
+            self.in_progress = true;
+        }
+    };
+}
+
+pub fn onVblank(bus: *System.Bus7) void {
+    inline for (0..4) |i| bus.dma[i].poll(.vblank);
+}
+
+pub fn step(cpu: *System.Arm7tdmi) bool {
+    const bus: *System.Bus7 = @ptrCast(@alignCast(cpu.bus.ptr));
+
+    inline for (0..4) |i| {
+        if (bus.dma[i].in_progress) {
+            bus.dma[i].step(cpu);
+            return true;
+        }
+    }
+
+    return false;
+}
+
+const Adjustment = enum(u2) {
+    Increment = 0,
+    Decrement = 1,
+    Fixed = 2,
+    IncrementReload = 3,
+};
+
+const Kind = enum(u2) {
+    immediate = 0,
+    vblank,
+    cartridge_slot,
+    special,
+};

src/core/nds7/io.zig

@@ -12,6 +12,8 @@ const masks = @import("../io.zig").masks;
 const IntEnable = @import("../io.zig").IntEnable;
 const IntRequest = @import("../io.zig").IntEnable;
 
+const dma = @import("dma.zig");
+
 const log = std.log.scoped(.nds7_io);
 
 pub const Io = struct {
@@ -52,10 +54,10 @@ pub fn read(bus: *const Bus, comptime T: type, address: u32) T {
     return switch (T) {
         u32 => switch (address) {
             // DMA Transfers
-            0x0400_00B0...0x0400_00DC => warn("TODO: impl DMA", .{}),
+            0x0400_00B0...0x0400_00DC => dma.read(T, &bus.dma, address) orelse 0x000_0000,
 
             // Timers
-            0x0400_0100...0x0400_010C => warn("TODO: impl timer", .{}),
+            0x0400_0100...0x0400_010C => warn("TODO(timer): read(T: {}, addr: 0x{X:0>8}) {}", .{ T, address, T }),
 
             0x0400_0180 => bus.io.shr.ipc._nds7.sync.raw,
             0x0400_0208 => @intFromBool(bus.io.ime),
@@ -68,22 +70,27 @@ pub fn read(bus: *const Bus, comptime T: type, address: u32) T {
         u16 => switch (address) {
             0x0400_0004 => bus.io.ppu.?.nds7.dispstat.raw,
             // DMA Transfers
-            0x0400_00B0...0x0400_00DE => warn("TODO: impl DMA", .{}),
+            0x0400_00B0...0x0400_00DE => dma.read(T, &bus.dma, address) orelse 0x0000,
 
             // Timers
-            0x0400_0100...0x0400_010E => warn("TODO: impl timer", .{}),
+            0x0400_0100...0x0400_010E => warn("TODO(timer): read(T: {}, addr: 0x{X:0>8}) {}", .{ T, address, T }),
+
+            0x0400_0130 => bus.io.shr.input.keyinput().raw,
+            0x0400_0136 => bus.io.shr.input.extkeyin().raw,
 
-            0x0400_0130 => bus.io.shr.keyinput.load(.Monotonic),
             0x0400_0180 => @truncate(bus.io.shr.ipc._nds7.sync.raw),
             0x0400_0184 => @truncate(bus.io.shr.ipc._nds7.cnt.raw),
             else => warn("unexpected: read(T: {}, addr: 0x{X:0>8}) {} ", .{ T, address, T }),
         },
         u8 => switch (address) {
             // DMA Transfers
-            0x0400_00B0...0x0400_00DF => warn("TODO: impl DMA", .{}),
+            0x0400_00B0...0x0400_00DF => dma.read(T, &bus.dma, address) orelse 0x00,
 
             // Timers
-            0x0400_0100...0x0400_010F => warn("TODO: impl timer", .{}),
+            0x0400_0100...0x0400_010F => warn("TODO(timer): read(T: {}, addr: 0x{X:0>8}) {}", .{ T, address, T }),
+
+            // RTC
+            0x0400_0138 => warn("TODO(rtc): read(T: {}, addr: 0x{X:0>8}) {}", .{ T, address, T }),
 
             0x0400_0240 => bus.vram.stat().raw,
             0x0400_0241 => bus.io.shr.wramcnt.raw,
@@ -99,10 +106,10 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
     switch (T) {
         u32 => switch (address) {
             // DMA Transfers
-            0x0400_00B0...0x0400_00DC => log.warn("TODO: impl DMA", .{}),
+            0x0400_00B0...0x0400_00DC => dma.write(T, &bus.dma, address, value),
 
             // Timers
-            0x0400_0100...0x0400_010C => log.warn("TODO: impl timer", .{}),
+            0x0400_0100...0x0400_010C => log.warn("TODO(timer): write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8})", .{ T, address, value }),
 
             0x0400_0180 => bus.io.shr.ipc.setIpcSync(.nds7, value),
             0x0400_0208 => bus.io.ime = value & 1 == 1,
@@ -113,11 +120,13 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
             else => log.warn("unexpected: write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8})", .{ T, address, value }),
         },
         u16 => switch (address) {
+            0x0400_0004 => bus.io.ppu.?.nds7.dispstat.raw = value,
+
             // DMA Transfers
-            0x0400_00B0...0x0400_00DE => log.warn("TODO: impl DMA", .{}),
+            0x0400_00B0...0x0400_00DE => dma.write(T, &bus.dma, address, value),
 
             // Timers
-            0x0400_0100...0x0400_010E => log.warn("TODO: impl timer", .{}),
+            0x0400_0100...0x0400_010E => log.warn("TODO(timer): write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8})", .{ T, address, value }),
 
             0x0400_0180 => bus.io.shr.ipc.setIpcSync(.nds7, value),
             0x0400_0184 => bus.io.shr.ipc.setIpcFifoCnt(.nds7, value),
@@ -127,12 +136,24 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
         },
         u8 => switch (address) {
             // DMA Transfers
-            0x0400_00B0...0x0400_00DF => log.warn("TODO: impl DMA", .{}),
+            0x0400_00B0...0x0400_00DF => dma.write(T, &bus.dma, address, value),
 
             // Timers
-            0x0400_0100...0x0400_010F => log.warn("TODO: impl timer", .{}),
+            0x0400_0100...0x0400_010F => log.warn("TODO(timer): write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8})", .{ T, address, value }),
+
+            // RTC
+            0x0400_0138 => log.warn("TODO(rtc): write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8})", .{ T, address, value }),
 
             0x0400_0208 => bus.io.ime = value & 1 == 1,
+
+            0x0400_0301 => switch ((value >> 6) & 0b11) {
+                0b00 => bus.io.haltcnt = .execute,
+                0b10 => bus.io.haltcnt = .halt,
+                else => |val| {
+                    const tag: Haltcnt = @enumFromInt(val);
+                    log.err("TODO: Implement {}", .{tag});
+                },
+            },
             else => log.warn("unexpected: write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>2})", .{ T, address, value }),
         },
         else => @compileError(T ++ " is an unsupported bus write type"),
@@ -158,3 +179,14 @@ const Haltcnt = enum(u2) {
 };
 
 const PostFlag = enum(u8) { in_progress = 0, completed };
+
+pub const DmaCnt = extern union {
+    dad_adj: Bitfield(u16, 5, 2),
+    sad_adj: Bitfield(u16, 7, 2),
+    repeat: Bit(u16, 9),
+    transfer_type: Bit(u16, 10),
+    start_timing: Bitfield(u16, 12, 2),
+    irq: Bit(u16, 14),
+    enabled: Bit(u16, 15),
+    raw: u16,
+};

src/core/nds9/Bios.zig

@@ -31,7 +31,6 @@ pub fn deinit(self: @This(), allocator: Allocator) void {
 
 // Note: Parts of 16MiB addrspace that aren't mapped to BIOS are typically undefined
 pub fn read(self: *const @This(), comptime T: type, address: u32) T {
-    const readInt = std.mem.readIntLittle;
     const byte_count = @divExact(@typeInfo(T).Int.bits, 8);
 
     // if (address >= len) return 0x0000_0000; // TODO: What is undefined actually?
@@ -41,7 +40,7 @@ pub fn read(self: *const @This(), comptime T: type, address: u32) T {
         @panic("TODO: ability to load in NDS9 BIOS just-in-time");
     };
 
-    return readInt(T, ptr[address & (len - 1) ..][0..byte_count]);
+    return std.mem.readInt(T, ptr[address & (len - 1) ..][0..byte_count], .little);
 }
 
 pub fn write(_: *const @This(), comptime T: type, address: u32, value: T) void {

src/core/nds9/Bus.zig

@@ -8,6 +8,8 @@ const Wram = @import("../emu.zig").Wram;
 const Bios = @import("Bios.zig");
 const forceAlign = @import("../emu.zig").forceAlign;
 
+const Controllers = @import("dma.zig").Controllers;
+
 const Allocator = std.mem.Allocator;
 
 const Mode = enum { normal, debug };
@@ -18,8 +20,11 @@ const log = std.log.scoped(.nds9_bus);
 
 main: *[4 * MiB]u8,
 wram: *Wram,
+makeshift_palram: *[2 * KiB]u8,
 scheduler: *Scheduler,
 
+dma: Controllers = .{},
+
 io: io.Io,
 ppu: Ppu,
 bios: Bios,
@@ -31,6 +36,7 @@ pub fn init(allocator: Allocator, scheduler: *Scheduler, ctx: SharedCtx) !@This(
     return .{
         .main = ctx.main,
         .wram = ctx.wram,
+        .makeshift_palram = try allocator.create([2 * KiB]u8),
         .ppu = try Ppu.init(allocator, ctx.vram),
         .scheduler = scheduler,
         .io = io.Io.init(ctx.io),
@@ -42,6 +48,8 @@ pub fn init(allocator: Allocator, scheduler: *Scheduler, ctx: SharedCtx) !@This(
 pub fn deinit(self: *@This(), allocator: Allocator) void {
     self.ppu.deinit(allocator);
     self.bios.deinit(allocator);
+
+    allocator.destroy(self.makeshift_palram);
 }
 
 pub fn reset(_: *@This()) void {
@@ -58,8 +66,6 @@ pub fn dbgRead(self: *@This(), comptime T: type, address: u32) T {
 
 fn _read(self: *@This(), comptime T: type, comptime mode: Mode, address: u32) T {
     const byte_count = @divExact(@typeInfo(T).Int.bits, 8);
-    const readInt = std.mem.readIntLittle;
-
     const aligned_addr = forceAlign(T, address);
 
     switch (mode) {
@@ -69,11 +75,13 @@ fn _read(self: *@This(), comptime T: type, comptime mode: Mode, address: u32) T
     }
 
     return switch (aligned_addr) {
-        0x0200_0000...0x02FF_FFFF => readInt(T, self.main[aligned_addr & 0x003F_FFFF ..][0..byte_count]),
+        0x0200_0000...0x02FF_FFFF => std.mem.readInt(T, self.main[aligned_addr & (4 * MiB - 1) ..][0..byte_count], .little),
         0x0300_0000...0x03FF_FFFF => self.wram.read(T, .nds9, aligned_addr),
         0x0400_0000...0x04FF_FFFF => io.read(self, T, aligned_addr),
+        0x0500_0000...0x05FF_FFFF => std.mem.readInt(T, self.makeshift_palram[aligned_addr & (2 * KiB - 1) ..][0..@sizeOf(T)], .little),
         0x0600_0000...0x06FF_FFFF => self.ppu.vram.read(T, .nds9, aligned_addr),
-        0xFFFF_0000...0xFFFF_FFFF => self.bios.read(T, address),
+        0x0700_0000...0x07FF_FFFF => std.mem.readInt(T, self.ppu.oam.buf[aligned_addr & (2 * KiB - 1) ..][0..byte_count], .little),
+        0xFFFF_0000...0xFFFF_FFFF => self.bios.read(T, aligned_addr),
         else => warn("unexpected: read(T: {}, addr: 0x{X:0>8}) {} ", .{ T, address, T }),
     };
 }
@@ -88,8 +96,6 @@ pub fn dbgWrite(self: *@This(), comptime T: type, address: u32, value: T) void {
 
 fn _write(self: *@This(), comptime T: type, comptime mode: Mode, address: u32, value: T) void {
     const byte_count = @divExact(@typeInfo(T).Int.bits, 8);
-    const writeInt = std.mem.writeIntLittle;
-
     const aligned_addr = forceAlign(T, address);
 
     switch (mode) {
@@ -99,11 +105,13 @@ fn _write(self: *@This(), comptime T: type, comptime mode: Mode, address: u32, v
     }
 
     switch (aligned_addr) {
-        0x0200_0000...0x02FF_FFFF => writeInt(T, self.main[aligned_addr & 0x003F_FFFF ..][0..byte_count], value),
+        0x0200_0000...0x02FF_FFFF => std.mem.writeInt(T, self.main[aligned_addr & (4 * MiB - 1) ..][0..byte_count], value, .little),
         0x0300_0000...0x03FF_FFFF => self.wram.write(T, .nds9, aligned_addr, value),
         0x0400_0000...0x04FF_FFFF => io.write(self, T, aligned_addr, value),
+        0x0500_0000...0x05FF_FFFF => std.mem.writeInt(T, self.makeshift_palram[aligned_addr & (2 * KiB - 1) ..][0..@sizeOf(T)], value, .little),
         0x0600_0000...0x06FF_FFFF => self.ppu.vram.write(T, .nds9, aligned_addr, value),
-        0xFFFF_0000...0xFFFF_FFFF => self.bios.write(T, address, value),
+        0x0700_0000...0x07FF_FFFF => std.mem.writeInt(T, self.ppu.oam.buf[aligned_addr & (2 * KiB - 1) ..][0..@sizeOf(T)], value, .little),
+        0xFFFF_0000...0xFFFF_FFFF => self.bios.write(T, aligned_addr, value),
         else => log.warn("unexpected: write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8})", .{ T, address, value }),
     }
 }

src/core/nds9/Cp15.zig

@@ -4,7 +4,7 @@ const log = std.log.scoped(.cp15);
 
 const panic_on_unimplemented: bool = false;
 
-control: u32 = 0x0005_2078,
+control: u32 = 0x0001_2078,
 dtcm_size_base: u32 = 0x0300_000A,
 itcm_size_base: u32 = 0x0000_0020,
 

src/core/nds9/dma.zig

@@ -0,0 +1,411 @@
+const std = @import("std");
+
+const System = @import("../emu.zig").System;
+const DmaCnt = @import("io.zig").DmaCnt;
+
+const rotr = std.math.rotr;
+const shift = @import("../../util.zig").shift;
+const subset = @import("../../util.zig").subset;
+
+const handleInterrupt = @import("../emu.zig").handleInterrupt;
+
+const log = std.log.scoped(.nds9_dma_transfer);
+
+pub const Controllers = struct {
+    Controller(0) = Controller(0){},
+    Controller(1) = Controller(1){},
+    Controller(2) = Controller(2){},
+    Controller(3) = Controller(3){},
+};
+
+pub fn read(comptime T: type, dma: *const Controllers, addr: u32) ?T {
+    const byte_addr: u8 = @truncate(addr);
+
+    return switch (T) {
+        u32 => switch (byte_addr) {
+            0xB0, 0xB4 => null, // DMA0SAD, DMA0DAD,
+            0xB8 => @as(T, dma.*[0].dmacntH()) << 16, // DMA0CNT_L is write-only
+            0xBC, 0xC0 => null, // DMA1SAD, DMA1DAD
+            0xC4 => @as(T, dma.*[1].dmacntH()) << 16, // DMA1CNT_L is write-only
+            0xC8, 0xCC => null, // DMA2SAD, DMA2DAD
+            0xD0 => @as(T, dma.*[2].dmacntH()) << 16, // DMA2CNT_L is write-only
+            0xD4, 0xD8 => null, // DMA3SAD, DMA3DAD
+            0xDC => @as(T, dma.*[3].dmacntH()) << 16, // DMA3CNT_L is write-only
+            else => warn("unaligned {} read from 0x{X:0>8}", .{ T, addr }),
+        },
+        u16 => switch (byte_addr) {
+            0xB0, 0xB2, 0xB4, 0xB6 => null, // DMA0SAD, DMA0DAD
+            0xB8 => 0x0000, // DMA0CNT_L, suite.gba expects 0x0000 instead of 0xDEAD
+            0xBA => dma.*[0].dmacntH(),
+
+            0xBC, 0xBE, 0xC0, 0xC2 => null, // DMA1SAD, DMA1DAD
+            0xC4 => 0x0000, // DMA1CNT_L
+            0xC6 => dma.*[1].dmacntH(),
+
+            0xC8, 0xCA, 0xCC, 0xCE => null, // DMA2SAD, DMA2DAD
+            0xD0 => 0x0000, // DMA2CNT_L
+            0xD2 => dma.*[2].dmacntH(),
+
+            0xD4, 0xD6, 0xD8, 0xDA => null, // DMA3SAD, DMA3DAD
+            0xDC => 0x0000, // DMA3CNT_L
+            0xDE => dma.*[3].dmacntH(),
+            else => warn("unaligned {} read from 0x{X:0>8}", .{ T, addr }),
+        },
+        u8 => switch (byte_addr) {
+            0xB0...0xB7 => null, // DMA0SAD, DMA0DAD
+            0xB8, 0xB9 => 0x00, // DMA0CNT_L
+            0xBA, 0xBB => @truncate(dma.*[0].dmacntH() >> shift(u16, byte_addr)),
+
+            0xBC...0xC3 => null, // DMA1SAD, DMA1DAD
+            0xC4, 0xC5 => 0x00, // DMA1CNT_L
+            0xC6, 0xC7 => @truncate(dma.*[1].dmacntH() >> shift(u16, byte_addr)),
+
+            0xC8...0xCF => null, // DMA2SAD, DMA2DAD
+            0xD0, 0xD1 => 0x00, // DMA2CNT_L
+            0xD2, 0xD3 => @truncate(dma.*[2].dmacntH() >> shift(u16, byte_addr)),
+
+            0xD4...0xDB => null, // DMA3SAD, DMA3DAD
+            0xDC, 0xDD => 0x00, // DMA3CNT_L
+            0xDE, 0xDF => @truncate(dma.*[3].dmacntH() >> shift(u16, byte_addr)),
+            else => warn("unexpected {} read from 0x{X:0>8}", .{ T, addr }),
+        },
+        else => @compileError("DMA: Unsupported read width"),
+    };
+}
+
+pub fn write(comptime T: type, dma: *Controllers, addr: u32, value: T) void {
+    const byte_addr: u8 = @truncate(addr);
+
+    switch (T) {
+        u32 => switch (byte_addr) {
+            0xB0 => dma.*[0].setDmasad(value),
+            0xB4 => dma.*[0].setDmadad(value),
+            0xB8 => dma.*[0].setDmacnt(value),
+
+            0xBC => dma.*[1].setDmasad(value),
+            0xC0 => dma.*[1].setDmadad(value),
+            0xC4 => dma.*[1].setDmacnt(value),
+
+            0xC8 => dma.*[2].setDmasad(value),
+            0xCC => dma.*[2].setDmadad(value),
+            0xD0 => dma.*[2].setDmacnt(value),
+
+            0xD4 => dma.*[3].setDmasad(value),
+            0xD8 => dma.*[3].setDmadad(value),
+            0xDC => dma.*[3].setDmacnt(value),
+            else => log.warn("Tried to write 0x{X:0>8}{} to 0x{X:0>8}", .{ value, T, addr }),
+        },
+        u16 => switch (byte_addr) {
+            0xB0, 0xB2 => dma.*[0].setDmasad(subset(u32, u16, byte_addr, dma.*[0].sad, value)),
+            0xB4, 0xB6 => dma.*[0].setDmadad(subset(u32, u16, byte_addr, dma.*[0].dad, value)),
+            0xB8 => dma.*[0].setDmacntL(value),
+            0xBA => dma.*[0].setDmacntH(value),
+
+            0xBC, 0xBE => dma.*[1].setDmasad(subset(u32, u16, byte_addr, dma.*[1].sad, value)),
+            0xC0, 0xC2 => dma.*[1].setDmadad(subset(u32, u16, byte_addr, dma.*[1].dad, value)),
+            0xC4 => dma.*[1].setDmacntL(value),
+            0xC6 => dma.*[1].setDmacntH(value),
+
+            0xC8, 0xCA => dma.*[2].setDmasad(subset(u32, u16, byte_addr, dma.*[2].sad, value)),
+            0xCC, 0xCE => dma.*[2].setDmadad(subset(u32, u16, byte_addr, dma.*[2].dad, value)),
+            0xD0 => dma.*[2].setDmacntL(value),
+            0xD2 => dma.*[2].setDmacntH(value),
+
+            0xD4, 0xD6 => dma.*[3].setDmasad(subset(u32, u16, byte_addr, dma.*[3].sad, value)),
+            0xD8, 0xDA => dma.*[3].setDmadad(subset(u32, u16, byte_addr, dma.*[3].dad, value)),
+            0xDC => dma.*[3].setDmacntL(value),
+            0xDE => dma.*[3].setDmacntH(value),
+            else => log.warn("Tried to write 0x{X:0>4}{} to 0x{X:0>8}", .{ value, T, addr }),
+        },
+        u8 => switch (byte_addr) {
+            0xB0, 0xB1, 0xB2, 0xB3 => dma.*[0].setDmasad(subset(u32, u8, byte_addr, dma.*[0].sad, value)),
+            0xB4, 0xB5, 0xB6, 0xB7 => dma.*[0].setDmadad(subset(u32, u8, byte_addr, dma.*[0].dad, value)),
+            0xB8, 0xB9 => dma.*[0].setDmacntL(subset(u16, u8, byte_addr, @as(u16, @truncate(dma.*[0].word_count)), value)), // FIXME: How wrong is this? lol
+            0xBA, 0xBB => dma.*[0].setDmacntH(subset(u16, u8, byte_addr, dma.*[0].cnt.raw, value)),
+
+            0xBC, 0xBD, 0xBE, 0xBF => dma.*[1].setDmasad(subset(u32, u8, byte_addr, dma.*[1].sad, value)),
+            0xC0, 0xC1, 0xC2, 0xC3 => dma.*[1].setDmadad(subset(u32, u8, byte_addr, dma.*[1].dad, value)),
+            0xC4, 0xC5 => dma.*[1].setDmacntL(subset(u16, u8, byte_addr, @as(u16, @truncate(dma.*[1].word_count)), value)),
+            0xC6, 0xC7 => dma.*[1].setDmacntH(subset(u16, u8, byte_addr, dma.*[1].cnt.raw, value)),
+
+            0xC8, 0xC9, 0xCA, 0xCB => dma.*[2].setDmasad(subset(u32, u8, byte_addr, dma.*[2].sad, value)),
+            0xCC, 0xCD, 0xCE, 0xCF => dma.*[2].setDmadad(subset(u32, u8, byte_addr, dma.*[2].dad, value)),
+            0xD0, 0xD1 => dma.*[2].setDmacntL(subset(u16, u8, byte_addr, @as(u16, @truncate(dma.*[2].word_count)), value)),
+            0xD2, 0xD3 => dma.*[2].setDmacntH(subset(u16, u8, byte_addr, dma.*[2].cnt.raw, value)),
+
+            0xD4, 0xD5, 0xD6, 0xD7 => dma.*[3].setDmasad(subset(u32, u8, byte_addr, dma.*[3].sad, value)),
+            0xD8, 0xD9, 0xDA, 0xDB => dma.*[3].setDmadad(subset(u32, u8, byte_addr, dma.*[3].dad, value)),
+            0xDC, 0xDD => dma.*[3].setDmacntL(subset(u16, u8, byte_addr, @as(u16, @truncate(dma.*[3].word_count)), value)),
+            0xDE, 0xDF => dma.*[3].setDmacntH(subset(u16, u8, byte_addr, dma.*[3].cnt.raw, value)),
+            else => log.warn("Tried to write 0x{X:0>2}{} to 0x{X:0>8}", .{ value, T, addr }),
+        },
+        else => @compileError("DMA: Unsupported write width"),
+    }
+}
+
+fn warn(comptime format: []const u8, args: anytype) u0 {
+    log.warn(format, args);
+    return 0;
+}
+
+/// Function that creates a DMAController. Determines unique DMA Controller behaiour at compile-time
+fn Controller(comptime id: u2) type {
+    return struct {
+        const Self = @This();
+
+        const sad_mask: u32 = 0x0FFF_FFFE;
+        const dad_mask: u32 = 0x0FFF_FFFE;
+        const WordCount = u21;
+
+        /// Write-only. The first address in a DMA transfer. (DMASAD)
+        /// Note: use writeSrc instead of manipulating src_addr directly
+        sad: u32 = 0x0000_0000,
+        /// Write-only. The final address in a DMA transffer. (DMADAD)
+        /// Note: Use writeDst instead of manipulatig dst_addr directly
+        dad: u32 = 0x0000_0000,
+        /// Write-only. The Word Count for the DMA Transfer (DMACNT_L)
+        word_count: WordCount = 0,
+        /// Read / Write. DMACNT_H
+        /// Note: Use writeControl instead of manipulating cnt directly.
+        cnt: DmaCnt = .{ .raw = 0x0000 },
+
+        /// Internal. The last successfully read value
+        data_latch: u32 = 0x0000_0000,
+        /// Internal. Currrent Source Address
+        sad_latch: u32 = 0x0000_0000,
+        /// Internal. Current Destination Address
+        dad_latch: u32 = 0x0000_0000,
+        /// Internal. Word Count
+        _word_count: WordCount = 0,
+
+        /// Some DMA Transfers are enabled during Hblank / VBlank and / or
+        /// have delays. Thefore bit 15 of DMACNT isn't actually something
+        /// we can use to control when we do or do not execute a step in a DMA Transfer
+        in_progress: bool = false,
+
+        pub fn reset(self: *Self) void {
+            self.* = Self.init();
+        }
+
+        pub fn setDmasad(self: *Self, addr: u32) void {
+            self.sad = addr & sad_mask;
+        }
+
+        pub fn setDmadad(self: *Self, addr: u32) void {
+            self.dad = addr & dad_mask;
+        }
+
+        pub fn setDmacntL(self: *Self, halfword: u16) void {
+            self.word_count = halfword;
+        }
+
+        pub fn dmacntH(self: *const Self) u16 {
+            return self.cnt.raw & if (id == 3) 0xFFE0 else 0xF7E0;
+        }
+
+        pub fn setDmacntH(self: *Self, halfword: u16) void {
+            const new = DmaCnt{ .raw = halfword };
+
+            if (!self.cnt.enabled.read() and new.enabled.read()) {
+                // Reload Internals on Rising Edge.
+                self.sad_latch = self.sad;
+                self.dad_latch = self.dad;
+                self._word_count = if (self.word_count == 0) std.math.maxInt(WordCount) else self.word_count;
+
+                // Only a Start Timing of 00 has a DMA Transfer immediately begin
+                self.in_progress = new.start_timing.read() == 0b00;
+
+                // this is just for debug purposes
+                const start_timing: Kind = @enumFromInt(new.start_timing.read());
+
+                switch (start_timing) {
+                    .immediate, .vblank, .hblank => {},
+                    else => log.err("TODO: Implement DMA({}) {s} mode", .{ id, @tagName(start_timing) }),
+                }
+
+                // Debug stuff
+                {
+                    const sad_adj: Adjustment = @enumFromInt(new.sad_adj.read());
+                    const dad_adj: Adjustment = @enumFromInt(new.dad_adj.read());
+                    const byte_count = @as(u32, @sizeOf(u16)) << @intFromBool(new.transfer_type.read());
+
+                    const sad_final = switch (sad_adj) {
+                        .Increment, .IncrementReload => self.sad_latch +% self._word_count * byte_count,
+                        .Decrement => self.sad_latch -% self._word_count * byte_count,
+                        .Fixed => self.sad_latch,
+                    };
+
+                    const dad_final = switch (dad_adj) {
+                        .Increment, .IncrementReload => self.dad_latch +% self._word_count * byte_count,
+                        .Decrement => self.dad_latch -% self._word_count * byte_count,
+                        .Fixed => self.dad_latch,
+                    };
+
+                    log.debug("configured {s} transfer from 0x{X:0>8} -> 0x{X:0>8} to 0x{X:0>8} -> 0x{X:0>8} ({} words) for DMA{}", .{
+                        @tagName(start_timing),
+                        self.sad_latch,
+                        sad_final,
+                        self.dad_latch,
+                        dad_final,
+                        self._word_count,
+                        id,
+                    });
+                }
+            }
+
+            self.cnt.raw = halfword;
+        }
+
+        pub fn setDmacnt(self: *Self, word: u32) void {
+            self.setDmacntL(@truncate(word));
+            self.setDmacntH(@truncate(word >> 16));
+        }
+
+        pub fn step(self: *Self, cpu: *System.Arm946es) void {
+            const bus_ptr: *System.Bus9 = @ptrCast(@alignCast(cpu.bus.ptr));
+
+            const is_fifo = (id == 1 or id == 2) and self.cnt.start_timing.read() == 0b11;
+            const sad_adj: Adjustment = @enumFromInt(self.cnt.sad_adj.read());
+            const dad_adj: Adjustment = if (is_fifo) .Fixed else @enumFromInt(self.cnt.dad_adj.read());
+
+            const transfer_type = is_fifo or self.cnt.transfer_type.read();
+            const offset: u32 = if (transfer_type) @sizeOf(u32) else @sizeOf(u16);
+
+            const mask = if (transfer_type) ~@as(u32, 3) else ~@as(u32, 1);
+            const sad_addr = self.sad_latch & mask;
+            const dad_addr = self.dad_latch & mask;
+
+            if (transfer_type) {
+                if (sad_addr >= 0x0200_0000) self.data_latch = cpu.bus.read(u32, sad_addr);
+                cpu.bus.write(u32, dad_addr, self.data_latch);
+            } else {
+                if (sad_addr >= 0x0200_0000) {
+                    const value: u32 = cpu.bus.read(u16, sad_addr);
+                    self.data_latch = value << 16 | value;
+                }
+
+                cpu.bus.write(u16, dad_addr, @as(u16, @truncate(rotr(u32, self.data_latch, 8 * (dad_addr & 3)))));
+            }
+
+            switch (@as(u8, @truncate(sad_addr >> 24))) {
+                // according to fleroviux, DMAs with a source address in ROM misbehave
+                // the resultant behaviour is that the source address will increment despite what DMAXCNT says
+                0x08...0x0D => self.sad_latch +%= offset, // obscure behaviour
+                else => switch (sad_adj) {
+                    .Increment => self.sad_latch +%= offset,
+                    .Decrement => self.sad_latch -%= offset,
+                    .IncrementReload => log.err("{} is a prohibited adjustment on SAD", .{sad_adj}),
+                    .Fixed => {},
+                },
+            }
+
+            switch (dad_adj) {
+                .Increment, .IncrementReload => self.dad_latch +%= offset,
+                .Decrement => self.dad_latch -%= offset,
+                .Fixed => {},
+            }
+
+            self._word_count -= 1;
+
+            if (self._word_count == 0) {
+                if (self.cnt.irq.read()) {
+                    switch (id) {
+                        0 => bus_ptr.io.irq.dma0.set(),
+                        1 => bus_ptr.io.irq.dma1.set(),
+                        2 => bus_ptr.io.irq.dma2.set(),
+                        3 => bus_ptr.io.irq.dma3.set(),
+                    }
+
+                    handleInterrupt(.nds9, cpu);
+                }
+
+                // If we're not repeating, Fire the IRQs and disable the DMA
+                if (!self.cnt.repeat.read()) self.cnt.enabled.unset();
+
+                // We want to disable our internal enabled flag regardless of repeat
+                // because we only want to step A DMA that repeats during it's specific
+                // timing window
+                self.in_progress = false;
+            }
+        }
+
+        fn poll(self: *Self, comptime kind: Kind) void {
+            if (self.in_progress) return; // If there's an ongoing DMA Transfer, exit early
+
+            // No ongoing DMA Transfer, We want to check if we should repeat an existing one
+            // Determined by the repeat bit and whether the DMA is in the right start_timing
+
+            switch (kind) {
+                .vblank => self.in_progress = self.cnt.enabled.read() and self.cnt.start_timing.read() == 0b01,
+                .hblank => self.in_progress = self.cnt.enabled.read() and self.cnt.start_timing.read() == 0b10,
+                else => {},
+            }
+
+            // If we determined that the repeat bit is set (and now the Hblank / Vblank DMA is now in progress)
+            // Reload internal word count latch
+            // Reload internal DAD latch if we are in IncrementRelaod
+            if (self.in_progress) {
+                self._word_count = if (self.word_count == 0) std.math.maxInt(@TypeOf(self._word_count)) else self.word_count;
+                if (@as(Adjustment, @enumFromInt(self.cnt.dad_adj.read())) == .IncrementReload) self.dad_latch = self.dad;
+            }
+        }
+
+        pub fn requestAudio(self: *Self, _: u32) void {
+            comptime std.debug.assert(id == 1 or id == 2);
+            if (self.in_progress) return; // APU must wait their turn
+
+            // DMA May not be configured for handling DMAs
+            if (self.cnt.start_timing.read() != 0b11) return;
+
+            // We Assume the Repeat Bit is Set
+            // We Assume that DAD is set to 0x0400_00A0 or 0x0400_00A4 (fifo_addr)
+            // We Assume DMACNT_L is set to 4
+
+            // FIXME: Safe to just assume whatever DAD is set to is the FIFO Address?
+            // self.dad_latch = fifo_addr;
+            self.cnt.repeat.set();
+            self._word_count = 4;
+            self.in_progress = true;
+        }
+    };
+}
+
+pub fn onVblank(bus: *System.Bus9) void {
+    inline for (0..4) |i| bus.dma[i].poll(.vblank);
+}
+
+pub fn onHblank(bus: *System.Bus9) void {
+    inline for (0..4) |i| bus.dma[i].poll(.hblank);
+}
+
+pub fn step(cpu: *System.Arm946es) bool {
+    const bus: *System.Bus9 = @ptrCast(@alignCast(cpu.bus.ptr));
+
+    inline for (0..4) |i| {
+        if (bus.dma[i].in_progress) {
+            bus.dma[i].step(cpu);
+            return true;
+        }
+    }
+
+    return false;
+}
+
+const Adjustment = enum(u2) {
+    Increment = 0,
+    Decrement = 1,
+    Fixed = 2,
+    IncrementReload = 3,
+};
+
+const Kind = enum(u3) {
+    immediate = 0,
+    vblank,
+    hblank,
+
+    display_start_sync,
+    main_mem_display,
+    cartridge_slot,
+    pak_slot,
+    geo_cmd_fifo,
+};

src/core/nds9/io.zig

@@ -10,12 +10,16 @@ const masks = @import("../io.zig").masks;
 const IntEnable = @import("../io.zig").IntEnable;
 const IntRequest = @import("../io.zig").IntEnable;
 
+const dma = @import("dma.zig");
+
 const sext = @import("../../util.zig").sext;
 const shift = @import("../../util.zig").shift;
 
 const log = std.log.scoped(.nds9_io);
 
 pub const Io = struct {
+    const fill_len = 0x10 * @sizeOf(u32);
+
     shr: *SharedCtx.Io,
 
     /// Interrupt Master Enable
@@ -38,6 +42,9 @@ pub const Io = struct {
     div: Divisor = .{},
     sqrt: SquareRootUnit = .{},
 
+    // TODO: move somewhere else?
+    dma_fill: [fill_len]u8 = [_]u8{0} ** fill_len,
+
     pub fn init(io: *SharedCtx.Io) @This() {
         return .{ .shr = io };
     }
@@ -47,36 +54,48 @@ pub fn read(bus: *const Bus, comptime T: type, address: u32) T {
     return switch (T) {
         u32 => switch (address) {
             // DMA Transfers
-            0x0400_00B0...0x0400_00DC => warn("TODO: impl DMA", .{}),
+            0x0400_00B0...0x0400_00DC => dma.read(T, &bus.dma, address) orelse 0x0000_0000,
-            0x0400_00E0...0x0400_00EC => warn("TODO: impl DMA fill", .{}),
+            0x0400_00E0...0x0400_00EC => std.mem.readInt(T, bus.io.dma_fill[address & 0xF ..][0..@sizeOf(T)], .little),
 
             // Timers
-            0x0400_0100...0x0400_010C => warn("TODO: impl timer", .{}),
+            0x0400_0100...0x0400_010C => warn("TODO(timer): read(T: {}, addr: 0x{X:0>8}) {} ", .{ T, address, T }),
 
             0x0400_0180 => bus.io.shr.ipc._nds9.sync.raw,
             0x0400_0208 => @intFromBool(bus.io.ime),
             0x0400_0210 => bus.io.ie.raw,
             0x0400_0214 => bus.io.irq.raw,
 
+            // zig fmt: off
+            0x0400_0240 => @as(u32, bus.ppu.vram.io.cnt_d.raw) << 24
+                | @as(u32, bus.ppu.vram.io.cnt_c.raw) << 16
+                | @as(u32, bus.ppu.vram.io.cnt_b.raw) << 8
+                | bus.ppu.vram.io.cnt_a.raw << 0,
+            // zig fmt: on
+
+            0x0400_0280 => bus.io.div.cnt.raw,
             0x0400_02A0, 0x0400_02A4 => @truncate(bus.io.div.result >> shift(u64, address)),
             0x0400_02A8, 0x0400_02AC => @truncate(bus.io.div.remainder >> shift(u64, address)),
             0x0400_02B4 => @truncate(bus.io.sqrt.result),
 
+            0x0400_1000 => bus.ppu.engines[1].dispcnt.raw,
+
             0x0410_0000 => bus.io.shr.ipc.recv(.nds9),
 
             0x0400_4000, 0x0400_4008 => 0x0000_0000, // Lets software know this is NOT a DSi
             else => warn("unexpected: read(T: {}, addr: 0x{X:0>8}) {} ", .{ T, address, T }),
         },
         u16 => switch (address) {
+            0x0400_0006 => bus.ppu.io.nds9.vcount.raw,
+
             // DMA Transfers
-            0x0400_00B0...0x0400_00DE => warn("TODO: impl DMA", .{}),
+            0x0400_00B0...0x0400_00DE => dma.read(T, &bus.dma, address) orelse 0x0000,
-            0x0400_00E0...0x0400_00EE => warn("TODO: impl DMA fill", .{}),
+            0x0400_00E0...0x0400_00EE => std.mem.readInt(T, bus.io.dma_fill[address & 0xF ..][0..@sizeOf(T)], .little),
 
             // Timers
-            0x0400_0100...0x0400_010E => warn("TODO: impl timer", .{}),
+            0x0400_0100...0x0400_010E => warn("TODO(timer): read(T: {}, addr: 0x{X:0>8}) {} ", .{ T, address, T }),
 
             0x0400_0004 => bus.ppu.io.nds9.dispstat.raw,
-            0x0400_0130 => bus.io.shr.keyinput.load(.Monotonic),
+            0x0400_0130 => bus.io.shr.input.keyinput().raw,
 
             0x0400_0180 => @truncate(bus.io.shr.ipc._nds9.sync.raw),
             0x0400_0184 => @truncate(bus.io.shr.ipc._nds9.cnt.raw),
@@ -84,15 +103,29 @@ pub fn read(bus: *const Bus, comptime T: type, address: u32) T {
             0x0400_0280 => @truncate(bus.io.div.cnt.raw),
             0x0400_02B0 => @truncate(bus.io.sqrt.cnt.raw),
 
+            0x0400_1008 => bus.ppu.engines[1].bg[0].cnt.raw,
+            0x0400_100A => bus.ppu.engines[1].bg[1].cnt.raw,
+            0x0400_100C => bus.ppu.engines[1].bg[2].cnt.raw,
+            0x0400_100E => bus.ppu.engines[1].bg[3].cnt.raw,
+
+            0x0400_1010 => bus.ppu.engines[1].bg[0].hofs.raw,
+            0x0400_1012 => bus.ppu.engines[1].bg[0].vofs.raw,
+            0x0400_1014 => bus.ppu.engines[1].bg[1].hofs.raw,
+            0x0400_1016 => bus.ppu.engines[1].bg[1].vofs.raw,
+            0x0400_1018 => bus.ppu.engines[1].bg[2].hofs.raw,
+            0x0400_101A => bus.ppu.engines[1].bg[2].vofs.raw,
+            0x0400_101C => bus.ppu.engines[1].bg[3].hofs.raw,
+            0x0400_101E => bus.ppu.engines[1].bg[3].vofs.raw,
+
             else => warn("unexpected: read(T: {}, addr: 0x{X:0>8}) {} ", .{ T, address, T }),
         },
         u8 => switch (address) {
             // DMA Transfers
-            0x0400_00B0...0x0400_00DF => warn("TODO: impl DMA", .{}),
+            0x0400_00B0...0x0400_00DF => dma.read(T, &bus.dma, address) orelse 0x00,
-            0x0400_00E0...0x0400_00EF => warn("TODO: impl DMA fill", .{}),
+            0x0400_00E0...0x0400_00EF => std.mem.readInt(T, bus.io.dma_fill[address & 0xF ..][0..@sizeOf(T)], .little),
 
             // Timers
-            0x0400_0100...0x0400_010F => warn("TODO: impl timer", .{}),
+            0x0400_0100...0x0400_010F => warn("TODO(timer): read(T: {}, addr: 0x{X:0>8}) {} ", .{ T, address, T }),
 
             0x0400_0208 => @intFromBool(bus.io.ime),
 
@@ -108,28 +141,70 @@ const subset = @import("../../util.zig").subset;
 pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
     switch (T) {
         u32 => switch (address) {
+            0x0400_0000 => bus.ppu.engines[0].dispcnt.raw = value,
+            0x0400_0004 => bus.ppu.io.nds9.dispstat.raw = @truncate(value),
+            0x0400_0008 => {
+                bus.ppu.engines[0].bg[0].cnt.raw = @truncate(value >> 0); // 0x0400_0008
+                bus.ppu.engines[0].bg[1].cnt.raw = @truncate(value >> 16); // 0x0400_000A
+            },
+            0x0400_000C => {
+                bus.ppu.engines[0].bg[2].cnt.raw = @truncate(value >> 0); // 0x0400_000A
+                bus.ppu.engines[0].bg[3].cnt.raw = @truncate(value >> 16); // 0x0400_000C
+            },
+            0x00400_0010 => {
+                bus.ppu.engines[0].bg[0].hofs.raw = @truncate(value >> 0); // 0x0400_0010
+                bus.ppu.engines[0].bg[0].vofs.raw = @truncate(value >> 16); // 0x0400_0012
+            },
+            0x00400_0014 => {
+                bus.ppu.engines[0].bg[1].hofs.raw = @truncate(value >> 0); // 0x0400_0014
+                bus.ppu.engines[0].bg[1].vofs.raw = @truncate(value >> 16); // 0x0400_0016
+            },
+            0x00400_0018 => {
+                bus.ppu.engines[0].bg[2].hofs.raw = @truncate(value >> 0); // 0x0400_0018
+                bus.ppu.engines[0].bg[2].vofs.raw = @truncate(value >> 16); // 0x0400_001A
+            },
+            0x00400_001C => {
+                bus.ppu.engines[0].bg[3].hofs.raw = @truncate(value >> 0); // 0x0400_001C
+                bus.ppu.engines[0].bg[3].vofs.raw = @truncate(value >> 16); // 0x0400_001E
+            },
+
             // DMA Transfers
-            0x0400_00B0...0x0400_00DC => log.warn("TODO: impl DMA", .{}),
+            0x0400_00B0...0x0400_00DC => dma.write(T, &bus.dma, address, value),
-            0x0400_00E0...0x0400_00EC => log.warn("TODO: impl DMA fill", .{}),
+            0x0400_00E0...0x0400_00EC => std.mem.writeInt(T, bus.io.dma_fill[address & 0xF ..][0..@sizeOf(T)], value, .little),
 
             // Timers
-            0x0400_0100...0x0400_010C => log.warn("TODO: impl timer", .{}),
+            0x0400_0100...0x0400_010C => log.warn("TODO(timer): write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8})", .{ T, address, 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),
 
+            0x0400_0208 => bus.io.ime = value & 1 == 1,
+            0x0400_0210 => bus.io.ie.raw = value,
+            0x0400_0214 => bus.io.irq.raw &= ~value,
+
             0x0400_0240 => {
                 bus.ppu.vram.io.cnt_a.raw = @truncate(value >> 0); // 0x0400_0240
                 bus.ppu.vram.io.cnt_b.raw = @truncate(value >> 8); // 0x0400_0241
                 bus.ppu.vram.io.cnt_c.raw = @truncate(value >> 16); // 0x0400_0242
                 bus.ppu.vram.io.cnt_d.raw = @truncate(value >> 24); // 0x0400_0243
+
+                bus.ppu.vram.update();
+            },
+            0x0400_0244 => {
+                bus.ppu.vram.io.cnt_e.raw = @truncate(value >> 0); // 0x0400_0244
+                bus.ppu.vram.io.cnt_f.raw = @truncate(value >> 8); // 0x0400_0245
+                bus.ppu.vram.io.cnt_g.raw = @truncate(value >> 16); // 0x0400_0246
+                bus.io.shr.wramcnt.raw = @truncate(value >> 24); // 0x0400_0247
+
+                bus.ppu.vram.update();
+                bus.wram.update(bus.io.shr.wramcnt);
             },
 
-            0x0400_0208 => bus.io.ime = value & 1 == 1,
+            0x0400_0280 => {
-            0x0400_0210 => bus.io.ie.raw = value,
+                bus.io.div.cnt.raw = value;
-            0x0400_0214 => bus.io.irq.raw &= ~value,
+                bus.io.div.schedule(bus.scheduler);
+            },
 
             0x0400_0290, 0x0400_0294 => {
                 bus.io.div.numerator = subset(u64, u32, address, bus.io.div.numerator, value);
@@ -141,6 +216,11 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
                 bus.io.div.schedule(bus.scheduler);
             },
 
+            0x0400_02B0 => {
+                bus.io.sqrt.cnt.raw = value;
+                bus.io.sqrt.schedule(bus.scheduler);
+            },
+
             0x0400_02B8, 0x0400_02BC => {
                 bus.io.sqrt.param = subset(u64, u32, address, bus.io.sqrt.param, value);
                 bus.io.sqrt.schedule(bus.scheduler);
@@ -150,6 +230,30 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
             0x0400_0304 => bus.ppu.io.powcnt.raw = value,
 
             0x0400_1000 => bus.ppu.engines[1].dispcnt.raw = value,
+            0x0400_1008 => {
+                bus.ppu.engines[1].bg[0].cnt.raw = @truncate(value >> 0); // 0x0400_1008
+                bus.ppu.engines[1].bg[1].cnt.raw = @truncate(value >> 16); // 0x0400_100A
+            },
+            0x0400_100C => {
+                bus.ppu.engines[1].bg[2].cnt.raw = @truncate(value >> 0); // 0x0400_100A
+                bus.ppu.engines[1].bg[3].cnt.raw = @truncate(value >> 16); // 0x0400_100C
+            },
+            0x00400_1010 => {
+                bus.ppu.engines[1].bg[0].hofs.raw = @truncate(value >> 0); // 0x0400_1010
+                bus.ppu.engines[1].bg[0].vofs.raw = @truncate(value >> 16); // 0x0400_1012
+            },
+            0x00400_1014 => {
+                bus.ppu.engines[1].bg[1].hofs.raw = @truncate(value >> 0); // 0x0400_1014
+                bus.ppu.engines[1].bg[1].vofs.raw = @truncate(value >> 16); // 0x0400_1016
+            },
+            0x00400_1018 => {
+                bus.ppu.engines[1].bg[2].hofs.raw = @truncate(value >> 0); // 0x0400_1018
+                bus.ppu.engines[1].bg[2].vofs.raw = @truncate(value >> 16); // 0x0400_101A
+            },
+            0x00400_101C => {
+                bus.ppu.engines[1].bg[3].hofs.raw = @truncate(value >> 0); // 0x0400_101C
+                bus.ppu.engines[1].bg[3].vofs.raw = @truncate(value >> 16); // 0x0400_101E
+            },
 
             else => log.warn("unexpected: write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8})", .{ T, address, value }),
         },
@@ -157,11 +261,11 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
             0x0400_0004 => bus.ppu.io.nds9.dispstat.raw = value,
 
             // DMA Transfers
-            0x0400_00B0...0x0400_00DE => log.warn("TODO: impl DMA", .{}),
+            0x0400_00B0...0x0400_00DE => dma.write(T, &bus.dma, address, value),
-            0x0400_00E0...0x0400_00EE => log.warn("TODO: impl DMA fill", .{}),
+            0x0400_00E0...0x0400_00EE => std.mem.writeInt(T, bus.io.dma_fill[address & 0xF ..][0..@sizeOf(T)], value, .little),
 
             // Timers
-            0x0400_0100...0x0400_010E => log.warn("TODO: impl timer", .{}),
+            0x0400_0100...0x0400_010E => log.warn("TODO(timer): write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8})", .{ T, address, value }),
 
             0x0400_0180 => bus.io.shr.ipc.setIpcSync(.nds9, value),
             0x0400_0184 => bus.io.shr.ipc.setIpcFifoCnt(.nds9, value),
@@ -179,15 +283,29 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
 
             0x0400_0304 => bus.ppu.io.powcnt.raw = value,
 
+            0x0400_1008 => bus.ppu.engines[1].bg[0].cnt.raw = value,
+            0x0400_100A => bus.ppu.engines[1].bg[1].cnt.raw = value,
+            0x0400_100C => bus.ppu.engines[1].bg[2].cnt.raw = value,
+            0x0400_100E => bus.ppu.engines[1].bg[3].cnt.raw = value,
+
+            0x0400_1010 => bus.ppu.engines[1].bg[0].hofs.raw = value,
+            0x0400_1012 => bus.ppu.engines[1].bg[0].vofs.raw = value,
+            0x0400_1014 => bus.ppu.engines[1].bg[1].hofs.raw = value,
+            0x0400_1016 => bus.ppu.engines[1].bg[1].vofs.raw = value,
+            0x0400_1018 => bus.ppu.engines[1].bg[2].hofs.raw = value,
+            0x0400_101A => bus.ppu.engines[1].bg[2].vofs.raw = value,
+            0x0400_101C => bus.ppu.engines[1].bg[3].hofs.raw = value,
+            0x0400_101E => bus.ppu.engines[1].bg[3].vofs.raw = value,
+
             else => log.warn("unexpected: write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>4})", .{ T, address, value }),
         },
         u8 => switch (address) {
             // DMA Transfers
-            0x0400_00B0...0x0400_00DF => log.warn("TODO: impl DMA", .{}),
+            0x0400_00B0...0x0400_00DF => dma.write(T, &bus.dma, address, value),
-            0x0400_00E0...0x0400_00EF => log.warn("TODO: impl DMA fill", .{}),
+            0x0400_00E0...0x0400_00EF => std.mem.writeInt(T, bus.io.dma_fill[address & 0xF ..][0..@sizeOf(T)], value, .little),
 
             // Timers
-            0x0400_0100...0x0400_010F => log.warn("TODO: impl timer", .{}),
+            0x0400_0100...0x0400_010F => log.warn("TODO(timer): write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8})", .{ T, address, value }),
 
             0x0400_0208 => bus.io.ime = value & 1 == 1,
 
@@ -400,7 +518,7 @@ pub const DispcntA = extern union {
     tile_obj_1d_boundary: Bitfield(u32, 20, 2),
     bitmap_obj_1d_boundary: Bit(u32, 22),
     obj_during_hblank: Bit(u32, 23),
-    character_base: Bitfield(u32, 24, 3),
+    char_base: Bitfield(u32, 24, 3),
     screen_base: Bitfield(u32, 27, 3),
     bg_ext_pal_enable: Bit(u32, 30),
     obj_ext_pal_enable: Bit(u32, 31),
@@ -476,3 +594,34 @@ pub const Dispstat = extern union {
     lyc: Bitfield(u16, 7, 9),
     raw: u16,
 };
+
+pub const Bgcnt = extern union {
+    priority: Bitfield(u16, 0, 2),
+    char_base: Bitfield(u16, 2, 4),
+    mosaic_enable: Bit(u16, 6),
+    colour_mode: Bit(u16, 7),
+    screen_base: Bitfield(u16, 8, 5),
+    display_overflow: Bit(u16, 13),
+    size: Bitfield(u16, 14, 2),
+    raw: u16,
+};
+
+/// Write Only
+const BackgroundOffset = extern union {
+    offset: Bitfield(u16, 0, 9),
+    raw: u16,
+};
+
+pub const Hofs = BackgroundOffset;
+pub const Vofs = BackgroundOffset;
+
+pub const DmaCnt = extern union {
+    dad_adj: Bitfield(u16, 5, 2),
+    sad_adj: Bitfield(u16, 7, 2),
+    repeat: Bit(u16, 9),
+    transfer_type: Bit(u16, 10),
+    start_timing: Bitfield(u16, 11, 3),
+    irq: Bit(u16, 14),
+    enabled: Bit(u16, 15),
+    raw: u16,
+};

src/core/ppu.zig

@@ -5,9 +5,14 @@ const Scheduler = @import("Scheduler.zig");
 const System = @import("emu.zig").System;
 
 const Vram = @import("ppu/Vram.zig");
+const Oam = @import("ppu/Oam.zig");
+
 const EngineA = @import("ppu/engine.zig").EngineA;
 const EngineB = @import("ppu/engine.zig").EngineB;
 
+const dma7 = @import("nds7/dma.zig");
+const dma9 = @import("nds9/dma.zig");
+
 const handleInterrupt = @import("emu.zig").handleInterrupt;
 
 pub const screen_width = 256;
@@ -21,7 +26,10 @@ pub const Ppu = struct {
 
     vram: *Vram,
 
-    engines: struct { EngineA, EngineB } = .{ .{}, .{} },
+    // FIXME: do I need a pointer here?
+    oam: *Oam,
+
+    engines: struct { EngineA, EngineB },
 
     io: Io = .{},
 
@@ -44,20 +52,29 @@ pub const Ppu = struct {
     pub fn init(allocator: Allocator, vram: *Vram) !@This() {
         return .{
             .fb = try FrameBuffer.init(allocator),
+            .engines = .{ try EngineA.init(allocator), try EngineB.init(allocator) },
             .vram = vram,
+            .oam = blk: {
+                var oam = try allocator.create(Oam);
+                oam.init();
+
+                break :blk oam;
+            },
         };
     }
 
     pub fn deinit(self: @This(), allocator: Allocator) void {
         self.fb.deinit(allocator);
+        inline for (self.engines) |eng| eng.deinit(allocator);
+        allocator.destroy(self.oam);
     }
 
     pub fn drawScanline(self: *@This(), bus: *System.Bus9) void {
         if (self.io.powcnt.engine2d_a.read())
-            self.engines[0].drawScanline(bus, &self.fb, &self.io);
+            self.engines[0].drawScanline(bus, &self.fb);
 
         if (self.io.powcnt.engine2d_b.read())
-            self.engines[1].drawScanline(bus, &self.fb, &self.io);
+            self.engines[1].drawScanline(bus, &self.fb);
     }
 
     /// HDraw -> HBlank
@@ -72,7 +89,9 @@ pub const Ppu = struct {
             handleInterrupt(.nds7, system.arm7tdmi);
         }
 
-        // TODO: Run DMAs on HBlank
+        if (!self.io.nds9.dispstat.vblank.read()) { // ensure we aren't in VBlank
+            dma9.onHblank(system.bus9);
+        }
 
         self.io.nds9.dispstat.hblank.set();
         self.io.nds7.dispstat.hblank.set();
@@ -159,7 +178,11 @@ pub const Ppu = struct {
             self.io.nds7.dispstat.vblank.set();
 
             // TODO: Affine BG Latches
-            // TODO: VBlank DMA Transfers
+
+            dma7.onVblank(system.bus7);
+            dma9.onVblank(system.bus9);
+
+            // TODO: VBlank DMA9 Transfers
         }
 
         if (scanline == 262) {

src/core/ppu/Oam.zig

@@ -0,0 +1,7 @@
+const KiB = 0x400;
+
+buf: [2 * KiB]u8,
+
+pub fn init(self: *@This()) void {
+    @memset(self.buf[0..], 0);
+}

src/core/ppu/Vram.zig

@@ -1,6 +1,8 @@
 const std = @import("std");
 const KiB = 0x400;
 
+const System = @import("../emu.zig").System;
+
 const Allocator = std.mem.Allocator;
 const IntFittingRange = std.math.IntFittingRange;
 
@@ -253,15 +255,12 @@ pub fn update(self: *@This()) void {
     }
 }
 
-// TODO: Rename
+pub fn read(self: @This(), comptime T: type, comptime proc: System.Process, address: u32) T {
-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;
+    const table = if (proc == .nds9) self.nds9_table else self.nds7_table;
 
     if (table[page]) |some_ptr| {
         const ptr: [*]const T = @ptrCast(@alignCast(some_ptr));
@@ -269,16 +268,16 @@ pub fn read(self: @This(), comptime T: type, comptime dev: Device, address: u32)
         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 });
+    log.err("{s}: read(T: {}, addr: 0x{X:0>8}) was in un-mapped VRAM space", .{ @tagName(proc), T, address });
     return 0x00;
 }
 
-pub fn write(self: *@This(), comptime T: type, comptime dev: Device, address: u32, value: T) void {
+pub fn write(self: *@This(), comptime T: type, comptime proc: System.Process, 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;
+    const table = if (proc == .nds9) self.nds9_table else self.nds7_table;
 
     if (table[page]) |some_ptr| {
         const ptr: [*]T = @ptrCast(@alignCast(some_ptr));
@@ -287,5 +286,5 @@ pub fn write(self: *@This(), comptime T: type, comptime dev: Device, address: u3
         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 });
+    log.err("{s}: write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8}) was in un-mapped VRA< space", .{ @tagName(proc), T, address, value });
 }

src/core/ppu/engine.zig

@@ -11,14 +11,15 @@ const Ppu = @import("../ppu.zig").Ppu;
 const width = @import("../ppu.zig").screen_width;
 const height = @import("../ppu.zig").screen_height;
 
+const KiB = 0x400;
+
 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);
+    const log = std.log.scoped(.engine2d); // TODO: specify between 2D-A and 2D-B
-    _ = log; // TODO: specify between 2D-A and 2D-B
 
     // FIXME: don't commit zig crimes
     const Type = struct {
@@ -30,25 +31,76 @@ fn Engine(comptime kind: EngineKind) type {
     return struct {
         dispcnt: Type(DispcntA, DispcntB) = .{ .raw = 0x0000_0000 },
 
-        pub fn drawScanline(self: *@This(), bus: *Bus, fb: *FrameBuffer, io: *Ppu.Io) void {
+        bg: [4]bg.Text = .{ .{}, .{}, .{}, .{} },
+
+        // TODO: Rename
+        scanline: Scanline,
+
+        pub fn init(allocator: std.mem.Allocator) !@This() {
+            return .{
+                .scanline = try Scanline.init(allocator),
+            };
+        }
+
+        pub fn deinit(self: @This(), allocator: std.mem.Allocator) void {
+            self.scanline.deinit(allocator);
+        }
+
+        pub fn drawScanline(self: *@This(), bus: *Bus, fb: *FrameBuffer) void {
             const disp_mode = self.dispcnt.display_mode.read();
 
             switch (disp_mode) {
                 0 => { // Display Off
                     const buf = switch (kind) {
-                        .a => if (io.powcnt.display_swap.read()) fb.top(.back) else fb.btm(.back),
+                        .a => if (bus.ppu.io.powcnt.display_swap.read()) fb.top(.back) else fb.btm(.back),
-                        .b => if (io.powcnt.display_swap.read()) fb.btm(.back) else fb.top(.back),
+                        .b => if (bus.ppu.io.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)"),
+                1 => {
+                    const bg_mode = self.dispcnt.bg_mode.read();
+                    const bg_enable = self.dispcnt.bg_enable.read();
+                    const scanline: u32 = bus.ppu.io.nds9.vcount.scanline.read();
+
+                    switch (bg_mode) {
+                        //  BG0     BG1     BG2     BG3
+                        //  Text/3D Text    Text    Text
+                        0 => {
+                            // TODO: Fetch Sprites
+
+                            for (0..4) |layer| {
+                                // TODO: Draw Sprites
+
+                                inline for (0..4) |i| {
+                                    if (layer == self.bg[i].cnt.priority.read() and (bg_enable >> i) & 1 == 1) self.drawBackground(i, bus);
+                                }
+                            }
+
+                            const buf = switch (kind) {
+                                .a => if (bus.ppu.io.powcnt.display_swap.read()) fb.top(.back) else fb.btm(.back),
+                                .b => if (bus.ppu.io.powcnt.display_swap.read()) fb.btm(.back) else fb.top(.back),
+                            };
+
+                            const scanline_buf = blk: {
+                                const rgba_ptr: *[width * height]u32 = @ptrCast(@alignCast(buf));
+                                break :blk rgba_ptr[width * scanline ..][0..width];
+                            };
+
+                            self.renderTextMode(bus.dbgRead(u16, 0x0500_0000), scanline_buf);
+                        },
+                        else => |mode| {
+                            log.err("TODO: Implement Mode {}", .{mode});
+                            @panic("fatal error");
+                        },
+                    }
+                },
                 2 => { // VRAM display
                     if (kind == .b) return;
                     // TODO: Master Brightness can still affect this mode
 
-                    const scanline: u32 = io.nds9.vcount.scanline.read();
+                    const scanline: u32 = bus.ppu.io.nds9.vcount.scanline.read();
-                    const buf = if (io.powcnt.display_swap.read()) fb.top(.back) else fb.btm(.back);
+                    const buf = if (bus.ppu.io.powcnt.display_swap.read()) fb.top(.back) else fb.btm(.back);
 
                     const scanline_buf = blk: {
                         const rgba_ptr: *[width * height]u32 = @ptrCast(@alignCast(buf));
@@ -69,9 +121,211 @@ fn Engine(comptime kind: EngineKind) type {
                 },
             }
         }
+
+        fn drawBackground(self: *@This(), comptime layer: u2, bus: *Bus) void {
+            const screen_base = blk: {
+                const bgcnt_off: u32 = self.bg[layer].cnt.screen_base.read();
+                const dispcnt_off: u32 = if (kind == .a) self.dispcnt.screen_base.read() else 0;
+
+                break :blk (2 * KiB) * bgcnt_off + (64 * KiB) * dispcnt_off;
+            };
+
+            const char_base = blk: {
+                const bgcnt_off: u32 = self.bg[layer].cnt.char_base.read();
+                const dispcnt_off: u32 = if (kind == .a) self.dispcnt.char_base.read() else 0;
+
+                break :blk (16 * KiB) * bgcnt_off + (64 * KiB) * dispcnt_off;
+            };
+
+            const is_8bpp = self.bg[layer].cnt.colour_mode.read();
+            const size = self.bg[layer].cnt.size.read();
+
+            // In 4bpp: 1 byte represents two pixels so the length is (8 x 8) / 2
+            // In 8bpp: 1 byte represents one pixel so the length is 8 x 8
+            const tile_len: u32 = if (is_8bpp) 0x40 else 0x20;
+            const tile_row_offset: u32 = if (is_8bpp) 0x8 else 0x4;
+
+            const vofs: u32 = self.bg[layer].vofs.offset.read();
+            const hofs: u32 = self.bg[layer].hofs.offset.read();
+
+            const y: u32 = vofs + bus.ppu.io.nds9.vcount.scanline.read();
+
+            for (0..width) |idx| {
+                const i: u32 = @intCast(idx);
+                const x = hofs + i;
+
+                // TODO: Windowing
+
+                // Grab the Screen Entry from VRAM
+                const entry_addr = screen_base + tilemapOffset(size, x, y);
+                const entry: bg.Screen.Entry = @bitCast(bus.read(u16, 0x0600_0000 + entry_addr));
+
+                // Calculate the Address of the Tile in the designated Charblock
+                // We also take this opportunity to flip tiles if necessary
+                const tile_id: u32 = entry.tile_id.read();
+
+                // Calculate row and column offsets. Understand that
+                // `tile_len`, `tile_row_offset` and `col` are subject to different
+                // values depending on whether we are in 4bpp or 8bpp mode.
+                const row = @as(u3, @truncate(y)) ^ if (entry.v_flip.read()) 7 else @as(u3, 0);
+                const col = @as(u3, @truncate(x)) ^ if (entry.h_flip.read()) 7 else @as(u3, 0);
+                const tile_addr = char_base + (tile_id * tile_len) + (row * tile_row_offset) + if (is_8bpp) col else col >> 1;
+
+                const tile = bus.read(u8, 0x0600_0000 + tile_addr);
+                // If we're in 8bpp, then the tile value is an index into the palette,
+                // If we're in 4bpp, we have to account for a pal bank value in the Screen entry
+                // and then we can index the palette
+                const pal_addr: u32 = if (!is_8bpp) get4bppTilePalette(entry.pal_bank.read(), col, tile) else tile;
+
+                if (pal_addr != 0) {
+                    self.drawBackgroundPixel(layer, i, bus.read(u16, 0x0500_0000 + pal_addr * 2));
+                }
+            }
+        }
+
+        inline fn get4bppTilePalette(pal_bank: u4, col: u3, tile: u8) u8 {
+            const nybble_tile = tile >> ((col & 1) << 2) & 0xF;
+            if (nybble_tile == 0) return 0;
+
+            return (@as(u8, pal_bank) << 4) | nybble_tile;
+        }
+
+        fn renderTextMode(self: *@This(), backdrop: u16, frame_buf: []u32) void {
+            for (self.scanline.top(), self.scanline.btm(), frame_buf) |maybe_top, maybe_btm, *rgba| {
+                _ = maybe_btm;
+
+                const bgr555 = switch (maybe_top) {
+                    .set => |px| px,
+                    else => backdrop,
+                };
+
+                rgba.* = rgba888(bgr555);
+            }
+
+            self.scanline.reset();
+        }
+
+        // TODO: Comment this + get a better understanding
+        fn tilemapOffset(size: u2, x: u32, y: u32) u32 {
+            // Current Row: (y % PIXEL_COUNT) / 8
+            // Current COlumn: (x % PIXEL_COUNT) / 8
+            // Length of 1 row of Screen Entries: 0x40
+            // Length of 1 Screen Entry: 0x2 is the size of a screen entry
+            @setRuntimeSafety(false);
+
+            return switch (size) {
+                0 => (x % 256 / 8) * 2 + (y % 256 / 8) * 0x40, // 256 x 256
+                1 => blk: {
+                    // 512 x 256
+                    const offset: u32 = if (x & 0x1FF > 0xFF) 0x800 else 0;
+                    break :blk offset + (x % 256 / 8) * 2 + (y % 256 / 8) * 0x40;
+                },
+                2 => blk: {
+                    // 256 x 512
+                    const offset: u32 = if (y & 0x1FF > 0xFF) 0x800 else 0;
+                    break :blk offset + (x % 256 / 8) * 2 + (y % 256 / 8) * 0x40;
+                },
+                3 => blk: {
+                    // 512 x 512
+                    const offset: u32 = if (x & 0x1FF > 0xFF) 0x800 else 0;
+                    const offset_2: u32 = if (y & 0x1FF > 0xFF) 0x800 else 0;
+                    break :blk offset + offset_2 + (x % 256 / 8) * 2 + (y % 512 / 8) * 0x40;
+                },
             };
         }
 
+        fn drawBackgroundPixel(self: *@This(), comptime layer: u2, i: u32, bgr555: u16) void {
+            _ = layer;
+
+            self.scanline.top()[i] = Scanline.Pixel.from(.Background, bgr555);
+        }
+    };
+}
+
+const Scanline = struct {
+    const Pixel = union(enum) {
+        // TODO: Rename
+        const Layer = enum { Background, Sprite };
+
+        set: u16,
+        obj_set: u16,
+        unset: void,
+        hidden: void,
+
+        fn from(comptime layer: Layer, bgr555: u16) Pixel {
+            return switch (layer) {
+                .Background => .{ .set = bgr555 },
+                .Sprite => .{ .obj_set = bgr555 },
+            };
+        }
+
+        pub fn isSet(self: @This()) bool {
+            return switch (self) {
+                .set, .obj_set => true,
+                .unset, .hidden => false,
+            };
+        }
+    };
+
+    layers: [2][]Pixel,
+    buf: []Pixel,
+
+    fn init(allocator: std.mem.Allocator) !@This() {
+        const buf = try allocator.alloc(Pixel, width * 2); // Top & Bottom Scanline
+        @memset(buf, .unset);
+
+        return .{
+            // Top & Bototm Layers
+            .layers = [_][]Pixel{ buf[0..][0..width], buf[width..][0..width] },
+            .buf = buf,
+        };
+    }
+
+    fn reset(self: *@This()) void {
+        @memset(self.buf, .unset);
+    }
+
+    fn deinit(self: @This(), allocator: std.mem.Allocator) void {
+        allocator.free(self.buf);
+    }
+
+    fn top(self: *@This()) []Pixel {
+        return self.layers[0];
+    }
+
+    fn btm(self: *@This()) []Pixel {
+        return self.layers[1];
+    }
+};
+
+const bg = struct {
+    const Text = struct {
+        const io = @import("../nds9/io.zig");
+
+        /// Read / Write
+        cnt: io.Bgcnt = .{ .raw = 0x0000 },
+        /// Write Only
+        hofs: io.Hofs = .{ .raw = 0x0000 },
+        /// Write Only
+        vofs: io.Vofs = .{ .raw = 0x0000 },
+    };
+
+    const Screen = struct {
+        const Entry = extern union {
+            const Bitfield = @import("bitfield").Bitfield;
+            const Bit = @import("bitfield").Bit;
+
+            tile_id: Bitfield(u16, 0, 10),
+            h_flip: Bit(u16, 10),
+            v_flip: Bit(u16, 11),
+            pal_bank: Bitfield(u16, 12, 4),
+            raw: u16,
+        };
+    };
+
+    const Affine = @compileError("TODO: Implement Affine Backgrounds");
+};
+
 inline fn rgba888(bgr555: u16) u32 {
     const b: u32 = bgr555 >> 10 & 0x1F;
     const g: u32 = bgr555 >> 5 & 0x1F;

src/main.zig

@@ -6,6 +6,7 @@ const emu = @import("core/emu.zig");
 const Ui = @import("platform.zig").Ui;
 const SharedCtx = @import("core/emu.zig").SharedCtx;
 const System = @import("core/emu.zig").System;
+const Sync = @import("core/emu.zig").Sync;
 const Scheduler = @import("core/Scheduler.zig");
 
 const Allocator = std.mem.Allocator;
@@ -14,6 +15,7 @@ const ClapResult = clap.Result(clap.Help, &cli_params, clap.parsers.default);
 const cli_params = clap.parseParamsComptime(
     \\-h, --help        Display this help and exit.
     \\-f, --firm <str>  Path to NDS Firmware Directory
+    \\--gdb              Run Turbo in GDB Mode
     \\<str>             Path to the NDS ROM
     \\
 );
@@ -26,7 +28,7 @@ pub fn main() !void {
 
     const allocator = gpa.allocator();
 
-    const result = try clap.parse(clap.Help, &cli_params, clap.parsers.default, .{});
+    const result = try clap.parse(clap.Help, &cli_params, clap.parsers.default, .{ .allocator = allocator });
     defer result.deinit();
 
     const rom_path = try handlePositional(result);
@@ -65,11 +67,23 @@ pub fn main() !void {
     const rom_title = try emu.load(allocator, system, rom_path);
     if (firm_path) |path| try emu.loadFirm(allocator, system, path);
 
+    emu.fastBoot(system);
+
     var ui = try Ui.init(allocator);
     defer ui.deinit(allocator);
 
     ui.setTitle(rom_title);
-    try ui.run(&scheduler, system);
+
+    const sync = try allocator.create(Sync);
+    defer allocator.destroy(sync);
+
+    sync.init();
+
+    if (result.args.gdb == 0) {
+        try ui.run(&scheduler, system, sync);
+    } else {
+        try emu.debug.run(allocator, &ui, &scheduler, system, sync);
+    }
 }
 
 fn handlePositional(result: ClapResult) ![]const u8 {

src/platform.zig

@@ -8,8 +8,11 @@ const imgui = @import("ui/imgui.zig");
 const emu = @import("core/emu.zig");
 
 const System = @import("core/emu.zig").System;
+const Sync = @import("core/emu.zig").Sync;
 const KeyInput = @import("core/io.zig").KeyInput;
+const ExtKeyIn = @import("core/io.zig").ExtKeyIn;
 const Scheduler = @import("core/Scheduler.zig");
+const FrameBuffer = @import("core/ppu.zig").FrameBuffer;
 
 const Allocator = std.mem.Allocator;
 
@@ -33,7 +36,7 @@ pub const Ui = struct {
     state: imgui.State,
 
     pub fn init(allocator: Allocator) !Self {
-        var state = imgui.State{};
+        const state = imgui.State{};
 
         if (SDL.SDL_Init(SDL.SDL_INIT_VIDEO | SDL.SDL_INIT_EVENTS | SDL.SDL_INIT_AUDIO) < 0) panic();
         if (SDL.SDL_GL_SetAttribute(SDL.SDL_GL_CONTEXT_PROFILE_MASK, SDL.SDL_GL_CONTEXT_PROFILE_CORE) < 0) panic();
@@ -85,108 +88,42 @@ pub const Ui = struct {
         return SDL.SDL_GL_GetProcAddress(proc.ptr);
     }
 
-    pub fn run(self: *Self, scheduler: *Scheduler, system: System) !void {
+    pub fn setTitle(self: *@This(), title: [12]u8) void {
-        // TODO: Sort this out please
+        self.state.title = title ++ [_:0]u8{};
+    }
 
-        const vao_id = opengl_impl.vao();
+    pub fn run(self: *Self, scheduler: *Scheduler, system: System, sync: *Sync) !void {
-        defer gl.deleteVertexArrays(1, &[_]GLuint{vao_id});
+        const id = try opengl_impl.runInit(&system.bus9.ppu.fb);
-
+        defer id.deinit();
-        const top_tex = opengl_impl.screenTex(system.bus9.ppu.fb.top(.front));
-        const btm_tex = opengl_impl.screenTex(system.bus9.ppu.fb.btm(.front));
-        const top_out_tex = opengl_impl.outTex();
-        const btm_out_tex = opengl_impl.outTex();
-        defer gl.deleteTextures(4, &[_]GLuint{ top_tex, top_out_tex, btm_tex, btm_out_tex });
-
-        const top_fbo = try opengl_impl.frameBuffer(top_out_tex);
-        const btm_fbo = try opengl_impl.frameBuffer(btm_out_tex);
-        defer gl.deleteFramebuffers(2, &[_]GLuint{ top_fbo, btm_fbo });
-
-        const prog_id = try opengl_impl.program();
-        defer gl.deleteProgram(prog_id);
 
         var event: SDL.SDL_Event = undefined;
 
-        emu_loop: while (true) {
+        while (!sync.should_quit.load(.Monotonic)) {
-            emu.runFrame(scheduler, system);
+            emu.runFrame(scheduler, system); // TODO: run emu in separate thread
 
             while (SDL.SDL_PollEvent(&event) != 0) {
                 _ = zgui.backend.processEvent(&event);
-
+                handleInput(&event, system, &self.state, sync);
-                switch (event.type) {
-                    SDL.SDL_QUIT => break :emu_loop,
-                    SDL.SDL_WINDOWEVENT => {
-                        if (event.window.event == SDL.SDL_WINDOWEVENT_RESIZED) {
-                            std.log.debug("window resized to: {}x{}", .{ event.window.data1, event.window.data2 });
-
-                            self.state.dim.width = @intCast(event.window.data1);
-                            self.state.dim.height = @intCast(event.window.data2);
-                        }
-                    },
-                    SDL.SDL_KEYDOWN => {
-                        // TODO: Make use of compare_and_xor?
-                        const key_code = event.key.keysym.sym;
-                        var keyinput: KeyInput = .{ .raw = 0x0000 };
-
-                        switch (key_code) {
-                            SDL.SDLK_UP => keyinput.up.set(),
-                            SDL.SDLK_DOWN => keyinput.down.set(),
-                            SDL.SDLK_LEFT => keyinput.left.set(),
-                            SDL.SDLK_RIGHT => keyinput.right.set(),
-                            SDL.SDLK_x => keyinput.a.set(),
-                            SDL.SDLK_z => keyinput.b.set(),
-                            SDL.SDLK_a => keyinput.shoulder_l.set(),
-                            SDL.SDLK_s => keyinput.shoulder_r.set(),
-                            SDL.SDLK_RETURN => keyinput.start.set(),
-                            SDL.SDLK_RSHIFT => keyinput.select.set(),
-                            else => {},
-                        }
-
-                        system.bus9.io.shr.keyinput.fetchAnd(~keyinput.raw, .Monotonic);
-                    },
-                    SDL.SDL_KEYUP => {
-                        // TODO: Make use of compare_and_xor?
-                        const key_code = event.key.keysym.sym;
-                        var keyinput: KeyInput = .{ .raw = 0x0000 };
-
-                        switch (key_code) {
-                            SDL.SDLK_UP => keyinput.up.set(),
-                            SDL.SDLK_DOWN => keyinput.down.set(),
-                            SDL.SDLK_LEFT => keyinput.left.set(),
-                            SDL.SDLK_RIGHT => keyinput.right.set(),
-                            SDL.SDLK_x => keyinput.a.set(),
-                            SDL.SDLK_z => keyinput.b.set(),
-                            SDL.SDLK_a => keyinput.shoulder_l.set(),
-                            SDL.SDLK_s => keyinput.shoulder_r.set(),
-                            SDL.SDLK_RETURN => keyinput.start.set(),
-                            SDL.SDLK_RSHIFT => keyinput.select.set(),
-                            else => {},
-                        }
-
-                        system.bus9.io.shr.keyinput.fetchOr(keyinput.raw, .Monotonic);
-                    },
-                    else => {},
-                }
             }
 
             {
-                gl.bindFramebuffer(gl.FRAMEBUFFER, top_fbo);
+                gl.bindFramebuffer(gl.FRAMEBUFFER, id.top_fbo);
                 defer gl.bindFramebuffer(gl.FRAMEBUFFER, 0);
 
                 gl.viewport(0, 0, nds_width, nds_height);
-                opengl_impl.drawScreen(top_tex, prog_id, vao_id, system.bus9.ppu.fb.top(.front));
+                opengl_impl.drawScreen(id.top_tex, id.prog_id, id.vao_id, system.bus9.ppu.fb.top(.front));
             }
 
             {
-                gl.bindFramebuffer(gl.FRAMEBUFFER, btm_fbo);
+                gl.bindFramebuffer(gl.FRAMEBUFFER, id.btm_fbo);
                 defer gl.bindFramebuffer(gl.FRAMEBUFFER, 0);
 
                 gl.viewport(0, 0, nds_width, nds_height);
-                opengl_impl.drawScreen(btm_tex, prog_id, vao_id, system.bus9.ppu.fb.btm(.front));
+                opengl_impl.drawScreen(id.btm_tex, id.prog_id, id.vao_id, system.bus9.ppu.fb.btm(.front));
             }
 
-            const zgui_redraw = imgui.draw(&self.state, top_out_tex, btm_out_tex, system);
+            imgui.draw(&self.state, id.top_out_tex, id.btm_out_tex, system);
 
-            if (zgui_redraw) {
             // Background Colour
             const size = zgui.io.getDisplaySize();
             gl.viewport(0, 0, @intFromFloat(size[0]), @intFromFloat(size[1]));
@@ -194,14 +131,118 @@ pub const Ui = struct {
             gl.clear(gl.COLOR_BUFFER_BIT);
 
             zgui.backend.draw();
-            }
-
             SDL.SDL_GL_SwapWindow(self.window);
         }
     }
 
-    pub fn setTitle(self: *@This(), title: [12]u8) void {
+    pub fn debug_run(self: *Self, _: *Scheduler, system: System, sync: *Sync) !void {
-        self.state.title = title ++ [_:0]u8{};
+        const id = try opengl_impl.runInit(&system.bus9.ppu.fb);
+        defer id.deinit();
+
+        var event: SDL.SDL_Event = undefined;
+
+        while (!sync.should_quit.load(.Monotonic)) {
+            while (SDL.SDL_PollEvent(&event) != 0) {
+                _ = zgui.backend.processEvent(&event);
+                handleInput(&event, system, &self.state, sync);
+            }
+
+            {
+                gl.bindFramebuffer(gl.FRAMEBUFFER, id.top_fbo);
+                defer gl.bindFramebuffer(gl.FRAMEBUFFER, 0);
+
+                gl.viewport(0, 0, nds_width, nds_height);
+                opengl_impl.drawScreen(id.top_tex, id.prog_id, id.vao_id, system.bus9.ppu.fb.top(.front));
+            }
+
+            {
+                gl.bindFramebuffer(gl.FRAMEBUFFER, id.btm_fbo);
+                defer gl.bindFramebuffer(gl.FRAMEBUFFER, 0);
+
+                gl.viewport(0, 0, nds_width, nds_height);
+                opengl_impl.drawScreen(id.btm_tex, id.prog_id, id.vao_id, system.bus9.ppu.fb.btm(.front));
+            }
+
+            imgui.draw(&self.state, id.top_out_tex, id.btm_out_tex, system);
+
+            // Background Colour
+            const size = zgui.io.getDisplaySize();
+            gl.viewport(0, 0, @intFromFloat(size[0]), @intFromFloat(size[1]));
+            gl.clearColor(0, 0, 0, 1.0);
+            gl.clear(gl.COLOR_BUFFER_BIT);
+
+            zgui.backend.draw();
+            SDL.SDL_GL_SwapWindow(self.window);
+        }
+    }
+
+    fn handleInput(event: *SDL.SDL_Event, system: System, state: *imgui.State, sync: *Sync) void {
+        switch (event.type) {
+            SDL.SDL_QUIT => sync.should_quit.store(true, .Monotonic),
+            SDL.SDL_WINDOWEVENT => {
+                if (event.window.event == SDL.SDL_WINDOWEVENT_RESIZED) {
+                    std.log.debug("window resized to: {}x{}", .{ event.window.data1, event.window.data2 });
+
+                    state.dim.width = @intCast(event.window.data1);
+                    state.dim.height = @intCast(event.window.data2);
+
+                    zgui.io.setDisplaySize(@floatFromInt(event.window.data1), @floatFromInt(event.window.data2));
+                }
+            },
+            SDL.SDL_KEYDOWN => {
+                // TODO: Make use of compare_and_xor?
+                const key_code = event.key.keysym.sym;
+
+                var keyinput: KeyInput = .{ .raw = 0x0000 };
+                var extkeyin: ExtKeyIn = .{ .raw = 0x0000 };
+
+                switch (key_code) {
+                    SDL.SDLK_UP => keyinput.up.set(),
+                    SDL.SDLK_DOWN => keyinput.down.set(),
+                    SDL.SDLK_LEFT => keyinput.left.set(),
+                    SDL.SDLK_RIGHT => keyinput.right.set(),
+                    SDL.SDLK_c => keyinput.a.set(),
+                    SDL.SDLK_x => keyinput.b.set(),
+                    SDL.SDLK_d => extkeyin.x.set(),
+                    SDL.SDLK_s => extkeyin.y.set(),
+                    SDL.SDLK_a => keyinput.shoulder_l.set(),
+                    SDL.SDLK_f => keyinput.shoulder_r.set(),
+                    SDL.SDLK_RETURN => keyinput.start.set(),
+                    SDL.SDLK_RSHIFT => keyinput.select.set(),
+                    else => {},
+                }
+
+                const input = (@as(u32, extkeyin.raw) << 16) | keyinput.raw;
+                system.bus9.io.shr.input.set(.And, ~input);
+            },
+            SDL.SDL_KEYUP => {
+                // TODO: Make use of compare_and_xor?
+                const key_code = event.key.keysym.sym;
+
+                var keyinput: KeyInput = .{ .raw = 0x0000 };
+                var extkeyin: ExtKeyIn = .{ .raw = 0x0000 };
+
+                switch (key_code) {
+                    SDL.SDLK_UP => keyinput.up.set(),
+                    SDL.SDLK_DOWN => keyinput.down.set(),
+                    SDL.SDLK_LEFT => keyinput.left.set(),
+                    SDL.SDLK_RIGHT => keyinput.right.set(),
+                    SDL.SDLK_c => keyinput.a.set(),
+                    SDL.SDLK_x => keyinput.b.set(),
+                    SDL.SDLK_d => extkeyin.x.set(),
+                    SDL.SDLK_s => extkeyin.y.set(),
+                    SDL.SDLK_a => keyinput.shoulder_l.set(),
+                    SDL.SDLK_f => keyinput.shoulder_r.set(),
+                    SDL.SDLK_RETURN => keyinput.start.set(),
+                    SDL.SDLK_RSHIFT => keyinput.select.set(),
+                    else => {},
+                }
+
+                const input = (@as(u32, extkeyin.raw) << 16) | keyinput.raw;
+                system.bus9.io.shr.input.set(.Or, input);
+            },
+            else => {},
+        }
     }
 };
 
@@ -211,6 +252,46 @@ fn panic() noreturn {
 }
 
 const opengl_impl = struct {
+    const Ids = struct {
+        vao_id: GLuint,
+
+        top_tex: GLuint,
+        btm_tex: GLuint,
+        top_out_tex: GLuint,
+        btm_out_tex: GLuint,
+
+        top_fbo: GLuint,
+        btm_fbo: GLuint,
+
+        prog_id: GLuint,
+
+        fn deinit(self: Ids) void {
+            gl.deleteProgram(self.prog_id);
+            gl.deleteFramebuffers(2, &[_]GLuint{ self.top_fbo, self.btm_fbo });
+            gl.deleteTextures(4, &[_]GLuint{ self.top_tex, self.top_out_tex, self.btm_tex, self.btm_out_tex });
+            gl.deleteVertexArrays(1, &[_]GLuint{self.vao_id});
+        }
+    };
+
+    fn runInit(fb: *const FrameBuffer) !Ids {
+        const top_out_tex = opengl_impl.outTex();
+        const btm_out_tex = opengl_impl.outTex();
+
+        return .{
+            .vao_id = opengl_impl.vao(),
+
+            .top_tex = opengl_impl.screenTex(fb.top(.front)),
+            .btm_tex = opengl_impl.screenTex(fb.btm(.front)),
+            .top_out_tex = top_out_tex,
+            .btm_out_tex = btm_out_tex,
+
+            .top_fbo = try opengl_impl.frameBuffer(top_out_tex),
+            .btm_fbo = try opengl_impl.frameBuffer(btm_out_tex),
+
+            .prog_id = try opengl_impl.program(),
+        };
+    }
+
     fn drawScreen(tex_id: GLuint, prog_id: GLuint, vao_id: GLuint, buf: []const u8) void {
         gl.bindTexture(gl.TEXTURE_2D, tex_id);
         defer gl.bindTexture(gl.TEXTURE_2D, 0);

src/ui/imgui.zig

@@ -18,7 +18,7 @@ pub const State = struct {
     dim: Dimensions = .{ .width = 1600, .height = 900 },
 };
 
-pub fn draw(state: *const State, top_tex: GLuint, btm_tex: GLuint, system: System) bool {
+pub fn draw(state: *const State, top_tex: GLuint, btm_tex: GLuint, system: System) void {
     _ = system;
 
     zgui.backend.newFrame(@floatFromInt(state.dim.width), @floatFromInt(state.dim.height));
@@ -36,6 +36,4 @@ pub fn draw(state: *const State, top_tex: GLuint, btm_tex: GLuint, system: Syste
         zgui.image(@ptrFromInt(top_tex), .{ .w = w, .h = h });
         zgui.image(@ptrFromInt(btm_tex), .{ .w = w, .h = h });
     }
-
-    return true;
 }