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Gopher2600 - RetroBIOS
Type standalone
Classification Other
Source https://github.com/JetSetIlly/Gopher2600
Version v0.57.0
Profiled 2026-08-08
Cores gopher2600
Systems atari-2600
Technical notes

Atari 2600 emulator written in Go. The 6507, TIA and RIOT are emulated in software and the console needs no ROM of its own, so a plain cartridge boots with nothing supplied.

Supercharger emulation is the only path that reads a BIOS. NewSupercharger branches three ways (supercharger.go:93-119). A tape held as WAV or MP3 sets Loader.IsSoundData and calls loadBIOS, and the error is returned, so the cartridge fails to attach without the file. A demo unit image calls loadBIOS and substitutes fastloadOnlyBIOS() on failure. Everything else, including the usual Supercharger BIN, takes fastloadOnlyBIOS() without ever looking for the file: a 2048 byte stub holding a touch of the tape load register and the CPU jump table (bios.go:151-166).

loadBIOS reads the current working directory, then the directory holding the tape or BIN, then the configuration directory (bios.go:53-116). Each candidate name is tried in turn and the content is gated on MD5 before the caller checks the 2048 byte length, so a file under the right name with the wrong content is refused. ReqSpec selects the PAL table and the PAL hash (bios.go:56-59); ReqSpec comes from the television specification, the stella.pro entry or the filename (cartridgeloader/loader.go:194-201).

The demo unit is recognised by MD5 of the 256 bytes at 0x300 of the loaded image (demounit.go:58,78). When that image carries more than 2048 bytes it holds the Schweber chip and the carousel together; otherwise the eight ROMs are read from the directory of the loaded file (demounit_controller.go: 178-200). A read error or a length other than 8192 logs and returns nil, and the peripheral is left unplugged.

stella.pro is Stella's cartridge properties database, read from the configuration directory (properties.go:28,48-58). It is loaded by NewDebugger (debugger.go:356), which drives play as well as debug (gopher2600.go:261,307,326), so it applies to the plain gopher2600 <rom> invocation. A missing file is logged and start-up continues; the ROM selector then falls back to the filename and no television specification is inferred from the cartridge name.

The ROM selector also reads a Named_Boxarts directory from the configuration directory, listing it at start-up and fuzzy matching the cartridge name against the entries before reading one image (win_rom_select.go:92,127-138, 678-689). It holds the box art of the libretro-thumbnails Atari 2600 set, pinned upstream at commit 4ea759821724d6c7bcf2f46020d79fc4270ed2f6 (win_rom_select.go:91). Its content is whatever the user copies in and no name is fixed by the code, so it carries no file entry here.

Fonts, shaders, bevels, the CPU instruction table and the Movie Cart core are compiled in with go:embed. The remaining paths under the configuration directory are written by the emulator or authored by hand: preferences, debugger_imgui.ini, managerState, managerHotkeys, savekey, fa2_nvram, elf_nvram, regression, patches and setupDB. ARM map files and DWARF sources are read from a project build tree beside the ROM. AtariVox speech calls the festival binary as a process, with the path taken from preferences (atarivox_preferences.go:51).

12 files | 0 required, 12 optional | 10 in repo, 2 missing | 2 with HLE fallback

Supercharger BIOS.bin optional in repo HLE fallback
Starpath Supercharger BIOS, required to load a tape held as WAV or MP3

Supercharger BIOS PAL.bin optional missing HLE fallback
PAL Supercharger BIOS, selected when the loader resolves a PAL specification

Schweber OQ.bin optional in repo
Schweber chip image, the load that turns the Supercharger into the demo unit

Starpath Demonstration Unit 1P.bin optional in repo
Demo unit carousel ROM 1, read from the directory of the loaded image

Starpath Demonstration Unit 2P.bin optional in repo
Demo unit carousel ROM 2, read from the directory of the loaded image

Starpath Demonstration Unit 3P.bin optional missing
Demo unit carousel ROM 3, read from the directory of the loaded image

Starpath Demonstration Unit 4P.bin optional in repo
Demo unit carousel ROM 4, read from the directory of the loaded image

Starpath Demonstration Unit 5P.bin optional in repo
Demo unit carousel ROM 5, read from the directory of the loaded image

Starpath Demonstration Unit 6P.bin optional in repo
Demo unit carousel ROM 6, read from the directory of the loaded image

Starpath Demonstration Unit 7P.bin optional in repo
Demo unit carousel ROM 7, read from the directory of the loaded image

Starpath Demonstration Unit 8P.bin optional in repo
Demo unit carousel ROM 8, read from the directory of the loaded image

stella.pro optional in repo
Stella cartridge properties database, keyed by cartridge MD5

Generated on 2026-08-23T16:12:06Z