issues: the AMD row's staged fault reds every T14 testcases boot, and the tone underran once in nine

issues/a-metal-row-names-no-machine-so-another-benchs-boot-carries-it.md

@@ -19,6 +19,32 @@ The stick's controller is no longer pinned per machine (the `@boot` place), so
 which spare a row claims is decided at boot. Which bench a row runs on is still
 not declared, and the harness has nothing to refuse it by.
 
+The T14's `00:0d.0` [8086:9a13] is a spare under both boot layouts. Off the
+stick, `00:14.0` is the boot controller. Off the NVMe (#1095), no xHCI is. The
+AMD row claims the spare and its fault arm runs:
+`iommu: DMA FAULT owner=process unit3 stream=00:0d.0 addr=0x0000000050200000`,
+1 GiB past the grant at `0x10200000`. `klogd_hosted` then reds on
+`must_be_clean`. The fault ran on each of PR #1074's four stick boots
+(sessions 2–5), and `klogd_hosted` red on every one judged (sessions 2–4;
+[sessions 2 and 3](https://github.com/ToyOSOrg/evidence/tree/b1c036144b4c8a39415cb60145a823d0c0d2d652/r3)).
+The same happened on its NVMe landing boot (head 094323f29,
+[evidence](https://github.com/ToyOSOrg/evidence/tree/3cb575aadca9e85f33b4c5690c7e1ea4ca15822f/r8)).
+
+Four more rows red on that boot by this record's mechanism, because they are
+AMD-bench rows judged against a T14 readback:
+- `amdvi_usbd_drives_its_own_entry`: `test_rs_usbd_spare_vector` finds no
+  MSI-X on the T14's MSI-only xHCI;
+- `idle_entered`: "this row runs on the AMD bench";
+- `amdvi_translates_the_boot_controller` and
+  `amdvi_remaps_the_boot_controller`: no AMD-Vi unit is translating.
+
+The boot's two other reds have records of their own:
+`i219_messages_on_its_msi_vector` (`issues/i219-msi-passes-only-when-the-network-sends-it-a-frame.md`)
+and `hda_tone` (`issues/the-t14-tone-underran-one-period-once-in-nine-boots.md`).
+
+**Owner**: the metal harness (`tests/common/metal.rs`, and the row table in
+`tests/toyos.rs`).
+
 **Exit**: every metal row declares the machines it runs on, by the SMBIOS
 identity the machine's record carries. A selection run on one bench takes no
 row that is not declared for it, and says which rows it left out.

issues/the-t14-tone-underran-one-period-once-in-nine-boots.md

@@ -0,0 +1,49 @@
+---
+status: open
+kind: defect
+opened: 2026-10-28
+---
+
+# The T14 tone underran one period once in nine boots
+
+`hda_tone` reds when soundserver fills a period the tone client had not
+covered (`tests/common/audio.rs`'s `tone_on_metal`). On one T14 `testcases`
+boot it read `underruns=1 starve_max=1` in the stream's first 2 s stats
+window (11.772–13.773 s of a stream that closed at 14.977 s): one isolated
+period, somewhere in that window. The second window and `hda_tone_resampled`
+in that boot read 0.
+
+Distinct T14 boots judged for this row:
+- 7 of PR #1074's branch. Four are stick boots of earlier revisions on older
+  mains, and three are NVMe boots. The NVMe three include the red one (head
+  094323f29) and the same image booted again 24 minutes later.
+- 2 of main 370d7d9f6 alone, NVMe.
+
+If both trees underran at one rate, the red would land on a branch boot 7
+times in 9 (3 in 5 counting NVMe boots alone), so the counts attribute it to
+neither.
+([landing boot](https://github.com/ToyOSOrg/evidence/tree/3cb575aadca9e85f33b4c5690c7e1ea4ca15822f/r8),
+[every boot's judgement](https://github.com/ToyOSOrg/evidence/tree/9d0ed9325f33f34ba7714fe68ca1261129c27f0a/r9))
+
+There is no candidate cause. The samples cross a shared-memory ring.
+soundserver counts an underrun only once a client is streaming, that is once
+it has delivered (`ClientStream::is_streaming`). The one pipe on the path is
+the signal bell, and after delivery `signal_clients` (`system/soundserver/src/mix.rs`)
+rings it once per mix wake. It drops every error but `Gone`, and a bell
+refused for memory would be dropped too. But neither tree can refuse that
+write for memory in a stream this short:
+- on main 370d7d9f6, a pipe holds its page from its first write;
+- with #1074, a pipe that has held a byte needs another frame only when its
+  held bytes cross a frame's 4096 bytes (`kernel/pure/pipe.rs`'s `wants`, and
+  `consume` restarts a drained pipe at its frame's start). That takes about
+  4096 bells, and this stream rang at most about 1400 (one per mix wake,
+  871 + 515).
+
+**Owner**: soundserver and the hda driver.
+
+**Exit**: soundserver's underrun record names the period, how late the
+client's fill was and how late the device's completion was. A recurrence
+then names its cause, and the fix lands. The record does not close on a
+count of clean boots. At the observed 1 in 9, 26 consecutive clean boots
+are needed to exclude that rate with 95 % confidence, and about 300 to
+bound it under 1 in 100.