From d7b5bb0f0ba75de70e651202deaee86ab0f3cc6b Mon Sep 17 00:00:00 2001
From: acidburns <neon22@web.de>
Date: Tue, 17 Feb 2026 01:14:38 +0100
Subject: [PATCH] Adapt sender ACK receive window based on observed timing

---
 src/main.cpp | 51 +++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 41 insertions(+), 10 deletions(-)

diff --git a/src/main.cpp b/src/main.cpp
index fa3218a..85c13b2 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -105,6 +105,7 @@ static uint32_t g_sender_ack_timeout_total = 0;
 static uint32_t g_sender_ack_retry_total = 0;
 static uint32_t g_sender_ack_rtt_last_ms = 0;
 static uint32_t g_sender_ack_rtt_ewma_ms = 0;
+static uint32_t g_sender_ack_miss_streak = 0;
 static RxRejectReason g_sender_rx_reject_reason = RxRejectReason::None;
 static uint32_t g_sender_rx_reject_log_ms = 0;
 static RxRejectReason g_receiver_rx_reject_reason = RxRejectReason::None;
@@ -203,7 +204,7 @@ static void sender_log_diagnostics(uint32_t now_ms) {
   }
 
   serial_debug_printf(
-      "diag: q_depth=%lu q_hi=%lu q_drop=%lu batch_q=%u build=%u ack_pending=%u ack_retry_cur=%u ack_retry_total=%lu ack_timeout_total=%lu ack_rtt_last_ms=%lu ack_rtt_ewma_ms=%lu meter_ok=%lu meter_fail=%lu meter_ovf=%lu meter_timeout=%lu meter_age_ms=%lu rx_win_ms=%lu sleep_ms=%lu",
+      "diag: q_depth=%lu q_hi=%lu q_drop=%lu batch_q=%u build=%u ack_pending=%u ack_retry_cur=%u ack_retry_total=%lu ack_timeout_total=%lu ack_rtt_last_ms=%lu ack_rtt_ewma_ms=%lu ack_miss_streak=%lu meter_ok=%lu meter_fail=%lu meter_ovf=%lu meter_timeout=%lu meter_age_ms=%lu rx_win_ms=%lu sleep_ms=%lu",
       static_cast<unsigned long>(queue_depth),
       static_cast<unsigned long>(g_meter_queue_high_water),
       static_cast<unsigned long>(g_meter_queue_drop_count),
@@ -215,6 +216,7 @@ static void sender_log_diagnostics(uint32_t now_ms) {
       static_cast<unsigned long>(g_sender_ack_timeout_total),
       static_cast<unsigned long>(g_sender_ack_rtt_last_ms),
       static_cast<unsigned long>(g_sender_ack_rtt_ewma_ms),
+      static_cast<unsigned long>(g_sender_ack_miss_streak),
       static_cast<unsigned long>(meter_stats.frames_ok),
       static_cast<unsigned long>(meter_stats.frames_parse_fail),
       static_cast<unsigned long>(meter_stats.rx_overflow),
@@ -1384,26 +1386,49 @@ static void sender_loop() {
     LoraPacket ack_pkt = {};
     constexpr size_t ack_len = lora_frame_size(LORA_ACK_DOWN_PAYLOAD_LEN);
     uint32_t ack_air_ms = lora_airtime_ms(ack_len);
-    uint32_t ack_window_ms = ack_air_ms + 300;
-    if (ack_window_ms < 1200) {
-      ack_window_ms = 1200;
+    uint32_t ack_window_first_ms = ack_air_ms + 200;
+    if (g_sender_ack_rtt_ewma_ms > 0) {
+      uint32_t rtt_based_ms = g_sender_ack_rtt_ewma_ms + 150;
+      if (rtt_based_ms > ack_window_first_ms) {
+        ack_window_first_ms = rtt_based_ms;
+      }
     }
-    if (ack_window_ms > 4000) {
-      ack_window_ms = 4000;
+    uint32_t miss_boost_ms = g_sender_ack_miss_streak * 150;
+    if (miss_boost_ms > 1200) {
+      miss_boost_ms = 1200;
+    }
+    ack_window_first_ms += miss_boost_ms;
+    if (ack_window_first_ms < 600) {
+      ack_window_first_ms = 600;
+    }
+    if (ack_window_first_ms > 2500) {
+      ack_window_first_ms = 2500;
+    }
+    uint32_t ack_window_second_ms = ack_window_first_ms + (ack_window_first_ms / 2);
+    uint32_t min_second_ms = ack_air_ms + 400;
+    if (ack_window_second_ms < min_second_ms) {
+      ack_window_second_ms = min_second_ms;
+    }
+    if (ack_window_second_ms > 5000) {
+      ack_window_second_ms = 5000;
     }
     if (SERIAL_DEBUG_MODE) {
-      serial_debug_printf("ack: rx window=%lu airtime=%lu", static_cast<unsigned long>(ack_window_ms),
-                          static_cast<unsigned long>(ack_air_ms));
+      serial_debug_printf("ack: rx windows=%lu/%lu airtime=%lu miss_streak=%lu",
+                          static_cast<unsigned long>(ack_window_first_ms),
+                          static_cast<unsigned long>(ack_window_second_ms),
+                          static_cast<unsigned long>(ack_air_ms),
+                          static_cast<unsigned long>(g_sender_ack_miss_streak));
     }
     uint32_t rx_start = millis();
-    bool got_ack = lora_receive_window(ack_pkt, ack_window_ms);
+    bool got_ack = lora_receive_window(ack_pkt, ack_window_first_ms);
     if (!got_ack) {
-      got_ack = lora_receive_window(ack_pkt, ack_window_ms / 2);
+      got_ack = lora_receive_window(ack_pkt, ack_window_second_ms);
     }
     uint32_t rx_elapsed = millis() - rx_start;
     if (SERIAL_DEBUG_MODE) {
       g_sender_rx_window_ms += rx_elapsed;
     }
+    bool ack_accepted = false;
     if (!got_ack) {
       RxRejectReason reason = lora_get_last_rx_reject_reason();
       sender_note_rx_reject(reason, "ack");
@@ -1445,6 +1470,7 @@ static void sender_loop() {
       uint32_t ack_epoch = read_u32_be(&ack_pkt.payload[3]);
       bool set_time = false;
       if (g_batch_ack_pending && ack_id == g_last_sent_batch_id) {
+        ack_accepted = true;
         g_sender_ack_rtt_last_ms = rx_elapsed;
         if (g_sender_ack_rtt_ewma_ms == 0) {
           g_sender_ack_rtt_ewma_ms = rx_elapsed;
@@ -1475,6 +1501,11 @@ static void sender_loop() {
         }
       }
     }
+    if (ack_accepted) {
+      g_sender_ack_miss_streak = 0;
+    } else if (g_sender_ack_miss_streak < UINT32_MAX) {
+      g_sender_ack_miss_streak++;
+    }
   }
   if (!g_batch_ack_pending) {
     lora_sleep();