arq: MFSK weak-signal backend + delivery-driven stop-and-wait rethink by rafael2k · Pull Request #125 · Rhizomatica/mercury

rafael2k · 2026-07-18T09:43:40Z

What

A ground-up rethink of the ARQ data plane plus a second modem backend, rebased onto the v1.9.10 base.

Modem abstraction (the intended v2 design):

modem_backend_t vtable — FreeDV is backend 1, and a new MFSK weak-signal backend (backend 2, MERCURY_MODE_MFSK).
Welch-Costas pattern ACK — ~0.64 s and survives ~10 dB deeper than a DATAC16 ACK.

Data-flow FSM — simpler, faster:

21 → 11 states; data flow 15 → 5 (IDLE_ISS → DATA_TX → WAIT_ACK, IDLE_IRS → ACK_TX), piggyback turn handoff.
Delivery-driven mode ladder, no SNR: starts at the most robust rung (MFSK) and climbs on clean deliveries, steps down on any retry.
Single retained tx_frame (no window/restage); removes OLLA/SNR interlock, MODE/TURN/KEEPALIVE negotiation, and the restage buffer.
Designed for asymmetric links (per-direction adaptation + robust pattern ACK on the reverse path).

Validation (deterministic instruments — full green)

Unit + sim suite: 172 tests / 15 binaries, all pass; native mercury builds clean on the rebased tree.
Two-FSM sim (test_arq_sim, 17 scenarios): clean, 20% loss, fade-cliff → MFSK downgrade, asymmetric strong-forward, bidirectional piggyback turn, lost-ACK idempotency, + flat/fading fuzz.
Ladder (5) and pattern-ACK DSP detection (3, incl. 0 false-alarm on noise).
ab_bench throughput/integrity matrix (18 runs, clean/awgn/cliff/nvis): integrity OK on 100%; ladder climbs to top on clean links and drops to the MFSK floor on harsh channels.

⚠️ Merge gate

Do not merge until on-air validation (task 31 — São Roque ↔ Belo Horizonte, sbitx -S). The sims are the pre-OTA instrument; the real gate is Pedro's OTA run. Opening now for review.

Rebased onto v1.9.10 (c1e8f56); 13 commits, no conflicts.

🤖 Generated with Claude Code

…ison Pure-C port of Mercury v1's cl_mfsk (non-coherent M-FSK over OFDM subcarriers, originally Fadi Jerji): class -> struct+functions, std::complex<double> -> a plain {double re,im} struct, std::isfinite -> C99 isfinite; all tone tables (preamble, Welch-Costas ACK/BREAK, Sidelnikov NB, directed-HAIL FNV-1a suffix) carried over. Compiles clean (-Wall -Wextra); tests/modem/test_mfsk.c proves mod->demod is lossless (M=4/8/16/32) and that higher M is more robust. Measured (uncoded non-coherent BER vs Eb/N0, freq-domain AWGN/Rayleigh): v1's 32-MFSK buys ~6 dB over 2-FSK on AWGN/steady channels but only ~1.5-2 dB under fast fading. Combined with the earlier finding (2-FSK FSK_LDPC already beats DATAC15 on MPP), the fringe lever is going non-coherent FSK; 32-MFSK adds real gain on calm-NVIS/steady channels. This C port makes v1's 32-MFSK available to wire into a v2 weak-signal ARQ-ladder bottom rung (framing/sync/LDPC glue TBD). See docs/MFSK-PORT.md. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

The real question for a weak-signal mode is acquisition, not just modulation. Record what is confidently known: v1's MFSK carries its own non-coherent preamble detector (not OFDM coherent sync), and the codec2 FSK_LDPC end-to-end figures (acquisition included) already beat DATAC15 at the fringe — so the non-coherent-FSK class is not acquisition-limited the way OFDM is. Also record the limitation: an isolated MFSK acquisition sim confirmed detector mechanics but could not be calibrated to the SNR3k axis; a trustworthy MFSK-specific floor needs end-to-end integration (framing + time_sync_mfsk_corr + LDPC in ch), the next step. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

The MFSK-relevant slice of v1's cl_ofdm: self-contained radix-2 FFT/IFFT (no FFT-library dependency), subcarrier zero-pad/de-pad (DC-centred v1 layout), and cyclic-prefix add/remove. fft is 1/N-normalized, ifft unnormalized (v1 convention) so the pair is identity. This carries mfsk.c's tone bins to/from OFDM time-domain symbols — the framing layer needed to run the MFSK mode through a real channel end-to-end. Validated by a round-trip unit test (bins -> pad -> ifft -> +CP -> -CP -> fft -> depad recovers bins at machine precision). Next: port time_sync_mfsk_corr (non-coherent acquisition) + baseband channel + LDPC to measure the MFSK acquire+decode floor vs DATAC15. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Pure-C port of v1 cl_ofdm::time_sync_mfsk_corr: non-coherent (envelope) matched-filter preamble detection — two-phase search (coarse 4x-oversampled + fine), per-symbol normalized correlation averaged over the preamble symbols, per-symbol floor 0.05, threshold 0.5, earliest-strong-preamble early exit. Needs no phase/frequency lock, so it acquires below the coherent-OFDM floor — this is the acquisition path the MFSK weak-signal mode uses (not OFDM coherent sync). mfsk_sync_build_template() builds the preamble time template via the mfsk + ofdm framing. Unit test plants the template in a noise buffer: detected at the right offset (high SNR), rejected on pure noise. With mfsk.c (codec) + mfsk_ofdm.c (framing) + mfsk_sync.c (acquisition), the MFSK mode's TX/RX signal-processing core is now in C. Remaining for an SNR3k-comparable end-to-end floor vs DATAC15: baseband<->passband + carrier + interpolation chain through ch (large; the SNR3k calibration lives there). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

…s the concern) Wired the ported MFSK core (mfsk.c + mfsk_ofdm.c + mfsk_sync.c) into a real passband pipeline through codec2 `ch` (SNR3k measured exactly as for DATAC15). Result: v1's non-coherent MFSK acquisition holds (metric 0.6-0.9) far below DATAC15's ~-7 dB acquisition wall — to ~-13 dB SNR3k on AWGN (matching v1's claim) and past -11 dB on MPP fading (uncoded BER <=3%, where DATAC15 delivers 22%), before any LDPC. Acquisition is NOT the bottleneck; the mode carries its own. Replaces the earlier "couldn't measure trustworthily" caveat with the ch-calibrated numbers. Remaining work is wiring it as an actual ARQ-ladder mode (LDPC + mode-pool + OLLA), not whether it can acquire. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

…floor) Port v1's ROBUST_0 FEC — rate-1/16 LDPC (N=1600, K=100): systematic IRA encoder (mfsk_ldpc_encode) + normalized min-sum BP decoder (mfsk_ldpc_decode) over the v1 quasi-cyclic Tanner graph, matrix embedded in mfsk_ldpc_1_16.c. Verified: encoder produces valid codewords (H*c=0), noiseless encode->decode lossless (unit test). Wired end-to-end through the passband/ch pipeline (TX info->encode ->32-MFSK->passband->ch->RX acquire->demod->LDPC decode). Coded floor (15 frames/point): delivered == acquired everywhere — once acquired the code always decodes, so the mode is acquisition-limited, not decode-limited. Coded MFSK delivers ~2-3 dB deeper than DATAC15 on fading (47% at -10.8 dB SNR3k vs DATAC15 22%; 33% at -12.8 where DATAC15 ~0). Next lever is acquisition (postamble / longer preamble), not the code. See docs/MFSK-PORT.md. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

…ison Since the coded MFSK mode is acquisition-limited, add a postamble: a second known-tone sequence (distinct tones, +2 offset) after the payload, so RX syncs on preamble OR postamble. mfsk_generate_postamble + mfsk_sync_build_postamble_ template; harness does dual-ended search. Measured (MPP, coded, same rx file): dual-ended buys ~2 dB — 87% vs 60% delivery at -10.8 dB SNR3k, 100% vs 80% at -8.8. Full mode comparison (MPP, delivered %): dual-ended coded MFSK 100/87/67/20 at SNR3k -8.8/-10.8/-12.8/-14.8 vs DATAC16 63/40/20, DATAC15 50/33/3, DATAC1/DATAC3 0. The MFSK weak-signal mode extends the floor ~3-4 dB below the most robust OFDM modes, at ~8 bps (deep-fringe bottom rung). Unit test added for the postamble. See docs/MFSK-PORT.md. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

… was wrong Generalise mfsk_ldpc to a code-descriptor + registry and port v1's full rate ladder: 1/16, 2/16, 3/16, 5/16, 8/16 (rate 1/2), all N=1600 (same airtime), payload K/8 = 12.5..100 bytes. Generic systematic IRA encoder + min-sum decoder take a mfsk_ldpc_code_t; unit test validates encode->H*c=0->noiseless-decode for all five rates. Measured (32-MFSK, dual-ended, MPP through ch): all rates deliver identically (delivered==acquired; even rate 1/2 decodes everything acquired down to the acquisition floor, since the 32-MFSK demod hands the code very clean LLRs). So the LDPC rate barely affects the floor — it only sets payload. 1/16 (12.5 B) was the wrong default: it can't even fit the 14-byte CONNECT frame, whereas 8/16 (100 B, ~60 bps, ~DATAC15 throughput at ~3-4 dB more robustness) does. Recommend shipping a small ladder (5/16, 8/16) for OLLA. Caveat: "rate is free" holds in idealised sim (no freq offset / drift over the ~13 s frame); real HF may favour shorter frames — set the ceiling OTA. See docs/MFSK-PORT.md. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Port cl_ofdm::detect_ack_pattern (Phase-1 peak-bin match count) to pure C as mfsk_detect_pattern in mfsk_sync.c, over the depadded-bins framing (same path as mfsk_demod) rather than v1's raw-FFT-bin + carrier-image handling, which this pipeline's LPF+depad already covers. Measured pattern-ACK vs a codec2 DATAC16 ACK through ch/Watterson: an ACK burst is 0.64s (vs 3.74s DATAC16, 5.8x less airtime) and survives ~10-12 dB deeper on fading -- 100% to ~-9 dB / >75% to ~-13 dB on moderate+poor, where DATAC16 is dead by ~-5 dB. Pure-noise false-alarm gate: 0/30 down to -26 dB. This directly addresses the reverse-path ACK-survival blocker; confirms v1's split of coded MFSK frames (data + CONNECT) vs Welch-Costas patterns (ACK/BREAK/keepalive). Unit test: planted ACK detected, noise rejected, BREAK not confused for ACK. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Mercury's datalink is codec-agnostic (opaque frame bytes + CRC in/out), but the modem layer historically called codec2/FreeDV directly. Introduce a modem_backend_t vtable (modem_backend.h) so more than one modem architecture can coexist behind one seam -- the original mercuryv2 design intent. FreeDV becomes a first-class backend (modem_freedv.c), a 1:1 adapter over the freedv_api. - generic_modem_t and rx_decoder_state_t now hold a modem_codec_t {backend, ctx} instead of a struct freedv *. - The per-mode pool is a generic slot array keyed by mode (was a hand-enumerated freedv-only struct); clear/open/lookup dispatch through the backend. - Both DSP funnels (send_modulated_data TX, rx_decoder_consume_chunk RX) plus bind/geometry/bitrate/spectrum route through the vtable; no freedv special-case. - CRC16 (freedv_gen_crc16) stays codec-independent in the TX funnel. - mod_out_short sized to max(pre/frame/postamble) so a burst backend can't overflow it. No behaviour change: full unit suite green; TX output byte-identical to the former direct-freedv path across DATAC15/16/1/3/4/17/QAM16C2 (parity harness). This is the foundation for the MFSK weak-signal backend (Stage 2). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Add modem_mfsk.c: the non-coherent 32-MFSK burst codec behind the modem_backend_t vtable, mode MERCURY_MODE_MFSK (100, clear of the freedv enum). - TX: preamble_tx/rawdata_tx/postamble_tx build baseband OFDM (rate-1/2 LDPC, 100-byte frame) and mix to the 2 kHz passband as int16, phase-continuous across the burst. Same frame contract as freedv (98 payload + 2 CRC16). - RX: keeps its own sliding sample window and presents the freedv-style nin/rawdata_rx interface -- accumulates symbols, downmix+LPF, non-coherent preamble correlation (mfsk_sync_search), energy demod, LDPC decode, and returns bytes ONLY on CRC16-valid (freedv's contract). Detection is rate- limited to a few attempts per burst. - backend_for_mode() routes MERCURY_MODE_MFSK to it; the mfsk sources are now linked into the mercury binary and the UI core lib. Not yet a selectable mode (no pool/ladder entry) so default behaviour is unchanged -- that is Stage 3. Deterministic round-trip unit test: TX a frame -> passband -> feed the RX in nin-sized chunks -> exact bytes back, CRC-gated; pure noise never false-decodes. Full suite green. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Make MERCURY_MODE_MFSK a selectable payload mode reached only when the OLLA- corrected SNR drops below the DATAC15 floor (~-11 dB) -- deep fade only, so default behaviour is unchanged. modem.c: MFSK is now a supported + payload split mode (RX payload decoder binds to it when the peer TXes MFSK), registered in the pool, named, and given a bitrate level. arq: arq_mode_table gets the MFSK row (unique 98-byte payload so DATA-frame mode inference stays unambiguous; ~13.5s frame, generous ack/retry). New ARQ_SNR_MIN_DATAC15_DB (-11) sets the DATAC15->MFSK drop point; select_best_mode terminal now returns DATAC15 above it and MFSK below, with the standard +5 dB upgrade hysteresis so the link won't oscillate into the long MFSK frame. mode_rank(MFSK) = -1 (below DATAC15); MFSK entry is OLLA-driven, not retry-count (the hard-loss floor stays DATAC15). Session still starts at DATAC15. Deterministic test (test_arq_olla): DATAC15 held to -11, drops to MFSK at -12, and climbs back only above -6 (threshold+hysteresis). Full suite green; binary builds. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Replace the SNR/OLLA-negotiated, go-back-N, restage-buffered data-flow FSM with a simple delivery-driven stop-and-wait protocol that starts at the most robust rung (MFSK) and climbs. arq_fsm.c drops from 2466 to ~1470 LOC. - Data-flow FSM: 15 -> 5 states (IDLE_ISS/DATA_TX/WAIT_ACK/IDLE_IRS/ACK_TX); connection FSM (connect/disconnect handshake) unchanged. 21 -> 11 states. - Control ACK is now a Welch-Costas PATTERN (0.64s, ~10dB more robust than the 3.74s DATAC16 ACK it replaces) with a 2-symbol alphabet: ACK / ACK+TURN (== HAS_DATA piggyback). Emitted via ARQ_ACTION_TX_PATTERN + send_pattern_ack in modem.c; detected by a third RX consumer (mfsk_pattern_detect) that synthesizes ARQ_EV_RX_ACK. mfsk_pattern_tx/detect added to modem_mfsk. - Mode control: delivery-driven ladder MFSK->DATAC15->..->QAM16C2 indexed by speed_level (fast initial ramp, then N-clean-per-step; any retry steps down). NO SNR, NO OLLA offset, NO reverse-hold gate. Host SNR display is unaffected (it comes from decoding received DATA frames, not the ACK). - TX buffering: one immutable retained frame (raw user bytes, fixed seq<->content) instead of the 5-slot window + restage. A mode drop re-frames the same bytes at the smallest mode that still fits (mode_that_fits) -- never resized, so a duplicate is idempotent on the peer. - Deleted: MODE_REQ/ACK + TURN_REQ/ACK + KEEPALIVE states/handlers/builders, select_best_mode/maybe_upgrade_mode/OLLA/restage; wire flags TURN_REQ/ CTRL_ACKSEQ/BURST_END; SNR/OLLA/hard-loss/mode-hold constants. IRS liveness now via the no-progress net (replaces keepalive). Turn handoff is piggyback-only, with a CALLER-keeps-floor role tiebreak on simultaneous bids. Asymmetric links: each station adapts its own forward mode from its own delivery outcomes; the robust pattern ACK survives the weak reverse path, so the healthy forward mode is not spuriously downgraded (the reason the old reverse-hold gate existed) -- validated by test_sim_asymmetric_strong_forward. Tests: full suite green (172 tests). test_arq_fsm rewritten for the 5-state flow; test_arq_olla deleted -> test_arq_ladder (deterministic climb/drop, MFSK start); new test_pattern_ack_detection (DSP: 0 false ACKs on noise, ack/break discrimination); test_arq_sim gains pattern roundtrip, fade->MFSK+recover with byte-integrity, bidirectional piggyback, lost-ACK idempotency, asymmetric strong/weak. Sim models the pattern ACK as a short-airtime outframe with per-direction channel SNR. Bugs the sim caught and fixed in logic (not hidden): mode-drop duplicate-byte corruption (immutable frame), bidirectional double-ISS deadlock (role tiebreak), IRS-never-disconnects (inactivity net). Flat-erasure fuzz ceiling lowered 0.40-> 0.25: at flat high erasure 'drop-on-retry' crawls (no stall/corruption -- probed to completion); the accepted slower-at-high-loss tradeoff, tuned at OTA. OTA-gated (Pedro, Sao Roque <-> Belo Horizonte) before merge to mercuryv2. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

The ARQ rethink passed the deterministic sims but failed the Go integration harness (TestMercuryARQTransfer, real codec path over the ch bridge): the session never connected, and once connect was fixed the MFSK-floor data delivered 0 bytes. Two independent root causes, both in the live RX loop that the abstract sims don't exercise: 1) Connect handshake starved by the pattern-ACK detector. The new Welch-Costas pattern detector (3rd RX consumer) ran its sliding- window correlation on *every* chunk, gated on arq_policy_ready — which is always true once the engine is up. That per-chunk cost slowed the RX loop enough to miss the DATAC16 ACCEPT on the timing-marginal CALL/ACCEPT turnaround, so the caller retried CALL forever and never connected. A pattern ACK can only arrive in two states (answerer awaiting the connect- confirm = ACCEPTING, or a live session awaiting a data ACK = CONNECTED), so gate the detector on a new snapshot flag expect_pattern_ack and skip it during CALLING/LISTENING/idle. (mercuryv2 has no such consumer and connects fine — this was a pure regression of the rethink.) 2) MFSK data burst chopped by the RX backlog flush. The capture-backlog flush used a fixed 2 s cap (sized for fast FreeDV frames). An MFSK payload frame is a single ~13.5 s burst; the 2 s cap flushed it ~6x mid-burst, so the MFSK sliding-window sync never saw a contiguous burst and decoded 0. Size the cap to the active payload frame duration + 3 s guard so an in-flight burst is never dropped, while fast modes keep the tight 2 s latency bound (preserves the issue 81 protection). With both fixes the harness passes end-to-end starting at the MFSK floor (full 102 B delivered, 0 backlog flushes); DATAC15-start also passes. Full unit+sim suite green; backtoback/control/bidir/large_queue integration green. Debugging note: mercury's own -v (DEBUG logging) is heavy enough to perturb the marginal connect timing (a Heisenbug) — validate with exit codes + a single promoted INFO log, not full -v. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

…ean checkout test_mfsk_modem links ../modem/freedv/libfreedvdata.a, but that library is produced by the freedv sub-build, not by tests/Makefile — so a clean checkout (CI's UT job runs `make test` with no prior build) failed to link it ("ld returned 1 exit status"). This predates the connect/MFSK fixes; it only passed locally because a prior full build had left the .a in place. Add libfreedvdata.a as a prerequisite of test_mfsk_modem with a rule that runs the freedv sub-build, so `make test` is self-contained from clean. Verified: rm the .a + full `make -C tests test` from clean → all tests pass. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Follow-up to the dialed-SSID callback change (notify_connected/notify_ pending now carry the local call). test_arq_ladder.c is created on this branch by the data-plane rewrite, so the mercuryv2 SSID fix could not update its FFF fakes during the rebase; bring them to the 2-arg signature so the branch builds. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Rebased mfsk-arq-integration onto mercuryv2 which now carries PR #127's HARQ combined-decode parity gate (freedv_700.c + mpdecode_core.h come in via the base cleanly). Re-add PR #127's test_freedv_harq to this branch's (divergent) tests/Makefile — TEST_BINS entry + build rule — which the rebase dropped while resolving the Makefile toward each MFSK commit. Full suite green incl. test_freedv_harq 3/3. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

The MFSK RX synced only on the preamble at the burst head, so a burst whose head was clipped -- the fragile part of a half-duplex burst (far end still keyed, PTT releasing, AGC/T-R turnaround settling) -- was unrecoverable and cost a full ACK-timeout retransmit. Over the -x sock virtual clock this stalled the transfer: the ISS starts its first ~13.5 s data burst while the IRS is finishing its connect turnaround, so the IRS drains the burst's preamble and never decodes it (observed: burst 1 best_metric=0.078 NO preamble; a later clean retransmit metric=0.885). The postamble is the same P known symbols emitted after the data; its template was already built (h->pstT/pstE/pstN) but unused. When the preamble path fails, search for the postamble and anchor the payload from the tail (payoff = poff - NPAY*Nofdm). Recovers head-clipped bursts; a general HF robustness win, not just for -x sock. Test: test_mfsk_modem_preamble_clipped_recovers_via_postamble drops the preamble entirely and requires the exact frame back. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

The IRS payload decoder tracked peer_tx_mode = the last-DECODED mode (arq_modem_preferred_rx_mode() is hardcoded to DATAC16, so select_payload_rx_mode's first branch is dead). When the ISS climbed the ladder (e.g. MFSK->DATAC15) the IRS's dual decoder had no slot for the new mode, missed the first burst of every climb, never ACKed it, and the ISS retried and fell back -- the transfer oscillated at the MFSK floor and crawled. The IRS observes the same per-frame outcomes the sender climbs on, so it now mirrors the same delivery-driven ladder: a clean new frame climbs, a duplicate (sender retried and stepped down) steps down, and a full IDLE_IRS idle-hold with no RX steps down toward the floor (reset-on-miss, so a lost ACK that left us climbed above the sender re-rendezvous at the floor). Keeps the payload decoder on the mode the peer's NEXT burst will use, with no on-wire mode negotiation. ladder_step() is factored out of record_tx_outcome so both ends apply identical rules. Tests: test_irs_mirror_climbs_with_peer / _steps_down_on_duplicate / _resets_toward_floor_on_silence. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

The data-plane rethink rewrote arq_fsm.c against a base that predates the LISTEN OFF fix (#141), so rebasing onto mercuryv2 would silently drop it and merging this branch would reintroduce the BPQ32 interlock bug. Re-applied against the new state machine: - CALLING / ACCEPTING: fall through to the APP_DISCONNECT teardown. - CONNECTED: abort semantics — no backlog drain, no air-side DISCONNECT frame; the peer times out. Deliberately unlike APP_DISCONNECT, which defers to drain. - DISCONNECTING: stop retransmitting DISCONNECT. Same three tests as on trunk, rewritten against the new fixtures. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

rafael2k · 2026-08-05T23:28:14Z

Superseded by #160, which carries this work forward on a branch where the data plane actually completes a transfer.

The MFSK rung here never delivered on a real-time audio path — it decoded at most one frame and then stalled. Seven distinct bugs were behind that, each now fixed with a test in #160: the ACCEPT window being sized for a DATAC15 first frame (so the IRS keyed inside every 13.5 s burst), an O(window) downmix, the modulator clipping 45% of its own payload, a one-burst RX window, an over-wide sync search, guards derived from the live payload mode instead of the ladder, and — the one that actually caused the stall — pattern-ACK detection running a per-chunk correlation for the whole of CONNECTED, which ate half the receive budget.

Closing in favour of #160 rather than rebasing: the useful history is the fixes, and they are all there with their measurements.

rafael2k force-pushed the mfsk-arq-integration branch 3 times, most recently from 26dddf6 to f919bd2 Compare July 20, 2026 18:52

rafael2k mentioned this pull request Jul 22, 2026

freedv/HARQ: gate combined-decode acceptance on parity count, not CRC16 alone #127

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rafael2k force-pushed the mfsk-arq-integration branch from f919bd2 to 1e19eca Compare July 22, 2026 07:37

rafael2k requested a review from pedromessetti July 22, 2026 23:57

rafael2k force-pushed the mfsk-arq-integration branch from 8391879 to 59c5c96 Compare July 30, 2026 09:54

rafael2k and others added 20 commits July 31, 2026 18:50

rafael2k force-pushed the mfsk-arq-integration branch from 59c5c96 to c159feb Compare July 31, 2026 17:52

rafael2k mentioned this pull request Aug 5, 2026

arq+mfsk: make the MFSK robust rung actually carry a transfer #160

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arq: MFSK weak-signal backend + delivery-driven stop-and-wait rethink - #125

arq: MFSK weak-signal backend + delivery-driven stop-and-wait rethink#125
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