From d985eac0fc9e6b707d857f16a509caac8b56c81a Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Thu, 23 Feb 2023 22:12:06 -0600
Subject: [PATCH] tmp: implement mechanisms for a emu reset fn (currently
 crashes)

---
 src/core/Bus.zig                 | 26 ++++++++++++++++++++++
 src/core/apu.zig                 | 38 ++++++++++++++++++++++++++++----
 src/core/apu/device/Envelope.zig |  9 ++++----
 src/core/apu/device/Length.zig   |  6 ++---
 src/core/apu/device/Sweep.zig    | 20 +++++------------
 src/core/bus/Bios.zig            |  4 ++++
 src/core/bus/Ewram.zig           |  4 ++++
 src/core/bus/Iwram.zig           |  4 ++++
 src/core/bus/dma.zig             |  4 ++++
 src/core/bus/io.zig              |  4 ++++
 src/core/bus/timer.zig           |  6 +++++
 src/core/cpu.zig                 |  8 +++++++
 src/core/emu.zig                 |  7 ++++++
 src/core/scheduler.zig           | 15 +++++++++++--
 src/imgui.zig                    |  6 +++--
 15 files changed, 131 insertions(+), 30 deletions(-)

diff --git a/src/core/Bus.zig b/src/core/Bus.zig
index 29e9076..925f1ba 100644
--- a/src/core/Bus.zig
+++ b/src/core/Bus.zig
@@ -102,6 +102,32 @@ pub fn deinit(self: *Self) void {
     self.* = undefined;
 }
 
+pub fn reset(self: *Self) void {
+    self.bios.reset();
+    // TODO: deinit ppu
+    self.apu.reset();
+    self.iwram.reset();
+    self.ewram.reset();
+
+    // https://github.com/ziglang/zig/issues/14705
+    {
+        comptime var i: usize = 0;
+        inline while (i < self.dma.len) : (i += 1) {
+            self.dma[0].reset();
+        }
+    }
+
+    // https://github.com/ziglang/zig/issues/14705
+    {
+        comptime var i: usize = 0;
+        inline while (i < self.tim.len) : (i += 1) {
+            self.tim[0].reset();
+        }
+    }
+
+    self.io.reset();
+}
+
 fn fillReadTable(self: *Self, table: *[table_len]?*const anyopaque) void {
     const vramMirror = @import("ppu/Vram.zig").mirror;
 
diff --git a/src/core/apu.zig b/src/core/apu.zig
index 05b6cea..8730290 100644
--- a/src/core/apu.zig
+++ b/src/core/apu.zig
@@ -289,7 +289,28 @@ pub const Apu = struct {
         return apu;
     }
 
-    fn reset(self: *Self) void {
+    /// Used when resetting the emulator
+    pub fn reset(self: *Self) void {
+        // FIXME: These reset functions are meant to emulate obscure APU behaviour. Write proper emu reset fns
+        self.ch1.reset();
+        self.ch2.reset();
+        self.ch3.reset();
+        self.ch4.reset();
+
+        self.chA.reset();
+        self.chB.reset();
+
+        self.psg_cnt = .{ .raw = 0 };
+        self.dma_cnt = .{ .raw = 0 };
+        self.cnt = .{ .raw = 0 };
+        self.bias = .{ .raw = 0x200 };
+
+        self.sampling_cycle = 0;
+        self.fs.reset();
+    }
+
+    /// Emulates the reset behaviour of the APU
+    fn _reset(self: *Self) void {
         // All PSG Registers between 0x0400_0060..0x0400_0081 are zeroed
         // 0x0400_0082 and 0x0400_0088 retain their values
         self.ch1.reset();
@@ -351,7 +372,7 @@ pub const Apu = struct {
             // Rest Noise
             self.ch4.lfsr.reset();
         } else {
-            self.reset();
+            self._reset();
         }
     }
 
@@ -528,6 +549,11 @@ pub fn DmaSound(comptime kind: DmaSoundKind) type {
             };
         }
 
+        /// Used when resetting hte emulator (not emulation code)
+        fn reset(self: *Self) void {
+            self.* = Self.init();
+        }
+
         pub fn push(self: *Self, value: u32) void {
             if (!self.enabled) self.enable();
 
@@ -562,10 +588,14 @@ pub const FrameSequencer = struct {
     const Self = @This();
     pub const interval = (1 << 24) / 512;
 
-    step: u3,
+    step: u3 = 0,
 
     pub fn init() Self {
-        return .{ .step = 0 };
+        return .{};
+    }
+
+    pub fn reset(self: *Self) void {
+        self.* = .{};
     }
 
     pub fn tick(self: *Self) void {
diff --git a/src/core/apu/device/Envelope.zig b/src/core/apu/device/Envelope.zig
index 9eee8fe..49ea53c 100644
--- a/src/core/apu/device/Envelope.zig
+++ b/src/core/apu/device/Envelope.zig
@@ -3,17 +3,16 @@ const io = @import("../../bus/io.zig");
 const Self = @This();
 
 /// Period Timer
-timer: u3,
+timer: u3 = 0,
 /// Current Volume
-vol: u4,
+vol: u4 = 0,
 
 pub fn create() Self {
-    return .{ .timer = 0, .vol = 0 };
+    return .{};
 }
 
 pub fn reset(self: *Self) void {
-    self.timer = 0;
-    self.vol = 0;
+    self.* = .{};
 }
 
 pub fn tick(self: *Self, nrx2: io.Envelope) void {
diff --git a/src/core/apu/device/Length.zig b/src/core/apu/device/Length.zig
index 420daf0..8478188 100644
--- a/src/core/apu/device/Length.zig
+++ b/src/core/apu/device/Length.zig
@@ -1,13 +1,13 @@
 const Self = @This();
 
-timer: u9,
+timer: u9 = 0,
 
 pub fn create() Self {
-    return .{ .timer = 0 };
+    return .{};
 }
 
 pub fn reset(self: *Self) void {
-    self.timer = 0;
+    self.* = .{};
 }
 
 pub fn tick(self: *Self, enabled: bool, ch_enable: *bool) void {
diff --git a/src/core/apu/device/Sweep.zig b/src/core/apu/device/Sweep.zig
index 605697d..82877e8 100644
--- a/src/core/apu/device/Sweep.zig
+++ b/src/core/apu/device/Sweep.zig
@@ -3,26 +3,18 @@ const ToneSweep = @import("../ToneSweep.zig");
 
 const Self = @This();
 
-timer: u8,
-enabled: bool,
-shadow: u11,
+timer: u8 = 0,
+enabled: bool = false,
+shadow: u11 = 0,
 
-calc_performed: bool,
+calc_performed: bool = false,
 
 pub fn create() Self {
-    return .{
-        .timer = 0,
-        .enabled = false,
-        .shadow = 0,
-        .calc_performed = false,
-    };
+    return .{};
 }
 
 pub fn reset(self: *Self) void {
-    self.timer = 0;
-    self.enabled = false;
-    self.shadow = 0;
-    self.calc_performed = false;
+    self.* = .{};
 }
 
 pub fn tick(self: *Self, ch1: *ToneSweep) void {
diff --git a/src/core/bus/Bios.zig b/src/core/bus/Bios.zig
index 84e6e7d..6743ffc 100644
--- a/src/core/bus/Bios.zig
+++ b/src/core/bus/Bios.zig
@@ -77,6 +77,10 @@ pub fn init(allocator: Allocator, maybe_path: ?[]const u8) !Self {
     return Self{ .buf = buf, .allocator = allocator };
 }
 
+pub fn reset(self: *Self) void {
+    self.addr_latch = 0;
+}
+
 pub fn deinit(self: *Self) void {
     if (self.buf) |buf| self.allocator.free(buf);
     self.* = undefined;
diff --git a/src/core/bus/Ewram.zig b/src/core/bus/Ewram.zig
index c36d998..a1ad801 100644
--- a/src/core/bus/Ewram.zig
+++ b/src/core/bus/Ewram.zig
@@ -35,6 +35,10 @@ pub fn init(allocator: Allocator) !Self {
     };
 }
 
+pub fn reset(self: *Self) void {
+    std.mem.set(u8, self.buf, 0);
+}
+
 pub fn deinit(self: *Self) void {
     self.allocator.free(self.buf);
     self.* = undefined;
diff --git a/src/core/bus/Iwram.zig b/src/core/bus/Iwram.zig
index 383075e..0356460 100644
--- a/src/core/bus/Iwram.zig
+++ b/src/core/bus/Iwram.zig
@@ -35,6 +35,10 @@ pub fn init(allocator: Allocator) !Self {
     };
 }
 
+pub fn reset(self: *Self) void {
+    std.mem.set(u8, self.buf, 0);
+}
+
 pub fn deinit(self: *Self) void {
     self.allocator.free(self.buf);
     self.* = undefined;
diff --git a/src/core/bus/dma.zig b/src/core/bus/dma.zig
index e1f1b1c..7d75d18 100644
--- a/src/core/bus/dma.zig
+++ b/src/core/bus/dma.zig
@@ -195,6 +195,10 @@ fn DmaController(comptime id: u2) type {
             };
         }
 
+        pub fn reset(self: *Self) void {
+            self.* = Self.init();
+        }
+
         pub fn setDmasad(self: *Self, addr: u32) void {
             self.sad = addr & sad_mask;
         }
diff --git a/src/core/bus/io.zig b/src/core/bus/io.zig
index 3b62d1f..2cbbb32 100644
--- a/src/core/bus/io.zig
+++ b/src/core/bus/io.zig
@@ -38,6 +38,10 @@ pub const Io = struct {
         };
     }
 
+    pub fn reset(self: *Self) void {
+        self.* = Self.init();
+    }
+
     fn setIrqs(self: *Io, word: u32) void {
         self.ie.raw = @truncate(u16, word);
         self.irq.raw &= ~@truncate(u16, word >> 16);
diff --git a/src/core/bus/timer.zig b/src/core/bus/timer.zig
index ad7b5f0..93ff7c4 100644
--- a/src/core/bus/timer.zig
+++ b/src/core/bus/timer.zig
@@ -128,6 +128,12 @@ fn Timer(comptime id: u2) type {
             };
         }
 
+        pub fn reset(self: *Self) void {
+            const scheduler = self.sched;
+
+            self.* = Self.init(scheduler);
+        }
+
         /// TIMCNT_L Getter
         pub fn timcntL(self: *const Self) u16 {
             if (self.cnt.cascade.read() or !self.cnt.enabled.read()) return self._counter;
diff --git a/src/core/cpu.zig b/src/core/cpu.zig
index 669d195..e005c9e 100644
--- a/src/core/cpu.zig
+++ b/src/core/cpu.zig
@@ -314,6 +314,14 @@ pub const Arm7tdmi = struct {
         };
     }
 
+    // FIXME: Resetting disables logging (if enabled)
+    pub fn reset(self: *Self) void {
+        const bus_ptr = self.bus;
+        const scheduler_ptr = self.sched;
+
+        self.* = Self.init(scheduler_ptr, bus_ptr, null);
+    }
+
     pub inline fn hasSPSR(self: *const Self) bool {
         const mode = getModeChecked(self, self.cpsr.mode.read());
         return switch (mode) {
diff --git a/src/core/emu.zig b/src/core/emu.zig
index 11931d7..215173f 100644
--- a/src/core/emu.zig
+++ b/src/core/emu.zig
@@ -222,3 +222,10 @@ pub const EmuThing = struct {
         }
     }
 };
+
+pub fn reset(cpu: *Arm7tdmi) void {
+    // @breakpoint();
+    cpu.sched.reset(); // Yes this is order sensitive, see the PPU reset for why
+    cpu.bus.reset();
+    cpu.reset();
+}
diff --git a/src/core/scheduler.zig b/src/core/scheduler.zig
index 8a57183..86ebab1 100644
--- a/src/core/scheduler.zig
+++ b/src/core/scheduler.zig
@@ -11,11 +11,11 @@ const log = std.log.scoped(.Scheduler);
 pub const Scheduler = struct {
     const Self = @This();
 
-    tick: u64,
+    tick: u64 = 0,
     queue: PriorityQueue(Event, void, lessThan),
 
     pub fn init(allocator: Allocator) Self {
-        var sched = Self{ .tick = 0, .queue = PriorityQueue(Event, void, lessThan).init(allocator, {}) };
+        var sched = Self{ .queue = PriorityQueue(Event, void, lessThan).init(allocator, {}) };
         sched.queue.add(.{ .kind = .HeatDeath, .tick = std.math.maxInt(u64) }) catch unreachable;
 
         return sched;
@@ -26,6 +26,17 @@ pub const Scheduler = struct {
         self.* = undefined;
     }
 
+    pub fn reset(self: *Self) void {
+        // `std.PriorityQueue` provides no reset function, so we will just create a new one
+        const allocator = self.queue.allocator;
+        self.queue.deinit();
+
+        var new_queue = PriorityQueue(Event, void, lessThan).init(allocator, {});
+        new_queue.add(.{ .kind = .HeatDeath, .tick = std.math.maxInt(u64) }) catch unreachable;
+
+        self.* = .{ .queue = new_queue };
+    }
+
     pub inline fn now(self: *const Self) u64 {
         return self.tick;
     }
diff --git a/src/imgui.zig b/src/imgui.zig
index 2dcf60f..1d62181 100644
--- a/src/imgui.zig
+++ b/src/imgui.zig
@@ -48,7 +48,7 @@ pub const State = struct {
     }
 };
 
-pub fn draw(state: *State, tex_id: GLuint, cpu: *const Arm7tdmi) void {
+pub fn draw(state: *State, tex_id: GLuint, cpu: *Arm7tdmi) void {
     const win_scale = config.config().host.win_scale;
 
     {
@@ -77,7 +77,9 @@ pub fn draw(state: *State, tex_id: GLuint, cpu: *const Arm7tdmi) void {
         if (zgui.beginMenu("Emulation", true)) {
             defer zgui.endMenu();
 
-            if (zgui.menuItem("Restart", .{})) log.warn("TODO: Restart Emulator", .{});
+            if (zgui.menuItem("Restart", .{})) {
+                emu.reset(cpu);
+            }
         }
     }