NAK=69/~1060 lamp commands explains the observed stuck-bright/missed
lamps (fire-and-forget writes turn each corrupt 4-byte burst into a
visible state error) while 2-byte traffic is pristine (analog 88.1%,
counters flat, zero wedges, worst gap 0.14s). The HC11 RX ISR's worst
path sits right at ~320 E-cycles. Ladder: 9600 production, 31250v2
CLEAN (FastRIO), 62500 needs host NAK-retransmit, 125000 CPU-walled.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Board->PC near-perfect at 125k (framing 5) while PC->board shredded by
packet length (2-byte polls 60% delivered, 4-byte lamp cmds ~2/3 NAKed
as checksum-corrupt): the 2MHz HC11 RX ISR can't drain back-to-back
bytes at 80us. MAX232 acquitted; zero wedges even at 40% inbound loss.
62500 image built as the sweet-spot candidate (RIOv4_2_patched_62500.bin).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
192s mash at 31250 with the $D9E7 wait fix: framing 5655 -> 54
(-99.4%), AbandonCount 65 -> +0, duplicate replies gone (215% -> 88.6%
of poll slots — identical to the healthy 9600 profile, the structural
$D758 drop-gate ratio), zero wedges, counters perfectly flat. The
byte-clocked ACK-wait theory is confirmed end to end: disassembly
predicted the mechanism, one operand byte fixed it, the wire went
quiet. Evidence log archived; results table in ANALYSIS.md.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
testlogs/ carries the raw records behind the CONFIRMED verdict:
baseline wedged at 0.62s and stayed dead 300s; patched ran clean
through 152s of heavier mash, worst gap 0.58s self-recovered.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
CydandClaude Fable 5