CydandClaude Fable 5
83fcb198c8
The display has a third use: serial error annunciator. $D5F2 renders 'E0' + three live counters (TX-ring overflow $3187, reply retries $3184, give-up teardowns $3185); $DAB8/$DAB2 is a terminal crash screen spelling 'dEAd' when the TX dispatcher meets an unknown command byte. Also recorded: RX overrun is unhandled (checksum NAKs are the only symptom), unused vectors hang in BRA-self stubs, FAULT LED = MAX690 PFO, manual/remote reset works by pulling PFI low, RUN LED = buffered AS*, and the MAX690 watchdog is unconnected/unserviced — software wedges persist until reset, matching bench observations. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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). sha25660a88718835c654b6135dbec7721c40ef99dca07df2ad4b57eedeb24037a5f73. 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 longJSRinit chain — textbook HC11 bring-up. - Vector table (
$FFD6-$FFFF, big-endian):$FFFERESET →$C000$FFD6SCI (serial) →$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 →$DB07..$DB3Dstubs.
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.
Patched images (built by make_patch.py; see RIOv4_2-ANALYSIS.md)
RIOv4_2_patched.bin— the reply-latch wedge fix, 23 bytes changed. sha2563fc8170caf60e2580641724ff995176c93c4f2e706f31487beded8233142493f.RIOv4_2_patched_31250.bin(make_patch.py --baud31250) — wedge fix- SCI retuned 9600 → 31250 baud (one more byte,
$D62B: 30→02). sha2569f866cf353d04906e1d3e3847b6375eaae251c987b656f68f093e61ba1bd545b. Bench/RIOJoy-only until the native games get baud patches; needs an FTDI-class adapter (16550s can't make 31250). Test tools take--baud 31250.
- SCI retuned 9600 → 31250 baud (one more byte,