RIO board firmware

• RIOv4_2.bin — RIO cockpit I/O board firmware v4.2, dumped 2026-07-04 from one of our own boards' EPROM: an AMD AM27C512-150 (64K x 8 UV EPROM, 150ns — the image fills it exactly). sha256 60a88718835c654b6135dbec7721c40ef99dca07df2ad4b57eedeb24037a5f73. For the eventual patched burn: a pin-compatible Winbond W27C512 (electrically erasable, TL866-friendly) drops straight into the socket; the original AMD chip gets labeled and preserved unmodified.

First-look analysis (from the image alone, confirmed on hardware)

• MCU: Toshiba TMP68HC11 (read off the chip; the code fingerprint agrees — 6800-family opcodes with writes into the 68HC11 internal register block at $10xx).
• Memory map: image is FF up to 0xC000; 16KB of code occupies $C000-$FFFF (EPROM mapped at the top of the HC11 address space).
• Startup at $C000: SEI; LDS #$8000; STAA $1024 (TMSK2); STAA $1022 (TMSK1); ... then a long JSR init chain — textbook HC11 bring-up.
• Vector table ($FFD6-$FFFF, big-endian):
  • $FFFE RESET → $C000
  • $FFD6 SCI (serial) → $D630 — the entry point of the board's receive/protocol interrupt handler. The suspected board-side DISABLE_AND_DIE-style wedge (see RIO-NOTES.md: the board mirrors the game's PCSPAK state machine, and mash-stress leaves the reply path dead while the button/event path stays alive) is reachable from here.
  • $FFE4 → $C1B2, $FFE6 → $C18E (timer output-compares); most other vectors → $DB07..$DB3D stubs.

Why this exists

The remaining RIO reliability issue is board-side: under button-mash stress the board's reply/analog state machine wedges (RX dead, TX alive; a button press or power cycle revives it), reproduced identically on two different USB serial adapters. The game-side half of the protocol was binary-patched for tolerance (BTL4OPT patches v2-v4); the board firmware is the other half. Plan (RIO-NOTES.md "Board firmware patch plan"): disassemble as 68HC11 from $C000 with the vector entries as roots, find the SCI state machine (protocol constants FC=ACK FD=NAK FE=RESTART FF=IDLE, idle-reload-4 patterns), patch the early-ACK/error wedge path or widen its window, burn a new EPROM, keep this original safe.

Current work candidate — RIOv4_3rc1.bin

Built by make_patch.py --e0thresh=5 --checkrepaint RIOv4_2.bin RIOv4_3rc1.bin; sha256 dc59bd51cae34781cf42f338e44a020b249a4030acc3c584af916aee9ca881e3 (68 bytes changed vs stock). 9600 baud, native-game compatible. On the stock v4.2 base it carries:

1. Reply-latch wedge fix (edits 1-2) — bench-certified.
2. E0-display threshold, N=5 (edit 5) — bench-certified 2026-07-19 (held F0000000 sub-threshold, flipped to E0000105 at the 5th teardown; mash regression clean).
3. Check self-test display repaint (edit 6, NEW) — the CheckRequest handler previously left a stale 04000000 frame on the display; a 10-byte cave at $E020 now repaints F0000000 after every check, then re-renders the E0 readout only if a counter is at/over threshold. Needs on-hardware verification: after a burn, any version+check exchange (tray connect, monitor, mash start) must leave the display reading F0000000, not 04000000; then re-run --e0test (expect the certified behavior unchanged) and a mash spot-check.

Once edit 6 is verified on the cockpit, this image is christened RIO 4.3.

Archive

All prior generations live in archive/ with their disassemblies: RIOv4_2_patched (wedge fix only), _31250/_31250v2 (FastRIO speed builds), _62500/_125000 (speed-ladder science runs), and the _e0t5 pair (threshold without check-repaint; the 9600 one is in the socket as of 2026-07-19 until rc1 is burned). Bench verdicts and per-edit history: RIOv4_2-ANALYSIS.md. The pristine dump RIOv4_2.bin stays at top level — it is the source every patch builds from.