# mfsk-core
[](https://github.com/jl1nie/mfsk-core/actions/workflows/ci.yml)
[](https://crates.io/crates/mfsk-core)
[](https://docs.rs/mfsk-core)
[](LICENSE)
Pure-Rust library for **WSJT-family digital amateur-radio modes** — a
single crate that implements FT8, FT4, FST4, WSPR, JT9, JT65 and
Q65-30A decode / encode / synthesis on top of a small set of shared
primitives (DSP, sync correlation, LLR, LDPC / convolutional /
Reed-Solomon / QRA FEC, message codecs).
## Why this exists
[WSJT-X](https://sourceforge.net/projects/wsjt/) is the reference
implementation of these modes and will stay that way — it is
battle-tested on the desktop, heavily optimised, and the source of
truth for every protocol constant you will find in this crate. But
it is also a mixed Fortran / C / Qt application built around a
specific desktop workflow. That makes it a poor fit whenever you
want to run the decoders *somewhere else*:
- in a **browser** as a WASM PWA,
- on **Android or iOS** for portable operation, where linking a
Fortran runtime is a non-starter,
- in a **headless Rust application** (skimmer, monitoring station,
remote SDR front end),
- on **embedded MCUs** (ESP32-S3 with esp-dsp, RP2350 with CMSIS-DSP,
Cortex-M) via `no_std + alloc` — the M5Stack Core2 PoC decodes 3–7
FT8 results per 15 s cycle on Xtensa LX6 with the fixed-point hot
path,
- or as the core of a **new protocol experiment** that reuses FT8's
LDPC and sync machinery for a different modulation / FEC /
message recipe.
The seven protocols share roughly 80 % of their signal path. In the
Fortran codebase that commonality is expressed by copy-and-paste
between per-mode source files; here it is expressed by traits.
## The abstraction
```text
┌────────────────────────────────────────────────────────┐
│ ft8 ft4 fst4 wspr jt9 jt65 q65 │ per-protocol ZSTs
│ (each implements Protocol + FrameLayout) │ (feature-gated)
└─────────────┬─────────────────┬────────────────────────┘
│ │
┌────────▼─────────┐ ┌────▼─────────┐
│ msg │ │ fec │ shared codecs
│ Wsjt77 · Jt72 │ │ LDPC · RS │ behind traits
│ Wspr50 · Q65 │ │ ConvFano·QRA │
│ · Hash table │ │ │
└────────┬─────────┘ └────┬─────────┘
│ │
┌───▼─────────────────▼───┐
│ core │ Protocol trait, DSP
│ sync · llr · equalize · │ (resample / GFSK /
│ pipeline · tx · dsp │ downsample / subtract)
└─────────────────────────┘
```
Each protocol declares its slot length, tone count, Gray map, Costas
/ sync pattern, FEC codec and message codec at compile time via the
`Protocol` trait. The generic code in `core` — coarse sync, fine
sync, LLR computation, LDPC / RS / convolutional decode, GFSK
synthesis — works for any type that satisfies the trait. Dispatch is
monomorphised, so the machine code is byte-identical to a hand-
written per-protocol decoder.
Adding a new protocol is a trait impl on a ZST, not a cross-cutting
refactor: FST4-60A joined the crate post-hoc without changing any
shared pipeline code.
The receive path is a chain of free functions in `core::sync` →
`core::llr` → `core::equalize` → `core::pipeline` (each generic
over `P: Protocol`), not a `Demodulator` / `Receiver` trait. See
[`docs/LIBRARY.md` §4](https://github.com/jl1nie/mfsk-core/blob/main/docs/LIBRARY.md#4-shared-primitives-core)
for the data-flow diagram.
```toml
[dependencies]
mfsk-core = { version = "0.6", features = ["ft8", "ft4"] }
```
## Attribution
Every algorithm in this crate is derived from
[WSJT-X](https://sourceforge.net/projects/wsjt/) (Joe Taylor K1JT and
collaborators). Source files cite the corresponding upstream
`lib/ft8/*`, `lib/ft4/*`, `lib/fst4/*`, `lib/wsprd/*`, `lib/jt65_*`,
`lib/jt9_*`, `lib/packjt.f90`, etc. that they port from. This is a
Rust re-implementation aimed at broadening the set of platforms
(browser / WASM, Android, embedded) that can host the decoders —
**not** a replacement for WSJT-X itself, which remains the reference
implementation.
License matches upstream: **GPL-3.0-or-later**.
## Protocols
| FT8 | 15 s | LDPC(174, 91) + CRC-14 | 77 bit | 3 × Costas-7 | `ft8` |
| FT4 | 7.5 s | LDPC(174, 91) + CRC-14 | 77 bit | 4 × Costas-4 | `ft4` |
| FST4-60A | 60 s | LDPC(240, 101) + CRC-24 | 77 bit | 5 × Costas-8 | `fst4` |
| WSPR | 120 s | Convolutional r=½ K=32 + Fano | 50 bit | Per-symbol LSB (npr3) | `wspr` |
| JT9 | 60 s | Convolutional r=½ K=32 + Fano | 72 bit | 16 distributed slots | `jt9` |
| JT65 | 60 s | Reed-Solomon(63, 12) GF(2⁶) | 72 bit | 63 distributed slots | `jt65` |
| Q65-30A | 30 s | QRA(15, 65) GF(2⁶) + CRC-12 | 77 bit | 22 distributed slots | `q65` |
| Q65-60A‥E | 60 s | (same QRA codec) | 77 bit | (same sync layout) | `q65` |
Seven protocol families, eleven wired ZSTs in the registry: Q65 contributes one
30-s sub-mode (Q65-30A) plus five 60-s EME sub-modes (Q65-60A‥E) that share
the FEC, message codec and sync layout but differ in NSPS / tone spacing.
[`PROTOCOLS`](https://docs.rs/mfsk-core/latest/mfsk_core/static.PROTOCOLS.html)
exposes one entry per wired ZST; `uvpacket` (when enabled) adds four
more for its rate ladder.
### Static set of protocols
`PROTOCOLS` is a `const` slice — the set of supported protocols is
fixed at compile time by Cargo features. There is no runtime
`register_protocol()` API by design: every wired ZST is verified by
`tests/protocol_invariants.rs` to satisfy the trait surface, and that
guarantee can't be extended to types unknown at compile time. UI /
FFI consumers should iterate `PROTOCOLS` (or filter via `by_id` /
`by_name`) at startup; if you need a new protocol, add the ZST + a
`protocol_meta!` line and rebuild.
### Applied example: `uvpacket` (experimental)
The `uvpacket` module (`--features uvpacket`, off by default) is
an in-tree example showing the trait abstractions extend beyond
WSJT-X — a π/4-DQPSK packet protocol for NFM / SSB voice channels
that reuses the shared `Ldpc240_101` codec. **Experimental and
its public API may change** — pin to an exact version. See
[`docs/UVPACKET.md`](https://github.com/jl1nie/mfsk-core/blob/main/docs/UVPACKET.md)
([日本語](https://github.com/jl1nie/mfsk-core/blob/main/docs/UVPACKET.ja.md))
for the design narrative, modulation / equaliser / framing details
and per-mode performance characterisation.
## Modules
- `mfsk_core::core` — protocol traits, DSP (resample / downsample /
GFSK / subtract), sync, LLR, equaliser, pipeline driver.
- `mfsk_core::fec` — `Ldpc174_91` / `Ldpc240_101` / `ConvFano` /
`ConvFano232` / `Rs63_12` / `qra::Q65Codec` (with the
`qra15_65_64::QRA15_65_64_IRR_E23` code instance) for Q65.
- `mfsk_core::msg` — 77-bit (`Wsjt77Message`), 72-bit (`Jt72Codec`),
50-bit (`Wspr50Message`) and Q65 (`Q65Message`, 77-bit ↔ 13-symbol
packing helpers) message codecs; callsign hash table.
- `mfsk_core::{ft8, ft4, fst4, wspr, jt9, jt65, q65}` — per-protocol
ZSTs, decoders and synthesisers (each feature-gated). The `q65`
module exposes one ZST per wired sub-mode — `Q65a30` for
terrestrial work, plus `Q65a60` / `Q65b60` / `Q65c60` / `Q65d60` /
`Q65e60` for EME at 6 m through 10 GHz+ — with generic
`synthesize_standard_for<P>` / `decode_at_for<P>` / `decode_scan_for<P>`
helpers that pick the right NSPS and tone spacing from the type
parameter.
## Features
| `ft8` | ✓ | FT8 decode / synth |
| `ft4` | ✓ | FT4 decode / synth |
| `fst4` | | FST4-60A decode / synth |
| `wspr` | | WSPR decode / synth |
| `jt9` | | JT9 decode / synth |
| `jt65` | | JT65 decode / synth (+ erasure-aware RS) |
| `q65` | | Q65-30A decode / synth (QRA soft-decision) |
| `uvpacket` | | Applied example *(experimental)*: NFM voice-channel packet protocol (QPSK + LDPC), reuses `Ldpc240_101` |
| `full` | | Aggregate of all seven WSJT protocols + uvpacket + packet-bytes |
| `parallel` | ✓ | Rayon-parallel candidate processing |
| `fft-rustfft` | ✓ | Default host FFT backend (`rustfft`, requires `std`) |
| `fft-extern` | | Pluggable FFT trait — caller binary supplies an `FftPlanner` impl (esp-dsp on ESP32-S3, CMSIS-DSP on RP2350, …) |
| `fixed-point` | | Embedded integer pipeline: u16 spectrogram + i16 DFT + Q11i16 LLR + integer NMS BP |
| `profile-coarse` | | Always-on coarse_sync sub-stage profiling (host has `MFSK_PROFILE_COARSE` env var alternative) |
## Quick example
```rust
use mfsk_core::ft8::{
decode::{decode_frame, DecodeDepth},
wave_gen::{message_to_tones, tones_to_i16},
};
use mfsk_core::msg::wsjt77::{pack77, unpack77};
// 1. Synthesise an FT8 frame and pad it into a 15-second slot.
let msg77 = pack77("CQ", "JA1ABC", "PM95").unwrap();
let tones = message_to_tones(&msg77);
let frame = tones_to_i16(&tones, /* freq */ 1500.0, /* amp */ 20_000);
let mut audio = vec![0i16; 180_000]; // 15 s @ 12 kHz
let start = (0.5 * 12_000.0) as usize;
for (i, &s) in frame.iter().enumerate() {
if start + i < audio.len() { audio[start + i] = s; }
}
// 2. Decode it back.
for r in decode_frame(&audio, 100.0, 3_000.0, 1.0, None, DecodeDepth::BpAllOsd, 50) {
if let Some(text) = unpack77(&r.message77) {
println!("{:7.1} Hz dt={:+.2} s SNR={:+.0} dB {}",
r.freq_hz, r.dt_sec, r.snr_db, text);
}
}
```
Each protocol module documents its top-level entry points and
carries its own Quick example:
- [`mfsk_core::ft8`](https://docs.rs/mfsk-core/latest/mfsk_core/ft8/)
— `decode_frame` + `decode_sniper_ap` (narrow-band "sniper" mode)
- [`mfsk_core::ft4`](https://docs.rs/mfsk-core/latest/mfsk_core/ft4/)
— `decode_frame`
- [`mfsk_core::fst4`](https://docs.rs/mfsk-core/latest/mfsk_core/fst4/)
— FST4-60A `decode_frame`
- [`mfsk_core::wspr`](https://docs.rs/mfsk-core/latest/mfsk_core/wspr/)
— `decode::decode_scan_default`
- [`mfsk_core::jt9`](https://docs.rs/mfsk-core/latest/mfsk_core/jt9/)
— `decode_scan_default`
- [`mfsk_core::jt65`](https://docs.rs/mfsk-core/latest/mfsk_core/jt65/)
— `decode_scan_default` + `decode_at_with_erasures` (for low SNR)
- [`mfsk_core::q65`](https://docs.rs/mfsk-core/latest/mfsk_core/q65/)
— `decode_scan_default` (Q65-30A); generic `decode_scan_for<P>`
for any wired sub-mode including the Q65-60A‥E EME variants;
`decode_scan_with_ap` / `decode_scan_with_ap_for<P>` for AP-hint
decoding (~2 dB threshold gain when call signs are known); and
`decode_scan_fading_for<P>` for the fast-fading metric (Gaussian
/ Lorentzian channel models) that recovers 5–8 dB on Doppler-spread
channels — required for microwave EME at 5.7 / 10 / 24 GHz; and
`decode_scan_with_ap_list_for<P>` (paired with `standard_qso_codewords`)
for BP-free template matching against the full WSJT-X "AP list"
of standard exchanges (~3 dB threshold gain when the callsign pair
is known up-front)
## C / C++ / Kotlin
The `mfsk-ffi` sibling crate in this repository builds a
`libmfsk.{so,a,dylib}` + `mfsk.h` (via `cbindgen`) that exposes the
same decoder and synthesiser surface through an opaque-handle C ABI.
`mfsk-ffi` is not published to crates.io — consumers clone this repo and run:
```
cargo build -p mfsk-ffi --release
```
See `mfsk-ffi/examples/cpp_smoke/` for an end-to-end driver test
(including multi-threaded usage) and `mfsk-ffi/examples/kotlin_jni/`
for an Android/JNI skeleton.
## Contributing
PRs welcome — recent forks have shipped FT4 SIC, FT4/FST4 depth +
strictness controls, and the FT8 wide-band AP path. The local-fence
+ CI gates are uniform across direct commits and fork PRs:
- **Pre-commit hook**: `.githooks/pre-commit` runs `cargo fmt --check`,
`cargo clippy --workspace --all-targets --features full -- -D warnings`,
and `RUSTDOCFLAGS=-D warnings cargo doc -p mfsk-core --features full
--no-deps` (~10–20 s on a warm cache). Enable once per clone:
```sh
git config core.hooksPath .githooks
```
The hook deliberately skips the full `cargo test` suite (kept in
CI to keep commits snappy); fmt / clippy / rustdoc each catch a
failure mode that would otherwise trip CI after the push.
- **CI gates** (`.github/workflows/ci.yml`): same fmt + clippy
fence, plus `cargo test -p mfsk-core --features full --release --
--include-ignored` (slow synthetic-SNR / AP / fast-fading sweeps
enabled), a 13-cell feature matrix that builds every protocol in
isolation + the embedded `alloc + ft8 + fft-extern + fixed-point`
preset, the C++ driver against `mfsk-ffi`, rustdoc with `-D warnings`,
and a `cargo publish --dry-run` for `mfsk-core`.
- **Release**: tag-driven (`v0.6.x`). Pushing a tag that matches
`mfsk-core/Cargo.toml::version` and is reachable from `main`
triggers `release.yml`, which publishes to crates.io and cuts a
GitHub release with auto-generated notes. Embedded `mfsk-ffi-ft8`
binaries follow on the same tag.
For non-trivial changes, please open an issue first so the
WSJT-X-source-faithfulness lineage of any DSP or FEC change is
visible in review (every protocol constant in this crate cites the
upstream `lib/*.f90` it ports from — drift from that lineage tends
to be the failure mode caught by the WSJT-X golden harnesses).
## Architecture & ABI reference
For a deeper look at the design — trait hierarchy with worked
examples, shared DSP / sync / LLR / pipeline primitives, the C ABI
memory model, Kotlin/Android scaffolding — see the library
reference:
- **English:** [`docs/LIBRARY.md`](https://github.com/jl1nie/mfsk-core/blob/main/docs/LIBRARY.md)
- **日本語:** [`docs/LIBRARY.ja.md`](https://github.com/jl1nie/mfsk-core/blob/main/docs/LIBRARY.ja.md)
- **Embedded targets:**
[English `docs/EMBEDDED.md`](https://github.com/jl1nie/mfsk-core/blob/main/docs/EMBEDDED.md)
/ [日本語 `docs/EMBEDDED.ja.md`](https://github.com/jl1nie/mfsk-core/blob/main/docs/EMBEDDED.ja.md)
— generic-scalar architecture (one codebase for f32 host and
fixed-point embedded), feature-flag map, FFT / dot-product extern
contracts, BASIS scratch placement, Q-format reference, Core2 perf
ballpark + footprint.
## Status
`0.6.x` — API is deliberately not frozen. Breaking changes follow
cargo-style minor bumps (`0.5 → 0.6`). The 0.5.x line landed the
embedded baseline (`no_std + alloc`, pluggable FFT backend,
caller-buffer TX APIs) and the first end-to-end real-audio embedded
port. The **0.6.x line consolidates the FT8 sync + per-candidate
pipeline**: host (`decode_frame*`) and embedded (`decode_block`) now
share `decode_block::coarse_sync` (WSJT-X `sync8.f90`-faithful 16-bin
allsum estimator) and a unified `process_one_candidate_inner` for the
LLR / BP / OSD / AP staircase. See `CHANGELOG.md` for the full per-
release breakdown.
Latest M5StickS3 (Xtensa LX7) ship config decodes **6 / 18 JTDX-golden
FT8 callsigns + 1 bonus = 7 total** on the WSJT-X-distributed busy-band
reference (`samples/FT8/210703_133430.wav`) in **~1.19 s post-SlotEnd**
via the streaming pipeline (FFT overlapped with capture). The 0.6.2
LLR migration (`Q3i8 → Q11i16`, double-width but better precision under
esp-dsp i16 spectrogram noise) added one entry (XE2X HA2NP RR73) over
the 0.5.x baseline. M5Stack Core2 (LX6) on the same WAV ~2.8 s. See
[`docs/EMBEDDED.md`](https://github.com/jl1nie/mfsk-core/blob/main/docs/EMBEDDED.md)
for the integration contract, runtime BP / `nstep-half` tuning knobs,
and the structural recall ceiling (no `fine_refine_pass1` on Xtensa
without 192k FFT — investigated and deferred);
`embedded-poc/m5stack-s3-app/` and `embedded-poc/m5stack-core2-app/`
are the production FT8 controller crates (LCD UI + QSO FSM +
WiFi-UDP log streaming) — both consume the board-agnostic
`embedded-poc/mfsk-app-shared/` (carved out as part of
[#61](https://github.com/jl1nie/mfsk-core/issues/61), closed in
0.6.3). `embedded-poc/m5stack-s3/` is the remaining decoder-only
compute-bench crate for S3 timing-regression tracking; the matching
Core2 bench was retired in #61 Phase 3 (M5Stack Core2 timing is
now measured through `m5stack-core2-app` itself).
Host AP-on multipass recall on the same WAV is materially higher.
After 0.6.2's host pipeline catch-up (cs-source unification +
`subtract_signal_lpf` matching `decode_block_multipass`),
`decode_frame_subtract_with_ap` produces **18 decodes** including
**5 / 6 of the JTDX AP-on extras** (was 1 / 6 pre-0.6.2). The single
remaining AP-on extra (K1BZM DK8NE -19 dB) needs a wider AP-list /
callsign hash table — out of 0.6.x scope.
Algorithm correctness is covered by the workspace test suite:
end-to-end synth → decode roundtrips for every protocol, an AWGN
sensitivity sweep that confirms Q65-30A hits its WSJT-X-published
−24 dB threshold, an AP-vs-plain comparison that shows the expected
~2 dB gain from a-priori call sign information, an AP-list
(template matching) comparison that decodes 6/6 frames at SNR −25 dB
where plain BP fails 0/6, a real 6 m EME recording (W7GJ exchanges
from the WSJT-X reference set), and a real 10 GHz EME recording that
the fast-fading metric is required to decode. The trait surface
itself is pinned by `tests/protocol_invariants.rs` — a single generic
`<P: Protocol>` checker run across every wired ZST. Run with
`--features full` for the eleven-ZST coverage; the default features
(`ft8`, `ft4`) only exercise the two default protocols.
Recall against the **WSJT-X-distributed reference recordings**
(`samples/{WSPR,FT4,JT9}/*.wav`) is locked by golden harnesses in
`tests/{wspr,ft4,jt9}_wsjtx_samples.rs` (run only when the WSJT-X
tree is present at the expected sibling path):
| `WSPR/150426_0918.wav` (8 frames) | **8 / 8** | sub-bin demod + neg-dt |
| `FT4/000000_000002.wav` (6 frames) | **6 / 6** | Nuttall + sync4d |
| `JT9/130418_1742.wav` (5 frames) | **5 / 5** | full WSJT-X-faithful softsym pipeline (afc9 + chkss2 + xx0 mettab + sync9 collapse) |
| `MSK144/181211_120500.wav` (n/a) | — | not implemented — [#25](https://github.com/jl1nie/mfsk-core/issues/25) |
| `JT65/*` (n/a) | — | golden harness pending — [#24](https://github.com/jl1nie/mfsk-core/issues/24) |
| `FST4/210115_0058.wav` (1 frame) | — | golden harness pending — [#23](https://github.com/jl1nie/mfsk-core/issues/23) |
#### Known limitations / quirks
- **JT65** — `decode_scan` decodes synthesised JT65A frames cleanly
via the Reed-Solomon(63, 12) FEC and the AP-list path lifts weak
signals to within ~2 dB of WSJT-X. There's no golden WAV in this
crate's regression set because the WSJT-X v3 reference samples
themselves don't decode cleanly without the soft-symbol erasure
metadata that lives in private WSJT-X branches. Tracked in
[#24](https://github.com/jl1nie/mfsk-core/issues/24).
- **FST4** — only the FST4-60A long-period variant is wired (sample
duration / Costas layout for FST4-15 / FST4W are out of scope of
the 0.5.x line). Recall against `samples/FST4/210115_0058.wav` is
not yet locked by a golden harness — tracked in
[#23](https://github.com/jl1nie/mfsk-core/issues/23).
- **MSK144** — not implemented in 0.5.x. The decode path needs a
different correlator geometry from the rest of the FT/JT/Q-family
decoders this crate is built around. Tracked in
[#25](https://github.com/jl1nie/mfsk-core/issues/25).
#### What's solid
- **FT8** — synth → decode round-trip lib tests green, real WSJT-X
reference (`210703_133430.wav`):
- **WSJT-X 8-entry golden: 7 / 8** (host `decode_frame_with_ap` and
embedded `decode_block` both, post-0.6.0 sync consolidation +
`i_start as i32` fix).
- **JTDX 18-entry golden: 16 / 18** (`decode_block`).
- **Host AP-on multipass JTDX-extras: 5 / 6** (was 1 / 6 pre-0.6.2)
via `decode_frame_subtract_with_ap` after the cs-source +
`subtract_signal_lpf` unification.
- **Embedded S3 fixed-point: 6 / 18 + 1 bonus = 7 total** in
~1.19 s post-SlotEnd. AP-hint biasing exposed on the narrow-band
(`decode_sniper_ap`), wide-band single-pass (`decode_frame_with_ap`),
multipass (`decode_frame_subtract_with_ap`) and embedded
(`decode_block_with_ap`, new in 0.6.1) paths.
- **WSPR** — 8 / 8 WSJT-X golden, ~0.88 s end-to-end on a desktop
build. Sub-bin demod + 2-pass subtract+re-coarse + OSD-2 fallback +
Type-3 phantom filter.
- **FT4** — 6 / 6 WSJT-X golden after the 0.5.9 multi-slice port of
the WSJT-X demod path (Nuttall window, `nsym = 4` LLR aggregation,
`sync4d` 2-pass refine, `rvec` scrambler). Successive-interference
cancellation primitives (`subtract_signal*`, `refine_signal_freq`)
ported from `lib/ft4_subtract.f90`. WSJT-X Decode menu (Fast /
Normal / Deep) exposed via `decode_frame_with_options` for FT4
and FST4-60A.
- **JT9** — 5 / 5 WSJT-X golden on `samples/JT9/130418_1742.wav`
via the full WSJT-X-faithful softsym pipeline (`afc9` + `chkss2`
+ `xx0` mettab + `sync9` per-freq collapse). Closed [#19](https://github.com/jl1nie/mfsk-core/issues/19).
- **Q65** — fast-fading + AP-list paths exercise both the WSJT-X
6 m EME and the 10 GHz EME reference recordings.
- **SNR (FT8)** — `xsnr2_db_simple` calibration (0.5.7 + 0.5.8) lands
reported SNR within ±3 dB of JTDX absolute on real silicon.