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+# Bus-reset edge events + review fix wave — design
+
+Date: 2026-08-15
+Branch: `fix-ci-hs` (unpushed, 6 commits over master `53fef2833`)
+
+## Problem
+
+A max-effort review of the branch produced 15 findings. Four are regressions the branch
+itself introduced; the rest are pre-existing or cross-cutting. The load-bearing one:
+
+`dcd_ci_hs.c` now runs the RM-prescribed reset cleanup at the URI (reset-start) interrupt
+but does not tell usbd until the Port Change Detect that ends the reset. For the whole
+reset window — a minimum of 3 ms, typically 10–50 ms — usbd still believes the device is
+configured while the DCD's queue heads have been zeroed. A class driver writing in that
+window (`tud_hid_n_report()`, `tud_cdc_write_flush()`) primes a disabled endpoint over a
+zeroed dQH, *after* the cleanup's flush, so the stale prime survives re-enumeration over a
+buffer usbd has already released. On a 600 MHz M7 that window is enormous. Master had no
+gap: cleanup and event were adjacent statements.
+
+The stack has no way to express "reset started" — `DCD_EVENT_BUS_RESET` carries the
+negotiated speed, which does not exist until the reset ends. That missing vocabulary is
+the actual defect; the driver-level workarounds considered (deferring the memclr, guarding
+primes with a private flag) only shrink the window.
+
+## Design
+
+### 1. Stack: split the bus-reset event into two edges
+
+`src/device/dcd.h`:
+
+```c
+DCD_EVENT_BUS_RESET_START, // reset signaling detected; bus unusable, speed unknown
+DCD_EVENT_BUS_RESET_END,   // reset complete; .bus_reset.speed is final
+...
+#define DCD_EVENT_BUS_RESET DCD_EVENT_BUS_RESET_END  // backward compatibility
+```
+
+No new helper: `dcd_event_bus_reset(rhport, speed, in_isr)` keeps its name and emits
+`_END`, so every other port is bit-identical to today; `_START` uses the existing
+payload-free `dcd_event_bus_signal()`. The alias keeps unit-test/fuzz references
+compiling.
+
+**Contract (documented in `dcd.h`):** `_START` is optional. A DCD that cannot distinguish
+the two edges emits only `_END`, which stays self-sufficient — it performs the full
+teardown with or without a preceding `_START`.
+
+`src/device/usbd.c`:
+- `case DCD_EVENT_BUS_RESET_START:` → `usbd_reset(rhport)` only; speed untouched.
+- `case DCD_EVENT_BUS_RESET_END:` → unchanged (`usbd_reset()` + latch speed).
+- `_usbd_event_str[]` gains both names.
+- `TODO:` note that a DCD signalling both edges should not pay for two teardowns — track
+  a per-rhport "start seen" flag and skip the redundant `usbd_reset()` in `_END`, keeping
+  the unconditional teardown for the legacy single-event path.
+
+Cost, accepted deliberately: one extra queued event and one extra `usbd_reset()` per
+enumeration on ci_hs only, bounded at one per reset against a default
+`CFG_TUD_TASK_QUEUE_SZ` of 16 (queue pressure is the failure PR #3817 fixed, hence the
+explicit note).
+
+### 2. ci_hs: split `bus_reset()` along the register/software line
+
+- **`bus_reset_begin()` — at URI, inside the reset window (UM10503 25.10.3):** ENDPTCTRL
+  type-reset loop, `ENDPTNAK`/`ENDPTNAKEN`, `ENDPTSETUPSTAT` and `ENDPTCOMPLETE`
+  write-back clears, bounded `ENDPTPRIME` drain, `ENDPTFLUSH` all. Emit `_START`.
+  Registers only — nothing in `_dcd_data` is touched, so no software structure is pulled
+  out from under a task mid-`dcd_edpt_xfer`.
+- **`bus_reset_complete()` — at the PCI ending the reset:** re-flush, `tu_memclr(&_dcd_data)`,
+  EP0 queue-head re-init, dcache clean. Emit `_END` with the final PSPD speed.
+
+Two properties fall out: the re-flush kills any prime armed during the window without a
+new state flag, and the memclr now happens at the same instant usbd is told, so the
+"configured over zeroed queue heads" mismatch is eliminated rather than shrunk. Residual
+exposure (a task priming exactly as the ISR memclrs) equals master's.
+
+The reason-dispatch (`pci_reason`, suspend/URI ordering) is unchanged; only the reset
+case's body moves.
+
+### 3. ci_hs: one bounded-flush helper
+
+Extract `flush_endpoints(dcd_reg, mask)` — writes `ENDPTFLUSH = mask`, spins bounded by
+`CI_HS_BUSY_SPIN` until those bits clear, returns `true` if they cleared — and route all
+five flush sites through it (`bus_reset_begin`, `bus_reset_complete`, `dcd_deinit`,
+`dcd_edpt_iso_activate`, the setup-time EP0 flush). The unified part is the mechanism
+(one bound, one spin idiom, one return convention); callers keep their existing reactions,
+all of which currently proceed regardless, and that stays true here — no caller gains new
+error handling in this wave. Without this, §2 adds a fifth site to a file that already
+carried four hand-rolled variants.
+
+### 4. Mechanical fixes
+
+`dcd_ci_hs.c`
+- Setup-time EP0 flush waits for completion (via §3's helper) before the SETUP event is
+  queued, so the flush can no longer still be asserted when the task primes the response —
+  which also dissolves its interaction with the post-prime verify. This adds a bounded
+  spin in ISR context; the RM notes a flush waits out any packet already in progress, so
+  the wait is one packet time (microseconds at HS) and the existing `CI_HS_BUSY_SPIN`
+  bound caps the pathological case, consistent with the file's other flush sites.
+- `dcd_set_address()` writes `DEVICEADDR` only if the status-ZLP prime took. A refused
+  prime means a newer SETUP superseded the transfer; staging an address whose ACK will
+  never arrive is wrong.
+- Emit `DCD_EVENT_RESUME` only when `!(PORTSC1 & PORTSC1_SUSPEND)` (restores master's
+  hardware guard, lost in the rework).
+
+`dcd_lpc_ip3511.c`
+- Deliver the setup copy only when known-good:
+  `if (latch still set) { INTSETSTAT = TU_BIT(0); } else { dcd_event_setup_received(...); }`.
+- `TODO:` token on the USB.13 deferral so backlog sweeps surface it.
+
+`usbd.c`
+- The DCD-refusal path in `usbd_edpt_xfer` stops routing through the breakpoint-carrying
+  assert: a DCD declining a prime is documented and self-healing, not a programming error,
+  and `TU_BREAKPOINT()` is not gated on `CFG_TUSB_DEBUG` — with a probe attached (always,
+  on the rig) it halts the target. Log and return false instead.
+
+BSP
+- Delete the seven-line RHPORT block in `lpcxpresso55s28/board.cmake` (byte-identical to
+  `family.cmake`'s own guards; `board.mk`'s `?=` stays as the idiomatic Make form).
+- `lpc11u37.ld`: correct the stale comment (nothing lands in RamUsb2 in either build
+  system now — the stack owns the whole bank) and keep the ASSERT, re-labelled as
+  future-proofing.
+
+## Findings improved for free (documented, no code)
+
+A reset that starts and never completes — cable pulled mid-reset — now delivers `_START`
+and tears usbd down, where before usbd stayed configured on a dead bus. This softens both
+the adjudicated UNPLUGGED-removal finding and the deferred aborted-reset item: a stray
+later PCI delivering `_END` becomes harmless (usbd already torn down, just latches a
+speed) instead of deconfiguring a live device. True detach detection still requires OTGSC
+B-session-valid VBUS sensing — board-dependent, still a follow-up.
+
+## Explicitly deferred
+
+- Prime verification generalized to all endpoints and all causes (RM 25.10.8.2); the
+  EP0/SETUP-gated form stays, its flush interaction fixed by §4.
+- usbd discards `usbd_control_xfer_cb`/`tud_control_xfer` returns — cross-DCD behavior
+  change needing its own regression pass, despite `usbd.c` being open here.
+- Timed-out flush still proceeds to the memclr (now confined to one helper).
+- LPC55S2x USB.3 FORCE_FS workaround; iso-IN 1023 enforcement; 8-byte OUT-spill
+  enforcement; USB.13 INTONNAK workaround.
+- Gating `TU_BREAKPOINT()` on `CFG_TUSB_DEBUG` stack-wide.
+- Unguarded `set()` RHPORT knobs in ~14 sibling `board.cmake` files.
+
+## Verification
+
+1. `pre-commit run --all-files`; builds for mimxrt1064_evk, lpcxpresso18s37,
+   lpcxpresso11u37, lpcxpresso55s28, plus Make link checks for the two previously-broken
+   targets (`host/cdc_msc_hid` on 55s28, `device/cdc_msc_throughput` on 11u37).
+2. Cross-DCD build guard: one non-ci_hs, non-ip3511 board (e.g. `stm32f407disco`) to prove
+   the `DCD_EVENT_BUS_RESET` alias keeps legacy ports compiling untouched.
+3. HIL on byte-verified flash (`verifyfile` on every J-Link load — the 1064's silent
+   flash no-op has struck twice): usbtest 30/30 on mimxrt1064_evk, lpcxpresso55s28,
+   lpcxpresso11u37; 50× case-9/10 loops on the 1064; 10× case-11/12/24 unlink loops.
+4. Reset-path specific: confirm HS enumeration (480) and, with `LOG=2`, that a single
+   enumeration shows exactly one `_START`/`_END` pair and no spurious RESUME.
+5. Suspend/resume exercise on the 1064 (host-side autosuspend on the port) confirming
+   `SUSPEND`/`RESUME` pairing and no reset misclassification.
+
+## Success criteria
+
+All four regressions closed, no new findings in a scoped re-review of the wave diff, every
+listed HIL result green on verified flash, and legacy DCDs provably untouched (alias build
+check + unchanged `_END` semantics).
diff --git a/docs/superpowers/specs/2026-08-16-drop-ep0-prime-verify-design.md b/docs/superpowers/specs/2026-08-16-drop-ep0-prime-verify-design.md
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+# Drop the EP0 post-prime verify — design
+
+Date: 2026-08-16
+Branch: `fix-ci-hs` (unpushed, 19 commits over merge-base `53fef2833`)
+
+## Context
+
+The branch grew while chasing a wedge on `mimxrt1064_evk`: the board would stop answering a
+host transfer, the URB would never complete, `testusb` would block uninterruptibly and the
+whole rig would follow it down. Eight occurrences over four days, across the Linux usbtest
+battery's queued control and bulk tests.
+
+The cause turned out to be silicon: **Errata i.MX RT1064_A / RT1060_A ERR050101**. While an
+isochronous IN endpoint is active, an IN token addressed to that same endpoint number on
+another device sharing the host silently unprimes one of this device's OUT endpoints —
+control, bulk, interrupt or isochronous. NXP states it cannot be detected by software and
+raises no interrupt. Moving the usbtest example's iso IN endpoint from 3 to 7 (commit
+`42870b15b`) cleared it: 340 consecutive wedge-free runs, where the board previously
+re-wedged within hours.
+
+Before that was known, an earlier theory — a SETUP arriving mid-prime silently cancelling an
+EP0 prime — produced a post-prime verification block in `qhd_start_xfer()`. That theory's
+supporting capture (EP0's status ZLP armed but unprimed, the device a control transfer ahead
+of the host) is explained by ERR050101 just as well, because the errata explicitly covers
+*control* OUT endpoints and a control status stage **is** an OUT endpoint. The generalized
+version of that verify was already reverted (`565bb0d99`) as both regression-prone and aimed
+at a failure the vendor documents as undetectable in software. This spec removes what
+remains of it.
+
+## Change
+
+Delete the post-prime block in `qhd_start_xfer()` (`src/portable/chipidea/ci_hs/dcd_ci_hs.c`):
+the bounded `ENDPTPRIME` drain, the `ENDPTFLUSH`-on-timeout, and the
+`ENDPTSTAT | ENDPTCOMPLETE` / `ENDPTSETUPSTAT` verdict. The tail becomes:
+
+```c
+  // start transfer
+  dcd_reg->ENDPTPRIME = TU_BIT(epnum + (dir ? 16 : 0));
+  return true;
+```
+
+This removes two register spins and four volatile reads from every EP0 transfer, and with
+them the false-fail path a reviewer flagged: a transfer the interrupt handler has already
+completed reads identically to a cancelled prime.
+
+## Deliberately kept
+
+- **The pre-prime setup-lockout guard** directly above it — UM10503 25.10.8.1.1 step 4
+  verbatim ("Before priming for status/handshake phases ensure that ENDPTSETUPSTAT is '0'"),
+  and older than the wedge theory. It also keeps `qhd_start_xfer()` returning `bool`, so
+  `dcd_set_address()`'s gating and the usbd breakpoint removal stay meaningful — no cascade.
+- **The setup-time EP0 flush and its completion wait** — the flush is the 25.10.8.1.1 step-3
+  remark; the wait exists because an unfinished flush can retire a freshly primed response,
+  an interaction independent of the verify.
+- **The `BUS_RESET_START`/`END` split** and the rest of the review-driven hardening.
+- Everything hardware-proven: the rf_tv fix, the lpc11u37 stack move, the lpc55s28
+  onboarding, the lpc55 Make OHCI link, and the ERR050101 endpoint move itself.
+
+The commit message records the corrected attribution of the handoff capture, so the next
+reader does not re-derive the superseded theory from the same evidence.
+
+## Validation
+
+The "with it" arm is already banked from 2026-08-16: 10x 30/30 batteries plus 15x TEST 27,
+15x tests 9/10 and 10x tests 11/12/24, all clean. This is the second half of an A/B.
+
+1. **Rebase onto current master first** (master has moved: midi2/usbtmc/video), then rebuild —
+   otherwise the validated tree is not the tree that merges.
+2. **Software gates:** `pre-commit run --all-files`; full example builds for
+   mimxrt1064_evk, lpcxpresso18s37, lpcxpresso11u37, lpcxpresso55s28; the two Make link
+   canaries (`host/cdc_msc_hid` on lpcxpresso55s28, `device/cdc_msc_throughput` on
+   lpcxpresso11u37); `ceedling test:all`.
+3. **Hardware — mimxrt1064_evk only.** It is the only ci_hs board on the rig; the other two
+   run ip3511, which this change does not touch. Preconditions: CI idle
+   (`pgrep -f "hil_test.py [-]-retry"`), board lock held for the whole run. Flash with
+   `loadfile` (its built-in Program & Verify — JLinkExe V9.66 has no `verifyfile`), then
+   confirm re-enumeration as `cafe:4010` with serial `BAE96FB95AFA6DBB8F00005002001200`, and
+   confirm `lsusb -v` still reports the iso IN endpoint as **0x87** so a stale image cannot
+   masquerade as a pass.
+4. **Runs:** 5x the full 30-case battery, then 15x `--tests 9,10,14,21` (queued control, ch9
+   subset, both ctrl_out cases) — the control paths the verify actually protected, which a
+   plain battery samples only once per run. Print a `testusb` D-state scan after every
+   iteration.
+
+**Acceptance:** 5/5 batteries at 30/30, 15/15 loops, and no `testusb` D-state outliving its
+case runtime.
+
+**Rollback trigger:** any control-case failure (errno 110 or 71 on cases 9, 10, 14, 21) or a
+lingering D-state means the verify was load-bearing after all — restore it and record that
+result in the commit message. A negative result is a finding, not a setback.