Rhizomatica · rafael2k · Jul 15, 2026 · Jul 15, 2026 · Jul 15, 2026 · Jul 15, 2026
diff --git a/.gitignore b/.gitignore
@@ -70,8 +70,16 @@ context-*.txt
 copilot-*.txt
 screen.jpg
 
-# utils build outputs
+# dependency files from -MMD
+*.d
+
+# test/bench binaries and their output dirs
 utils/watterson_test
+tests/connect_bench
+/results/
+
+utils/shortframe_sweep
 utils/acquire_vs_decode
+utils/hail_suffix_sweep
 utils/resampler_bench
 utils/rxcost_bench
diff --git a/Makefile b/Makefile
@@ -125,8 +125,11 @@ MERCURY_LINK_INPUTS = \
 	main.o common/cfg_utils.o common/iniparser/iniparser.o common/iniparser/dictionary.o \
 	datalink_arq/arq.o datalink_arq/arq_tnc.o datalink_arq/arith.o datalink_arq/arq_channels.o \
 	datalink_arq/arq_fsm.o datalink_arq/arq_protocol.o datalink_arq/arq_timing.o datalink_arq/arq_modem.o \
-	datalink_broadcast/broadcast.o datalink_broadcast/kiss.o modem/modem.o modem/framer.o modem/channel_busy.o modem/freedv/libfreedvdata.a \
-	audioio/audioio.a common/os_interop.o common/ring_buffer_posix.o common/shm_posix.o common/crc6.o common/hermes_log.o common/virtual_clock.o \
+	datalink_broadcast/broadcast.o datalink_broadcast/kiss.o modem/modem.o modem/modem_freedv.o \
+	modem/modem_mfsk.o modem/mfsk.o modem/mfsk_ofdm.o modem/mfsk_sync.o modem/mfsk_ldpc.o modem/mfsk_ldpc_1_16.o \
+	modem/mfsk_ldpc_2_16.o modem/mfsk_ldpc_3_16.o modem/mfsk_ldpc_5_16.o modem/mfsk_ldpc_8_16.o modem/framer.o \
+	modem/channel_busy.o modem/freedv/libfreedvdata.a audioio/audioio.a common/os_interop.o \
+	common/ring_buffer_posix.o common/shm_posix.o common/crc6.o common/hermes_log.o common/virtual_clock.o \
 	common/chan.o common/queue.o common/mercury_engine.o common/mercury_cli.o data_interfaces/tcp_interfaces.o data_interfaces/net.o \
 	gui_interface/ui_communication.o gui_interface/ui_status.o \
 	gui_interface/websocket/mongoose.o gui_interface/websocket/mercury_websocket.o \
@@ -196,8 +199,10 @@ MERCURY_CORE_OBJS = \
 	datalink_arq/arq.o datalink_arq/arq_tnc.o datalink_arq/arith.o datalink_arq/arq_channels.o \
 	datalink_arq/arq_fsm.o datalink_arq/arq_protocol.o datalink_arq/arq_timing.o datalink_arq/arq_modem.o \
 	datalink_broadcast/broadcast.o datalink_broadcast/kiss.o \
-	modem/modem.o modem/framer.o modem/channel_busy.o \
-	common/os_interop.o common/ring_buffer_posix.o common/shm_posix.o common/crc6.o common/hermes_log.o common/virtual_clock.o \
+	modem/modem.o modem/modem_freedv.o modem/modem_mfsk.o modem/mfsk.o modem/mfsk_ofdm.o modem/mfsk_sync.o \
+	modem/mfsk_ldpc.o modem/mfsk_ldpc_1_16.o modem/mfsk_ldpc_2_16.o modem/mfsk_ldpc_3_16.o \
+	modem/mfsk_ldpc_5_16.o modem/mfsk_ldpc_8_16.o modem/framer.o modem/channel_busy.o common/os_interop.o \
+	common/ring_buffer_posix.o common/shm_posix.o common/crc6.o common/hermes_log.o common/virtual_clock.o \
 	common/chan.o common/queue.o common/mercury_engine.o common/mercury_cli.o \
 	data_interfaces/tcp_interfaces.o data_interfaces/net.o \
 	gui_interface/ui_communication.o gui_interface/ui_status.o \

diff --git a/claude_context2.txt b/claude_context2.txt
@@ -0,0 +1 @@
+claude --resume a74b8149-410c-4d71-bf03-4dd2f3841699
diff --git a/common/cfg_utils.c b/common/cfg_utils.c
@@ -61,10 +61,7 @@ void cfg_set_defaults(mercury_config *cfg)
     cfg->retry_downgrade_threshold   = ARQ_RETRY_DOWNGRADE_THRESHOLD_DEFAULT;
     cfg->channel_guard_ms            = ARQ_CHANNEL_GUARD_MS_DEFAULT;
     cfg->iss_post_ack_guard_ms       = ARQ_ISS_POST_ACK_GUARD_MS_DEFAULT;
-    cfg->keepalive_interval_s        = ARQ_KEEPALIVE_INTERVAL_S_DEFAULT;
-    cfg->keepalive_miss_limit        = ARQ_KEEPALIVE_MISS_LIMIT_DEFAULT;
     cfg->peer_payload_hold_s         = ARQ_PEER_PAYLOAD_HOLD_S_DEFAULT;
-    cfg->startup_max_s               = ARQ_STARTUP_MAX_S_DEFAULT;
     cfg->busy_detect                 = false;
     cfg->busy_threshold_db           = 10;
     cfg->busy_hysteresis_db          = 3;
@@ -211,17 +208,11 @@ bool cfg_read(mercury_config *cfg, const char *ini_path)
     i = iniparser_getint(ini, CFG_KEY_ARQ_ISS_POST_ACK_GUARD_MS, cfg->iss_post_ack_guard_ms);
     if (i >= 200 && i <= 3000) cfg->iss_post_ack_guard_ms = i;
 
-    i = iniparser_getint(ini, CFG_KEY_ARQ_KEEPALIVE_INTERVAL_S, cfg->keepalive_interval_s);
-    if (i >= 5 && i <= 120)  cfg->keepalive_interval_s = i;
 
-    i = iniparser_getint(ini, CFG_KEY_ARQ_KEEPALIVE_MISS_LIMIT, cfg->keepalive_miss_limit);
-    if (i >= 2 && i <= 20)   cfg->keepalive_miss_limit = i;
 
     i = iniparser_getint(ini, CFG_KEY_ARQ_PEER_PAYLOAD_HOLD_S, cfg->peer_payload_hold_s);
     if (i >= 1 && i <= 120)  cfg->peer_payload_hold_s = i;
 
-    i = iniparser_getint(ini, CFG_KEY_ARQ_STARTUP_MAX_S, cfg->startup_max_s);
-    if (i >= 2 && i <= 60)   cfg->startup_max_s = i;
 
     cfg->busy_detect = (bool) iniparser_getboolean(ini, CFG_KEY_BUSY_DETECT,
                                                    cfg->busy_detect ? 1 : 0);
@@ -338,10 +329,7 @@ bool cfg_write(const mercury_config *cfg, const char *ini_path)
     fprintf(f, "retry_downgrade_threshold = %d\n", cfg->retry_downgrade_threshold);
     fprintf(f, "channel_guard_ms = %d\n", cfg->channel_guard_ms);
     fprintf(f, "iss_post_ack_guard_ms = %d\n", cfg->iss_post_ack_guard_ms);
-    fprintf(f, "keepalive_interval_s = %d\n", cfg->keepalive_interval_s);
-    fprintf(f, "keepalive_miss_limit = %d\n", cfg->keepalive_miss_limit);
     fprintf(f, "peer_payload_hold_s = %d\n", cfg->peer_payload_hold_s);
-    fprintf(f, "startup_max_s = %d\n", cfg->startup_max_s);
 
     fprintf(f, "\n[channel]\n");
     fprintf(f, "busy_detect = %s\n", cfg->busy_detect ? "true" : "false");

diff --git a/common/cfg_utils.h b/common/cfg_utils.h
@@ -53,10 +53,7 @@
 #define CFG_KEY_ARQ_RETRY_DOWNGRADE_THRESHOLD "arq:retry_downgrade_threshold"
 #define CFG_KEY_ARQ_CHANNEL_GUARD_MS          "arq:channel_guard_ms"
 #define CFG_KEY_ARQ_ISS_POST_ACK_GUARD_MS     "arq:iss_post_ack_guard_ms"
-#define CFG_KEY_ARQ_KEEPALIVE_INTERVAL_S      "arq:keepalive_interval_s"
-#define CFG_KEY_ARQ_KEEPALIVE_MISS_LIMIT      "arq:keepalive_miss_limit"
 #define CFG_KEY_ARQ_PEER_PAYLOAD_HOLD_S       "arq:peer_payload_hold_s"
-#define CFG_KEY_ARQ_STARTUP_MAX_S             "arq:startup_max_s"
 #define CFG_KEY_BUSY_DETECT                   "channel:busy_detect"
 #define CFG_KEY_BUSY_THRESHOLD_DB             "channel:busy_threshold_db"
 #define CFG_KEY_BUSY_HYSTERESIS_DB            "channel:busy_hysteresis_db"
@@ -99,14 +96,8 @@ typedef struct {
                                          * Default 700, clamped 200..3000.      */
     int      iss_post_ack_guard_ms;     /* ARQ: ISS guard before resuming DATA
                                          * TX after ACK. Default 900, 200..3000.*/
-    int      keepalive_interval_s;      /* ARQ: keepalive TX interval. Default
-                                         * 20, clamped 5..120.                  */
-    int      keepalive_miss_limit;      /* ARQ: missed keepalives before drop.
-                                         * Default 5, clamped 2..20.            */
     int      peer_payload_hold_s;       /* ARQ: hold peer payload mode after
                                          * activity. Default 15, clamped 1..120.*/
-    int      startup_max_s;             /* ARQ: control-mode-only startup
-                                         * window. Default 10, clamped 2..60.   */
     float    tx_gain_db;            /* Linear-equivalent gain on the modulator
                                     * TX samples, in dB. 0.0 = no change.
                                     * Range -20.0 .. +20.0 (clamped). */

diff --git a/common/mercury_engine.c b/common/mercury_engine.c
@@ -125,10 +125,7 @@ int mercury_engine_init(const mercury_config *cfg,
     arq_set_retry_downgrade_threshold(cfg->retry_downgrade_threshold);
     arq_set_channel_guard_ms(cfg->channel_guard_ms);
     arq_set_iss_post_ack_guard_ms(cfg->iss_post_ack_guard_ms);
-    arq_set_keepalive_interval_s(cfg->keepalive_interval_s);
-    arq_set_keepalive_miss_limit(cfg->keepalive_miss_limit);
     arq_set_peer_payload_hold_s(cfg->peer_payload_hold_s);
-    arq_set_startup_max_s(cfg->startup_max_s);
     modem_set_tx_gain(powf(10.0f, cfg->tx_gain_db / 20.0f));
     modem_set_tx_delay_ms(cfg->tx_delay_ms);
     modem_set_busy_cfg((float)cfg->busy_threshold_db,

diff --git a/datalink_arq/arq.c b/datalink_arq/arq.c
@@ -224,6 +224,22 @@ static void cb_send_tx_frame(int packet_type, int mode,
     arq_modem_enqueue(&action);
 }
 
+/* Enqueue a Welch-Costas MFSK pattern ACK for the modem TX worker.  Carries no
+ * coded frame — the modem synthesises the ack/break tone burst directly (see
+ * send_pattern_ack in modem.c).  `mode` is the current payload mode, used only
+ * so the worker can key at the right passband geometry. */
+static void cb_send_pattern_ack(int mode, int pattern_kind)
+{
+    arq_action_t action = {
+        .type         = ARQ_ACTION_TX_PATTERN,
+        .mode         = mode,
+        .frame_size   = 0,
+        .frame_count  = 1,
+        .pattern_kind = pattern_kind,
+    };
+    arq_modem_enqueue(&action);
+}
+
 static void cb_notify_connected(const char *remote_call, const char *local_call)
 {
     pthread_mutex_lock(&g_conn_lock);
@@ -857,22 +873,11 @@ void arq_handle_incoming_frame(uint8_t *data, size_t frame_size, float rx_snr)
     {
         switch (hdr.subtype)
         {
+        /* ACK: the coded DATAC16 ACK is used only for the post-ACCEPT connect
+         * confirmation now; in-session ACKs are the MFSK pattern (synthesised
+         * in modem.c), not a control frame here. */
         case ARQ_SUBTYPE_ACK:          ev.id = ARQ_EV_RX_ACK;           break;
         case ARQ_SUBTYPE_DISCONNECT:   ev.id = ARQ_EV_RX_DISCONNECT;    break;
-        case ARQ_SUBTYPE_TURN_REQ:     ev.id = ARQ_EV_RX_TURN_REQ;      break;
-        case ARQ_SUBTYPE_TURN_ACK:     ev.id = ARQ_EV_RX_TURN_ACK;      break;
-        case ARQ_SUBTYPE_KEEPALIVE:    ev.id = ARQ_EV_RX_KEEPALIVE;     break;
-        case ARQ_SUBTYPE_KEEPALIVE_ACK: ev.id = ARQ_EV_RX_KEEPALIVE_ACK; break;
-        case ARQ_SUBTYPE_MODE_REQ:
-            ev.id   = ARQ_EV_RX_MODE_REQ;
-            ev.mode = (frame_size > ARQ_FRAME_HDR_SIZE)
-                      ? (int)data[ARQ_FRAME_HDR_SIZE] : 0;
-            break;
-        case ARQ_SUBTYPE_MODE_ACK:
-            ev.id   = ARQ_EV_RX_MODE_ACK;
-            ev.mode = (frame_size > ARQ_FRAME_HDR_SIZE)
-                      ? (int)data[ARQ_FRAME_HDR_SIZE] : 0;
-            break;
         default:
             return;
         }
@@ -885,6 +890,16 @@ void arq_handle_incoming_frame(uint8_t *data, size_t frame_size, float rx_snr)
     evq_push(&ev);
 }
 
+void arq_post_pattern_ack(bool is_break)
+{
+    arq_event_t ev = {0};
+    ev.id       = ARQ_EV_RX_ACK;
+    ev.rx_flags = is_break ? ARQ_FLAG_HAS_DATA : 0;
+    /* session_id left 0: patterns carry none, and the dispatch session-ID
+     * gate treats 0 as "unknown/accept". */
+    evq_push(&ev);
+}
+
 /* ======================================================================
  * Public arq.h API
  * ====================================================================== */
@@ -924,6 +939,7 @@ int arq_init(size_t frame_size, int mode)
 
     static const arq_fsm_callbacks_t cbs = {
         .send_tx_frame       = cb_send_tx_frame,
+        .send_pattern_ack    = cb_send_pattern_ack,
         .notify_connected    = cb_notify_connected,
         .notify_pending      = cb_notify_pending,
         .notify_cancelpending = cb_notify_cancelpending,
@@ -1088,8 +1104,36 @@ bool arq_get_runtime_snapshot(arq_runtime_snapshot_t *snapshot)
     pthread_mutex_lock(&g_sess_lock);
     snapshot->initialized      = true;
     snapshot->connected        = (g_sess.conn_state == ARQ_CONN_CONNECTED);
+    /* Only while a pattern ACK could actually arrive.
+     *
+     * This gates a correlation that modem.c runs over a ~3-burst window on
+     * EVERY capture chunk, so leaving it on for all of CONNECTED cost about
+     * half the RX budget for the whole session: measured 3.5k samp/s consumed
+     * against 8k arriving, the capture ring growing to ~400 kB, and the backlog
+     * guard then flushing bursts that were still arriving.  Trunk, which has no
+     * pattern ACK, holds 7.99k samp/s on the same bench.
+     *
+     * WAIT_ACK is by definition the only state where a pattern ACK is due
+     * (see ARQ_DFLOW_WAIT_ACK).  Everywhere else -- above all IDLE_IRS, where
+     * the receiver is busy demodulating a 13.5 s burst -- there is nothing to
+     * detect and the CPU is needed elsewhere.
+     *
+     * ACCEPTING is the one other state where a pattern is due -- the caller's
+     * connect confirm -- but it is emphatically NOT the whole ~18 s ACCEPT
+     * window, which is how this was first written and what cost the RX budget
+     * at exactly the wrong moment.  The confirm's arrival time is predictable
+     * (one ISS post-ACK guard after our ACCEPT leaves the air), so the FSM opens
+     * a bounded few-second window at ACCEPT PTT-OFF and closes it on any state
+     * change: see confirm_listen_until_ms / ARQ_CONNECT_CONFIRM_LISTEN_MS. */
+    snapshot->expect_pattern_ack =
+        (g_sess.conn_state == ARQ_CONN_CONNECTED &&
+         g_sess.dflow_state == ARQ_DFLOW_WAIT_ACK) ||
+        (g_sess.conn_state == ARQ_CONN_ACCEPTING &&
+         g_sess.confirm_listen_until_ms != 0 &&
+         time_now_ms() < g_sess.confirm_listen_until_ms);
     snapshot->trx              = trx;
-    snapshot->tx_backlog_bytes = backlog + g_sess.tx_inflight_bytes;
+    snapshot->tx_backlog_bytes = backlog +
+        (g_sess.tx_frame_present ? g_sess.tx_frame_len : 0);
     snapshot->speed_level      = g_sess.speed_level;
     snapshot->payload_mode      = g_sess.payload_mode;
     snapshot->peer_tx_mode      = g_sess.peer_tx_mode;
@@ -1197,22 +1241,6 @@ void arq_set_iss_post_ack_guard_ms(int ms)
     HLOGI(LOG_COMP, "iss_post_ack_guard_ms = %d", atomic_load(&arq_iss_post_ack_guard_ms));
 }
 
-void arq_set_keepalive_interval_s(int s)
-{
-    if (s < 5)   s = (s <= 0) ? ARQ_KEEPALIVE_INTERVAL_S_DEFAULT : 5;
-    if (s > 120) s = 120;
-    atomic_store(&arq_keepalive_interval_s, s);
-    HLOGI(LOG_COMP, "keepalive_interval_s = %d", atomic_load(&arq_keepalive_interval_s));
-}
-
-void arq_set_keepalive_miss_limit(int n)
-{
-    if (n < 2)  n = (n <= 0) ? ARQ_KEEPALIVE_MISS_LIMIT_DEFAULT : 2;
-    if (n > 20) n = 20;
-    atomic_store(&arq_keepalive_miss_limit, n);
-    HLOGI(LOG_COMP, "keepalive_miss_limit = %d", atomic_load(&arq_keepalive_miss_limit));
-}
-
 void arq_set_ladder_up_successes(int n)
 {
     if (n < 1)  n = (n <= 0) ? ARQ_LADDER_UP_SUCCESSES_DEFAULT : 1;
@@ -1245,14 +1273,6 @@ void arq_set_peer_payload_hold_s(int s)
     HLOGI(LOG_COMP, "peer_payload_hold_s = %d", atomic_load(&arq_peer_payload_hold_s));
 }
 
-void arq_set_startup_max_s(int s)
-{
-    if (s < 2)  s = (s <= 0) ? ARQ_STARTUP_MAX_S_DEFAULT : 2;
-    if (s > 60) s = 60;
-    atomic_store(&arq_startup_max_s, s);
-    HLOGI(LOG_COMP, "startup_max_s = %d", atomic_load(&arq_startup_max_s));
-}
-
 void reset_arq_info(arq_info *conn)
 {
     if (!conn) return;

diff --git a/datalink_arq/arq.h b/datalink_arq/arq.h
@@ -69,9 +69,19 @@ typedef enum
     ARQ_ACTION_NONE = 0,
     ARQ_ACTION_TX_CONTROL = 1,
     ARQ_ACTION_TX_PAYLOAD = 2,
-    ARQ_ACTION_MODE_SWITCH = 3
+    ARQ_ACTION_MODE_SWITCH = 3,
+    ARQ_ACTION_TX_PATTERN = 4  /* emit a Welch-Costas MFSK pattern ACK — no
+                                * coded frame; pattern_kind selects ACK vs
+                                * ACK+TURN (break).  Airtime ~0.64 s.        */
 } arq_action_type_t;
 
+/** @brief Pattern-ACK symbol kind (ARQ_ACTION_TX_PATTERN). */
+typedef enum
+{
+    ARQ_PATTERN_ACK   = 0,  /* plain ACK: "got your frame, keep the floor"   */
+    ARQ_PATTERN_BREAK = 1   /* ACK+TURN: "got it AND I have data" (HAS_DATA) */
+} arq_pattern_kind_t;
+
 /** @brief Single modem action item popped by modem TX worker. */
 typedef struct
 {
@@ -81,13 +91,20 @@ typedef struct
     int frame_count;     /* frames in this PTT burst (>= 1); the modem reads
                           * frame_count * frame_size bytes and modulates them
                           * behind a single preamble                          */
+    int pattern_kind;    /* arq_pattern_kind_t, valid for ARQ_ACTION_TX_PATTERN */
 } arq_action_t;
 
 /** @brief Snapshot of current ARQ runtime state for telemetry/decision making. */
 typedef struct
 {
     bool initialized;
     bool connected;
+    /* True when a Welch-Costas pattern ACK could legitimately arrive: the
+     * answerer awaiting the caller's connect-confirm (ACCEPTING) or an active
+     * session (CONNECTED).  The RX pattern detector runs its per-chunk
+     * correlation only when this is set — running it during CALLING/LISTENING/
+     * idle is pure overhead that slows the connect-critical DATAC16 decode. */
+    bool expect_pattern_ack;
     int trx;
     int tx_backlog_bytes;
     int speed_level;
@@ -266,6 +283,17 @@ void arq_notify_cq_tx_complete(void);
  */
 void arq_handle_incoming_frame(uint8_t *data, size_t frame_size, float rx_snr);
 
+/**
+ * @brief Post a synthesized pattern-ACK event (from the RX pattern detector).
+ *
+ * A Welch-Costas pattern ACK carries no coded header, so the modem RX worker
+ * synthesizes the FSM event directly.  In stop-and-wait only one frame is
+ * outstanding, so an ACK unambiguously acks it.
+ *
+ * @param is_break true = ACK+TURN (HAS_DATA piggyback), false = plain ACK.
+ */
+void arq_post_pattern_ack(bool is_break);
+
 /**
  * @brief Feed decoder/link metrics into ARQ adaptation.
  * @param sync Decoder sync flag.
@@ -342,13 +370,10 @@ void arq_set_data_retry_slots(int slots);
 /* Setters for the newly-atomic ARQ timing/ladder tunables. */
 void arq_set_channel_guard_ms(int ms);
 void arq_set_iss_post_ack_guard_ms(int ms);
-void arq_set_keepalive_interval_s(int s);
-void arq_set_keepalive_miss_limit(int n);
 void arq_set_ladder_up_successes(int n);
 void arq_set_retry_downgrade_threshold(int n);
 void arq_set_mode_hold_after_downgrade_s(int s);
 void arq_set_peer_payload_hold_s(int s);
-void arq_set_startup_max_s(int s);
 
 /**
  * @brief Trigger outgoing call attempt using current ARQ addresses.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		claude --resume a74b8149-410c-4d71-bf03-4dd2f3841699