feat: implement SRAM saving and loading

.gitmodules

@@ -4,3 +4,6 @@
 [submodule "lib/zig-clap"]
 	path = lib/zig-clap
 	url = https://github.com/Hejsil/zig-clap
+[submodule "lib/known-folders"]
+	path = lib/known-folders
+	url = https://github.com/ziglibs/known-folders

build.zig

@@ -14,6 +14,9 @@ pub fn build(b: *std.build.Builder) void {
 
     const exe = b.addExecutable("zba", "src/main.zig");
     
+    // Known Folders (%APPDATA%, XDG, etc.)
+    exe.addPackagePath("known_folders", "lib/known-folders/known-folders.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/known-folders

@@ -0,0 +1 @@
+Subproject commit 9db1b99219c767d5e24994b1525273fe4031e464

src/Bus.zig

@@ -29,10 +29,10 @@ ewram: Ewram,
 
 io: Io,
 
-pub fn init(alloc: Allocator, sched: *Scheduler, rom_path: []const u8, maybe_bios: ?[]const u8) !Self {
+pub fn init(alloc: Allocator, sched: *Scheduler, rom_path: []const u8, bios_path: ?[]const u8, save_path: ?[]const u8) !Self {
     return Self{
-        .pak = try GamePak.init(alloc, rom_path),
-        .bios = try Bios.init(alloc, maybe_bios),
+        .pak = try GamePak.init(alloc, rom_path, save_path),
+        .bios = try Bios.init(alloc, bios_path),
         .ppu = try Ppu.init(alloc, sched),
         .apu = Apu.init(),
         .iwram = try Iwram.init(alloc),

src/bus/GamePak.zig

@@ -10,8 +10,8 @@ buf: []u8,
 alloc: Allocator,
 backup: Backup,
 
-pub fn init(alloc: Allocator, path: []const u8) !Self {
-    const file = try std.fs.cwd().openFile(path, .{});
+pub fn init(alloc: Allocator, rom_path: []const u8, save_path: ?[]const u8) !Self {
+    const file = try std.fs.cwd().openFile(rom_path, .{});
     defer file.close();
 
     const len = try file.getEndPos();
@@ -24,7 +24,7 @@ pub fn init(alloc: Allocator, path: []const u8) !Self {
         .buf = buf,
         .alloc = alloc,
         .title = title,
-        .backup = try Backup.init(alloc, kind),
+        .backup = try Backup.init(alloc, kind, title, save_path),
     };
     pak.parseHeader();
 
@@ -40,7 +40,7 @@ fn parseHeader(self: *const Self) void {
     log.info("Title: {s}", .{title});
     if (version != 0) log.info("Version: {}", .{version});
     log.info("Game Code: {s}", .{code});
-    if (lookupMaker(maker)) |c| log.info("Maker Code: {s}", .{c}) else log.info("Maker: {s}", .{maker});
+    if (lookupMaker(maker)) |c| log.info("Maker: {s}", .{c}) else log.info("Maker Code: {s}", .{maker});
 }
 
 fn parseTitle(buf: []u8) [12]u8 {

src/bus/backup.zig

@@ -1,8 +1,9 @@
 const std = @import("std");
-
 const Allocator = std.mem.Allocator;
 const log = std.log.scoped(.Backup);
 
+const correctTitle = @import("../util.zig").correctTitle;
+
 const backup_kinds = [5]Needle{
     .{ .str = "EEPROM_V", .kind = .Eeprom },
     .{ .str = "SRAM_V", .kind = .Sram },
@@ -18,7 +19,10 @@ pub const Backup = struct {
     alloc: Allocator,
     kind: BackupKind,
 
-    pub fn init(alloc: Allocator, kind: BackupKind) !Self {
+    title: [12]u8,
+    save_path: ?[]const u8,
+
+    pub fn init(alloc: Allocator, kind: BackupKind, title: [12]u8, path: ?[]const u8) !Self {
         const buf_len: usize = switch (kind) {
             .Sram => 0x8000, // 32K
             .Flash => 0x10000, // 64K
@@ -29,11 +33,16 @@ pub const Backup = struct {
         const buf = try alloc.alloc(u8, buf_len);
         std.mem.set(u8, buf, 0);
 
-        return Self{
+        var backup = Self{
             .buf = buf,
             .alloc = alloc,
             .kind = kind,
+            .title = title,
+            .save_path = path,
         };
+        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 {
@@ -52,9 +61,58 @@ pub const Backup = struct {
     }
 
     pub fn deinit(self: Self) void {
+        if (self.save_path) |path| self.writeSaveToDisk(path) catch |e| log.err("Failed to save {}", .{e});
+
         self.alloc.free(self.buf);
     }
 
+    fn loadSaveFromDisk(self: *Self, path: []const u8) !void {
+        const file_path = try self.getSaveFilePath(path);
+        defer self.alloc.free(file_path);
+
+        const file: std.fs.File = try std.fs.openFileAbsolute(file_path, .{});
+
+        const len = try file.getEndPos();
+        const file_buf = try file.readToEndAlloc(self.alloc, len);
+        defer self.alloc.free(file_buf);
+
+        switch (self.kind) {
+            .Sram => {
+                std.mem.copy(u8, self.buf, file_buf);
+                log.info("Loaded Save from {s}", .{file_path});
+            },
+            else => return SaveError.UnsupportedBackupKind,
+        }
+    }
+
+    fn getSaveFilePath(self: *const Self, path: []const u8) ![]const u8 {
+        const filename = try self.getSaveFilename();
+        defer self.alloc.free(filename);
+
+        return try std.fs.path.join(self.alloc, &[_][]const u8{ path, filename });
+    }
+
+    fn getSaveFilename(self: *const Self) ![]const u8 {
+        const title = correctTitle(self.title);
+        return try std.mem.concat(self.alloc, u8, &[_][]const u8{ title, ".sav" });
+    }
+
+    fn writeSaveToDisk(self: Self, path: []const u8) !void {
+        const file_path = try self.getSaveFilePath(path);
+        defer self.alloc.free(file_path);
+
+        const file = try std.fs.createFileAbsolute(file_path, .{});
+        defer file.close();
+
+        switch (self.kind) {
+            .Sram => {
+                try file.writeAll(self.buf);
+                log.info("Dumped SRAM 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) {
@@ -96,3 +154,7 @@ const Needle = struct {
         };
     }
 };
+
+const SaveError = error{
+    UnsupportedBackupKind,
+};

src/main.zig

@@ -1,6 +1,7 @@
 const std = @import("std");
 const SDL = @import("sdl2");
 const clap = @import("clap");
+const known_folders = @import("known_folders");
 
 const emu = @import("emu.zig");
 const Bus = @import("Bus.zig");
@@ -21,6 +22,9 @@ const expected_rate = @import("emu.zig").frame_rate;
 
 pub const enable_logging: bool = false;
 const is_binary: bool = false;
+const log = std.log.scoped(.GUI);
+
+const correctTitle = @import("util.zig").correctTitle;
 
 pub fn main() anyerror!void {
     // Allocator for Emulator + CLI
@@ -40,7 +44,7 @@ pub fn main() anyerror!void {
 
     if (args.flag("--help")) return clap.help(std.io.getStdErr().writer(), &params);
 
-    const maybe_bios: ?[]const u8 = if (args.option("--bios")) |p| p else null;
+    const bios_path: ?[]const u8 = if (args.option("--bios")) |p| p else null;
 
     const positionals = args.positionals();
     const stderr = std.io.getStdErr();
@@ -58,11 +62,16 @@ pub fn main() anyerror!void {
         },
     };
 
+    // Determine Save Directory
+    const save_path = try setupSavePath(alloc);
+    defer if (save_path) |path| alloc.free(path);
+    log.info("Save Path: {s}", .{save_path});
+
     // Initialize Emulator
     var scheduler = Scheduler.init(alloc);
     defer scheduler.deinit();
 
-    var bus = try Bus.init(alloc, &scheduler, rom_path, maybe_bios);
+    var bus = try Bus.init(alloc, &scheduler, rom_path, bios_path, save_path);
     defer bus.deinit();
 
     var cpu = Arm7tdmi.init(&scheduler, &bus);
@@ -88,12 +97,13 @@ pub fn main() anyerror!void {
     if (status < 0) sdlPanic();
     defer SDL.SDL_Quit();
 
+    const title = correctTitle(bus.pak.title);
+
     var title_buf: [0x20]u8 = std.mem.zeroes([0x20]u8);
-    var title = try std.fmt.bufPrint(&title_buf, "ZBA | {s}", .{bus.pak.title});
-    correctTitleSlice(&title);
+    const window_title = try std.fmt.bufPrint(&title_buf, "ZBA | {s}", .{title});
 
     var window = SDL.SDL_CreateWindow(
-        title.ptr,
+        window_title.ptr,
         SDL.SDL_WINDOWPOS_CENTERED,
         SDL.SDL_WINDOWPOS_CENTERED,
         gba_width * window_scale,
@@ -163,7 +173,7 @@ pub fn main() anyerror!void {
         SDL.SDL_RenderPresent(renderer);
 
         const actual = emu_rate.calc();
-        const dyn_title = std.fmt.bufPrint(&dyn_title_buf, "{s} [Emu: {d:0>3.2}fps, {d:0>3.2}%] ", .{ title, actual, actual * 100 / expected_rate }) catch unreachable;
+        const dyn_title = std.fmt.bufPrint(&dyn_title_buf, "{s} [Emu: {d:0>3.2}fps, {d:0>3.2}%] ", .{ window_title, actual, actual * 100 / expected_rate }) catch unreachable;
         SDL.SDL_SetWindowTitle(window, dyn_title.ptr);
     }
 
@@ -180,14 +190,22 @@ const CliError = error{
     UnneededOptions,
 };
 
-/// The slice considers some null values to be a part of the string
-/// so change the length of the slice so that isn't the case
-// FIXME: This is awful and bad
-fn correctTitleSlice(title: *[]u8) void {
-    for (title.*) |char, i| {
-        if (char == 0) {
-            title.len = i;
-            break;
-        }
+// FIXME: Superfluous allocations?
+fn setupSavePath(alloc: std.mem.Allocator) !?[]const u8 {
+    const save_subpath = try std.fs.path.join(alloc, &[_][]const u8{ "zba", "save" });
+    defer alloc.free(save_subpath);
+
+    const maybe_data_path = try known_folders.getPath(alloc, .data);
+    defer if (maybe_data_path) |path| alloc.free(path);
+
+    const save_path = if (maybe_data_path) |base| try std.fs.path.join(alloc, &[_][]const u8{ base, save_subpath }) else null;
+
+    if (save_path) |_| {
+        // If we've determined what our save path should be, ensure the prereq directories
+        // are present so that we can successfully write to the path when necessary
+        const maybe_data_dir = try known_folders.open(alloc, .data, .{});
+        if (maybe_data_dir) |data_dir| try data_dir.makePath(save_subpath);
     }
+
+    return save_path;
 }

src/util.zig

@@ -53,3 +53,50 @@ pub fn intToBytes(comptime T: type, value: anytype) [@sizeOf(T)]u8 {
 
     return result;
 }
+
+/// The Title from the GBA Cartridge may be null padded to a maximum
+/// length of 12 bytes. 
+///
+/// This function returns a slice of everything just before the first 
+/// `\0`
+pub fn correctTitle(title: [12]u8) []const u8 {
+    var len = title.len;
+    for (title) |char, i| {
+        if (char == 0) {
+            len = i;
+            break;
+        }
+    }
+
+    return title[0..len];
+}
+
+/// Copies a Title and returns either an identical or similar 
+/// array consisting of ASCII that won't make any file system angry
+///
+/// Currently Unused but I assume there's some ROM out there that will require this 
+pub fn safeTitle(title: [12]u8) [12]u8 {
+    var result: [12]u8 = title;
+
+    for (result) |*char| {
+        if (char.* == '-') char.* = '_';
+        if (char.* == 0) break;
+    }
+
+    return result;
+}
+
+pub fn fixTitle(alloc: std.mem.Allocator, title: [12]u8) ![]u8 {
+    var len: usize = 12;
+    for (title) |char, i| {
+        if (char == 0) {
+            len = i;
+            break;
+        }
+    }
+
+    const buf = try alloc.alloc(u8, len);
+    std.mem.copy(u8, buf, title[0..len]);
+
+    return buf;
+}