diff --git a/src/core/io.zig b/src/core/io.zig
index acd0210..6314677 100644
--- a/src/core/io.zig
+++ b/src/core/io.zig
@@ -10,31 +10,9 @@ const log = std.log.scoped(.shared_io);
 // every other "shared I/O register" is just duplicated on both CPUs. So they shouldn't be here
 
 pub const Io = struct {
-    /// Interrupt Master Enable
-    /// Read/Write
-    ime: bool = false,
-
-    /// Interrupt Enable
-    /// Read/Write
-    ///
-    /// Caller must cast the `u32` to either `nds7.IntEnable` or `nds9.IntEnable`
-    ie: u32 = 0x0000_0000,
-
-    /// IF - Interrupt Request
-    /// Read/Write
-    ///
-    /// Caller must cast the `u32` to either `nds7.IntRequest` or `nds9.IntRequest`
-    irq: u32 = 0x0000_0000,
-
     /// Inter Process Communication FIFO
     ipc_fifo: IpcFifo = .{},
 
-    /// Post Boot Flag
-    /// Read/Write
-    ///
-    /// Caller must cast the `u8` to either `nds7.PostFlg` or `nds9.PostFlg`
-    post_flg: u8 = @intFromEnum(nds7.PostFlag.in_progress),
-
     wramcnt: WramCnt = .{ .raw = 0x00 },
 
     // TODO: DS Cartridge I/O Ports
@@ -271,24 +249,7 @@ pub const masks = struct {
     }
 };
 
-pub const nds7 = struct {
-    pub const IntEnable = extern union {
-        raw: u32,
-    };
-
-    pub const IntRequest = IntEnable;
-    pub const PostFlag = enum(u8) { in_progress = 0, completed };
-};
-
-pub const nds9 = struct {
-    pub const IntEnable = extern union {
-        raw: u32,
-    };
-
-    pub const IntRequest = IntEnable;
-
-    pub const PostFlag = enum(u8) { in_progress = 0, completed };
-};
+pub const PostFlag = enum(u1) { in_progress = 0, completed };
 
 const Fifo = struct {
     const Index = u8;
diff --git a/src/core/nds7/io.zig b/src/core/nds7/io.zig
index 7d55468..2af9b90 100644
--- a/src/core/nds7/io.zig
+++ b/src/core/nds7/io.zig
@@ -5,6 +5,7 @@ const Bit = @import("bitfield").Bit;
 
 const Bus = @import("Bus.zig");
 const SharedIo = @import("../io.zig").Io;
+const PostFlag = @import("../io.zig").PostFlag;
 const masks = @import("../io.zig").masks;
 
 const log = std.log.scoped(.nds7_io);
@@ -12,6 +13,20 @@ const log = std.log.scoped(.nds7_io);
 pub const Io = struct {
     shared: *SharedIo,
 
+    // IME - Interrupt Master Enable
+    /// Read / Write
+    ime: bool = false,
+
+    /// IE - Interrupt Enable
+    /// Read / Write
+    ie: Interrupt = .{ .raw = 0x0000_0000 },
+
+    /// IF - Interrupt Request
+    /// Read / Write
+    irq: Interrupt = .{ .raw = 0x0000_0000 },
+
+    postflg: PostFlag = .in_progress,
+
     pub fn init(io: *SharedIo) @This() {
         return .{ .shared = io };
     }
@@ -20,9 +35,9 @@ pub const Io = struct {
 pub fn read(bus: *const Bus, comptime T: type, address: u32) T {
     return switch (T) {
         u32 => switch (address) {
-            0x0400_0208 => @intFromBool(bus.io.shared.ime),
-            0x0400_0210 => bus.io.shared.ie,
-            0x0400_0214 => bus.io.shared.irq,
+            0x0400_0208 => @intFromBool(bus.io.ime),
+            0x0400_0210 => bus.io.ie.raw,
+            0x0400_0214 => bus.io.irq.raw,
 
             0x0410_0000 => bus.io.shared.ipc_fifo.recv(.nds7),
             else => warn("unexpected: read(T: {}, addr: 0x{X:0>8}) {} ", .{ T, address, T }),
@@ -44,9 +59,9 @@ pub fn read(bus: *const Bus, comptime T: type, address: u32) T {
 pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
     switch (T) {
         u32 => switch (address) {
-            0x0400_0208 => bus.io.shared.ime = value & 1 == 1,
-            0x0400_0210 => bus.io.shared.ie = value,
-            0x0400_0214 => bus.io.shared.irq = value,
+            0x0400_0208 => bus.io.ime = value & 1 == 1,
+            0x0400_0210 => bus.io.ie.raw = value,
+            0x0400_0214 => bus.io.irq.raw = value,
 
             0x0400_0188 => bus.io.shared.ipc_fifo.send(.nds7, value) catch |e| std.debug.panic("FIFO error: {}", .{e}),
             else => log.warn("unexpected: write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8})", .{ T, address, value }),
@@ -73,3 +88,7 @@ pub const Vramstat = extern union {
     vramd_enabled: Bit(u8, 1),
     raw: u8,
 };
+
+const Interrupt = extern union {
+    raw: u32,
+};
diff --git a/src/core/nds9/io.zig b/src/core/nds9/io.zig
index ccf0bac..c7e2634 100644
--- a/src/core/nds9/io.zig
+++ b/src/core/nds9/io.zig
@@ -5,6 +5,7 @@ const Bit = @import("bitfield").Bit;
 
 const Bus = @import("Bus.zig");
 const SharedIo = @import("../io.zig").Io;
+const PostFlag = @import("../io.zig").PostFlag;
 const masks = @import("../io.zig").masks;
 
 const sext = @import("../../util.zig").sext;
@@ -14,6 +15,22 @@ const log = std.log.scoped(.nds9_io);
 pub const Io = struct {
     shared: *SharedIo,
 
+    // IME - Interrupt Master Enable
+    /// Read / Write
+    ime: bool = false,
+
+    /// IE - Interrupt Enable
+    /// Read / Write
+    ie: Interrupt = .{ .raw = 0x0000_0000 },
+
+    /// IF - Interrupt Request
+    /// Read / Write
+    irq: Interrupt = .{ .raw = 0x0000_0000 },
+
+    // TODO: move postflg
+
+    postflg: PostFlag = .in_progress,
+
     /// POWCNT1 - Graphics Power Control
     /// Read / Write
     powcnt: PowCnt = .{ .raw = 0x0000_0000 },
@@ -33,9 +50,9 @@ pub const Io = struct {
 pub fn read(bus: *const Bus, comptime T: type, address: u32) T {
     return switch (T) {
         u32 => switch (address) {
-            0x0400_0208 => @intFromBool(bus.io.shared.ime),
-            0x0400_0210 => bus.io.shared.ie,
-            0x0400_0214 => bus.io.shared.irq,
+            0x0400_0208 => @intFromBool(bus.io.ime),
+            0x0400_0210 => bus.io.ie.raw,
+            0x0400_0214 => bus.io.irq.raw,
 
             0x0400_02A0 => @truncate(bus.io.div.result),
             0x0400_02A4 => @truncate(bus.io.div.result >> 32),
@@ -80,9 +97,9 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
                 bus.ppu.vram.io.cnt_d.raw = @truncate(value >> 24); // 0x0400_0243
             },
 
-            0x0400_0208 => bus.io.shared.ime = value & 1 == 1,
-            0x0400_0210 => bus.io.shared.ie = value,
-            0x0400_0214 => bus.io.shared.irq = value,
+            0x0400_0208 => bus.io.ime = value & 1 == 1,
+            0x0400_0210 => bus.io.ie.raw = value,
+            0x0400_0214 => bus.io.irq.raw = value,
 
             0x0400_0290 => {
                 bus.io.div.numerator = masks.mask(bus.io.div.numerator, value, 0xFFFF_FFFF);
@@ -116,7 +133,7 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
         u16 => switch (address) {
             0x0400_0180 => bus.io.shared.ipc_fifo.setIpcSync(.nds9, value),
             0x0400_0184 => bus.io.shared.ipc_fifo.setIpcFifoCnt(.nds9, value),
-            0x0400_0208 => bus.io.shared.ime = value & 1 == 1,
+            0x0400_0208 => bus.io.ime = value & 1 == 1,
 
             0x0400_0280 => {
                 bus.io.div.cnt.raw = value;
@@ -437,3 +454,7 @@ const AtomicKeyInput = struct {
         _ = @atomicRmw(u16, &self.inner.raw, .And, value, ordering);
     }
 };
+
+const Interrupt = extern union {
+    raw: u32,
+};