commit ac165d1acd1947bb849482b663d1dbb493de49ab Author: Paul Montag Date: Mon May 11 22:51:12 2026 -0500 kind of in the middle of the checksum stuff diff --git a/.gitignore b/.gitignore new file mode 100644 index 0000000..0180838 --- /dev/null +++ b/.gitignore @@ -0,0 +1,3 @@ +.zig-cache/ +zig-out/ +*.o diff --git a/build.zig b/build.zig new file mode 100644 index 0000000..ea8ffcd --- /dev/null +++ b/build.zig @@ -0,0 +1,156 @@ +const std = @import("std"); + +// Although this function looks imperative, it does not perform the build +// directly and instead it mutates the build graph (`b`) that will be then +// executed by an external runner. The functions in `std.Build` implement a DSL +// for defining build steps and express dependencies between them, allowing the +// build runner to parallelize the build automatically (and the cache system to +// know when a step doesn't need to be re-run). +pub fn build(b: *std.Build) void { + // Standard target options allow the person running `zig build` to choose + // what target to build for. Here we do not override the defaults, which + // means any target is allowed, and the default is native. Other options + // for restricting supported target set are available. + const target = b.standardTargetOptions(.{}); + // Standard optimization options allow the person running `zig build` to select + // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall. Here we do not + // set a preferred release mode, allowing the user to decide how to optimize. + const optimize = b.standardOptimizeOption(.{}); + // It's also possible to define more custom flags to toggle optional features + // of this build script using `b.option()`. All defined flags (including + // target and optimize options) will be listed when running `zig build --help` + // in this directory. + + // This creates a module, which represents a collection of source files alongside + // some compilation options, such as optimization mode and linked system libraries. + // Zig modules are the preferred way of making Zig code available to consumers. + // addModule defines a module that we intend to make available for importing + // to our consumers. We must give it a name because a Zig package can expose + // multiple modules and consumers will need to be able to specify which + // module they want to access. + const mod = b.addModule("rom_dump", .{ + // The root source file is the "entry point" of this module. Users of + // this module will only be able to access public declarations contained + // in this file, which means that if you have declarations that you + // intend to expose to consumers that were defined in other files part + // of this module, you will have to make sure to re-export them from + // the root file. + .root_source_file = b.path("src/root.zig"), + // Later on we'll use this module as the root module of a test executable + // which requires us to specify a target. + .target = target, + }); + + // Here we define an executable. An executable needs to have a root module + // which needs to expose a `main` function. While we could add a main function + // to the module defined above, it's sometimes preferable to split business + // logic and the CLI into two separate modules. + // + // If your goal is to create a Zig library for others to use, consider if + // it might benefit from also exposing a CLI tool. A parser library for a + // data serialization format could also bundle a CLI syntax checker, for example. + // + // If instead your goal is to create an executable, consider if users might + // be interested in also being able to embed the core functionality of your + // program in their own executable in order to avoid the overhead involved in + // subprocessing your CLI tool. + // + // If neither case applies to you, feel free to delete the declaration you + // don't need and to put everything under a single module. + const exe = b.addExecutable(.{ + .name = "rom_dump", + .root_module = b.createModule(.{ + // b.createModule defines a new module just like b.addModule but, + // unlike b.addModule, it does not expose the module to consumers of + // this package, which is why in this case we don't have to give it a name. + .root_source_file = b.path("src/main.zig"), + // Target and optimization levels must be explicitly wired in when + // defining an executable or library (in the root module), and you + // can also hardcode a specific target for an executable or library + // definition if desireable (e.g. firmware for embedded devices). + .target = target, + .optimize = optimize, + // List of modules available for import in source files part of the + // root module. + .imports = &.{ + // Here "rom_dump" is the name you will use in your source code to + // import this module (e.g. `@import("rom_dump")`). The name is + // repeated because you are allowed to rename your imports, which + // can be extremely useful in case of collisions (which can happen + // importing modules from different packages). + .{ .name = "rom_dump", .module = mod }, + }, + }), + }); + + // This declares intent for the executable to be installed into the + // install prefix when running `zig build` (i.e. when executing the default + // step). By default the install prefix is `zig-out/` but can be overridden + // by passing `--prefix` or `-p`. + b.installArtifact(exe); + + // This creates a top level step. Top level steps have a name and can be + // invoked by name when running `zig build` (e.g. `zig build run`). + // This will evaluate the `run` step rather than the default step. + // For a top level step to actually do something, it must depend on other + // steps (e.g. a Run step, as we will see in a moment). + const run_step = b.step("run", "Run the app"); + + // This creates a RunArtifact step in the build graph. A RunArtifact step + // invokes an executable compiled by Zig. Steps will only be executed by the + // runner if invoked directly by the user (in the case of top level steps) + // or if another step depends on it, so it's up to you to define when and + // how this Run step will be executed. In our case we want to run it when + // the user runs `zig build run`, so we create a dependency link. + const run_cmd = b.addRunArtifact(exe); + run_step.dependOn(&run_cmd.step); + + // By making the run step depend on the default step, it will be run from the + // installation directory rather than directly from within the cache directory. + run_cmd.step.dependOn(b.getInstallStep()); + + // This allows the user to pass arguments to the application in the build + // command itself, like this: `zig build run -- arg1 arg2 etc` + if (b.args) |args| { + run_cmd.addArgs(args); + } + + // Creates an executable that will run `test` blocks from the provided module. + // Here `mod` needs to define a target, which is why earlier we made sure to + // set the releative field. + const mod_tests = b.addTest(.{ + .root_module = mod, + }); + + // A run step that will run the test executable. + const run_mod_tests = b.addRunArtifact(mod_tests); + + // Creates an executable that will run `test` blocks from the executable's + // root module. Note that test executables only test one module at a time, + // hence why we have to create two separate ones. + const exe_tests = b.addTest(.{ + .root_module = exe.root_module, + }); + + // A run step that will run the second test executable. + const run_exe_tests = b.addRunArtifact(exe_tests); + + // A top level step for running all tests. dependOn can be called multiple + // times and since the two run steps do not depend on one another, this will + // make the two of them run in parallel. + const test_step = b.step("test", "Run tests"); + test_step.dependOn(&run_mod_tests.step); + test_step.dependOn(&run_exe_tests.step); + + // Just like flags, top level steps are also listed in the `--help` menu. + // + // The Zig build system is entirely implemented in userland, which means + // that it cannot hook into private compiler APIs. All compilation work + // orchestrated by the build system will result in other Zig compiler + // subcommands being invoked with the right flags defined. You can observe + // these invocations when one fails (or you pass a flag to increase + // verbosity) to validate assumptions and diagnose problems. + // + // Lastly, the Zig build system is relatively simple and self-contained, + // and reading its source code will allow you to master it. +} diff --git a/build.zig.zon b/build.zig.zon new file mode 100644 index 0000000..d994621 --- /dev/null +++ b/build.zig.zon @@ -0,0 +1,81 @@ +.{ + // This is the default name used by packages depending on this one. For + // example, when a user runs `zig fetch --save `, this field is used + // as the key in the `dependencies` table. Although the user can choose a + // different name, most users will stick with this provided value. + // + // It is redundant to include "zig" in this name because it is already + // within the Zig package namespace. + .name = .rom_dump, + // This is a [Semantic Version](https://semver.org/). + // In a future version of Zig it will be used for package deduplication. + .version = "0.0.0", + // Together with name, this represents a globally unique package + // identifier. This field is generated by the Zig toolchain when the + // package is first created, and then *never changes*. This allows + // unambiguous detection of one package being an updated version of + // another. + // + // When forking a Zig project, this id should be regenerated (delete the + // field and run `zig build`) if the upstream project is still maintained. + // Otherwise, the fork is *hostile*, attempting to take control over the + // original project's identity. Thus it is recommended to leave the comment + // on the following line intact, so that it shows up in code reviews that + // modify the field. + .fingerprint = 0x9ea89f2f1f5395c9, // Changing this has security and trust implications. + // Tracks the earliest Zig version that the package considers to be a + // supported use case. + .minimum_zig_version = "0.16.0", + // This field is optional. + // Each dependency must either provide a `url` and `hash`, or a `path`. + // `zig build --fetch` can be used to fetch all dependencies of a package, recursively. + // Once all dependencies are fetched, `zig build` no longer requires + // internet connectivity. + .dependencies = .{ + // See `zig fetch --save ` for a command-line interface for adding dependencies. + //.example = .{ + // // When updating this field to a new URL, be sure to delete the corresponding + // // `hash`, otherwise you are communicating that you expect to find the old hash at + // // the new URL. If the contents of a URL change this will result in a hash mismatch + // // which will prevent zig from using it. + // .url = "https://example.com/foo.tar.gz", + // + // // This is computed from the file contents of the directory of files that is + // // obtained after fetching `url` and applying the inclusion rules given by + // // `paths`. + // // + // // This field is the source of truth; packages do not come from a `url`; they + // // come from a `hash`. `url` is just one of many possible mirrors for how to + // // obtain a package matching this `hash`. + // // + // // Uses the [multihash](https://multiformats.io/multihash/) format. + // .hash = "...", + // + // // When this is provided, the package is found in a directory relative to the + // // build root. In this case the package's hash is irrelevant and therefore not + // // computed. This field and `url` are mutually exclusive. + // .path = "foo", + // + // // When this is set to `true`, a package is declared to be lazily + // // fetched. This makes the dependency only get fetched if it is + // // actually used. + // .lazy = false, + //}, + }, + // Specifies the set of files and directories that are included in this package. + // Only files and directories listed here are included in the `hash` that + // is computed for this package. Only files listed here will remain on disk + // when using the zig package manager. As a rule of thumb, one should list + // files required for compilation plus any license(s). + // Paths are relative to the build root. Use the empty string (`""`) to refer to + // the build root itself. + // A directory listed here means that all files within, recursively, are included. + .paths = .{ + "build.zig", + "build.zig.zon", + "src", + // For example... + //"LICENSE", + //"README.md", + }, +} diff --git a/src/cartridge.zig b/src/cartridge.zig new file mode 100644 index 0000000..8a0fae1 --- /dev/null +++ b/src/cartridge.zig @@ -0,0 +1,3 @@ +const Reader = std.Io.Reader; + +// diff --git a/src/main.zig b/src/main.zig new file mode 100644 index 0000000..796b898 --- /dev/null +++ b/src/main.zig @@ -0,0 +1,38 @@ +const std = @import("std"); +const Io = std.Io; + +const snes = @import("snes/root.zig"); +const Rom = snes.rom.Rom; + +pub fn main(init: std.process.Init) !void { + var args = init.minimal.args.iterate(); + _ = args.skip(); + + while (args.next()) |arg| { + var file = try std.Io.Dir.cwd().openFile(init.io, arg, .{}); + defer file.close(init.io); + + var buf: [512]u8 = undefined; + var reader = file.reader(init.io, &buf); + + const rom = try Rom.parse(&reader); + const header = rom.header(); + + std.debug.print( + "Parsing {s}\n\ttitle: {s}\n\tmode: {d},\n\tchipset: {d}\n\tromSize: {B}\n\tramSize: {B}\n\tcountryCode: {d}\n\tdeveloperID: {d}\n\tromVersion: {d}\n\tchecksum:\n\t\tcomplement: {d}\n\t\tsum: {d}\n", + .{ + arg, + header.title, + header.mode, + header.chipset, + header.romSize.size(), + header.ramSize.size(), + header.countryCode, + header.developerID, + header.romVersion, + header.checksum.complement, + header.checksum.sum, + }, + ); + } +} diff --git a/src/root.zig b/src/root.zig new file mode 100644 index 0000000..a10c42d --- /dev/null +++ b/src/root.zig @@ -0,0 +1,4 @@ +//! By convention, root.zig is the root source file when making a package. +const std = @import("std"); + +pub const cartridge = @import("cartridge.zig"); diff --git a/src/snes/rom/error.zig b/src/snes/rom/error.zig new file mode 100644 index 0000000..ca497da --- /dev/null +++ b/src/snes/rom/error.zig @@ -0,0 +1,3 @@ +pub const Error = error{ + InvalidChecksum, +}; diff --git a/src/snes/rom/ex_hi_rom.zig b/src/snes/rom/ex_hi_rom.zig new file mode 100644 index 0000000..dfaea84 --- /dev/null +++ b/src/snes/rom/ex_hi_rom.zig @@ -0,0 +1,20 @@ +const std = @import("std"); +const rom = @import("root.zig"); + +const Header = rom.Header; +const FileReader = std.Io.File.Reader; + +pub const ExHiROM = struct { + header: Header, + romFile: *FileReader, + + pub const HeaderLocation = 0x40FFC0; + + // init create things + pub fn init(header: Header, romFile: *FileReader) @This() { + return .{ + .header = header, + .romFile = romFile, + }; + } +}; diff --git a/src/snes/rom/header.zig b/src/snes/rom/header.zig new file mode 100644 index 0000000..d4683f8 --- /dev/null +++ b/src/snes/rom/header.zig @@ -0,0 +1,50 @@ +const std = @import("std"); +const rom = @import("root.zig"); + +const Reader = std.Io.Reader; +const Error = rom.Error; +const Mode = rom.Mode; + +pub const Header = extern struct { + title: [21]u8, + mode: Mode, + chipset: u8, + romSize: Bytes, + ramSize: Bytes, + countryCode: u8, + developerID: u8, + romVersion: u8, + checksum: Checksum, + interupts: [32]u8, + + pub const Bytes = extern struct { + _shift: u8, + + pub fn size(self: @This()) usize { + return (@as(usize, 1) <<| self._shift) * 1024; + } + }; + + pub const Checksum = extern struct { + complement: u16, + sum: u16, + + pub fn valid(self: @This()) bool { + return self.sum +% self.complement +% 1 != 0; + } + }; + + /// parse assumes the reader is at the beggining of the rom, and + /// therefore skips any data in the copier section if there is one. + pub fn parse(from: *Reader) !@This() { + var data: [@sizeOf(@This())]u8 = undefined; + try from.readSliceAll(&data); + const header: @This() = @bitCast(data); + + if (header.checksum.valid()) { + return Error.InvalidChecksum; + } + + return header; + } +}; diff --git a/src/snes/rom/hi_rom.zig b/src/snes/rom/hi_rom.zig new file mode 100644 index 0000000..370391e --- /dev/null +++ b/src/snes/rom/hi_rom.zig @@ -0,0 +1,21 @@ +const std = @import("std"); +const rom = @import("root.zig"); + +const Header = rom.Header; +const FileReader = std.Io.File.Reader; + +pub const HiROM = struct { + header: Header, + romFile: *FileReader, + + // The Location of the header in this rom type + pub const HeaderLocation = 0x00FFC0; + + // init create things + pub fn init(header: Header, romFile: *FileReader) @This() { + return .{ + .header = header, + .romFile = romFile, + }; + } +}; diff --git a/src/snes/rom/lo_rom.zig b/src/snes/rom/lo_rom.zig new file mode 100644 index 0000000..d1145f6 --- /dev/null +++ b/src/snes/rom/lo_rom.zig @@ -0,0 +1,21 @@ +const std = @import("std"); +const rom = @import("root.zig"); + +const Header = rom.Header; +const FileReader = std.Io.File.Reader; + +pub const LoROM = struct { + header: Header, + romFile: *FileReader, + + // The location of the header in this rom mode + pub const HeaderLocation = 0x007FC0; + + // init create things + pub fn init(header: Header, romFile: *FileReader) @This() { + return .{ + .header = header, + .romFile = romFile, + }; + } +}; diff --git a/src/snes/rom/mode.zig b/src/snes/rom/mode.zig new file mode 100644 index 0000000..2e0323b --- /dev/null +++ b/src/snes/rom/mode.zig @@ -0,0 +1,12 @@ +// Ignoring the optional 512-byte header, the files contain the contents of the cartridge ROM in linear order. Depending on how the cartridge is mapped, there are 3 orderings: +// +// LoROM: 32k banks starting from $800000 +// HiROM: 64k banks starting from $C00000 +// ExHiROM: 64k banks starting from $C00000, then continuing from $400000 after 4MB. +// +// This means that the ROM header could be at one of 3 locations which maps to memory at $00FFC0: +pub const Mode = enum(u8) { + LoROM = 0, + HiROM = 1, + ExHiROM = 5, +}; diff --git a/src/snes/rom/rom.zig b/src/snes/rom/rom.zig new file mode 100644 index 0000000..fbb8f2d --- /dev/null +++ b/src/snes/rom/rom.zig @@ -0,0 +1,91 @@ +const std = @import("std"); +const rom = @import("root.zig"); + +const FileReader = std.Io.File.Reader; +const Reader = std.Io.Reader; + +const Error = rom.Error; +const ExHiROM = rom.ExHiROM; +const Header = rom.Header; +const HiROM = rom.HiROM; +const LoROM = rom.LoROM; +const Mode = rom.Mode; + +pub const Rom = union(Mode) { + // TODO: you need to make this into a struct and the memory layout a field + // since you should store the header in here and if the data was headered or + // unheadered + LoROM: LoROM, + HiROM: HiROM, + ExHiROM: ExHiROM, + + /// parse takes a rom file (seeked to 0) and parses it into a ROM + /// if the file is not a valid ROM file it will return Error.InvalidChecksum + pub fn parse(romFile: *FileReader) !Rom { + // The data contained in the file may be unheadered or headered. The only difference + // between these two is that the headered version has 512 extra bytes at the start of the file. + // + // The 512 byte header is not the same as the ROM header, which is a part of the on-cartridge + // ROM. Instead it is 512 bytes of metadata gathered by a Copier device used to dump the ROM. + // This extra data is generally considered useless, except to the specific copier device that + // it was originally used with. Modern common practice prefers unheadered ROM files. + inline for ([_]usize{ 0, 512 }) |offset| { + // Now lets loop through each of the different memory types + // Ignoring the optional 512-byte header, the files contain the contents of the cartridge + // ROM in linear order. Depending on how the cartridge is mapped, there are 3 orderings: + // LoROM: 32k banks starting from $800000 + // HiROM: 64k banks starting from $C00000 + // ExHiROM: 64k banks starting from $C00000, then continuing from $400000 after 4MB. + // + // This means that the ROM header could be at one of 3 locations which maps to memory at $00FFC0: + // + // LoROM: $007FC0 + // HiROM: $00FFC0 + // ExHiROM: $40FFC0 + inline for (std.meta.fields(@This())) |field| { + try romFile.seekTo(field.type.HeaderLocation + offset); + const maybe_header = Header.parse(&romFile.interface) catch null; + + if (maybe_header) |head| { + return @unionInit(@This(), field.name, field.type.init(head, romFile)); + } + } + } + + return Error.InvalidChecksum; + } + + /// header will return the header of the ROM file + pub fn header(self: *const @This()) *const Header { + switch (self.*) { + .LoROM => |*loRom| return &loRom.header, + .HiROM => |*hiRom| return &hiRom.header, + .ExHiROM => |*exHiRom| return &exHiRom.header, + } + } + + pub fn checksum(self: *const @This(), romReader: *Reader) !u16 { + var head = self.header().*; + head.checksum.complement = 0xFFFF; + head.checksum.sum = 0x0000; + + var sum: u16 = 0; + const headerBytes: [@sizeOf(@TypeOf(header))]u8 = @bitCast(header); + for (headerBytes) |b| { + sum +%= @as(u16, b); + } + + const header_location = switch (self.*) { + .LoROM => |*rom| rom.HeaderLocation, + .HiROM => |*rom| rom.HeaderLocation, + .ExHiROM => |*rom| rom.HeaderLocation, + }; + + for (@sizeOf(@TypeOf(header))..header.romSize.size()) |_| { + const b = try romReader.takeByte(); + sum +%= @intCast(b); + } + + return sum; + } +}; diff --git a/src/snes/rom/root.zig b/src/snes/rom/root.zig new file mode 100644 index 0000000..2bfcd40 --- /dev/null +++ b/src/snes/rom/root.zig @@ -0,0 +1,7 @@ +pub const Error = @import("error.zig").Error; +pub const ExHiROM = @import("ex_hi_rom.zig").ExHiROM; +pub const Header = @import("header.zig").Header; +pub const HiROM = @import("hi_rom.zig").HiROM; +pub const LoROM = @import("lo_rom.zig").LoROM; +pub const Mode = @import("mode.zig").Mode; +pub const Rom = @import("rom.zig").Rom; diff --git a/src/snes/root.zig b/src/snes/root.zig new file mode 100644 index 0000000..bc58deb --- /dev/null +++ b/src/snes/root.zig @@ -0,0 +1 @@ +pub const rom = @import("rom/root.zig");