fix(emu): share same main mem allocation between ARM7 + ARM9

src/core/emu.zig

@@ -3,6 +3,7 @@ const nds9 = @import("nds9.zig");
 const nds7 = @import("nds7.zig");
 
 const Header = @import("cartridge.zig").Header;
+const SharedIo = @import("io.zig").Io;
 const Arm946es = nds9.Arm946es;
 
 const Allocator = std.mem.Allocator;
@@ -107,3 +108,26 @@ pub fn runFrame(nds7_group: nds7.Group, nds9_group: nds9.Group) void {
         }
     }
 }
+
+// FIXME: Perf win to allocating on the stack instead?
+pub const SharedContext = struct {
+    const MiB = 0x100000;
+
+    io: *SharedIo,
+    main: *[4 * MiB]u8,
+
+    pub fn init(allocator: Allocator) !@This() {
+        const ctx = .{
+            .io = try allocator.create(SharedIo),
+            .main = try allocator.create([4 * MiB]u8),
+        };
+        ctx.io.* = .{};
+
+        return ctx;
+    }
+
+    pub fn deinit(self: @This(), allocator: Allocator) void {
+        allocator.destroy(self.io);
+        allocator.destroy(self.main);
+    }
+};

src/core/nds7/Bus.zig

@@ -4,6 +4,7 @@ const io = @import("io.zig");
 
 const Scheduler = @import("Scheduler.zig");
 const SharedIo = @import("../io.zig").Io;
+const SharedContext = @import("../emu.zig").SharedContext;
 
 const Allocator = std.mem.Allocator;
 
@@ -18,20 +19,16 @@ main: *[4 * MiB]u8,
 wram: *[64 * KiB]u8,
 io: io.Io,
 
-pub fn init(allocator: Allocator, scheduler: *Scheduler, shared_io: *SharedIo) !@This() {
-    const main_mem = try allocator.create([4 * MiB]u8);
-    errdefer allocator.destroy(main_mem);
-    @memset(main_mem, 0);
-
+pub fn init(allocator: Allocator, scheduler: *Scheduler, shared_ctx: SharedContext) !@This() {
     const wram = try allocator.create([64 * KiB]u8);
     errdefer allocator.destroy(wram);
     @memset(wram, 0);
 
     return .{
-        .main = main_mem,
+        .main = shared_ctx.main,
         .wram = wram,
         .scheduler = scheduler,
-        .io = io.Io.init(shared_io),
+        .io = io.Io.init(shared_ctx.io),
     };
 }
 

src/core/nds9/Bus.zig

@@ -2,7 +2,7 @@ const std = @import("std");
 
 const Ppu = @import("../ppu.zig").Ppu;
 const Scheduler = @import("Scheduler.zig");
-const SharedIo = @import("../io.zig").Io;
+const SharedContext = @import("../emu.zig").SharedContext;
 const io = @import("io.zig");
 
 const Allocator = std.mem.Allocator;
@@ -20,11 +20,7 @@ ppu: Ppu,
 
 scheduler: *Scheduler,
 
-pub fn init(allocator: Allocator, scheduler: *Scheduler, shared_io: *SharedIo) !@This() {
-    const main_mem = try allocator.create([4 * MiB]u8);
-    errdefer allocator.destroy(main_mem);
-    @memset(main_mem, 0);
-
+pub fn init(allocator: Allocator, scheduler: *Scheduler, shared_ctx: SharedContext) !@This() {
     const vram1_mem = try allocator.create([512 * KiB]u8);
     errdefer allocator.destroy(vram1_mem);
     @memset(vram1_mem, 0);
@@ -33,11 +29,11 @@ pub fn init(allocator: Allocator, scheduler: *Scheduler, shared_io: *SharedIo) !
     scheduler.push(.draw, 256 * dots_per_cycle);
 
     return .{
-        .main = main_mem,
+        .main = shared_ctx.main,
         .vram1 = vram1_mem,
         .ppu = try Ppu.init(allocator),
         .scheduler = scheduler,
-        .io = io.Io.init(shared_io),
+        .io = io.Io.init(shared_ctx.io),
     };
 }