feat: integrate zig-clap with ZBA

.gitmodules

@@ -1,3 +1,6 @@
 [submodule "lib/SDL.zig"]
 	path = lib/SDL.zig
 	url = https://github.com/MasterQ32/SDL.zig
+[submodule "lib/zig-clap"]
+	path = lib/zig-clap
+	url = https://github.com/Hejsil/zig-clap

build.zig

@@ -15,7 +15,11 @@ pub fn build(b: *std.build.Builder) void {
     const exe = b.addExecutable("zba", "src/main.zig");
 
     // Bitfield type from FlorenceOS: https://github.com/FlorenceOS/
-    exe.addPackage(.{ .name = "bitfield", .path = .{ .path = "lib/util/bitfield.zig" } });
+    // exe.addPackage(.{ .name = "bitfield", .path = .{ .path = "lib/util/bitfield.zig" } });
+    exe.addPackagePath("bitfield", "lib/util/bitfield.zig");
+
+    // Argument Parsing Library
+    exe.addPackagePath("clap", "lib/zig-clap/clap.zig");
 
     // Zig SDL Bindings: https://github.com/MasterQ32/SDL.zig
     const sdk = Sdk.init(b);

lib/zig-clap

@@ -0,0 +1 @@
+Subproject commit a2af4a9267c547ec0f91ea1a84b2a50760ca5483

src/Bus.zig

@@ -18,10 +18,10 @@ iwram: Iwram,
 ewram: Ewram,
 io: Io,
 
-pub fn init(alloc: Allocator, sched: *Scheduler, path: []const u8) !Self {
+pub fn init(alloc: Allocator, sched: *Scheduler, rom_path: []const u8, maybe_bios: ?[]const u8) !Self {
     return Self{
-        .pak = try GamePak.init(alloc, path),
-        .bios = try Bios.init(alloc, "./bin/gba_bios.bin"), // TODO: don't hardcode this + bundle open-sorce Boot ROM
+        .pak = try GamePak.init(alloc, rom_path),
+        .bios = try Bios.init(alloc, maybe_bios),
         .ppu = try Ppu.init(alloc, sched),
         .iwram = try Iwram.init(alloc),
         .ewram = try Ewram.init(alloc),

src/bus/Bios.zig

@@ -3,33 +3,46 @@ const std = @import("std");
 const Allocator = std.mem.Allocator;
 const Self = @This();
 
-buf: []u8,
+buf: ?[]u8,
 alloc: Allocator,
 
-pub fn init(alloc: Allocator, path: []const u8) !Self {
+pub fn init(alloc: Allocator, maybe_path: ?[]const u8) !Self {
+    var buf: ?[]u8 = null;
+    if (maybe_path) |path| {
         const file = try std.fs.cwd().openFile(path, .{});
         defer file.close();
 
         const len = try file.getEndPos();
+        buf = try file.readToEndAlloc(alloc, len);
+    }
 
     return Self{
-        .buf = try file.readToEndAlloc(alloc, len),
+        .buf = buf,
         .alloc = alloc,
     };
 }
 
 pub fn deinit(self: Self) void {
-    self.alloc.free(self.buf);
+    if (self.buf) |buf| self.alloc.free(buf);
 }
 
 pub fn get32(self: *const Self, idx: usize) u32 {
-    return (@as(u32, self.buf[idx + 3]) << 24) | (@as(u32, self.buf[idx + 2]) << 16) | (@as(u32, self.buf[idx + 1]) << 8) | (@as(u32, self.buf[idx]));
+    if (self.buf) |buf|
+        return (@as(u32, buf[idx + 3]) << 24) | (@as(u32, buf[idx + 2]) << 16) | (@as(u32, buf[idx + 1]) << 8) | (@as(u32, buf[idx]));
+
+    std.debug.panic("[CPU|BIOS:32] ZBA tried to read from 0x{X:0>8} but no BIOS was provided.", .{idx});
 }
 
 pub fn get16(self: *const Self, idx: usize) u16 {
-    return (@as(u16, self.buf[idx + 1]) << 8) | @as(u16, self.buf[idx]);
+    if (self.buf) |buf|
+        return (@as(u16, buf[idx + 1]) << 8) | @as(u16, buf[idx]);
+
+    std.debug.panic("[CPU|BIOS:16] ZBA tried to read from 0x{X:0>8} but no BIOS was provided.", .{idx});
 }
 
 pub fn get8(self: *const Self, idx: usize) u8 {
-    return self.buf[idx];
+    if (self.buf) |buf|
+        return buf[idx];
+
+    std.debug.panic("[CPU|BIOS:8] ZBA tried to read from 0x{X:0>8} but no BIOS was provided.", .{idx});
 }

src/main.zig

@@ -1,5 +1,6 @@
 const std = @import("std");
 const SDL = @import("sdl2");
+const clap = @import("clap");
 
 const emu = @import("emu.zig");
 const Bus = @import("Bus.zig");
@@ -25,25 +26,46 @@ pub fn main() anyerror!void {
     const alloc = gpa.allocator();
     defer std.debug.assert(!gpa.deinit());
 
-    // Handle CLI Arguments
-    const args = try std.process.argsAlloc(alloc);
-    defer std.process.argsFree(alloc, args);
+    // Parse CLI Arguments
+    const params = comptime [_]clap.Param(clap.Help){
+        clap.parseParam("-h, --help         Display this help and exit.     ") catch unreachable,
+        clap.parseParam("-b, --bios <PATH>  Optional Path to GBA BIOS ROM.  ") catch unreachable,
+        clap.parseParam("<PATH>             Path to GBA GamePak ROM         ") catch unreachable,
+    };
 
-    const zba_args: []const []const u8 = args[1..];
+    var args = try clap.parse(clap.Help, &params, .{});
+    defer args.deinit();
 
-    if (zba_args.len == 0) {
-        std.log.err("Expected PATH to Gameboy Advance ROM as a CLI argument", .{});
-        return;
-    } else if (zba_args.len > 1) {
-        std.log.err("Too many CLI arguments were provided", .{});
-        return;
+    if (args.flag("--help")) {
+        return clap.help(std.io.getStdErr().writer(), &params);
     }
 
+    var maybe_bios: ?[]const u8 = null;
+    if (args.option("--bios")) |path| {
+        maybe_bios = path;
+    }
+
+    const positionals = args.positionals();
+    const stderr = std.io.getStdErr();
+    defer stderr.close();
+
+    const rom_path = switch (positionals.len) {
+        1 => positionals[0],
+        0 => {
+            try stderr.writeAll("ZBA requires a positional path to a GamePak ROM.\n");
+            return CliError.InsufficientOptions;
+        },
+        else => {
+            try stderr.writeAll("ZBA received too many arguments.\n");
+            return CliError.UnneededOptions;
+        },
+    };
+
     // Initialize Emulator
     var scheduler = Scheduler.init(alloc);
     defer scheduler.deinit();
 
-    var bus = try Bus.init(alloc, &scheduler, zba_args[0]);
+    var bus = try Bus.init(alloc, &scheduler, rom_path, maybe_bios);
     defer bus.deinit();
 
     var cpu = Arm7tdmi.init(&scheduler, &bus);
@@ -158,3 +180,8 @@ fn sdlPanic() noreturn {
     const str = @as(?[*:0]const u8, SDL.SDL_GetError()) orelse "unknown error";
     @panic(std.mem.sliceTo(str, 0));
 }
+
+const CliError = error{
+    InsufficientOptions,
+    UnneededOptions,
+};