# Findings log

One entry per claim. Every claim carries evidence (kernel source reference or
blob offset + observed bytes). Claims that cannot be evidenced are registered
in the Unknowns section instead. Blobs referenced by filename are the
linux-firmware copies listed in `manifest.json` (SHA-256 TBD in fixtures).

Blobs observed: mt7981/mt7915/mt7916/mt7986 × {wm, wa, rom_patch}
(linux-firmware snapshot 2026-04-20, Debian).

## F1 — Connac2 RAM container layout

`[region data, packed from offset 0 in table order][optional hidden trailer
(see F2)][n_region × 40-byte region table][36-byte trailer at EOF]`

Evidence: `mt76_connac_mcu.c` `mt76_connac2_load_ram()` +
`mt76_connac2_send_ram()` (region data streamed sequentially from offset 0;
table and trailer located from EOF); `mt76_connac_mcu.h`
`struct mt76_connac2_fw_region` / `_fw_trailer`. Confirmed by exact layout
match on 8 RAM blobs (sum(region.len) + table + trailer (+ hidden trailer) ==
file size).

Region fields: `decomp_crc/decomp_len/decomp_blk_sz` (MCU-side decompression,
unused when decomp_len==0 — all observed blobs), `addr`, `len`,
`feature_set`, `type`.

## F2 — Hidden second trailer carries the full build string

Between region data and the kernel-parsed table sits a trailer the upstream
loader never reads. WM blobs: 100 bytes; WA blobs: 36 bytes (no string).
Observed family-wide (all 4 chips).

WM hidden trailer = 16×'#' + `40 00 00 00` + 1-byte string length + flags +
full build string + '#'-padding. Recovered strings:

- mt7981_wm: `t-neptune-main-mt7915-1953-MT7981_MP2111_IMP-20240823161204`
- mt7916_wm: `t-neptune-main-mt7915-1953-MT7916_MP2111_IMP-20240823170147`
- mt7986_wm: `t-neptune-main-mt7915-1953-MT7986_MP2111_IMP-20240823160608`
- mt7915_wm: `t-neptune-mp-mt7915-2045-MT7915_MP_7_4_2045-20220929103802`

Significance: the kernel-visible trailer's `fw_ver[10]` is stripped
(`____000000` WM / `DEV_000000` WA); the hidden trailer restores branch
("main"/"mp"), internal build number (1953/2045), MP tag, and build
timestamp. This is the version metadata the changelog tooling keys on.

Evidence: bytes at offset `sum(region.len)` in each blob (see
`manifest.json` → `hidden_trailer.raw_head`).

## F3 — region `type` is a content tag used by some loaders

All parsed mt79-family blobs: `type == 0` (`FW_TYPE_DEFAULT`). It is not
ignored upstream: mt7921's loader selects
`feature_set & FW_FEATURE_NON_DL && type == FW_TYPE_CLC` regions as
country/location-calibration data instead of downloading them to the MCU.

Evidence: `mt7921/mcu.c` CLC handling; `FW_TYPE_CLC` definition in
`mt76_connac_mcu.h`.

## F4 — Patch container format

92-byte big-endian header (16-byte build date, 4-byte platform tag —
"ALPS" on all four — hw_sw_ver, patch_ver, checksum, descriptor), 64-byte BE
section table, plaintext section data at explicit offsets. All observed
patch sections: `enc_type == 0` (plaintext).

Evidence: `mt76_connac2_load_patch()` + `struct mt76_connac2_patch_hdr/_sec`
in `mt76_connac_mcu.h`; exact parse of 4 patch blobs.

Section counts: mt7915 patch = 2 sections, all others = 1; section `type`
constant `0x30002` on every observed section (loader downloads all sections
regardless; field semantics otherwise unobserved).

## Unknowns registry

- **U1 — `feature_set` bit 7 (0x80):** observed only on WM regions at
  `0xf0xxxxxx` addresses (mt7981 r7–r10, mt7986 equivalents). Upstream
  defines bits 0–6 only; vendor-SDK search found no definition (2026-08-20).
  Correlation with address family noted; semantics undetermined. May relate
  to a second download destination or content class.
- **U2 — hidden-trailer non-string fields:** the `40 00 00 00` and flag
  bytes before/around the string (F2) are uninterpreted.
- **U3 — WO container:** `mt7981_wo.bin` uses the mtk_wed loader
  (`mtk_wed_mcu.c`), a different format; not yet parsed.

## Related verified facts

- NDS32LE target: `GCC: (2018-10-23_nds32le-elf-mculib-v3) 4.9.4` string in
  mt7981_wa region data; FreeRTOS v10.0.0 + `portable/GCC/NDS32/port.c`
  strings in mt7981_wo.
- No per-region encryption in any observed blob (`FW_FEATURE_SET_ENCRYPT`
  clear; patch `enc_type == 0`). Optional protocol support exists in the
  loader (key from EFUSE path) but is not exercised by shipped images.