feat: implement IPCFIFO IRQs

turbo now passes rockwrestler!!!

src/core/emu.zig

@@ -8,13 +8,16 @@ const Allocator = std.mem.Allocator;
 /// Load a NDS Cartridge
 ///
 /// intended to be used immediately after Emulator initialization
-pub fn load(allocator: Allocator, system: System, rom_file: std.fs.File) ![12]u8 {
+pub fn load(allocator: Allocator, system: System, rom_path: []const u8) ![12]u8 {
     const log = std.log.scoped(.load_rom);
 
-    const rom_buf = try rom_file.readToEndAlloc(allocator, try rom_file.getEndPos());
+    const file = try std.fs.cwd().openFile(rom_path, .{});
-    defer allocator.free(rom_buf);
+    defer file.close();
 
-    var stream = std.io.fixedBufferStream(rom_buf);
+    const buf = try file.readToEndAlloc(allocator, try file.getEndPos());
+    defer allocator.free(buf);
+
+    var stream = std.io.fixedBufferStream(buf);
     const header = try stream.reader().readStruct(Header);
 
     log.info("Title: \"{s}\"", .{std.mem.sliceTo(&header.title, 0)});
@@ -29,7 +32,7 @@ pub fn load(allocator: Allocator, system: System, rom_file: std.fs.File) ![12]u8
         log.debug("ARM9 Size: 0x{X:0>8}", .{header.arm9_size});
 
         // Copy ARM9 Code into Main Memory
-        for (rom_buf[header.arm9_rom_offset..][0..header.arm9_size], 0..) |value, i| {
+        for (buf[header.arm9_rom_offset..][0..header.arm9_size], 0..) |value, i| {
             const address = header.arm9_ram_address + @as(u32, @intCast(i));
             system.bus9.dbgWrite(u8, address, value);
         }
@@ -45,7 +48,7 @@ pub fn load(allocator: Allocator, system: System, rom_file: std.fs.File) ![12]u8
         log.debug("ARM7 Size: 0x{X:0>8}", .{header.arm7_size});
 
         // Copy ARM7 Code into Main Memory
-        for (rom_buf[header.arm7_rom_offset..][0..header.arm7_size], 0..) |value, i| {
+        for (buf[header.arm7_rom_offset..][0..header.arm7_size], 0..) |value, i| {
             const address = header.arm7_ram_address + @as(u32, @intCast(i));
             system.bus7.dbgWrite(u8, address, value);
         }
@@ -56,6 +59,41 @@ pub fn load(allocator: Allocator, system: System, rom_file: std.fs.File) ![12]u8
     return header.title;
 }
 
+/// Load NDS Firmware
+pub fn loadFirm(allocator: Allocator, system: System, firm_path: []const u8) !void {
+    const log = std.log.scoped(.load_firm);
+
+    { // NDS7 BIOS
+        const path = try std.mem.join(allocator, "/", &.{ firm_path, "bios7.bin" });
+        defer allocator.free(path);
+
+        log.debug("bios7 path: {s}", .{path});
+
+        const file = try std.fs.cwd().openFile(path, .{});
+        defer file.close();
+
+        const buf = try file.readToEndAlloc(allocator, try file.getEndPos());
+        defer allocator.free(buf);
+
+        @memcpy(system.bus7.bios[0..buf.len], buf);
+    }
+
+    { // NDS9 BIOS
+        const path = try std.mem.join(allocator, "/", &.{ firm_path, "bios9.bin" });
+        defer allocator.free(path);
+
+        log.debug("bios9 path: {s}", .{path});
+
+        const file = try std.fs.cwd().openFile(path, .{});
+        defer file.close();
+
+        const buf = try file.readToEndAlloc(allocator, try file.getEndPos());
+        defer allocator.free(buf);
+
+        @memcpy(system.bus9.bios[0..buf.len], buf);
+    }
+}
+
 const bus_clock = 33513982; // 33.513982 Hz
 const dot_clock = 5585664; //   5.585664 Hz
 const arm7_clock = bus_clock;
@@ -273,3 +311,27 @@ pub const System = struct {
         self.bus9.deinit(allocator);
     }
 };
+
+// FIXME: Using Wram.Device here is jank. System should probably carry an Enum + some Generic Type Fns
+pub fn handleInterrupt(comptime dev: Wram.Device, cpu: if (dev == .nds9) *System.Arm946es else *System.Arm7tdmi) void {
+    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
+
+    // TODO: Handle HALT
+    // HALTCNG (NDS7) and CP15 (NDS9)
+
+    const ret_addr = cpu.r[15] - if (cpu.cpsr.t.read()) 0 else @as(u32, 4);
+    const spsr = cpu.cpsr;
+
+    cpu.changeMode(.Irq);
+    cpu.cpsr.t.unset();
+    cpu.cpsr.i.set();
+
+    cpu.r[14] = ret_addr;
+    cpu.spsr.raw = spsr.raw;
+    cpu.r[15] = if (dev == .nds9) 0xFFFF_0018 else 0x0000_0018;
+    cpu.pipe.reload(cpu);
+}

src/core/io.zig

@@ -2,42 +2,16 @@ const std = @import("std");
 
 const Bitfield = @import("bitfield").Bitfield;
 const Bit = @import("bitfield").Bit;
+const System = @import("emu.zig").System;
+const handleInterrupt = @import("emu.zig").handleInterrupt;
 
 const log = std.log.scoped(.shared_io);
 
-// FIXME: This whole thing is bad bad bad bad bad
-// I think only the IPC stuff needs to be here, since they talk to each other.
-// 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 = .{},
+    ipc: Ipc = .{},
-
-    /// 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
 };
 
 fn warn(comptime format: []const u8, args: anytype) u0 {
@@ -45,13 +19,20 @@ fn warn(comptime format: []const u8, args: anytype) u0 {
     return 0;
 }
 
-const IpcFifo = struct {
+/// Inter-Process Communication
+const Ipc = struct {
     const Sync = IpcSync;
     const Control = IpcFifoCnt;
 
     _nds7: Impl = .{},
     _nds9: Impl = .{},
 
+    // we need access to the CPUs to handle IPC IRQs
+    arm7tdmi: ?*System.Arm7tdmi = null,
+    arm946es: ?*System.Arm946es = null,
+
+    // TODO: DS Cartridge I/O Ports
+
     const Source = enum { nds7, nds9 };
 
     const Impl = struct {
@@ -69,6 +50,11 @@ const IpcFifo = struct {
         last_read: ?u32 = null,
     };
 
+    pub fn configure(self: *@This(), system: System) void {
+        self.arm7tdmi = system.arm7tdmi;
+        self.arm946es = system.arm946es;
+    }
+
     /// IPCSYNC
     /// Read/Write
     pub fn setIpcSync(self: *@This(), comptime src: Source, value: anytype) void {
@@ -77,28 +63,42 @@ const IpcFifo = struct {
                 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);
 
+                if (value >> 13 & 1 == 1 and self._nds9.sync.recv_irq.read()) {
+                    const bus: *System.Bus9 = @ptrCast(@alignCast(self.arm946es.?.bus.ptr));
+
+                    bus.io.irq.ipcsync.set();
+                    handleInterrupt(.nds9, self.arm946es.?);
+                }
+
                 if (value >> 3 & 1 == 1) {
                     self._nds7.fifo.reset();
 
-                    self._nds7.cnt.send_fifo_empty.write(true);
+                    self._nds7.cnt.send_fifo_empty.set();
-                    self._nds9.cnt.recv_fifo_empty.write(true);
+                    self._nds9.cnt.recv_fifo_empty.set();
 
-                    self._nds7.cnt.send_fifo_full.write(false);
+                    self._nds7.cnt.send_fifo_full.unset();
-                    self._nds9.cnt.recv_fifo_full.write(false);
+                    self._nds9.cnt.recv_fifo_full.unset();
                 }
             },
             .nds9 => {
                 self._nds9.sync.raw = masks.ipcFifoSync(self._nds9.sync.raw, value);
                 self._nds7.sync.raw = masks.mask(self._nds7.sync.raw, (self._nds9.sync.raw >> 8) & 0xF, 0xF);
 
+                if (value >> 13 & 1 == 1 and self._nds7.sync.recv_irq.read()) {
+                    const bus: *System.Bus7 = @ptrCast(@alignCast(self.arm7tdmi.?.bus.ptr));
+
+                    bus.io.irq.ipcsync.set();
+                    handleInterrupt(.nds7, self.arm7tdmi.?);
+                }
+
                 if (value >> 3 & 1 == 1) {
                     self._nds9.fifo.reset();
 
-                    self._nds9.cnt.send_fifo_empty.write(true);
+                    self._nds9.cnt.send_fifo_empty.set();
-                    self._nds7.cnt.recv_fifo_empty.write(true);
+                    self._nds7.cnt.recv_fifo_empty.set();
 
-                    self._nds9.cnt.send_fifo_full.write(false);
+                    self._nds9.cnt.send_fifo_full.unset();
-                    self._nds7.cnt.recv_fifo_full.write(false);
+                    self._nds7.cnt.recv_fifo_full.unset();
                 }
             },
         }
@@ -121,23 +121,49 @@ const IpcFifo = struct {
                 if (!self._nds7.cnt.enable_fifos.read()) return;
                 try self._nds7.fifo.push(value);
 
+                const not_empty_cache = !self._nds9.cnt.recv_fifo_empty.read();
+
                 // update status bits
                 self._nds7.cnt.send_fifo_empty.write(self._nds7.fifo._len() == 0);
                 self._nds9.cnt.recv_fifo_empty.write(self._nds7.fifo._len() == 0);
 
                 self._nds7.cnt.send_fifo_full.write(self._nds7.fifo._len() == 0x10);
                 self._nds9.cnt.recv_fifo_full.write(self._nds7.fifo._len() == 0x10);
+
+                const not_empty = !self._nds9.cnt.recv_fifo_empty.read();
+
+                if (self._nds9.cnt.recv_fifo_irq_enable.read() and !not_empty_cache and not_empty) {
+                    // NDS7 Send | NDS9 RECV (Handling Not Empty)
+
+                    const bus: *System.Bus9 = @ptrCast(@alignCast(self.arm946es.?.bus.ptr));
+                    bus.io.irq.ipc_recv_not_empty.set();
+
+                    handleInterrupt(.nds9, self.arm946es.?);
+                }
             },
             .nds9 => {
                 if (!self._nds9.cnt.enable_fifos.read()) return;
                 try self._nds9.fifo.push(value);
 
+                const not_empty_cache = !self._nds7.cnt.recv_fifo_empty.read();
+
                 // update status bits
                 self._nds9.cnt.send_fifo_empty.write(self._nds9.fifo._len() == 0);
                 self._nds7.cnt.recv_fifo_empty.write(self._nds9.fifo._len() == 0);
 
                 self._nds9.cnt.send_fifo_full.write(self._nds9.fifo._len() == 0x10);
                 self._nds7.cnt.recv_fifo_full.write(self._nds9.fifo._len() == 0x10);
+
+                const not_empty = !self._nds7.cnt.recv_fifo_empty.read();
+
+                if (self._nds7.cnt.recv_fifo_irq_enable.read() and !not_empty_cache and not_empty) {
+                    // NDS9 Send | NDS7 RECV (Handling Not Empty)
+
+                    const bus: *System.Bus7 = @ptrCast(@alignCast(self.arm7tdmi.?.bus.ptr));
+                    bus.io.irq.ipc_recv_not_empty.set();
+
+                    handleInterrupt(.nds7, self.arm7tdmi.?);
+                }
             },
         }
     }
@@ -158,6 +184,8 @@ const IpcFifo = struct {
                     break :blk self._nds7.last_read orelse 0x0000_0000;
                 };
 
+                const empty_cache = self._nds9.cnt.send_fifo_empty.read();
+
                 // update status bits
                 self._nds7.cnt.recv_fifo_empty.write(self._nds9.fifo._len() == 0);
                 self._nds9.cnt.send_fifo_empty.write(self._nds9.fifo._len() == 0);
@@ -165,6 +193,15 @@ const IpcFifo = struct {
                 self._nds7.cnt.recv_fifo_full.write(self._nds9.fifo._len() == 0x10);
                 self._nds9.cnt.send_fifo_full.write(self._nds9.fifo._len() == 0x10);
 
+                const empty = self._nds9.cnt.send_fifo_empty.read();
+
+                if (self._nds9.cnt.send_fifo_irq_enable.read() and (!empty_cache and empty)) {
+                    const bus: *System.Bus9 = @ptrCast(@alignCast(self.arm946es.?.bus.ptr));
+                    bus.io.irq.ipc_send_empty.set();
+
+                    handleInterrupt(.nds9, self.arm946es.?);
+                }
+
                 return value;
             },
             .nds9 => {
@@ -179,6 +216,8 @@ const IpcFifo = struct {
                     break :blk self._nds7.last_read orelse 0x0000_0000;
                 };
 
+                const empty_cache = self._nds7.cnt.send_fifo_empty.read();
+
                 // update status bits
                 self._nds9.cnt.recv_fifo_empty.write(self._nds7.fifo._len() == 0);
                 self._nds7.cnt.send_fifo_empty.write(self._nds7.fifo._len() == 0);
@@ -186,6 +225,15 @@ const IpcFifo = struct {
                 self._nds9.cnt.recv_fifo_full.write(self._nds7.fifo._len() == 0x10);
                 self._nds7.cnt.send_fifo_full.write(self._nds7.fifo._len() == 0x10);
 
+                const empty = self._nds7.cnt.send_fifo_empty.read();
+
+                if (self._nds7.cnt.send_fifo_irq_enable.read() and (!empty_cache and empty)) {
+                    const bus: *System.Bus7 = @ptrCast(@alignCast(self.arm7tdmi.?.bus.ptr));
+                    bus.io.irq.ipc_send_empty.set();
+
+                    handleInterrupt(.nds7, self.arm7tdmi.?);
+                }
+
                 return value;
             },
         }
@@ -259,7 +307,6 @@ pub const masks = struct {
         const err_mask: u32 = 0x4000; // bit 14
 
         const err_bit = (cnt & err_mask) & ~(value & err_mask);
-        if (value & 0b1000 != 0) log.err("TODO: handle IPCFIFOCNT.3", .{});
 
         const without_err = (@as(u32, value) & _mask) | (cnt & ~_mask);
         return (without_err & ~err_mask) | err_bit;
@@ -271,23 +318,12 @@ pub const masks = struct {
     }
 };
 
-pub const nds7 = struct {
+// FIXME: bitfields depends on NDS9 / NDS7
-    pub const IntEnable = extern union {
+pub const IntEnable = extern union {
-        raw: u32,
+    ipcsync: Bit(u32, 16),
-    };
+    ipc_send_empty: Bit(u32, 17),
-
+    ipc_recv_not_empty: Bit(u32, 18),
-    pub const IntRequest = IntEnable;
+    raw: u32,
-    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 };
 };
 
 const Fifo = struct {

src/core/nds7/Bus.zig

@@ -22,10 +22,16 @@ wram: *[64 * KiB]u8,
 vram: *Vram,
 io: io.Io,
 
+bios: *[16 * KiB]u8,
+
 pub fn init(allocator: Allocator, scheduler: *Scheduler, ctx: SharedCtx) !@This() {
     const wram = try allocator.create([64 * KiB]u8);
-    errdefer allocator.destroy(wram);
     @memset(wram, 0);
+    errdefer allocator.destroy(wram);
+
+    const bios = try allocator.create([16 * KiB]u8);
+    @memset(bios, 0);
+    errdefer allocator.destroy(bios);
 
     return .{
         .main = ctx.main,
@@ -34,11 +40,14 @@ pub fn init(allocator: Allocator, scheduler: *Scheduler, ctx: SharedCtx) !@This(
         .wram = wram,
         .scheduler = scheduler,
         .io = io.Io.init(ctx.io),
+
+        .bios = bios,
     };
 }
 
 pub fn deinit(self: *@This(), allocator: Allocator) void {
     allocator.destroy(self.wram);
+    allocator.destroy(self.bios);
 }
 
 pub fn reset(_: *@This()) void {}
@@ -64,12 +73,13 @@ fn _read(self: *@This(), comptime T: type, comptime mode: Mode, address: u32) T
     }
 
     return switch (aligned_addr) {
+        0x0000_0000...0x01FF_FFFF => readInt(T, self.bios[address & 0x3FFF ..][0..byte_count]),
         0x0200_0000...0x02FF_FFFF => readInt(T, self.main[aligned_addr & 0x003F_FFFF ..][0..byte_count]),
         0x0300_0000...0x037F_FFFF => switch (self.io.shr.wramcnt.mode.read()) {
             0b00 => readInt(T, self.wram[aligned_addr & 0x0000_FFFF ..][0..byte_count]),
             else => self.shr_wram.read(T, .nds7, aligned_addr),
         },
-        0x0380_0000...0x0380_FFFF => readInt(T, self.wram[aligned_addr & 0x0000_FFFF ..][0..byte_count]),
+        0x0380_0000...0x03FF_FFFF => readInt(T, self.wram[aligned_addr & 0x0000_FFFF ..][0..byte_count]),
         0x0400_0000...0x04FF_FFFF => io.read(self, T, aligned_addr),
         0x0600_0000...0x06FF_FFFF => self.vram.read(T, .nds7, aligned_addr),
         else => warn("unexpected read: 0x{x:0>8} -> {}", .{ aligned_addr, T }),
@@ -97,6 +107,7 @@ fn _write(self: *@This(), comptime T: type, comptime mode: Mode, address: u32, v
     }
 
     switch (aligned_addr) {
+        0x0000_0000...0x01FF_FFFF => log.err("tried to read from NDS7 BIOS: 0x{X:0>8}", .{aligned_addr}),
         0x0200_0000...0x02FF_FFFF => writeInt(T, self.main[aligned_addr & 0x003F_FFFF ..][0..byte_count], value),
         0x0300_0000...0x037F_FFFF => switch (self.io.shr.wramcnt.mode.read()) {
             0b00 => writeInt(T, self.wram[aligned_addr & 0x0000_FFFF ..][0..byte_count], value),

src/core/nds7/io.zig

@@ -7,11 +7,36 @@ const Bus = @import("Bus.zig");
 const SharedCtx = @import("../emu.zig").SharedCtx;
 const masks = @import("../io.zig").masks;
 
+const IntEnable = @import("../io.zig").IntEnable;
+const IntRequest = @import("../io.zig").IntEnable;
+
 const log = std.log.scoped(.nds7_io);
 
 pub const Io = struct {
     shr: *SharedCtx.Io,
 
+    /// 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: IntEnable = .{ .raw = 0x0000_0000 },
+
+    /// IF - Interrupt Request
+    /// Read/Write
+    ///
+    /// Caller must cast the `u32` to either `nds7.IntRequest` or `nds9.IntRequest`
+    irq: IntRequest = .{ .raw = 0x0000_0000 },
+
+    /// Post Boot Flag
+    /// Read/Write
+    ///
+    /// Caller must cast the `u8` to either `nds7.PostFlg` or `nds9.PostFlg`
+    postflg: PostFlag = .in_progress,
+
     pub fn init(io: *SharedCtx.Io) @This() {
         return .{ .shr = io };
     }
@@ -20,21 +45,23 @@ 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.shr.ime),
+            0x0400_0208 => @intFromBool(bus.io.ime),
-            0x0400_0210 => bus.io.shr.ie,
+            0x0400_0210 => bus.io.ie.raw,
-            0x0400_0214 => bus.io.shr.irq,
+            0x0400_0214 => bus.io.irq.raw,
 
-            0x0410_0000 => bus.io.shr.ipc_fifo.recv(.nds7),
+            0x0410_0000 => bus.io.shr.ipc.recv(.nds7),
             else => warn("unexpected: read(T: {}, addr: 0x{X:0>8}) {} ", .{ T, address, T }),
         },
         u16 => switch (address) {
-            0x0400_0180 => @truncate(bus.io.shr.ipc_fifo._nds7.sync.raw),
+            0x0400_0180 => @truncate(bus.io.shr.ipc._nds7.sync.raw),
-            0x0400_0184 => @truncate(bus.io.shr.ipc_fifo._nds7.cnt.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) {
             0x0400_0240 => bus.vram.stat().raw,
             0x0400_0241 => bus.io.shr.wramcnt.raw,
+
+            0x0400_0300 => @intFromEnum(bus.io.postflg),
             else => warn("unexpected: read(T: {}, addr: 0x{X:0>8}) {} ", .{ T, address, T }),
         },
         else => @compileError(T ++ " is an unsupported bus read type"),
@@ -44,19 +71,20 @@ 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.shr.ime = value & 1 == 1,
+            0x0400_0208 => bus.io.ime = value & 1 == 1,
-            0x0400_0210 => bus.io.shr.ie = value,
+            0x0400_0210 => bus.io.ie.raw = value,
-            0x0400_0214 => bus.io.shr.irq = value,
+            0x0400_0214 => bus.io.irq.raw &= ~value,
 
-            0x0400_0188 => bus.io.shr.ipc_fifo.send(.nds7, value) catch |e| std.debug.panic("FIFO error: {}", .{e}),
+            0x0400_0188 => bus.io.shr.ipc.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 }),
         },
         u16 => switch (address) {
-            0x0400_0180 => bus.io.shr.ipc_fifo.setIpcSync(.nds7, value),
+            0x0400_0180 => bus.io.shr.ipc.setIpcSync(.nds7, value),
-            0x0400_0184 => bus.io.shr.ipc_fifo.setIpcFifoCnt(.nds7, value),
+            0x0400_0184 => bus.io.shr.ipc.setIpcFifoCnt(.nds7, value),
             else => log.warn("unexpected: write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8})", .{ T, address, value }),
         },
         u8 => switch (address) {
+            0x0400_0208 => bus.io.ime = value & 1 == 1,
             else => log.warn("unexpected: write(T: {}, addr: 0x{X:0>8}, value: 0x{X:0>8})", .{ T, address, value }),
         },
         else => @compileError(T ++ " is an unsupported bus write type"),
@@ -73,3 +101,5 @@ pub const Vramstat = extern union {
     vramd_enabled: Bit(u8, 1),
     raw: u8,
 };
+
+const PostFlag = enum(u8) { in_progress = 0, completed };

src/core/nds9/Bus.zig

@@ -20,23 +20,32 @@ wram: *Wram,
 io: io.Io,
 ppu: Ppu,
 
+bios: *[32 * KiB]u8,
+
 scheduler: *Scheduler,
 
 pub fn init(allocator: Allocator, scheduler: *Scheduler, ctx: SharedCtx) !@This() {
     const dots_per_cycle = 3; // ARM946E-S runs twice as fast as the ARM7TDMI
     scheduler.push(.{ .nds9 = .draw }, 256 * dots_per_cycle);
 
+    const bios = try allocator.create([32 * KiB]u8);
+    @memset(bios, 0);
+    errdefer allocator.destroy(bios);
+
     return .{
         .main = ctx.main,
         .wram = ctx.wram,
         .ppu = try Ppu.init(allocator, ctx.vram),
         .scheduler = scheduler,
         .io = io.Io.init(ctx.io),
+
+        .bios = bios,
     };
 }
 
 pub fn deinit(self: *@This(), allocator: Allocator) void {
     self.ppu.deinit(allocator);
+    allocator.destroy(self.bios);
 }
 
 pub fn reset(_: *@This()) void {
@@ -68,6 +77,7 @@ fn _read(self: *@This(), comptime T: type, comptime mode: Mode, address: u32) T
         0x0300_0000...0x03FF_FFFF => self.wram.read(T, .nds9, aligned_addr),
         0x0400_0000...0x04FF_FFFF => io.read(self, T, aligned_addr),
         0x0600_0000...0x06FF_FFFF => self.ppu.vram.read(T, .nds9, aligned_addr),
+        0xFFFF_0000...0xFFFF_FFFF => readInt(T, self.bios[address & 0x0000_7FFF ..][0..byte_count]),
         else => warn("unexpected read: 0x{x:0>8} -> {}", .{ aligned_addr, T }),
     };
 }
@@ -97,6 +107,7 @@ fn _write(self: *@This(), comptime T: type, comptime mode: Mode, address: u32, v
         0x0300_0000...0x03FF_FFFF => self.wram.write(T, .nds9, aligned_addr, value),
         0x0400_0000...0x04FF_FFFF => io.write(self, T, aligned_addr, value),
         0x0600_0000...0x06FF_FFFF => self.ppu.vram.write(T, .nds9, aligned_addr, value),
+        0xFFFF_0000...0xFFFF_FFFF => log.err("tried to read from NDS9 BIOS: 0x{X:0>8}", .{aligned_addr}),
         else => log.warn("unexpected write: 0x{X:}{} -> 0x{X:0>8}", .{ value, T, aligned_addr }),
     }
 }

src/core/nds9/io.zig

@@ -7,6 +7,9 @@ const Bus = @import("Bus.zig");
 const SharedCtx = @import("../emu.zig").SharedCtx;
 const masks = @import("../io.zig").masks;
 
+const IntEnable = @import("../io.zig").IntEnable;
+const IntRequest = @import("../io.zig").IntEnable;
+
 const sext = @import("../../util.zig").sext;
 
 const log = std.log.scoped(.nds9_io);
@@ -14,6 +17,22 @@ const log = std.log.scoped(.nds9_io);
 pub const Io = struct {
     shr: *SharedCtx.Io,
 
+    /// 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: IntEnable = .{ .raw = 0x0000_0000 },
+
+    /// IF - Interrupt Request
+    /// Read/Write
+    ///
+    /// Caller must cast the `u32` to either `nds7.IntRequest` or `nds9.IntRequest`
+    irq: IntRequest = .{ .raw = 0x0000_0000 },
+
     /// POWCNT1 - Graphics Power Control
     /// Read / Write
     powcnt: PowCnt = .{ .raw = 0x0000_0000 },
@@ -33,9 +52,9 @@ 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.shr.ime),
+            0x0400_0208 => @intFromBool(bus.io.ime),
-            0x0400_0210 => bus.io.shr.ie,
+            0x0400_0210 => bus.io.ie.raw,
-            0x0400_0214 => bus.io.shr.irq,
+            0x0400_0214 => bus.io.irq.raw,
 
             0x0400_02A0 => @truncate(bus.io.div.result),
             0x0400_02A4 => @truncate(bus.io.div.result >> 32),
@@ -43,15 +62,15 @@ pub fn read(bus: *const Bus, comptime T: type, address: u32) T {
             0x0400_02AC => @truncate(bus.io.div.remainder >> 32),
             0x0400_02B4 => @truncate(bus.io.sqrt.result),
 
-            0x0410_0000 => bus.io.shr.ipc_fifo.recv(.nds9),
+            0x0410_0000 => bus.io.shr.ipc.recv(.nds9),
             else => warn("unexpected: read(T: {}, addr: 0x{X:0>8}) {} ", .{ T, address, T }),
         },
         u16 => switch (address) {
             0x0400_0004 => bus.ppu.io.dispstat.raw,
             0x0400_0130 => bus.io.keyinput.load(.Monotonic),
 
-            0x0400_0180 => @truncate(bus.io.shr.ipc_fifo._nds9.sync.raw),
+            0x0400_0180 => @truncate(bus.io.shr.ipc._nds9.sync.raw),
-            0x0400_0184 => @truncate(bus.io.shr.ipc_fifo._nds9.cnt.raw),
+            0x0400_0184 => @truncate(bus.io.shr.ipc._nds9.cnt.raw),
 
             0x0400_0280 => @truncate(bus.io.div.cnt.raw),
             0x0400_02B0 => @truncate(bus.io.sqrt.cnt.raw),
@@ -69,9 +88,9 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
     switch (T) {
         u32 => switch (address) {
             0x0400_0000 => bus.ppu.io.dispcnt_a.raw = value,
-            0x0400_0180 => bus.io.shr.ipc_fifo.setIpcSync(.nds9, value),
+            0x0400_0180 => bus.io.shr.ipc.setIpcSync(.nds9, value),
-            0x0400_0184 => bus.io.shr.ipc_fifo.setIpcFifoCnt(.nds9, value),
+            0x0400_0184 => bus.io.shr.ipc.setIpcFifoCnt(.nds9, value),
-            0x0400_0188 => bus.io.shr.ipc_fifo.send(.nds9, value) catch |e| std.debug.panic("IPC FIFO Error: {}", .{e}),
+            0x0400_0188 => bus.io.shr.ipc.send(.nds9, value) catch |e| std.debug.panic("IPC FIFO Error: {}", .{e}),
 
             0x0400_0240 => {
                 bus.ppu.vram.io.cnt_a.raw = @truncate(value >> 0); // 0x0400_0240
@@ -80,9 +99,9 @@ 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.shr.ime = value & 1 == 1,
+            0x0400_0208 => bus.io.ime = value & 1 == 1,
-            0x0400_0210 => bus.io.shr.ie = value,
+            0x0400_0210 => bus.io.ie.raw = value,
-            0x0400_0214 => bus.io.shr.irq = value,
+            0x0400_0214 => bus.io.irq.raw &= ~value,
 
             0x0400_0290 => {
                 bus.io.div.numerator = masks.mask(bus.io.div.numerator, value, 0xFFFF_FFFF);
@@ -114,9 +133,9 @@ 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_0180 => bus.io.shr.ipc_fifo.setIpcSync(.nds9, value),
+            0x0400_0180 => bus.io.shr.ipc.setIpcSync(.nds9, value),
-            0x0400_0184 => bus.io.shr.ipc_fifo.setIpcFifoCnt(.nds9, value),
+            0x0400_0184 => bus.io.shr.ipc.setIpcFifoCnt(.nds9, value),
-            0x0400_0208 => bus.io.shr.ime = value & 1 == 1,
+            0x0400_0208 => bus.io.ime = value & 1 == 1,
 
             0x0400_0280 => {
                 bus.io.div.cnt.raw = value;

src/main.zig

@@ -13,6 +13,7 @@ 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
     \\<str>             Path to the NDS ROM
     \\
 );
@@ -31,10 +32,10 @@ pub fn main() !void {
     const rom_path = try handlePositional(result);
     log.debug("loading rom from: {s}", .{rom_path});
 
-    const rom_file = try std.fs.cwd().openFile(rom_path, .{});
+    const firm_path = result.args.firm;
-    defer rom_file.close();
+    log.debug("loading firmware from from: {?s}", .{firm_path});
 
-    const ctx = try SharedCtx.init(allocator);
+    var ctx = try SharedCtx.init(allocator);
     defer ctx.deinit(allocator);
 
     var scheduler = try Scheduler.init(allocator);
@@ -56,7 +57,10 @@ pub fn main() !void {
         break :blk .{ .arm7tdmi = &arm7tdmi, .arm946es = &arm946es, .bus7 = &bus7, .bus9 = &bus9, .cp15 = &cp15 };
     };
     defer system.deinit(allocator);
-    const rom_title = try emu.load(allocator, system, rom_file);
+
+    ctx.io.ipc.configure(system); // Shared I/O needs access to both CPUs (e.g. IPCSYNC)
+    const rom_title = try emu.load(allocator, system, rom_path);
+    if (firm_path) |path| try emu.loadFirm(allocator, system, path);
 
     var ui = try Ui.init(allocator);
     defer ui.deinit(allocator);