62500 SHELVED: chord-driven RX overrun is host-unfixable; 31250v2 is FastRIO

Slow chorded presses still glitch lamps at 62500 after three rounds of host-side hardening (NAK-race resend -> stop-and-wait -> typed resolution): a chord maximizes board ISR latency exactly when lamp replies arrive, and a 2-byte RX buffer loses bytes no protocol can recover. Full post-mortem in ANALYSIS.md; all bench evidence archived. Final ladder: 9600 production / 31250v2 FastRIO / 62500 shelved / 125000 not viable. Stop-and-wait stays on everywhere as cheap delivery insurance. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
2026-07-19 13:40:48 -05:00
parent 5dd7f78bc2
commit 61e7d0f600
2 changed files with 60 additions and 0 deletions
@@ -341,3 +341,36 @@ Host-side NAK-driven retransmit (the protocol's intended use of ACK/NAK;
 RioSerialLink currently fire-and-forgets outbound) would make 62500
 lamp-solid (1 retry -> ~0.4% residual, 2 -> ~0.03%) and is good
 robustness at any rate. Until then, 31250 v2 is the honest FastRIO.
+
+### 62500 final verdict (2026-07-19) — SHELVED. Chord-driven RX overrun.
+
+Three rounds of host-side hardening at 62500 (evidence in `testlogs/`,
+implementations in RioJoy.Core RioSerialLink):
+1. **NAK-race resend** — resends tracked NAKs 1:1 (321/321) yet lamps
+   still glitched: under bursts the NAK arrives after a newer command is
+   already "latest", so the wrong packet was resent; total shreds never
+   NAK at all.
+2. **Stop-and-wait** (one command in flight; ACK/NAK/50ms-timeout;
+   retransmit the SAME packet, limit 2) — still glitched: reply
+   resolution was type-blind, so an analog reply in USB transit from the
+   previous poll falsely confirmed the next lamp command.
+3. **Typed resolution** (a reply only resolves its matching request;
+   ACK/NAK safe type-blind because the board's TX ISR prioritizes them
+   ahead of reply data; 10ms settle after budget-exhausted drops) —
+   improved, but **chorded presses still glitch even at slow press
+   rates**.
+
+The chord observation closes the case: a chord makes the board scan,
+queue and transmit N button events at once — worst-case ISR latency —
+exactly when our 4-byte lamp replies arrive at 160us/byte into a 2-byte
+RX buffer. Corruption at 62500 is chord-shaped, not rate-shaped; no
+host-side protocol can prevent the board losing bytes it never latched,
+and retries can land in the same busy window. Fixing it for real means
+firmware ISR restructuring (or sequence numbers) — out of scope.
+
+**Final ladder verdict: 31250 v2 is the FastRIO standard** (3.3x stock,
+clean without any host-side compensation — NAK 5 in 192s of mash).
+The stop-and-wait + typed-resolution machinery stays enabled at every
+rate as delivery insurance (it hardens 9600 production cabinets against
+ordinary electrical noise, and its retries are near-zero on clean links).
+62500 images remain in the repo for future firmware work.
@@ -0,0 +1,27 @@
+== RIO mash test :: COM1 @ 62500 8N1, 300s, chip label 'patched-62500-sw' ==
+   lamp echo ON (drives reply/lamp collisions), wedge threshold 2.0s, app auto-recovery DISABLED
+   log: C:\VWE\riojoy\riomash-patched-62500-sw-20260719-133628.log
+   firmware: 4.2
+   counters before: RestartCount=0  AbandonCount=0  FullBufferCount=0  [board/lamp faults reported!]
+
+>>> MASH NOW: two hands, 8 lamp buttons, as fast as you can. <<<
+>>> Test runs 300s. A wedge alarm will beep + banner.   <<<
+>>> Ctrl+C ends the run early and still prints the summary.   <<<
+
+[  31.90s] progress: presses=72 (72/min) analog=497 maxGap=0.21s wedges=0
+[  58.27s] operator stop (Ctrl+C) — ending run, snapshotting counters...
+
+== MASH SUMMARY [patched-62500-sw] ==
+run              : 58s on COM1, lamps on, wedge threshold 2.0s
+firmware         : 4.2
+presses/releases : 123 / 123  (124 presses/min)
+analog replies   : 931 (~1054 poll slots; 88.3%), sentinels 0
+framing / NAK    : 7 / 20 (command resends NAK/timeout: 34)
+gap histogram    : <100ms:921  100-250ms:9  250-500ms:0  0.5-1s:0  1-2s:0  2-5s:0  >5s:0
+longest gaps     : 0.22s@58.3s, 0.21s@0.6s, 0.14s@41.9s, 0.14s@26.8s, 0.13s@23.6s, 0.11s@12.4s, 0.11s@24.4s, 0.10s@54.1s, 0.10s@53.4s, 0.10s@16.5s
+wedge events     : 0
+counters before  : RestartCount=0  AbandonCount=0  FullBufferCount=0  [board/lamp faults reported!]
+counters after   : RestartCount=0  AbandonCount=0  FullBufferCount=0  [board/lamp faults reported!]
+counter delta    : RestartCount=+0  AbandonCount=+0  FullBufferCount=+0
+verdict          : PASS — no wedge; compare gap histogram + counter delta to baseline
+log file         : C:\VWE\riojoy\riomash-patched-62500-sw-20260719-133628.log