# MediaTek Connac2 WiFi firmware container format

Scope: `mt7915/7916/7981/7986_{wm,wa,rom_patch}.bin` as shipped in
linux-firmware. All field layouts are transcribed from
`drivers/net/wireless/mediatek/mt76/mt76_connac_mcu.h` (structs
`mt76_connac2_fw_trailer`, `mt76_connac2_fw_region`,
`mt76_connac2_patch_hdr`, `mt76_connac2_patch_sec`); loader behavior from
`mt76_connac_mcu.c` (`mt76_connac2_load_patch`, `mt76_connac2_load_ram`,
`mt76_connac2_send_ram`). Verified against 54 historical blob revisions
(`dataset/history.jsonl`).

## RAM images (`*_wm.bin`, `*_wa.bin`) — little-endian

```
offset 0:  region data, packed back-to-back in region-table order
           (driver streams from offset 0, advancing by each region's len)
+sum(len): [optional] hidden second trailer — 100B on WM, 36B on WA
           (present on every observed revision; loader never reads it)
+gap:      region table: n_region × 40-byte records
end-36:    36-byte trailer
```

### Region record (40 bytes)

| off | size | field | notes |
|---|---|---|---|
| 0 | 4 | decomp_crc | CRC of decompressed data (unused when decomp_len==0) |
| 4 | 4 | decomp_len | 0 = stored uncompressed (all observed revisions) |
| 8 | 4 | decomp_blk_sz | MCU-side decompression block size |
| 12 | 4 | rsv | |
| 16 | 4 | addr | download destination (bus address) |
| 20 | 4 | len | stored length == download length |
| 24 | 1 | feature_set | bit0 ENCRYPT, bits1-2 KEY_IDX, bit4 ENCRY_MODE, bit5 OVERRIDE_ADDR, bit6 NON_DL, **bit7: undefined upstream — see U1** |
| 25 | 1 | type | content tag: 0 DEFAULT everywhere in this family; mt7921 uses 2 = CLC (country/location data, paired with NON_DL) |
| 26 | 14 | rsv1 | |

Observed `feature_set` bits in the wild: `0x20` (OVERRIDE_ADDR, WM region 0),
`0x80` (unknown, all `0xf0xxxxxx` regions), `0xc0` (NON_DL|0x80, zero-length
entries). No observed blob sets ENCRYPT.

### Trailer (36 bytes, at EOF)

| off | size | field | notes |
|---|---|---|---|
| 0 | 1 | chip_id | 0x0b mt7915, 0x13 mt7916, 0x14 mt7981, 0x0f mt7986 (WM); 0x00 on WA |
| 1 | 1 | eco_code | silicon eco |
| 2 | 1 | n_region | |
| 3 | 1 | format_ver | |
| 4 | 1 | format_flag | |
| 5 | 2 | rsv | |
| 6 | 10 | fw_ver[10] | **stripped by MTK**: `____000000` (WM) / `DEV_000000` (WA) |
| 16 | 15 | build_date[15] | `%Y%m%d%H%M%S` ASCII |
| 31 | 4 | crc | LE32 |

### Hidden second trailer (not read by the upstream loader)

WM (100B): `16×'#'`, `40 00 00 00`, 1-byte string length, flags, then the
full build string `t-neptune-<branch>-mt7915-<n>-<CHIP>_<MPTAG>_<MPVER>-<build-ts>`,
`'#'`-padded. WA (36B): no string. This restores the version metadata MTK
strips from fw_ver — the key input to version diffing (`tools/fw_history.py`).

Observed build strings per revision: `dataset/history.jsonl`.

## Patch images (`*_rom_patch.bin`) — big-endian

```
offset 0:    92-byte header
offset 92:   n_section × 64-byte section records
explicit:    section data at each section's `offs`
```

Header: `build_date[16]`, `platform[4]` ("ALPS" on all observed), `hw_sw_ver`,
`patch_ver`, `checksum(u16)`, `rsv(u16)`, descriptor (`patch_ver`, `subsys`,
`feature`, `n_section`, `crc`, `rsv[11]`).

Section record: `type`, `offs`, `size`, info union (`addr`, `len`,
`key_idx`/enc-mode, `align_len`). Observed: `type == 0x30002` on every
section; `enc_type == 0` (plaintext); download addresses `0x00900000`-range;
section counts 1 (7916/7981/7986) and 2 (7915, one small + one data section).

## WO images (`mt7981_wo.bin`, `mt7986_wo_{0,1}.bin`)

Different container, loaded by the ethernet-side WED driver
(`drivers/net/ethernet/mediatek/mtk_wed_mcu.c`), not mt76. Not yet parsed
(unknown U3). Firmware content: FreeRTOS v10.0 + NDS32 port, "coe/" source
paths (string evidence).

## Firmware ISA

NDS32 (Andes) 32-bit little-endian. Evidence: `GCC: (2018-10-23_nds32le-elf-mculib-v3) 4.9.4` in mt7981_wa data;
`portable/GCC/NDS32/port.c` in mt7981_wo. `tools/mtk_fw_elf.py` emits
`EM_NDS32`(167) ET_EXEC ELF for Ghidra import.

## Unknowns

U1 `feature_set` bit7 (0x80): correlated with `0xf0xxxxxx` destinations;
undefined upstream. U2 hidden-trailer non-string fields. U3 WO container
format. See `docs/findings.md`.