fix(input): make use of atomic rmw intrinsics when handling input

src/core/bus/io.zig

@@ -96,7 +96,7 @@ pub fn read(bus: *const Bus, comptime T: type, address: u32) ?T {
             0x0400_0128 => util.io.read.todo(log, "Read {} from SIOCNT", .{T}),
 
             // Keypad Input
-            0x0400_0130 => bus.io.keyinput.load(.Monotonic).raw,
+            0x0400_0130 => bus.io.keyinput.load(.Monotonic),
 
             // Serial Communication 2
             0x0400_0134 => util.io.read.todo(log, "Read {} from RCNT", .{T}),
@@ -366,7 +366,7 @@ const InterruptEnable = extern union {
 
 /// Read Only
 /// 0 = Pressed, 1 = Released
-const KeyInput = extern union {
+pub const KeyInput = extern union {
     a: Bit(u16, 0),
     b: Bit(u16, 1),
     select: Bit(u16, 2),
@@ -390,18 +390,19 @@ const AtomicKeyInput = struct {
         return .{ .inner = value };
     }
 
-    pub inline fn load(self: *const Self, comptime ordering: Ordering) KeyInput {
+    pub inline fn load(self: *const Self, comptime ordering: Ordering) u16 {
-        return .{ .raw = switch (ordering) {
+        return switch (ordering) {
             .AcqRel, .Release => @compileError("not supported for atomic loads"),
             else => @atomicLoad(u16, &self.inner.raw, ordering),
-        } };
+        };
     }
 
-    pub inline fn store(self: *Self, value: u16, comptime ordering: Ordering) void {
+    pub inline fn fetchOr(self: *Self, value: u16, comptime ordering: Ordering) void {
-        switch (ordering) {
+        _ = @atomicRmw(u16, &self.inner.raw, .Or, value, ordering);
-            .AcqRel, .Acquire => @compileError("not supported for atomic stores"),
-            else => @atomicStore(u16, &self.inner.raw, value, ordering),
     }
+
+    pub inline fn fetchAnd(self: *Self, value: u16, comptime ordering: Ordering) void {
+        _ = @atomicRmw(u16, &self.inner.raw, .And, value, ordering);
     }
 };
 

src/platform.zig

@@ -12,6 +12,7 @@ const Arm7tdmi = @import("core/cpu.zig").Arm7tdmi;
 const Scheduler = @import("core/scheduler.zig").Scheduler;
 const FpsTracker = @import("util.zig").FpsTracker;
 const TwoWayChannel = @import("zba-util").TwoWayChannel;
+const KeyInput = @import("core/bus/io.zig").KeyInput;
 
 const gba_width = @import("core/ppu.zig").width;
 const gba_height = @import("core/ppu.zig").height;
@@ -136,28 +137,7 @@ pub const Gui = struct {
                     SDL.SDL_KEYDOWN => {
                         // TODO: Make use of compare_and_xor?
                         const key_code = event.key.keysym.sym;
-                        var keyinput = cpu.bus.io.keyinput.load(.Monotonic);
+                        var keyinput: KeyInput = .{ .raw = 0x0000 };
-
-                        switch (key_code) {
-                            SDL.SDLK_UP => keyinput.up.unset(),
-                            SDL.SDLK_DOWN => keyinput.down.unset(),
-                            SDL.SDLK_LEFT => keyinput.left.unset(),
-                            SDL.SDLK_RIGHT => keyinput.right.unset(),
-                            SDL.SDLK_x => keyinput.a.unset(),
-                            SDL.SDLK_z => keyinput.b.unset(),
-                            SDL.SDLK_a => keyinput.shoulder_l.unset(),
-                            SDL.SDLK_s => keyinput.shoulder_r.unset(),
-                            SDL.SDLK_RETURN => keyinput.start.unset(),
-                            SDL.SDLK_RSHIFT => keyinput.select.unset(),
-                            else => {},
-                        }
-
-                        cpu.bus.io.keyinput.store(keyinput.raw, .Monotonic);
-                    },
-                    SDL.SDL_KEYUP => {
-                        // TODO: Make use of compare_and_xor?
-                        const key_code = event.key.keysym.sym;
-                        var keyinput = cpu.bus.io.keyinput.load(.Monotonic);
 
                         switch (key_code) {
                             SDL.SDLK_UP => keyinput.up.set(),
@@ -173,7 +153,28 @@ pub const Gui = struct {
                             else => {},
                         }
 
-                        cpu.bus.io.keyinput.store(keyinput.raw, .Monotonic);
+                        cpu.bus.io.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 => {},
+                        }
+
+                        cpu.bus.io.keyinput.fetchOr(keyinput.raw, .Monotonic);
                     },
                     SDL.SDL_WINDOWEVENT => {
                         if (event.window.event == SDL.SDL_WINDOWEVENT_RESIZED) {