From bf7b533b3c83fb09dc6c5803c9573a2c2ae96f16 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Mon, 28 Mar 2022 19:40:47 -0300
Subject: [PATCH 1/6] chore: stub more apu I/O addresses

---
 src/Bus.zig    |  1 +
 src/apu.zig    | 35 ++++++++++++++++++++++++++++++++++-
 src/bus/io.zig | 24 ++++++++++++++++++++++++
 3 files changed, 59 insertions(+), 1 deletion(-)

diff --git a/src/Bus.zig b/src/Bus.zig
index 72add6d..a1eec70 100644
--- a/src/Bus.zig
+++ b/src/Bus.zig
@@ -125,6 +125,7 @@ pub fn write16(self: *Self, addr: u32, halfword: u16) void {
         0x0500_0000...0x05FF_FFFF => self.ppu.palette.set16(addr & 0x3FF, halfword),
         0x0600_0000...0x0601_7FFF => self.ppu.vram.set16(addr - 0x0600_0000, halfword),
         0x0700_0000...0x07FF_FFFF => self.ppu.oam.set16(addr & 0x3FF, halfword),
+        0x0800_00C4, 0x0800_00C6, 0x0800_00C8 => log.warn("Tried to write 0x{X:0>4} to GPIO", .{halfword}),
 
         else => undWrite("Tried to write 0x{X:0>4} to 0x{X:0>8}", .{ halfword, addr }),
     }
diff --git a/src/apu.zig b/src/apu.zig
index 840a248..854db35 100644
--- a/src/apu.zig
+++ b/src/apu.zig
@@ -43,6 +43,10 @@ pub const Apu = struct {
         self.ch_vol_cnt.raw = (self.ch_vol_cnt.raw & 0xFF00) | byte;
     }
 
+    pub fn setSoundCntLHigh(self: *Self, byte: u8) void {
+        self.ch_vol_cnt.raw = @as(u16, byte) << 8 | (self.ch_vol_cnt.raw & 0xFF);
+    }
+
     pub fn setBiasHigh(self: *Self, byte: u8) void {
         self.bias.raw = (@as(u16, byte) << 8) | (self.bias.raw & 0xFF);
     }
@@ -51,9 +55,13 @@ pub const Apu = struct {
 const ToneSweep = struct {
     const Self = @This();
 
+    /// NR10
     sweep: io.Sweep,
+    /// NR11
     duty: io.Duty,
+    /// NR12
     envelope: io.Envelope,
+    /// NR13, NR14
     freq: io.Frequency,
 
     fn init() Self {
@@ -65,6 +73,10 @@ const ToneSweep = struct {
         };
     }
 
+    pub fn setFreqLow(self: *Self, byte: u8) void {
+        self.freq.raw = (self.freq.raw & 0xFF00) | byte;
+    }
+
     pub fn setFreqHigh(self: *Self, byte: u8) void {
         self.freq.raw = (@as(u16, byte) << 8) | (self.freq.raw & 0xFF);
     }
@@ -73,8 +85,11 @@ const ToneSweep = struct {
 const Tone = struct {
     const Self = @This();
 
+    /// NR21
     duty: io.Duty,
+    /// NR22
     envelope: io.Envelope,
+    /// NR23, NR24
     freq: io.Frequency,
 
     fn init() Self {
@@ -85,8 +100,12 @@ const Tone = struct {
         };
     }
 
+    pub fn setFreqLow(self: *Self, byte: u8) void {
+        self.freq.raw = (self.freq.raw & 0xFF00) | byte;
+    }
+
     pub fn setFreqHigh(self: *Self, byte: u8) void {
-        self.freq.raw = (self.freq.raw & 0x00FF) | (@as(u16, byte) << 8);
+        self.freq.raw = @as(u16, byte) << 8 | (self.freq.raw & 0xFF);
     }
 };
 
@@ -94,10 +113,13 @@ const Wave = struct {
     const Self = @This();
 
     /// Write-only
+    /// NR30
     select: io.WaveSelect,
     /// NR31    
     length: u8,
+    /// NR32
     vol: io.WaveVolume,
+    /// NR33, NR34
     freq: io.Frequency,
 
     fn init() Self {
@@ -108,6 +130,14 @@ const Wave = struct {
             .length = 0,
         };
     }
+
+    pub fn setFreqLow(self: *Self, byte: u8) void {
+        self.freq.raw = (self.freq.raw & 0xFF00) | byte;
+    }
+
+    pub fn setFreqHigh(self: *Self, byte: u8) void {
+        self.freq.raw = @as(u16, byte) << 8 | (self.freq.raw & 0xFF);
+    }
 };
 
 const Noise = struct {
@@ -116,8 +146,11 @@ const Noise = struct {
     /// Write-only
     /// NR41
     len: u6,
+    /// NR42
     envelope: io.Envelope,
+    /// NR43
     poly: io.PolyCounter,
+    /// NR44
     cnt: io.NoiseControl,
 
     fn init() Self {
diff --git a/src/bus/io.zig b/src/bus/io.zig
index b3ff351..b365004 100644
--- a/src/bus/io.zig
+++ b/src/bus/io.zig
@@ -124,6 +124,9 @@ pub fn read16(bus: *const Bus, addr: u32) u16 {
         // Sound
         0x0400_0088 => bus.apu.bias.raw,
 
+        // DMA Transfers
+        0x0400_00BA => bus.dma._0.cnt.raw,
+
         // Timers
         0x0400_0100 => bus.tim._0.counter(),
         0x0400_0102 => bus.tim._0.cnt.raw,
@@ -221,6 +224,8 @@ pub fn write16(bus: *Bus, addr: u32, halfword: u16) void {
 
         // Serial Communication 2
         0x0400_0134 => log.warn("Wrote 0x{X:0>4} to RCNT", .{halfword}),
+        0x0400_0140 => log.warn("Wrote 0x{X:0>4} to JOYCNT", .{halfword}),
+        0x0400_0158 => log.warn("Wrote 0x{X:0>4} to JOYSTAT", .{halfword}),
 
         // Interrupts
         0x0400_0200 => bus.io.ie.raw = halfword,
@@ -239,6 +244,13 @@ pub fn read8(bus: *const Bus, addr: u32) u8 {
         0x0400_0006 => @truncate(u8, bus.ppu.vcount.raw),
 
         // Sound
+        0x0400_0060 => bus.apu.ch1.sweep.raw,
+        0x0400_0063 => bus.apu.ch1.envelope.raw,
+        0x0400_0069 => bus.apu.ch2.envelope.raw,
+        0x0400_0073 => bus.apu.ch3.vol.raw,
+        0x0400_0079 => bus.apu.ch4.envelope.raw,
+        0x0400_007C => bus.apu.ch4.poly.raw,
+        0x0400_0081 => @truncate(u8, bus.apu.ch_vol_cnt.raw >> 8),
         0x0400_0089 => @truncate(u8, bus.apu.bias.raw >> 8),
 
         // Serial Communication 1
@@ -258,14 +270,26 @@ pub fn write8(bus: *Bus, addr: u32, byte: u8) void {
         0x0400_0005 => bus.ppu.dispstat.raw = (@as(u16, byte) << 8) | (bus.ppu.dispstat.raw & 0xFF),
 
         // Sound
+        0x0400_0060 => bus.apu.ch1.sweep.raw = byte,
+        0x0400_0062 => bus.apu.ch1.duty.raw = byte,
         0x0400_0063 => bus.apu.ch1.envelope.raw = byte,
+        0x0400_0064 => bus.apu.ch1.setFreqLow(byte),
         0x0400_0065 => bus.apu.ch1.setFreqHigh(byte),
+        0x0400_0068 => bus.apu.ch2.duty.raw = byte,
         0x0400_0069 => bus.apu.ch2.envelope.raw = byte,
+        0x0400_006C => bus.apu.ch2.setFreqLow(byte),
         0x0400_006D => bus.apu.ch2.setFreqHigh(byte),
         0x0400_0070 => bus.apu.ch3.select.raw = byte,
+        0x0400_0072 => bus.apu.ch3.length = byte,
+        0x0400_0073 => bus.apu.ch3.vol.raw = byte,
+        0x0400_0074 => bus.apu.ch3.setFreqLow(byte),
+        0x0400_0075 => bus.apu.ch3.setFreqHigh(byte),
+        0x0400_0078 => bus.apu.ch4.len = @truncate(u6, byte),
         0x0400_0079 => bus.apu.ch4.envelope.raw = byte,
+        0x0400_007C => bus.apu.ch4.poly.raw = byte,
         0x0400_007D => bus.apu.ch4.cnt.raw = byte,
         0x0400_0080 => bus.apu.setSoundCntLLow(byte),
+        0x0400_0081 => bus.apu.setSoundCntLHigh(byte),
         0x0400_0084 => bus.apu.setSoundCntX(byte >> 7 & 1 == 1),
         0x0400_0089 => bus.apu.setBiasHigh(byte),
 

From 29da7b294e5a803b18f621add327b1bd15164487 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Mon, 28 Mar 2022 19:41:22 -0300
Subject: [PATCH 2/6] feat: implement Flash backup cartrige kinds

---
 src/bus/backup.zig | 142 +++++++++++++++++++++++++++++++++++++++------
 1 file changed, 123 insertions(+), 19 deletions(-)

diff --git a/src/bus/backup.zig b/src/bus/backup.zig
index ce639b3..6199718 100644
--- a/src/bus/backup.zig
+++ b/src/bus/backup.zig
@@ -23,6 +23,9 @@ pub const Backup = struct {
     title: [12]u8,
     save_path: ?[]const u8,
 
+    // TODO: Implement EEPROM
+    flash: Flash,
+
     pub fn init(alloc: Allocator, kind: BackupKind, title: [12]u8, path: ?[]const u8) !Self {
         const buf_len: usize = switch (kind) {
             .Sram => 0x8000, // 32K
@@ -40,15 +43,14 @@ pub const Backup = struct {
             .kind = kind,
             .title = title,
             .save_path = path,
+            .flash = Flash.init(),
         };
-        if (backup.save_path) |p| backup.loadSaveFromDisk(p) catch |e| log.err("Failed to load save: {}", .{e});
 
+        if (backup.save_path) |p| backup.loadSaveFromDisk(p) catch |e| log.err("Failed to load save: {}", .{e});
         return backup;
     }
 
     pub fn guessKind(rom: []const u8) ?BackupKind {
-        @setRuntimeSafety(false);
-
         for (backup_kinds) |needle| {
             const needle_len = needle.str.len;
 
@@ -63,7 +65,6 @@ pub const Backup = struct {
 
     pub fn deinit(self: Self) void {
         if (self.save_path) |path| self.writeSaveToDisk(path) catch |e| log.err("Failed to write save: {}", .{e});
-
         self.alloc.free(self.buf);
     }
 
@@ -78,7 +79,7 @@ pub const Backup = struct {
         defer self.alloc.free(file_buf);
 
         switch (self.kind) {
-            .Sram => {
+            .Sram, .Flash, .Flash1M => {
                 std.mem.copy(u8, self.buf, file_buf);
                 log.info("Loaded Save from {s}", .{file_path});
             },
@@ -103,37 +104,70 @@ pub const Backup = struct {
         defer self.alloc.free(file_path);
 
         switch (self.kind) {
-            .Sram => {
+            .Sram, .Flash, .Flash1M => {
                 const file = try std.fs.createFileAbsolute(file_path, .{});
                 defer file.close();
 
                 try file.writeAll(self.buf);
-                log.info("Dumped SRAM to {s}", .{file_path});
+                log.info("Wrote Save to {s}", .{file_path});
             },
             else => return SaveError.UnsupportedBackupKind,
         }
     }
 
     pub fn get8(self: *const Self, idx: usize) u8 {
-        // TODO: Implement Flash and EEPROM
         switch (self.kind) {
-            .Flash => return switch (idx) {
-                0x0000 => 0x32, // Panasonic manufacturer ID
-                0x0001 => 0x1B, // Panasonic device ID
-                else => self.buf[idx],
+            .Flash => {
+                switch (idx) {
+                    0x0000 => if (self.flash.id_mode) return 0x32, // Panasonic manufacturer ID
+                    0x0001 => if (self.flash.id_mode) return 0x1B, // Panasonic device ID
+                    else => {},
+                }
+
+                return self.flash.read(self.buf, idx);
             },
-            .Flash1M => return switch (idx) {
-                0x0000 => 0x62, // Sanyo manufacturer ID
-                0x0001 => 0x13, // Sanyo device ID
-                else => self.buf[idx],
+            .Flash1M => {
+                switch (idx) {
+                    0x0000 => if (self.flash.id_mode) return 0x62, // Sanyo manufacturer ID
+                    0x0001 => if (self.flash.id_mode) return 0x13, // Sanyo device ID
+                    else => {},
+                }
+
+                return self.flash.read(self.buf, idx);
             },
             .Eeprom => return self.buf[idx],
-            .Sram => return self.buf[idx & 0x7FFF], // 32K SRAM chips are repeated
+            .Sram => return self.buf[idx & 0x7FFF], // 32K SRAM chip is mirrored
         }
     }
 
     pub fn set8(self: *Self, idx: usize, byte: u8) void {
-        self.buf[idx] = byte;
+        switch (self.kind) {
+            .Flash, .Flash1M => {
+                if (self.flash.prep_write) return self.flash.write(self.buf, idx, byte);
+                if (self.flash.shouldEraseSector(idx, byte)) return self.flash.eraseSector(self.buf, idx);
+
+                switch (idx) {
+                    0x0000 => if (self.kind == .Flash1M and self.flash.set_bank) {
+                        self.flash.bank = @truncate(u1, byte);
+                    },
+                    0x5555 => {
+                        if (self.flash.state == .Command) {
+                            self.flash.handleCommand(self.buf, byte);
+                        } else if (byte == 0xAA and self.flash.state == .Ready) {
+                            self.flash.state = .Set;
+                        } else if (byte == 0xF0) {
+                            self.flash.state = .Ready;
+                        }
+                    },
+                    0x2AAA => if (byte == 0x55 and self.flash.state == .Set) {
+                        self.flash.state = .Command;
+                    },
+                    else => {},
+                }
+            },
+            .Eeprom => self.buf[idx] = byte,
+            .Sram => self.buf[idx & 0x7FFF] = byte,
+        }
     }
 };
 
@@ -145,10 +179,12 @@ const BackupKind = enum {
 };
 
 const Needle = struct {
+    const Self = @This();
+
     str: []const u8,
     kind: BackupKind,
 
-    fn init(str: []const u8, kind: BackupKind) @This() {
+    fn init(str: []const u8, kind: BackupKind) Self {
         return .{
             .str = str,
             .kind = kind,
@@ -159,3 +195,71 @@ const Needle = struct {
 const SaveError = error{
     UnsupportedBackupKind,
 };
+
+const Flash = struct {
+    const Self = @This();
+
+    state: FlashState,
+
+    id_mode: bool,
+    set_bank: bool,
+    prep_erase: bool,
+    prep_write: bool,
+
+    bank: u1,
+
+    fn init() Self {
+        return .{
+            .state = .Ready,
+            .id_mode = false,
+            .set_bank = false,
+            .prep_erase = false,
+            .prep_write = false,
+            .bank = 0,
+        };
+    }
+
+    fn handleCommand(self: *Self, buf: []u8, byte: u8) void {
+        switch (byte) {
+            0x90 => self.id_mode = true,
+            0xF0 => self.id_mode = false,
+            0xB0 => self.set_bank = true,
+            0x80 => self.prep_erase = true,
+            0x10 => {
+                std.mem.set(u8, buf, 0xFF);
+                self.prep_erase = false;
+            },
+            0xA0 => self.prep_write = true,
+            else => std.debug.panic("Unhandled Flash Command: 0x{X:0>2}", .{byte}),
+        }
+
+        self.state = .Ready;
+    }
+
+    fn shouldEraseSector(self: *const Self, idx: usize, byte: u8) bool {
+        return self.prep_erase and idx & 0xFFF == 0x000 and byte == 0x30;
+    }
+
+    fn write(self: *Self, buf: []u8, idx: usize, byte: u8) void {
+        buf[idx + if (self.bank == 1) 0x1000 else @as(usize, 0)] = byte;
+        self.prep_write = false;
+    }
+
+    fn read(self: *const Self, buf: []u8, idx: usize) u8 {
+        return buf[idx + if (self.bank == 1) 0x1000 else @as(usize, 0)];
+    }
+
+    fn eraseSector(self: *Self, buf: []u8, idx: usize) void {
+        const start = (idx & 0xF000) + if (self.bank == 1) 0x1000 else @as(usize, 0);
+
+        std.mem.set(u8, buf[start..][0..0x1000], 0xFF);
+        self.prep_erase = false;
+        self.state = .Ready;
+    }
+};
+
+const FlashState = enum {
+    Ready,
+    Set,
+    Command,
+};

From 7f555095f2c49cbb06bca9fc2fd6cdee05a1b2cd Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Tue, 29 Mar 2022 08:50:12 -0300
Subject: [PATCH 3/6] chore: tick on memory access instead of 1cpi

---
 src/Bus.zig | 16 ++++++++++++++--
 src/emu.zig |  6 +++---
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/src/Bus.zig b/src/Bus.zig
index a1eec70..a805fec 100644
--- a/src/Bus.zig
+++ b/src/Bus.zig
@@ -27,6 +27,8 @@ tim: Timers,
 iwram: Iwram,
 ewram: Ewram,
 
+sched: *Scheduler,
+
 io: Io,
 
 pub fn init(alloc: Allocator, sched: *Scheduler, rom_path: []const u8, bios_path: ?[]const u8, save_path: ?[]const u8) !Self {
@@ -40,6 +42,7 @@ pub fn init(alloc: Allocator, sched: *Scheduler, rom_path: []const u8, bios_path
         .dma = DmaControllers.init(),
         .tim = Timers.init(sched),
         .io = Io.init(),
+        .sched = sched,
     };
 }
 
@@ -52,6 +55,8 @@ pub fn deinit(self: Self) void {
 }
 
 pub fn read32(self: *const Self, addr: u32) u32 {
+    self.sched.tick += 1;
+
     return switch (addr) {
         // General Internal Memory
         0x0000_0000...0x0000_3FFF => self.bios.get32(addr),
@@ -74,7 +79,7 @@ pub fn read32(self: *const Self, addr: u32) u32 {
 }
 
 pub fn write32(self: *Self, addr: u32, word: u32) void {
-    // TODO: write32 can write to GamePak Flash
+    self.sched.tick += 1;
 
     switch (addr) {
         // General Internal Memory
@@ -92,6 +97,8 @@ pub fn write32(self: *Self, addr: u32, word: u32) void {
 }
 
 pub fn read16(self: *const Self, addr: u32) u16 {
+    self.sched.tick += 1;
+
     return switch (addr) {
         // General Internal Memory
         0x0000_0000...0x0000_3FFF => self.bios.get16(addr),
@@ -114,7 +121,8 @@ pub fn read16(self: *const Self, addr: u32) u16 {
 }
 
 pub fn write16(self: *Self, addr: u32, halfword: u16) void {
-    // TODO: write16 can write to GamePak Flash
+    self.sched.tick += 1;
+
     switch (addr) {
         // General Internal Memory
         0x0200_0000...0x02FF_FFFF => self.ewram.set16(addr & 0x3FFFF, halfword),
@@ -132,6 +140,8 @@ pub fn write16(self: *Self, addr: u32, halfword: u16) void {
 }
 
 pub fn read8(self: *const Self, addr: u32) u8 {
+    self.sched.tick += 1;
+
     return switch (addr) {
         // General Internal Memory
         0x0000_0000...0x0000_3FFF => self.bios.get8(addr),
@@ -155,6 +165,8 @@ pub fn read8(self: *const Self, addr: u32) u8 {
 }
 
 pub fn write8(self: *Self, addr: u32, byte: u8) void {
+    self.sched.tick += 1;
+
     switch (addr) {
         // General Internal Memory
         0x0200_0000...0x02FF_FFFF => self.ewram.set8(addr & 0x3FFFF, byte),
diff --git a/src/emu.zig b/src/emu.zig
index 2ff3990..fd34689 100644
--- a/src/emu.zig
+++ b/src/emu.zig
@@ -43,9 +43,9 @@ pub fn run(kind: RunKind, quit: *Atomic(bool), fps: *FpsAverage, sched: *Schedul
 }
 
 pub fn runFrame(sched: *Scheduler, cpu: *Arm7tdmi, bus: *Bus) void {
-    var cycles: u64 = 0;
-    while (cycles < cycles_per_frame) : (cycles += 1) {
-        sched.tick += 1;
+    const frame_end = sched.tick + cycles_per_frame;
+
+    while (sched.tick < frame_end) {
         _ = cpu.step();
 
         while (sched.tick >= sched.nextTimestamp()) {

From e1276695497113bec80f7dff2146b41c11b4f12c Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Tue, 29 Mar 2022 08:58:57 -0300
Subject: [PATCH 4/6] Revert "chore: tick on memory access instead of 1cpi"

This reverts commit 7f555095f2c49cbb06bca9fc2fd6cdee05a1b2cd.
---
 src/Bus.zig | 16 ++--------------
 src/emu.zig |  6 +++---
 2 files changed, 5 insertions(+), 17 deletions(-)

diff --git a/src/Bus.zig b/src/Bus.zig
index a805fec..a1eec70 100644
--- a/src/Bus.zig
+++ b/src/Bus.zig
@@ -27,8 +27,6 @@ tim: Timers,
 iwram: Iwram,
 ewram: Ewram,
 
-sched: *Scheduler,
-
 io: Io,
 
 pub fn init(alloc: Allocator, sched: *Scheduler, rom_path: []const u8, bios_path: ?[]const u8, save_path: ?[]const u8) !Self {
@@ -42,7 +40,6 @@ pub fn init(alloc: Allocator, sched: *Scheduler, rom_path: []const u8, bios_path
         .dma = DmaControllers.init(),
         .tim = Timers.init(sched),
         .io = Io.init(),
-        .sched = sched,
     };
 }
 
@@ -55,8 +52,6 @@ pub fn deinit(self: Self) void {
 }
 
 pub fn read32(self: *const Self, addr: u32) u32 {
-    self.sched.tick += 1;
-
     return switch (addr) {
         // General Internal Memory
         0x0000_0000...0x0000_3FFF => self.bios.get32(addr),
@@ -79,7 +74,7 @@ pub fn read32(self: *const Self, addr: u32) u32 {
 }
 
 pub fn write32(self: *Self, addr: u32, word: u32) void {
-    self.sched.tick += 1;
+    // TODO: write32 can write to GamePak Flash
 
     switch (addr) {
         // General Internal Memory
@@ -97,8 +92,6 @@ pub fn write32(self: *Self, addr: u32, word: u32) void {
 }
 
 pub fn read16(self: *const Self, addr: u32) u16 {
-    self.sched.tick += 1;
-
     return switch (addr) {
         // General Internal Memory
         0x0000_0000...0x0000_3FFF => self.bios.get16(addr),
@@ -121,8 +114,7 @@ pub fn read16(self: *const Self, addr: u32) u16 {
 }
 
 pub fn write16(self: *Self, addr: u32, halfword: u16) void {
-    self.sched.tick += 1;
-
+    // TODO: write16 can write to GamePak Flash
     switch (addr) {
         // General Internal Memory
         0x0200_0000...0x02FF_FFFF => self.ewram.set16(addr & 0x3FFFF, halfword),
@@ -140,8 +132,6 @@ pub fn write16(self: *Self, addr: u32, halfword: u16) void {
 }
 
 pub fn read8(self: *const Self, addr: u32) u8 {
-    self.sched.tick += 1;
-
     return switch (addr) {
         // General Internal Memory
         0x0000_0000...0x0000_3FFF => self.bios.get8(addr),
@@ -165,8 +155,6 @@ pub fn read8(self: *const Self, addr: u32) u8 {
 }
 
 pub fn write8(self: *Self, addr: u32, byte: u8) void {
-    self.sched.tick += 1;
-
     switch (addr) {
         // General Internal Memory
         0x0200_0000...0x02FF_FFFF => self.ewram.set8(addr & 0x3FFFF, byte),
diff --git a/src/emu.zig b/src/emu.zig
index fd34689..2ff3990 100644
--- a/src/emu.zig
+++ b/src/emu.zig
@@ -43,9 +43,9 @@ pub fn run(kind: RunKind, quit: *Atomic(bool), fps: *FpsAverage, sched: *Schedul
 }
 
 pub fn runFrame(sched: *Scheduler, cpu: *Arm7tdmi, bus: *Bus) void {
-    const frame_end = sched.tick + cycles_per_frame;
-
-    while (sched.tick < frame_end) {
+    var cycles: u64 = 0;
+    while (cycles < cycles_per_frame) : (cycles += 1) {
+        sched.tick += 1;
         _ = cpu.step();
 
         while (sched.tick >= sched.nextTimestamp()) {

From 3046e6243a050a6080b23cba537fd9f34c41c2bd Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Tue, 29 Mar 2022 09:06:26 -0300
Subject: [PATCH 5/6] chore: don't assume 1cpi when stepping by a frame

---
 src/emu.zig | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/emu.zig b/src/emu.zig
index 2ff3990..74db05d 100644
--- a/src/emu.zig
+++ b/src/emu.zig
@@ -43,8 +43,9 @@ pub fn run(kind: RunKind, quit: *Atomic(bool), fps: *FpsAverage, sched: *Schedul
 }
 
 pub fn runFrame(sched: *Scheduler, cpu: *Arm7tdmi, bus: *Bus) void {
-    var cycles: u64 = 0;
-    while (cycles < cycles_per_frame) : (cycles += 1) {
+    const frame_end = sched.tick + cycles_per_frame;
+
+    while (sched.tick < frame_end) {
         sched.tick += 1;
         _ = cpu.step();
 

From 1bb3659df6c076d76187cc557a8aed1fc2df6b9e Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Tue, 29 Mar 2022 18:52:09 -0300
Subject: [PATCH 6/6] chore: update README

---
 README.md | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/README.md b/README.md
index 9242e2c..d3f8d4b 100644
--- a/README.md
+++ b/README.md
@@ -13,26 +13,27 @@ An in-progress Gameboy Advance Emulator written in Zig ⚡!
 * [ARM7TDMI Data Sheet](https://www.dca.fee.unicamp.br/cursos/EA871/references/ARM/ARM7TDMIDataSheet.pdf)
 
 ## Compiling
-Most recently built on Zig [v0.10.0-dev.1037+331cc810d](https://github.com/ziglang/zig/tree/331cc810d)
+Most recently built on Zig [v0.10.0-dev.1659+4dd65316b](https://github.com/ziglang/zig/tree/4dd65316b)
 
 ### Dependencies
 * [SDL.zig](https://github.com/MasterQ32/SDL.zig)
     * [SDL2](https://www.libsdl.org/download-2.0.php)
 * [zig-clap](https://github.com/Hejsil/zig-clap)
+* [known-folders](https://github.com/ziglibs/known-folders)
 * [`bitfields.zig`](https://github.com/FlorenceOS/Florence/blob/f6044db788d35d43d66c1d7e58ef1e3c79f10d6f/lib/util/bitfields.zig)
 
 `bitfields.zig` from [FlorenceOS](https://github.com/FlorenceOS) is included under `lib/util/bitfield.zig`.
 
-`SDL.zig` and `zig-clap` are git submodules you can init using `git submodule update --init` from your terminal. 
+Use `git submodule update --init` from the project root to pull the git submodules `SDL.zig`, `zig-clap`, and `known-folders`
 
-On Linux, be sure to have SDL2 installed using whatever package manager your distro uses. 
+Be sure to provide SDL2 using: 
+* Linux: Your distro's package manager
+* MacOS: ¯\\\_(ツ)_/¯
+* Windows: [`vcpkg`](https://github.com/Microsoft/vcpkg) (install `sdl2:x64-windows`)
 
-On Windows, it's easiest if you use [`vcpkg`](https://github.com/Microsoft/vcpkg) to install `sdl2:x64-windows`. If not, 
-`SDL2.zig` will provide a helpful compile error which should help you get what you need.
+`SDL.zig` will provide a helpful compile error if the zig compiler is unable to find SDL2. 
 
-On macOS? ¯\\\_(ツ)_/¯ I hope it isn't too hard to compile though. 
-
-Once you've got all the dependencies, run `zig build -Drelease-fast`. The executable is located at `zig-out/bin/`. 
+Once you've got all the dependencies, execute `zig build -Drelease-fast`. The executable is located at `zig-out/bin/`. 
 
 ## Controls
 Key | Button