chore: Guilty Gear X expects these I/O Registers

src/core/Bus.zig

@@ -88,7 +88,7 @@ pub fn dbgRead(self: *const Self, comptime T: type, address: u32) T {
         },
         0x02 => self.ewram.read(T, aligned_addr),
         0x03 => self.iwram.read(T, aligned_addr),
-        0x04 => io.read(self, T, aligned_addr),
+        0x04 => self.readIo(T, address),
 
         // Internal Display Memory
         0x05 => self.ppu.palette.read(T, aligned_addr),
@@ -113,6 +113,11 @@ pub fn dbgRead(self: *const Self, comptime T: type, address: u32) T {
     };
 }
 
+fn readIo(self: *const Self, comptime T: type, unaligned_address: u32) T {
+    const maybe_value = io.read(self, T, forceAlign(T, unaligned_address));
+    return if (maybe_value) |value| value else self.readOpenBus(T, unaligned_address);
+}
+
 fn readOpenBus(self: *const Self, comptime T: type, address: u32) T {
     const r15 = self.cpu.?.r[15];
 
@@ -168,7 +173,7 @@ pub fn read(self: *Self, comptime T: type, address: u32) T {
         },
         0x02 => self.ewram.read(T, aligned_addr),
         0x03 => self.iwram.read(T, aligned_addr),
-        0x04 => io.read(self, T, aligned_addr),
+        0x04 => self.readIo(T, address),
 
         // Internal Display Memory
         0x05 => self.ppu.palette.read(T, aligned_addr),

src/core/apu.zig

@@ -1,6 +1,7 @@
 const std = @import("std");
 const SDL = @import("sdl2");
 const io = @import("bus/io.zig");
+const util = @import("util.zig");
 
 const Arm7tdmi = @import("cpu.zig").Arm7tdmi;
 const Scheduler = @import("scheduler.zig").Scheduler;
@@ -9,13 +10,11 @@ const SoundFifo = std.fifo.LinearFifo(u8, .{ .Static = 0x20 });
 const AudioDeviceId = SDL.SDL_AudioDeviceID;
 
 const intToBytes = @import("util.zig").intToBytes;
-const readUndefined = @import("util.zig").readUndefined;
-const writeUndefined = @import("util.zig").writeUndefined;
 const log = std.log.scoped(.APU);
 
 pub const host_sample_rate = 1 << 15;
 
-pub fn read(comptime T: type, apu: *const Apu, addr: u32) T {
+pub fn read(comptime T: type, apu: *const Apu, addr: u32) ?T {
     const byte = @truncate(u8, addr);
 
     return switch (T) {
@@ -38,7 +37,7 @@ pub fn read(comptime T: type, apu: *const Apu, addr: u32) T {
             0x84 => apu.getSoundCntX(),
             0x88 => apu.bias.raw, // SOUNDBIAS
             0x90...0x9F => apu.ch3.wave_dev.read(T, apu.ch3.select, addr),
-            else => readUndefined(log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
+            else => util.io.read.undef(T, log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
         },
         u8 => switch (byte) {
             0x60 => apu.ch1.getSoundCntL(), // NR10
@@ -52,9 +51,9 @@ pub fn read(comptime T: type, apu: *const Apu, addr: u32) T {
             0x81 => @truncate(u8, apu.psg_cnt.raw >> 8), // NR51
             0x84 => apu.getSoundCntX(),
             0x89 => @truncate(u8, apu.bias.raw >> 8), // SOUNDBIAS_H
-            else => readUndefined(log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
+            else => util.io.read.undef(T, log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
         },
-        u32 => readUndefined(log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
+        u32 => util.io.read.undef(T, log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
         else => @compileError("APU: Unsupported read width"),
     };
 }
@@ -78,7 +77,7 @@ pub fn write(comptime T: type, apu: *Apu, addr: u32, value: T) void {
             0x90...0x9F => apu.ch3.wave_dev.write(T, apu.ch3.select, addr, value),
             0xA0 => apu.chA.push(value), // FIFO_A
             0xA4 => apu.chB.push(value), // FIFO_B
-            else => writeUndefined(log, "Tried to write 0x{X:0>8}{} to 0x{X:0>8}", .{ value, T, addr }),
+            else => util.io.write.undef(log, "Tried to write 0x{X:0>8}{} to 0x{X:0>8}", .{ value, T, addr }),
         },
         u16 => switch (byte) {
             0x60 => apu.ch1.setSoundCntL(@truncate(u8, value)), // SOUND1CNT_L
@@ -101,7 +100,7 @@ pub fn write(comptime T: type, apu: *Apu, addr: u32, value: T) void {
             0x88 => apu.bias.raw = value, // SOUNDBIAS
             // WAVE_RAM
             0x90...0x9F => apu.ch3.wave_dev.write(T, apu.ch3.select, addr, value),
-            else => writeUndefined(log, "Tried to write 0x{X:0>4}{} to 0x{X:0>8}", .{ value, T, addr }),
+            else => util.io.write.undef(log, "Tried to write 0x{X:0>4}{} to 0x{X:0>8}", .{ value, T, addr }),
         },
         u8 => switch (byte) {
             0x60 => apu.ch1.setSoundCntL(value),
@@ -133,7 +132,7 @@ pub fn write(comptime T: type, apu: *Apu, addr: u32, value: T) void {
             0x84 => apu.setSoundCntX(value >> 7 & 1 == 1), // NR52
             0x89 => apu.setSoundBiasH(value),
             0x90...0x9F => apu.ch3.wave_dev.write(T, apu.ch3.select, addr, value),
-            else => writeUndefined(log, "Tried to write 0x{X:0>2}{} to 0x{X:0>8}", .{ value, T, addr }),
+            else => util.io.write.undef(log, "Tried to write 0x{X:0>2}{} to 0x{X:0>8}", .{ value, T, addr }),
         },
         else => @compileError("APU: Unsupported write width"),
     }

src/core/bus/dma.zig

@@ -1,11 +1,10 @@
 const std = @import("std");
+const util = @import("../util.zig");
 
 const DmaControl = @import("io.zig").DmaControl;
 const Bus = @import("../Bus.zig");
 const Arm7tdmi = @import("../cpu.zig").Arm7tdmi;
 
-const readUndefined = @import("../util.zig").readUndefined;
-const writeUndefined = @import("../util.zig").writeUndefined;
 pub const DmaTuple = std.meta.Tuple(&[_]type{ DmaController(0), DmaController(1), DmaController(2), DmaController(3) });
 const log = std.log.scoped(.DmaTransfer);
 
@@ -13,7 +12,7 @@ pub fn create() DmaTuple {
     return .{ DmaController(0).init(), DmaController(1).init(), DmaController(2).init(), DmaController(3).init() };
 }
 
-pub fn read(comptime T: type, dma: *const DmaTuple, addr: u32) T {
+pub fn read(comptime T: type, dma: *const DmaTuple, addr: u32) ?T {
     const byte = @truncate(u8, addr);
 
     return switch (T) {
@@ -22,16 +21,16 @@ pub fn read(comptime T: type, dma: *const DmaTuple, addr: u32) T {
             0xC4 => @as(T, dma.*[1].cnt.raw) << 16,
             0xD0 => @as(T, dma.*[2].cnt.raw) << 16,
             0xDC => @as(T, dma.*[3].cnt.raw) << 16,
-            else => readUndefined(log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
+            else => util.io.read.undef(T, log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
         },
         u16 => switch (byte) {
             0xBA => dma.*[0].cnt.raw,
             0xC6 => dma.*[1].cnt.raw,
             0xD2 => dma.*[2].cnt.raw,
             0xDE => dma.*[3].cnt.raw,
-            else => readUndefined(log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
+            else => util.io.read.undef(T, log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
         },
-        u8 => readUndefined(log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
+        u8 => util.io.read.undef(T, log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
         else => @compileError("DMA: Unsupported read width"),
     };
 }
@@ -53,7 +52,7 @@ pub fn write(comptime T: type, dma: *DmaTuple, addr: u32, value: T) void {
             0xD4 => dma.*[3].setSad(value),
             0xD8 => dma.*[3].setDad(value),
             0xDC => dma.*[3].setCnt(value),
-            else => writeUndefined(log, "Tried to write 0x{X:0>8}{} to 0x{X:0>8}", .{ value, T, addr }),
+            else => util.io.write.undef(log, "Tried to write 0x{X:0>8}{} to 0x{X:0>8}", .{ value, T, addr }),
         },
         u16 => switch (byte) {
             0xB0 => dma.*[0].setSad(setU32L(dma.*[0].sad, value)),
@@ -83,9 +82,9 @@ pub fn write(comptime T: type, dma: *DmaTuple, addr: u32, value: T) void {
             0xDA => dma.*[3].setDad(setU32H(dma.*[3].dad, value)),
             0xDC => dma.*[3].setCntL(value),
             0xDE => dma.*[3].setCntH(value),
-            else => writeUndefined(log, "Tried to write 0x{X:0>4}{} to 0x{X:0>8}", .{ value, T, addr }),
+            else => util.io.write.undef(log, "Tried to write 0x{X:0>4}{} to 0x{X:0>8}", .{ value, T, addr }),
         },
-        u8 => writeUndefined(log, "Tried to write 0x{X:0>2}{} to 0x{X:0>8}", .{ value, T, addr }),
+        u8 => util.io.write.undef(log, "Tried to write 0x{X:0>2}{} to 0x{X:0>8}", .{ value, T, addr }),
         else => @compileError("DMA: Unsupported write width"),
     }
 }

src/core/bus/io.zig

@@ -1,5 +1,9 @@
 const std = @import("std");
 const builtin = @import("builtin");
+const timer = @import("timer.zig");
+const dma = @import("dma.zig");
+const apu = @import("../apu.zig");
+const util = @import("../util.zig");
 
 const Bit = @import("bitfield").Bit;
 const Bitfield = @import("bitfield").Bitfield;
@@ -7,12 +11,6 @@ const Bus = @import("../Bus.zig");
 const DmaController = @import("dma.zig").DmaController;
 const Scheduler = @import("../scheduler.zig").Scheduler;
 
-const timer = @import("timer.zig");
-const dma = @import("dma.zig");
-const apu = @import("../apu.zig");
-
-const readUndefined = @import("../util.zig").readUndefined;
-const writeUndefined = @import("../util.zig").writeUndefined;
 const log = std.log.scoped(.@"I/O");
 
 pub const Io = struct {
@@ -43,7 +41,7 @@ pub const Io = struct {
     }
 };
 
-pub fn read(bus: *const Bus, comptime T: type, address: u32) T {
+pub fn read(bus: *const Bus, comptime T: type, address: u32) ?T {
     return switch (T) {
         u32 => switch (address) {
             // Display
@@ -58,18 +56,18 @@ pub fn read(bus: *const Bus, comptime T: type, address: u32) T {
             0x0400_0100...0x0400_010C => timer.read(T, &bus.tim, address),
 
             // Serial Communication 1
-            0x0400_0128 => readTodo("Read {} from SIOCNT and SIOMLT_SEND", .{T}),
+            0x0400_0128 => util.io.read.todo(log, "Read {} from SIOCNT and SIOMLT_SEND", .{T}),
 
             // Keypad Input
-            0x0400_0130 => readTodo("Read {} from KEYINPUT", .{T}),
+            0x0400_0130 => util.io.read.todo(log, "Read {} from KEYINPUT", .{T}),
 
             // Serial Communication 2
-            0x0400_0150 => readTodo("Read {} from JOY_RECV", .{T}),
+            0x0400_0150 => util.io.read.todo(log, "Read {} from JOY_RECV", .{T}),
 
             // Interrupts
             0x0400_0200 => @as(T, bus.io.irq.raw) << 16 | bus.io.ie.raw,
             0x0400_0208 => @boolToInt(bus.io.ime),
-            else => readUndefined(log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, address }),
+            else => util.io.read.undef(T, log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, address }),
         },
         u16 => switch (address) {
             // Display
@@ -80,8 +78,10 @@ pub fn read(bus: *const Bus, comptime T: type, address: u32) T {
             0x0400_000A => bus.ppu.bg[1].cnt.raw,
             0x0400_000C => bus.ppu.bg[2].cnt.raw,
             0x0400_000E => bus.ppu.bg[3].cnt.raw,
-            0x0400_004C => readTodo("Read {} from MOSAIC", .{T}),
+            0x0400_004C => util.io.read.todo(log, "Read {} from MOSAIC", .{T}),
             0x0400_0050 => bus.ppu.bldcnt.raw,
+            0x0400_0052 => bus.ppu.bldalpha.raw,
+            0x0400_0054 => bus.ppu.bldy.raw,
 
             // Sound
             0x0400_0060...0x0400_009E => apu.read(T, &bus.apu, address),
@@ -93,20 +93,20 @@ pub fn read(bus: *const Bus, comptime T: type, address: u32) T {
             0x0400_0100...0x0400_010E => timer.read(T, &bus.tim, address),
 
             // Serial Communication 1
-            0x0400_0128 => readTodo("Read {} from SIOCNT", .{T}),
+            0x0400_0128 => util.io.read.todo(log, "Read {} from SIOCNT", .{T}),
 
             // Keypad Input
             0x0400_0130 => bus.io.keyinput.raw,
 
             // Serial Communication 2
-            0x0400_0134 => readTodo("Read {} from RCNT", .{T}),
+            0x0400_0134 => util.io.read.todo(log, "Read {} from RCNT", .{T}),
 
             // Interrupts
             0x0400_0200 => bus.io.ie.raw,
             0x0400_0202 => bus.io.irq.raw,
-            0x0400_0204 => readTodo("Read {} from WAITCNT", .{T}),
+            0x0400_0204 => util.io.read.todo(log, "Read {} from WAITCNT", .{T}),
             0x0400_0208 => @boolToInt(bus.io.ime),
-            else => readUndefined(log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, address }),
+            else => util.io.read.undef(T, log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, address }),
         },
         u8 => return switch (address) {
             // Display
@@ -123,18 +123,18 @@ pub fn read(bus: *const Bus, comptime T: type, address: u32) T {
             0x0400_0060...0x0400_00A7 => apu.read(T, &bus.apu, address),
 
             // Serial Communication 1
-            0x0400_0128 => readTodo("Read {} from SIOCNT_L", .{T}),
+            0x0400_0128 => util.io.read.todo(log, "Read {} from SIOCNT_L", .{T}),
 
             // Keypad Input
-            0x0400_0130 => readTodo("read {} from KEYINPUT_L", .{T}),
+            0x0400_0130 => util.io.read.todo(log, "read {} from KEYINPUT_L", .{T}),
 
             // Serial Communication 2
-            0x0400_0135 => readTodo("Read {} from RCNT_H", .{T}),
+            0x0400_0135 => util.io.read.todo(log, "Read {} from RCNT_H", .{T}),
 
             // Interrupts
             0x0400_0200 => @truncate(T, bus.io.ie.raw),
             0x0400_0300 => @enumToInt(bus.io.postflg),
-            else => readUndefined(log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, address }),
+            else => util.io.read.undef(T, log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, address }),
         },
         else => @compileError("I/O: Unsupported read width"),
     };
@@ -210,7 +210,7 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
             0x0400_0204 => log.debug("Wrote 0x{X:0>8} to WAITCNT", .{value}),
             0x0400_0208 => bus.io.ime = value & 1 == 1,
             0x0400_020C...0x0400_021C => {}, // Unused
-            else => writeUndefined(log, "Tried to write 0x{X:0>8}{} to 0x{X:0>8}", .{ value, T, address }),
+            else => util.io.write.undef(log, "Tried to write 0x{X:0>8}{} to 0x{X:0>8}", .{ value, T, address }),
         },
         u16 => switch (address) {
             // Display
@@ -292,7 +292,7 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
             0x0400_0204 => log.debug("Wrote 0x{X:0>4} to WAITCNT", .{value}),
             0x0400_0208 => bus.io.ime = value & 1 == 1,
             0x0400_0206, 0x0400_020A => {}, // Not Used
-            else => writeUndefined(log, "Tried to write 0x{X:0>4}{} to 0x{X:0>8}", .{ value, T, address }),
+            else => util.io.write.undef(log, "Tried to write 0x{X:0>4}{} to 0x{X:0>8}", .{ value, T, address }),
         },
         u8 => switch (address) {
             // Display
@@ -325,17 +325,12 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
             0x0400_0301 => bus.io.haltcnt = if (value >> 7 & 1 == 0) .Halt else std.debug.panic("TODO: Implement STOP", .{}),
 
             0x0400_0410 => log.debug("Wrote 0x{X:0>2} to the common yet undocumented 0x{X:0>8}", .{ value, address }),
-            else => writeUndefined(log, "Tried to write 0x{X:0>2}{} to 0x{X:0>8}", .{ value, T, address }),
+            else => util.io.write.undef(log, "Tried to write 0x{X:0>2}{} to 0x{X:0>8}", .{ value, T, address }),
         },
         else => @compileError("I/O: Unsupported write width"),
     };
 }
 
-fn readTodo(comptime format: []const u8, args: anytype) u8 {
-    log.debug(format, args);
-    return 0;
-}
-
 /// Read / Write
 pub const PostFlag = enum(u1) {
     FirstBoot = 0,

src/core/bus/timer.zig

@@ -1,4 +1,5 @@
 const std = @import("std");
+const util = @import("../util.zig");
 
 const TimerControl = @import("io.zig").TimerControl;
 const Io = @import("io.zig").Io;
@@ -6,8 +7,6 @@ const Scheduler = @import("../scheduler.zig").Scheduler;
 const Event = @import("../scheduler.zig").Event;
 const Arm7tdmi = @import("../cpu.zig").Arm7tdmi;
 
-const readUndefined = @import("../util.zig").readUndefined;
-const writeUndefined = @import("../util.zig").writeUndefined;
 pub const TimerTuple = std.meta.Tuple(&[_]type{ Timer(0), Timer(1), Timer(2), Timer(3) });
 const log = std.log.scoped(.Timer);
 
@@ -15,7 +14,7 @@ pub fn create(sched: *Scheduler) TimerTuple {
     return .{ Timer(0).init(sched), Timer(1).init(sched), Timer(2).init(sched), Timer(3).init(sched) };
 }
 
-pub fn read(comptime T: type, tim: *const TimerTuple, addr: u32) T {
+pub fn read(comptime T: type, tim: *const TimerTuple, addr: u32) ?T {
     const nybble = @truncate(u4, addr);
 
     return switch (T) {
@@ -24,7 +23,7 @@ pub fn read(comptime T: type, tim: *const TimerTuple, addr: u32) T {
             0x4 => @as(T, tim.*[1].cnt.raw) << 16 | tim.*[1].getCntL(),
             0x8 => @as(T, tim.*[2].cnt.raw) << 16 | tim.*[2].getCntL(),
             0xC => @as(T, tim.*[3].cnt.raw) << 16 | tim.*[3].getCntL(),
-            else => readUndefined(log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
+            else => util.io.read.undef(T, log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
         },
         u16 => switch (nybble) {
             0x0 => tim.*[0].getCntL(),
@@ -35,9 +34,9 @@ pub fn read(comptime T: type, tim: *const TimerTuple, addr: u32) T {
             0xA => tim.*[2].cnt.raw,
             0xC => tim.*[3].getCntL(),
             0xE => tim.*[3].cnt.raw,
-            else => readUndefined(log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
+            else => util.io.read.undef(T, log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
         },
-        u8 => readUndefined(log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
+        u8 => util.io.read.undef(T, log, "Tried to perform a {} read to 0x{X:0>8}", .{ T, addr }),
         else => @compileError("TIM: Unsupported read width"),
     };
 }
@@ -51,7 +50,7 @@ pub fn write(comptime T: type, tim: *TimerTuple, addr: u32, value: T) void {
             0x4 => tim.*[1].setCnt(value),
             0x8 => tim.*[2].setCnt(value),
             0xC => tim.*[3].setCnt(value),
-            else => writeUndefined(log, "Tried to write 0x{X:0>8}{} to 0x{X:0>8}", .{ value, T, addr }),
+            else => util.io.write.undef(log, "Tried to write 0x{X:0>8}{} to 0x{X:0>8}", .{ value, T, addr }),
         },
         u16 => switch (nybble) {
             0x0 => tim.*[0].setCntL(value),
@@ -62,9 +61,9 @@ pub fn write(comptime T: type, tim: *TimerTuple, addr: u32, value: T) void {
             0xA => tim.*[2].setCntH(value),
             0xC => tim.*[3].setCntL(value),
             0xE => tim.*[3].setCntH(value),
-            else => writeUndefined(log, "Tried to write 0x{X:0>4}{} to 0x{X:0>8}", .{ value, T, addr }),
+            else => util.io.write.undef(log, "Tried to write 0x{X:0>4}{} to 0x{X:0>8}", .{ value, T, addr }),
         },
-        u8 => writeUndefined(log, "Tried to write 0x{X:0>2}{} to 0x{X:0>8}", .{ value, T, addr }),
+        u8 => util.io.write.undef(log, "Tried to write 0x{X:0>2}{} to 0x{X:0>8}", .{ value, T, addr }),
         else => @compileError("TIM: Unsupported write width"),
     };
 }

src/core/emu.zig

@@ -13,10 +13,11 @@ const Atomic = std.atomic.Atomic;
 const Allocator = std.mem.Allocator;
 
 // TODO: Move these to a TOML File
-const sync_audio = true; // Enable Audio Sync
+const sync_audio = false; // Enable Audio Sync
 const sync_video: RunKind = .LimitedFPS; // Configure Video Sync
 pub const win_scale = 3; // 1x, 2x, 3x, etc. Window Scaling
 pub const cpu_logging = false; // Enable detailed CPU logging
+pub const allow_unhandled_io = true; // Only relevant in Debug Builds
 
 // 228 Lines which consist of 308 dots (which are 4 cycles long)
 const cycles_per_frame: u64 = 228 * (308 * 4); //280896

src/core/util.zig

@@ -3,6 +3,8 @@ const builtin = @import("builtin");
 const Log2Int = std.math.Log2Int;
 const Arm7tdmi = @import("cpu.zig").Arm7tdmi;
 
+const allow_unhandled_io = @import("emu.zig").allow_unhandled_io;
+
 // Sign-Extend value of type `T` to type `U`
 pub fn sext(comptime T: type, comptime U: type, value: T) T {
     // U must have less bits than T
@@ -102,6 +104,28 @@ pub const FilePaths = struct {
     save: ?[]const u8,
 };
 
+pub const io = struct {
+    pub const read = struct {
+        pub fn todo(comptime log: anytype, comptime format: []const u8, args: anytype) u8 {
+            log.debug(format, args);
+            return 0;
+        }
+
+        pub fn undef(comptime T: type, log: anytype, comptime format: []const u8, args: anytype) ?T {
+            log.warn(format, args);
+            if (builtin.mode == .Debug and !allow_unhandled_io) std.debug.panic("TODO: Implement I/O Register", .{});
+
+            return null;
+        }
+    };
+
+    pub const write = struct {
+        pub fn undef(log: anytype, comptime format: []const u8, args: anytype) void {
+            log.warn(format, args);
+            if (builtin.mode == .Debug and !allow_unhandled_io) std.debug.panic("TODO: Implement I/O Register", .{});
+        }
+    };
+};
 pub fn readUndefined(log: anytype, comptime format: []const u8, args: anytype) u8 {
     log.warn(format, args);
     if (builtin.mode == .Debug) std.debug.panic("TODO: Implement I/O Register", .{});