atari8bit

name: atari8bit description: >- Root router for Atari 8-bit XL/XE AI-agent skills. Load this file first, then choose the smallest matching topic file from this skill directory.

Atari 8-bit Agentic Programming Skills

Type: Root router and taxonomy Purpose: Route Atari XL/XE programming, reversing, and hardware questions to the smallest useful English skill file.

Use progressive disclosure:

1. Read this router.
2. Open exactly one or two topic files that match the task.
3. Use additional topic files only when the task crosses domains.

This skill is self-contained. The topic files below are the available reference material in this repository.

1. hardware/ — Silicon Reference

• hardware/cpu.md — 6502/65C02/65C816 flags, timing, undocumented opcodes, IRQ/NMI/BRK, opcode quick reference.
• hardware/antic.md — ANTIC DMA, display-list instruction bytes, scrolling registers, DLI timing, WSYNC, NMIEN/NMIST.
• hardware/gtia.md — GTIA registers, color model, GTIA modes, player/missile graphics, priority and collisions.
• hardware/pokey.md — POKEY audio, timers, IRQs, random/noise polynomials, keyboard/serial/SIO clocking.

2. system/ — OS, Memory, I/O, Compatibility

• system/memory-map.md — 64K memory map, zero page, PIA, PORTB banking, extended RAM detection.
• system/os-vectors-handlers.md — OS vectors, VBI/DLI/CIO/SIO entry points, IOCB lifecycle, handler tables, safe hook patterns.
• system/os-hardening.md — OS ROM disable, trampoline handlers, RESET survival, VCOUNT/VBLANK bare-metal sync.
• system/storage.md — SIO protocol, disk commands, XEX/ATR formats, CIO file access, SpartaDOS X, loader/depacker reversing.
• system/screen.md — ATASCII, screen codes, CIO GET/PUT/PRINT, keyboard codes, number display.
• system/input.md — Joysticks, paddles, mouse, light pen, console keys, trigger registers.
• system/compatibility.md — 400/800 vs XL/XE, PAL/NTSC, RAM expansions, CPU/chip/upgrades detection matrix.
• system/cartridges-pbi.md — Cartridge windows, banking, PBI devices, internal devices, reverse-engineering notes.

3. graphics/ — Rendering Techniques

• graphics/display-lists.md — DLI routines, display-list instruction set, LMS/JVB, WSYNC, multi-zone DLI patterns.
• graphics/character-modes.md — ANTIC text modes, fonts, CHBASE/CHACTL, blink/inversion, character-mode plotting.
• graphics/bitmap-modes.md — Hires and multicolor bitmap modes, 240-line tricks, custom video modes.
• graphics/pm-graphics.md — Hardware player/missile setup, movement, multiplexing, priority, and collision detection.
• graphics/software-sprites.md — CPU-rendered bitmap/character software sprites, save/restore, XOR, pre-shift tables, dirty buffers, collision tests.
• graphics/scrolling.md — Coarse/fine vertical and horizontal scroll, VSCROL/HSCROL, parallax, MWP buffering.
• graphics/advanced-fx.md — HIP, RIP, TIP, GTIA 9++, interlaced shade/color techniques.

4. audio/ — Sound and Music

• audio/synthesis.md — POKEY synthesis, distortion tables, filters, linked 16-bit channels, double POKEY.
• audio/digital-audio.md — 4-bit PCM/PDM playback, volume-only mode, VCOUNT-sync sample playback.
• audio/trackers.md — RMT and TMC2 playback engines, interrupt coexistence, tracker data layout.

5. algorithms/ — Code Patterns

• algorithms/math.md — 8/16/32-bit multiply/divide, modulo, LUT math, atan2, sqrt, distance.
• algorithms/bit-ops.md — Bit shifts/rotates, flag testing, zero-page idioms, INC/DEC hardware hazards.
• algorithms/optimization.md — 6502 size/speed patterns, jump tables, compare-free loops, flag-preserving tests.
• algorithms/compression.md — RLE, LZ4, Exomizer, DEFLATE decompression patterns.
• algorithms/3d-graphics.md — Matrix rotation, projection, shading, span buffers, culling.
• algorithms/sorting.md — 8/16-bit optimal sorts, bucket sort, CombSort, ShellSort, Quicksort.
• algorithms/macros.md — Reusable MADS macros for memory, arithmetic, shifting, interpolation.

6. tooling/ — Build, Examples, Reversing

• tooling/mads-assembler.md — Compact MADS syntax, directives, macros, procedures, banks, relocatables, 65816 addenda. For full MADS assembler documentation, use the standalone mads/ skill.
• tooling/code.md — Ready-to-read examples: sieve, Tetris, RLE, GTIA 9++, 40x40, demoscene catalog.
• tooling/reversing.md — XEX/ATR/source/listing triage, segment maps, depackers, Altirra tracing, hardware breakpoints.

7. exotics/ — Upgrades and Peripherals

• exotics/vbxe.md — VBXE FX core, detection, XDL, blitter, VRAM, palette, MEMAC windows, examples.
• exotics/sophia-rapidus.md — Sophia video upgrades, Rapidus/65C816 notes, APE-Time RTC, LDW/CA-2001 device protocol.

Navigation Rules

• Hardware-register behavior belongs in hardware/; software rendering recipes belong in graphics/.
• OS/device/file/vector questions belong in system/; build examples and reverse workflows belong in tooling/.
• Prefer the narrowest topic file that directly matches the request.
• If a task needs both hardware facts and implementation guidance, load the hardware topic first, then the graphics, audio, system, or tooling topic that covers the code path.
• When copying assembly snippets, copy the whole contract: routine, declared input/output registers or memory, scratch bytes, required lookup tables, and any init routine. If a topic provides generated tables, prefer those over incomplete symbolic table names.