From 0a99bf326878ad133136fe781d3e466d53d3d153 Mon Sep 17 00:00:00 2001
From: acidburns <neon22@web.de>
Date: Wed, 4 Feb 2026 00:36:40 +0100
Subject: [PATCH] Send batch ACKs immediately after reassembly

- Move ACK ahead of MQTT/web work to meet sender 400ms window
- Update ACK log format and document early-ACK behavior
---
 README.md    | 1 +
 src/main.cpp | 6 +++---
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/README.md b/README.md
index 4b34020..7787a0c 100644
--- a/README.md
+++ b/README.md
@@ -237,6 +237,7 @@ Notes:
 - Receiver reconstructs timestamps from `t_last` and `dt_s`.
 - Total power is computed on receiver as `p1 + p2 + p3`.
 - Sender error counters are carried in the batch header and applied to all samples.
+- Receiver ACKs MeterBatch as soon as the batch is reassembled, before MQTT/web/UI work, to avoid missing the sender ACK window.
 
 ## Device IDs
 - Derived from WiFi STA MAC.
diff --git a/src/main.cpp b/src/main.cpp
index 0f49a3f..875482d 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -498,7 +498,7 @@ static void send_batch_ack(uint16_t batch_id, uint16_t sender_id) {
   write_u16_le(&ack.payload[2], sender_id);
   write_u16_le(&ack.payload[4], g_short_id);
   if (SERIAL_DEBUG_MODE) {
-    serial_debug_printf("ack: tx batch_id=%u sender=%u receiver=%u", batch_id, sender_id, g_short_id);
+    serial_debug_printf("ack: tx batch_id=%u to sender=%04X", batch_id, sender_id);
   }
   lora_send(ack);
   lora_receive_continuous();
@@ -1007,6 +1007,8 @@ static void receiver_loop() {
         if (duplicate) {
           send_batch_ack(batch_id, pkt.device_id_short);
         } else {
+          g_last_batch_id_rx[sender_idx] = batch_id;
+          send_batch_ack(batch_id, pkt.device_id_short);
           count = batch.n;
           if (count == 0 || count > METER_BATCH_MAX_SAMPLES) {
             note_fault(g_receiver_faults, g_receiver_last_error, g_receiver_last_error_utc, g_receiver_last_error_ms, FaultType::Decode);
@@ -1080,8 +1082,6 @@ static void receiver_loop() {
                                        g_sender_last_error_remote[sender_idx], g_sender_last_error_remote_published[sender_idx],
                                        g_sender_last_error_remote_utc[sender_idx], g_sender_last_error_remote_ms[sender_idx]);
             }
-            g_last_batch_id_rx[sender_idx] = batch_id;
-            send_batch_ack(batch_id, pkt.device_id_short);
           }
         }
       } else if (decode_error) {