An original, open source replacement for Atari5200 startup/runtime services by StackBlender. The goal is to run supported cartridges without requiring or distributing Atari's BIOS. StackBlender is completing this as a goodwill gesture to the community; no community contribution is required.
Development software: not yet a complete BIOS replacement or general game runner.
An original6502 program executes in the2KiB F800..FFFF window through ordinary CPU, bus, video, audio and input hardware emulation. Qualified development services include cold startup, VBI clock/display shadows, DLI, analog scanning, IRQ/BRK/ timers, keypad windows and both fire sources for explicitly cooperating carts. The latest callback-bridge refactor uses1895of2048bytes with90reserved bytes untouched. Independent integration-owner Release/ASan diagnostics include input, interrupt nesting, frame/cache/state/process replay and refusal checks; see the attributed execution receipts.
These are limited development contracts, not original-hardware measurements or broad game compatibility. Current input services reserve0600..061F and cannot be silently applied to ordinary software using that RAM. The qualified opaque-title variant accepts arbitrary20title bytes with digit-only years; full text/ordinary-RAM/remaining reset and service compatibility are current work. Warm/CPU-only/host ControllerKey reset requests refuse; physical controller Reset is a separate input. Speed and battery efficiency take priority over fine timing accuracy, with dependable behavior and repeatable saves.
A separate original printable glyph asset contains 95new drawings. It has no Atari encoding, runtime-bank binding or provider target. Accepted runtime fonts and all thirteen pinned generation inputs remain unchanged.
Requires Python3.10+, CMake3.20+, Ninja and Git; no compiler, emulator, firmware, game download or network dependency is needed for offline authoring checks.
cmake -S . -B build -G Ninja
cmake --build build
ctest --test-dir build --output-on-failureOr run all237offline methods directly:
PYTHONDONTWRITEBYTECODE=1 python3 -m unittest discover -s tests -vThe ordinary suite includes real reproduction of all thirteen pinned development
exports and the CMake artifact consumer, plus rejection of altered bindings and
approval flags. Run it separately with python3 tools/verify_accepted_exports.py --cmake; see the catalog. Local source history is
required; the tool does not fetch it.
Generated images/maps/manifests/assets stay in ignored build directories. Candidate opt-in artifact targets bind full source revision and exact outputs; normal integration gates remain OFF. Export approval flags/capabilities remain unchanged even after independent native receipts. There is no supported firmware release, automatic BIOS fallback or bundled third-party cartridge.
No Atari BIOS bytes/disassembly, extracted font/logo/table, foreign replacement kernel/emulator implementation or firmware trace is used for reconstruction. Documentary facts, consumer requirements, proposed original policy and independent emulator observations are recorded separately. No original-system oracle or measurement corpus is available. Licensing alone does not establish authorship.
Roadmap, handoff, source ledger, testing, remaining services and contract preserve scope, provenance and open compatibility gaps. NTSC four-port is the initial target; other boards require explicit evidence.
A callable-reset generation rebuilds only the reset region of the cart-owned diagnostic parent: an instruction boundary at +$0F, fall-through to the cartridge handoff at +$8A, so software that copies the reset routine to RAM and calls it as a subroutine works. Offline tests pass (242); a licensed target reaches its menu through the stock external-bios debug path. Not Mars-qualified or admitted.
A compat generation adds VBI enable at handoff, the $0002 low frame counter byte and spurious-NMI return over callable-reset; not natively qualified.
A compat-v2 generation adds per-frame countdown service and default-vector fallback; not natively qualified.
Copyright (c)2026 StackBlender LLC.
GNU General Public License, version3 or (at your option) any later version
(GPL-3.0-or-later); see LICENSE. For other terms, contact
StackBlender.
A separately authored opaque-title generation removes only the digit restriction on20title bytes. Numeric years and entry validation remain. Mars d5c709f independently qualified it in both native builds; it remains unreleased; old generations/ABI/allocation/defaults remain unchanged.
A conditional timer memory audit inventories every original runtime code path/default-handler frontier without executing a CPU. It supports ordinary-RAM planning, not an approved profile or game-compatibility claim.
The separately authored original64 bank binds 64original development labels, preserving legacy digits/high bank/code. It is independently qualified by Mars938d829 in both native builds; no historical charset or ordinary software compatibility is claimed. Normative own geometry is available as source asset DATA in assets/printable-geometry.json for independent pixel oracles.
Separate B0ordinary-RAM identity and B1original diagnostic full-cold experiments are authored under Mars81025cf, NOT admitted. See docs/timer-experiments-proof.md (or timer-experiments-proof.md from docs).205offline methods include eight new contract/encoding/timing/pin/failure checks. Old13exports/flags/defaults preserved; no combined profile or unchanged-game run.
B2's separate conditional-year experiment permits any first year only with secondFF, retaining full cold initialization. It does not amend B1 or combine ordinary RAM, and requires independent admission. 212offline checks including exact committed CLI/CMake consumer; no game trial.
The explicitly combined cart-owned diagnostic profile now rebinds B0ownership onto byte-identical B2code under its own identity. It is independently qualified for its bounded development contract; see the native receipt. Game mapping and consumer trial decisions remain separate. All prior profiles/defaults stay unchanged.
A separately guarded Linear8K development identity keeps all2048combined ROM bytes unchanged and declares REQUIRED native immutable board/length/entry/handoff guards. Its exact pinned exporter/CMake and ORIGINAL 8192-byte diagnostic layout pass offline checks. Native integration/qualification is pending; this is not8KiB game admission or a new implemented6502validator.
An original startup/display diagnostic now exports twelve self-initializing cartridge controls (32KiB baseline/exact8KiB, direct MMIO versus VBI shadows, numeric/secondFF Cold). Counter and geometric bitmap expectations are independently specified. Offline authoring is qualified; native execution,8KiB guard and all product/compatibility gates remain separate.
The four32KiB startup/display controls now independently pass native Release and full-native ASan, including first fetch, CPU progress, actual display DMA, VBI shadow provenance and every geometric pixel. The eight8KiB controls await native guard qualification. This baseline result does not establish general game compatibility or a complete BIOS replacement.