> Historical snapshot (2026-09-26 working notes). Two claims are superseded:
> update entry is hold-PAD-while-powering-on (see ../firmware-update.md),
> and the cmtd checksum is solved (see ../../tools/README.md).

# Lofi-12 XT.bin — Reverse Engineering Notes (v1.1.156)

- File: `Lofi-12 XT.bin` (firmware v1.1.156)
- Size: 1,595,605 bytes (`0x1858D5`)
- SHA256: `617c3efea92399b0e3ed40890dd67a75013b0132059fa713076cae68a1908ac5`
- Folder also contains `.DS_Store`; no sample folders (unlike v1.5.205)
- Same SD-root `SYSTEM UPDATE` flow as v1.5.205

## Hardware context

Same platform as v1.5.205 (see `../Lofi-12XT_v1.5.205/Lofi-12XT_v1.5.205/reversed.md`):
TI TMS320C6748 (ARM9 + C674x DSP), DDR2 base `0xC0000000`. All `sect`
load addresses are `0xC2xxxxxx` (DDR2 snapshot loaded by the SPI-flash bootloader).

## Container format (same Sonicware custom format as v1.5.205)

```
[cmtd 48B][mmtd 36B][sect x7 -> EOF, exact fit]
```

### cmtd (0x00–0x2F)

| Off | Value | Meaning |
|-----|-------|---------|
| 0x00 | `cmtd` | magic |
| 0x04 | 1595605 | u32 LE filesize (matches) |
| 0x08 | `0xF58AF539` | u32 checksum (?) — differs per version, algorithm TBD |
| 0x10–0x2F | `(12, 1, 3, 1, 1, 156, 48, 1595557)` | container (?, 1, 3), fw (1, 1, 156), hdr len 48, remaining |

### mmtd (0x30–0x53)

| Off | Value | Meaning |
|-----|-------|---------|
| 0x30 | `mmtd` | magic |
| 0x34 | 1595557 | remaining size |
| 0x38 | `6e 25 13 20 ff ff ff ff` | timestamp/flags? (build-specific) |
| 0x40 | `(1, 1, 156)` | fw version |
| 0x4C | `0xC26C4820` | **entry point** (inside big code sect, verified below) |
| 0x50 | 7 | sect count |

### sects

| # | File off | Load addr | Len | End addr | Role |
|---|----------|-----------|-----|----------|------|
| 0 | 0x000054 | C27753B8 | 85912 (`0x14F98`) | C278A350 | asset/blob |
| 1 | 0x014FF8 | C2774C6C | 656 (`0x290`) | C2774EFC | float table |
| 2 | 0x015294 | C2775000 | 512 (`0x200`) | C2775200 | record table |
| 3 | 0x0154A0 | C2589800 | 1389120 (`0x153240`) | C26DCA40 | **main code (.text), C6000 DSP** |
| 4 | 0x1686EC | C2589508 | 8 | C2589510 | zeros (gap/patch slot, same as v1.5.205) |
| 5 | 0x168700 | C2755488 | 115561 (`0x1C369`) | C27718F1 | **.rodata/.data** (all readable strings) |
| 6 | 0x184A75 | C27737F8 | 3668 (`0xE54`) | C277464C | float ramp tail |

Chain verified: `next_off = off + 12 + len`, ends exactly at EOF (`0x1858D5`).
Memory tiling: code `C25895xx–C26DCA40`, data `C2755488–C277464C` (same
code→data→assets split as v1.5.205, just at lower DDR addresses).

## Code identification

- Entry `0xC26C4820` → file off `0x1504CC`. C64x-LE disassembly:
  `ZERO b0; mvc b0,ier; mvc b0,csr; mvk 0x37f4,b15; mvklh -0x3d89,b15;
  and -8,…` — identical reset prelude shape as v1.2.179/v1.5.205, only the
  stack immediates differ. Confirms C6000 DSP code.
- Big sect entropy 6.890, zeros 175,494 (12.6%) — same code+data mix as v1.5.205.
- String sect cross-refs: 5,854 words into code range + 2,932 self-pointers
  (vs 6,362 + 3,141 in v1.5.205 — table growth with features).
- Total `strings>=4`: 10,902 (vs 11,110 in v1.2.179; v1.5.205 higher).

## Data sect contents (file 0x168700–0x184A75)

- Same C674x crash dumper (`Legacy NMI Exception`, `IERR=`, `A0=…A31=`, `B0=…B31=`,
  `NTSR/ITSR/IRP/SSR/AMR`, `14AppSongBrowser`, `N3HAL…Driver`, libc++ `NSt3__`).
- Older `FileUtil` API shape: signatures use `(…S1_S1_PA256_c…Fv…)` /
  `(…S1_jjPjS2_…)`; **no `removeResourceFork`** symbols at all (present in v1.5.205),
  and no `Rb` (bool) params — file-DB / resource-fork handling postdates this build.
- v1.5-only feature strings absent: `Snip Loop` 0 hits, `PATTERN MIXDOWN` 0,
  `AUDIO EXPORT` 0. (`Isolator` 1 hit, `Reverse` 1, `Compressor` 2 — isolated
  pre-existing occurrences, not the v1.5 master-FX set.)

## Differences vs newer builds

| | v1.1.156 | v1.2.179 | v1.5.205 |
|---|---|---|---|
| size | 1,595,605 | 1,606,197 | 1,707,049 |
| nsect | 7 (with 8 B patch slot) | 6 (slot absent) | 7 (slot back) |
| code len | 1,389,120 | 1,399,200 | 1,490,112 |
| strings len | 115,561 | 117,825 | 125,081 |
| code base | C2589800 | C258D800 | C2B80C00 |
| entry | C26C4820 | C26CA4C0 | C2CD1AA0 |

v1.1→v1.2 is a small delta (+10 kB code); v1.2→v1.5 is the big jump (+91 kB code,
+7 kB strings: audio export, 4 new master FX, 16 slices, MIDI Note Map, …).