feat: put RTC Sync on Scheduler

TODO: Database to see what games have what GPIO devices

.gitmodules

@@ -7,3 +7,6 @@
 [submodule "lib/known-folders"]
 	path = lib/known-folders
 	url = https://github.com/ziglibs/known-folders
+[submodule "lib/zig-datetime"]
+	path = lib/zig-datetime
+	url = https://github.com/frmdstryr/zig-datetime

build.zig

@@ -13,10 +13,12 @@ pub fn build(b: *std.build.Builder) void {
     const mode = b.standardReleaseOptions();
 
     const exe = b.addExecutable("zba", "src/main.zig");
-    
     // Known Folders (%APPDATA%, XDG, etc.)
     exe.addPackagePath("known_folders", "lib/known-folders/known-folders.zig");
 
+    // DateTime Library
+    exe.addPackagePath("datetime", "lib/zig-datetime/src/main.zig");
+
     // Bitfield type from FlorenceOS: https://github.com/FlorenceOS/
     // exe.addPackage(.{ .name = "bitfield", .path = .{ .path = "lib/util/bitfield.zig" } });
     exe.addPackagePath("bitfield", "lib/util/bitfield.zig");

lib/zig-datetime

@@ -0,0 +1 @@
+Subproject commit 5ec1c36cf3791b3c6c5b330357bdb6feb93979ba

src/core/Bus.zig

@@ -51,7 +51,7 @@ sched: *Scheduler,
 
 pub fn init(self: *Self, allocator: Allocator, sched: *Scheduler, cpu: *Arm7tdmi, paths: FilePaths) !void {
     self.* = .{
-        .pak = try GamePak.init(allocator, paths.rom, paths.save),
+        .pak = try GamePak.init(allocator, cpu, paths.rom, paths.save),
         .bios = try Bios.init(allocator, paths.bios),
         .ppu = try Ppu.init(allocator, sched),
         .apu = Apu.init(sched),

src/core/bus/GamePak.zig

@@ -1,5 +1,7 @@
 const std = @import("std");
+const DateTime = @import("datetime").datetime.Datetime;
 
+const Arm7tdmi = @import("../cpu.zig").Arm7tdmi;
 const Bit = @import("bitfield").Bit;
 const Bitfield = @import("bitfield").Bitfield;
 const Backup = @import("backup.zig").Backup;
@@ -14,7 +16,7 @@ allocator: Allocator,
 backup: Backup,
 gpio: *Gpio,
 
-pub fn init(allocator: Allocator, rom_path: []const u8, save_path: ?[]const u8) !Self {
+pub fn init(allocator: Allocator, cpu: *Arm7tdmi, rom_path: []const u8, save_path: ?[]const u8) !Self {
     const file = try std.fs.cwd().openFile(rom_path, .{});
     defer file.close();
 
@@ -28,7 +30,7 @@ pub fn init(allocator: Allocator, rom_path: []const u8, save_path: ?[]const u8)
         .allocator = allocator,
         .title = title,
         .backup = try Backup.init(allocator, kind, title, save_path),
-        .gpio = try Gpio.init(allocator, .Rtc),
+        .gpio = try Gpio.init(allocator, cpu, .Rtc),
     };
 }
 
@@ -230,23 +232,18 @@ const Gpio = struct {
 
     const Device = struct {
         ptr: ?*anyopaque,
-        // TODO: Maybe make this comptime known? Removes some if statements
-        kind: Kind,
+        kind: Kind, // TODO: Make comptime known?
 
-        const Kind = enum {
-            Rtc,
-            None,
-        };
+        const Kind = enum { Rtc, None };
 
-        fn step(self: *Device, value: u4) void {
-            switch (self.kind) {
-                .Rtc => {
+        fn step(self: *Device, value: u4) u4 {
+            return switch (self.kind) {
+                .Rtc => blk: {
                     const clock = @ptrCast(*Clock, @alignCast(@alignOf(*Clock), self.ptr.?));
-
-                    clock.step(Clock.GpioData{ .raw = value });
+                    break :blk clock.step(Clock.Data{ .raw = value });
                 },
-                .None => {},
-            }
+                .None => value,
+            };
         }
 
         fn init(kind: Kind, ptr: ?*anyopaque) Device {
@@ -260,7 +257,7 @@ const Gpio = struct {
         Control,
     };
 
-    fn init(allocator: Allocator, kind: Device.Kind) !*This {
+    fn init(allocator: Allocator, cpu: *Arm7tdmi, kind: Device.Kind) !*This {
         const self = try allocator.create(This);
 
         self.* = .{
@@ -271,7 +268,7 @@ const Gpio = struct {
             .device = switch (kind) {
                 .Rtc => blk: {
                     const clock = try allocator.create(Clock);
-                    clock.init(self);
+                    clock.init(cpu, self);
 
                     break :blk Device{ .kind = kind, .ptr = clock };
                 },
@@ -294,17 +291,13 @@ const Gpio = struct {
     }
 
     fn write(self: *This, comptime reg: Register, value: if (reg == .Control) u1 else u4) void {
-        log.debug("RTC: Wrote 0b{b:0>4} to {}", .{ value, reg });
-
-        // if (reg == .Data)
-        // log.err("original: 0b{b:0>4} masked: 0b{b:0>4} result: 0b{b:0>4}", .{ self.data, value & self.direction, self.data | (value & self.direction) });
-
         switch (reg) {
             .Data => {
                 const masked_value = value & self.direction;
 
-                self.device.step(masked_value);
-                self.data = masked_value;
+                // The value which is actually stored in the GPIO register
+                // might be modified by the device implementing the GPIO interface e.g. RTC reads
+                self.data = self.device.step(masked_value);
             },
             .Direction => self.direction = value,
             .Control => self.cnt = value,
@@ -323,22 +316,23 @@ const Gpio = struct {
 };
 
 /// GBA Real Time Clock
-const Clock = struct {
+pub const Clock = struct {
     const This = @This();
 
-    cmd: Command,
     writer: Writer,
+    reader: Reader,
     state: State,
     cnt: Control,
 
     year: u8,
     month: u5,
     day: u6,
-    day_of_week: u3,
+    weekday: u3,
     hour: u6,
     minute: u7,
     second: u7,
 
+    cpu: *Arm7tdmi,
     gpio: *const Gpio,
 
     const Register = enum {
@@ -349,108 +343,126 @@ const Clock = struct {
 
     const State = union(enum) {
         Idle,
-        CommandInput,
+        Command,
         Write: Register,
         Read: Register,
     };
 
+    const Reader = struct {
+        i: u4,
+        count: u8,
+
+        /// Reads a bit from RTC registers. Which bit it reads is dependent on
+        ///
+        /// 1. The RTC State Machine, whitch tells us which register we're accessing
+        /// 2. A `count`, which keeps track of which byte is currently being read
+        /// 3. An index, which keeps track of which bit of the byte determined by `count` is being read
+        fn read(self: *Reader, clock: *const Clock, register: Register) u1 {
+            const idx = @intCast(u3, self.i);
+            defer self.i += 1;
+
+            // FIXME: What do I do about the unused bits?
+            return switch (register) {
+                .Control => @truncate(u1, switch (self.count) {
+                    0 => clock.cnt.raw >> idx,
+                    else => std.debug.panic("Tried to read from byte #{} of {} (hint: there's only 1 byte)", .{ self.count, register }),
+                }),
+                .DateTime => @truncate(u1, switch (self.count) {
+                    // Date
+                    0 => clock.year >> idx,
+                    1 => @as(u8, clock.month) >> idx,
+                    2 => @as(u8, clock.day) >> idx,
+                    3 => @as(u8, clock.weekday) >> idx,
+
+                    // Time
+                    4 => @as(u8, clock.hour) >> idx,
+                    5 => @as(u8, clock.minute) >> idx,
+                    6 => @as(u8, clock.second) >> idx,
+                    else => std.debug.panic("Tried to read from byte #{} of {} (hint: there's only 7 bytes)", .{ self.count, register }),
+                }),
+                .Time => @truncate(u1, switch (self.count) {
+                    0 => @as(u8, clock.hour) >> idx,
+                    1 => @as(u8, clock.minute) >> idx,
+                    2 => @as(u8, clock.second) >> idx,
+                    else => std.debug.panic("Tried to read from byte #{} of {} (hint: there's only 3 bytes)", .{ self.count, register }),
+                }),
+            };
+        }
+
+        /// Is true when a Reader has read a u8's worth of bits
+        fn finished(self: *const Reader) bool {
+            return self.i >= 8;
+        }
+
+        /// Resets the index used to shift bits out of RTC registers
+        /// and `count`, which is used to keep track of which byte we're reading
+        /// is incremeneted
+        fn lap(self: *Reader) void {
+            self.i = 0;
+            self.count += 1;
+        }
+
+        /// Resets the state of a `Reader` in preparation for a future
+        /// read command
+        fn reset(self: *Reader) void {
+            self.i = 0;
+            self.count = 0;
+        }
+    };
+
     const Writer = struct {
         buf: u8,
         i: u4,
 
-        /// The Number of bytes written to since last reset
+        /// The Number of bytes written since last reset
         count: u8,
 
+        /// Append a bit to the internal bit buffer (aka an integer)
         fn push(self: *Writer, value: u1) void {
             const idx = @intCast(u3, self.i);
             self.buf = (self.buf & ~(@as(u8, 1) << idx)) | @as(u8, value) << idx;
             self.i += 1;
         }
 
+        /// Takes the contents of the internal buffer and writes it to an RTC register
+        /// Where it writes to is dependent on:
+        ///
+        /// 1. The RTC State Machine, whitch tells us which register we're accessing
+        /// 2. A `count`, which keeps track of which byte is currently being read
+        fn write(self: *const Writer, clock: *Clock, register: Register) void {
+            // FIXME: What do do about unused bits?
+            switch (register) {
+                .Control => switch (self.count) {
+                    0 => clock.cnt.raw = (clock.cnt.raw & 0x80) | (self.buf & 0x7F), // Bit 7 read-only
+                    else => std.debug.panic("Tried to write to byte #{} of {} (hint: there's only 1 byte)", .{ self.count, register }),
+                },
+                .DateTime, .Time => log.debug("RTC: Ignoring {} write", .{register}),
+            }
+        }
+
+        /// Is true when 8 bits have been shifted into the internal buffer
+        fn finished(self: *const Writer) bool {
+            return self.i >= 8;
+        }
+
+        /// Resets the internal buffer
+        /// resets the index used to shift bits into the internal buffer
+        /// increments `count` (which keeps track of byte offsets) by one
         fn lap(self: *Writer) void {
             self.buf = 0;
             self.i = 0;
             self.count += 1;
         }
 
+        /// Resets `Writer` to a clean state in preparation for a future write command
         fn reset(self: *Writer) void {
             self.buf = 0;
             self.i = 0;
             self.count = 0;
         }
-
-        fn isFinished(self: *const Writer) bool {
-            return self.i >= 8;
-        }
-
-        fn getCount(self: *const Writer) u8 {
-            return self.count;
-        }
-
-        fn getValue(self: *const Writer) u8 {
-            return self.buf;
-        }
     };
 
-    const Command = struct {
-        buf: u8,
-        i: u4,
-
-        fn push(self: *Command, value: u1) void {
-            const idx = @intCast(u3, self.i);
-            self.buf = (self.buf & ~(@as(u8, 1) << idx)) | @as(u8, value) << idx;
-            self.i += 1;
-        }
-
-        fn reset(self: *Command) void {
-            self.buf = 0;
-            self.i = 0;
-        }
-
-        fn isFinished(self: *const Command) bool {
-            return self.i >= 8;
-        }
-
-        fn getCommand(self: *const Command) u8 {
-            // If high Nybble does not contain 0x6, reverse the order of the nybbles.
-            // For some reason RTC commands can be LSB or MSB which is funny
-            return if (self.buf >> 4 & 0xF == 0x6) self.buf else (self.buf & 0xF) << 4 | (self.buf >> 4 & 0xF);
-        }
-
-        fn handleCommand(self: *const Command, rtc: *Clock) State {
-            log.info("RTC: Failed to handle Command 0b{b:0>8} aka 0x{X:0>2}", .{ self.buf, self.buf });
-            const command = self.getCommand();
-
-            const is_write = command & 1 == 0;
-            const rtc_register = @intCast(u3, command >> 1 & 0x7); // TODO: Make Truncate
-
-            if (is_write) {
-                return switch (rtc_register) {
-                    0 => blk: {
-                        rtc.reset();
-                        break :blk .Idle;
-                    },
-                    1 => .{ .Write = .Control },
-                    2 => .{ .Write = .DateTime },
-                    3 => .{ .Write = .Time },
-                    6 => blk: {
-                        rtc.irq();
-                        break :blk .Idle;
-                    },
-                    4, 5, 7 => .Idle,
-                };
-            } else {
-                return switch (rtc_register) {
-                    1 => .{ .Read = .Control },
-                    2 => .{ .Read = .DateTime },
-                    3 => .{ .Read = .Time },
-                    0, 4, 5, 6, 7 => .Idle, // Do Nothing
-                };
-            }
-        }
-    };
-
-    const GpioData = extern union {
+    const Data = extern union {
         sck: Bit(u8, 0),
         sio: Bit(u8, 1),
         cs: Bit(u8, 2),
@@ -473,93 +485,196 @@ const Clock = struct {
         raw: u8,
     };
 
-    fn init(ptr: *This, gpio: *const Gpio) void {
+    fn init(ptr: *This, cpu: *Arm7tdmi, gpio: *const Gpio) void {
         ptr.* = .{
-            .cmd = .{ .buf = 0, .i = 0 },
             .writer = .{ .buf = 0, .i = 0, .count = 0 },
+            .reader = .{ .i = 0, .count = 0 },
             .state = .Idle,
             .cnt = .{ .raw = 0 },
-            .year = 0,
-            .month = 0,
-            .day = 0,
-            .day_of_week = 0,
-            .hour = 0,
-            .minute = 0,
-            .second = 0,
-            .gpio = gpio,
+            .year = 0x01,
+            .month = 0x6,
+            .day = 0x13,
+            .weekday = 0x3,
+            .hour = 0x23,
+            .minute = 0x59,
+            .second = 0x59,
+            .cpu = cpu,
+            .gpio = gpio, // Can't use Arm7tdmi ptr b/c not initialized yet
         };
+
+        cpu.sched.push(.RealTimeClock, 1 << 24); // Every Second
     }
 
-    fn attachGpio(self: *This, gpio: *const Gpio) void {
-        self.gpio = gpio;
+    pub fn updateTime(self: *This) void {
+        self.cpu.sched.push(.RealTimeClock, 1 << 24); // Reschedule
+
+        const now = DateTime.now();
+        self.year = toBcd(u8, @intCast(u8, now.date.year - 2000));
+        self.month = toBcd(u5, now.date.month);
+        self.day = toBcd(u3, now.date.day);
+        self.weekday = toBcd(u3, (now.date.weekday() + 1) % 7); // API is Monday = 0, Sunday = 6. We want Sunday = 0, Saturday = 6
+        self.hour = toBcd(u6, now.time.hour);
+        self.minute = toBcd(u7, now.time.minute);
+        self.second = toBcd(u7, now.time.second);
     }
 
-    fn step(self: *This, value: GpioData) void {
-        const cache: GpioData = .{ .raw = self.gpio.data };
+    fn step(self: *This, value: Data) u4 {
+        const cache: Data = .{ .raw = self.gpio.data };
 
-        switch (self.state) {
-            .Idle => {
-                // If SCK is high and CS rises, then prepare for Command
+        return switch (self.state) {
+            .Idle => blk: {
                 // FIXME: Maybe check incoming value to see if SCK is also high?
                 if (cache.sck.read()) {
                     if (!cache.cs.read() and value.cs.read()) {
-                        log.err("RTC: Entering Command Mode", .{});
-                        self.state = .CommandInput;
-                        self.cmd.reset();
+                        log.debug("RTC: Entering Command Mode", .{});
+                        self.state = .Command;
                     }
                 }
+
+                break :blk @truncate(u4, value.raw);
             },
-            .CommandInput => {
+            .Command => blk: {
                 if (!value.cs.read()) log.err("RTC: Expected CS to be set during {}, however CS was cleared", .{self.state});
 
-                if (!cache.sck.read() and value.sck.read()) {
                 // If SCK rises, sample SIO
-                    log.debug("RTC: Sampled 0b{b:0>1} from SIO", .{@boolToInt(value.sio.read())});
-                    self.cmd.push(@boolToInt(value.sio.read()));
-
-                    if (self.cmd.isFinished()) {
-                        self.state = self.cmd.handleCommand(self);
-                    }
-                }
-            },
-            State{ .Write = .Control } => {
-                if (!value.cs.read()) log.err("RTC: Expected CS to be set during {}, however CS was cleared", .{self.state});
-
                 if (!cache.sck.read() and value.sck.read()) {
-                    // If SCK rises, sample SIO
-
-                    log.debug("RTC: Sampled 0b{b:0>1} from SIO", .{@boolToInt(value.sio.read())});
                     self.writer.push(@boolToInt(value.sio.read()));
 
-                    if (self.writer.isFinished()) {
-                        self.writer.lap();
-                        self.cnt.raw = self.writer.getValue();
+                    if (self.writer.finished()) {
+                        self.state = self.processCommand(self.writer.buf);
+                        self.writer.reset();
 
-                        // FIXME: Move this to a constant or something
-                        if (self.writer.getCount() == 1) {
+                        log.debug("RTC: Switching to {}", .{self.state});
+                    }
+                }
+
+                break :blk @truncate(u4, value.raw);
+            },
+            .Write => |register| blk: {
+                if (!value.cs.read()) log.err("RTC: Expected CS to be set during {}, however CS was cleared", .{self.state});
+
+                // If SCK rises, sample SIO
+                if (!cache.sck.read() and value.sck.read()) {
+                    self.writer.push(@boolToInt(value.sio.read()));
+
+                    const register_width: u32 = switch (register) {
+                        .Control => 1,
+                        .DateTime => 7,
+                        .Time => 3,
+                    };
+
+                    if (self.writer.finished()) {
+                        self.writer.write(self, register); // write inner buffer to RTC register
+                        self.writer.lap();
+
+                        if (self.writer.count == register_width) {
                             self.writer.reset();
                             self.state = .Idle;
                         }
                     }
                 }
+
+                break :blk @truncate(u4, value.raw);
             },
-            else => {
-                // TODO: Implement Read/Writes for Date/Time and Time and Control
-                log.err("RTC: Ignored request to handle {} command", .{self.state});
+            .Read => |register| blk: {
+                if (!value.cs.read()) log.err("RTC: Expected CS to be set during {}, however CS was cleared", .{self.state});
+                var ret = value;
+
+                // if SCK rises, sample SIO
+                if (!cache.sck.read() and value.sck.read()) {
+                    ret.sio.write(self.reader.read(self, register) == 0b1);
+
+                    const register_width: u32 = switch (register) {
+                        .Control => 1,
+                        .DateTime => 7,
+                        .Time => 3,
+                    };
+
+                    if (self.reader.finished()) {
+                        self.reader.lap();
+
+                        if (self.reader.count == register_width) {
+                            self.reader.reset();
                             self.state = .Idle;
-            },
                         }
                     }
+                }
+
+                break :blk @truncate(u4, ret.raw);
+            },
+        };
+    }
 
     fn reset(self: *This) void {
-        // mGBA and NBA only zero the control register
-        // we'll do the same
+        // mGBA and NBA only zero the control register. We will do the same
+        log.debug("RTC: Reset (control register was zeroed)", .{});
+
         self.cnt.raw = 0;
-        log.info("RTC: Reset executed (control register was zeroed)", .{});
     }
 
-    fn irq(_: *const This) void {
-        // TODO: Force GamePak IRQ
-        log.err("RTC: TODO: Force GamePak IRQ", .{});
+    fn irq(self: *This) void {
+        // TODO: Confirm that this is the right behaviour
+        log.debug("RTC: Force GamePak IRQ", .{});
+
+        self.cpu.bus.io.irq.game_pak.set();
+        self.cpu.handleInterrupt();
+    }
+
+    fn processCommand(self: *This, raw_command: u8) State {
+        const command = blk: {
+            // If High Nybble is 0x6, no need to switch the endianness
+            if (raw_command >> 4 & 0xF == 0x6) break :blk raw_command;
+
+            // Turns out reversing the order of bits isn't trivial at all
+            // https://stackoverflow.com/questions/2602823/in-c-c-whats-the-simplest-way-to-reverse-the-order-of-bits-in-a-byte
+            var ret = raw_command;
+            ret = (ret & 0xF0) >> 4 | (ret & 0x0F) << 4;
+            ret = (ret & 0xCC) >> 2 | (ret & 0x33) << 2;
+            ret = (ret & 0xAA) >> 1 | (ret & 0x55) << 1;
+
+            break :blk ret;
+        };
+        log.debug("RTC: Handling Command 0x{X:0>2} [0b{b:0>8}]", .{ command, command });
+
+        const is_write = command & 1 == 0;
+        const rtc_register = @truncate(u3, command >> 1 & 0x7);
+
+        if (is_write) {
+            return switch (rtc_register) {
+                0 => blk: {
+                    self.reset();
+                    break :blk .Idle;
+                },
+                1 => .{ .Write = .Control },
+                2 => .{ .Write = .DateTime },
+                3 => .{ .Write = .Time },
+                6 => blk: {
+                    self.irq();
+                    break :blk .Idle;
+                },
+                4, 5, 7 => .Idle,
+            };
+        } else {
+            return switch (rtc_register) {
+                1 => .{ .Read = .Control },
+                2 => .{ .Read = .DateTime },
+                3 => .{ .Read = .Time },
+                0, 4, 5, 6, 7 => .Idle, // Do Nothing
+            };
+        }
     }
 };
+
+fn toBcd(comptime T: type, value: u8) T {
+    var input = value;
+    var ret: u8 = 0;
+    var shift: u3 = 0;
+
+    while (input > 0) {
+        ret |= (input % 10) << (shift << 2);
+        shift += 1;
+        input /= 10;
+    }
+
+    return @truncate(T, ret);
+}

src/core/scheduler.zig

@@ -2,6 +2,7 @@ const std = @import("std");
 
 const Bus = @import("Bus.zig");
 const Arm7tdmi = @import("cpu.zig").Arm7tdmi;
+const Clock = @import("bus/GamePak.zig").Clock;
 
 const Order = std.math.Order;
 const PriorityQueue = std.PriorityQueue;
@@ -60,6 +61,13 @@ pub const Scheduler = struct {
                         3 => cpu.bus.apu.ch4.channelTimerOverflow(late),
                     }
                 },
+                .RealTimeClock => {
+                    const device = &cpu.bus.pak.gpio.device;
+                    if (device.kind != .Rtc or device.ptr == null) return;
+
+                    const clock = @ptrCast(*Clock, @alignCast(@alignOf(*Clock), device.ptr.?));
+                    clock.updateTime();
+                },
                 .FrameSequencer => cpu.bus.apu.tickFrameSequencer(late),
                 .SampleAudio => cpu.bus.apu.sampleAudio(late),
                 .HBlank => cpu.bus.ppu.handleHBlankEnd(cpu, late), // The end of a HBlank
@@ -118,4 +126,5 @@ pub const EventKind = union(enum) {
     SampleAudio,
     FrameSequencer,
     ApuChannel: u2,
+    RealTimeClock,
 };