Cache encoded inflight payload for retry efficiency

src/main.cpp

@@ -90,6 +90,11 @@ static uint8_t g_inflight_count = 0;
 static uint16_t g_inflight_batch_id = 0;
 static bool g_inflight_active = false;
 static bool g_inflight_sync_request = false;
+static uint8_t g_inflight_encoded_payload[BATCH_MAX_COMPRESSED];
+static size_t g_inflight_encoded_payload_len = 0;
+static uint16_t g_inflight_encoded_batch_id = 0;
+static bool g_inflight_encoded_sync_request = false;
+static bool g_inflight_encoded_valid = false;
 static uint32_t g_last_debug_log_ms = 0;
 static uint32_t g_sender_rx_window_ms = 0;
 static uint32_t g_sender_sleep_ms = 0;
@@ -145,6 +150,7 @@ static TxBuildError g_last_tx_build_error = TxBuildError::None;
 
 static void watchdog_kick();
 static void finish_inflight_batch();
+static void invalidate_inflight_encode_cache();
 
 static void serial_debug_printf(const char *fmt, ...) {
   if (!SERIAL_DEBUG_MODE) {
@@ -218,6 +224,13 @@ static void sender_log_diagnostics(uint32_t now_ms) {
       static_cast<unsigned long>(g_sender_sleep_ms));
 }
 
+static void invalidate_inflight_encode_cache() {
+  g_inflight_encoded_payload_len = 0;
+  g_inflight_encoded_batch_id = 0;
+  g_inflight_encoded_sync_request = false;
+  g_inflight_encoded_valid = false;
+}
+
 static uint8_t bit_count32(uint32_t value) {
   uint8_t count = 0;
   while (value != 0) {
@@ -477,6 +490,7 @@ static bool batch_queue_drop_oldest() {
     g_inflight_count = 0;
     g_inflight_batch_id = 0;
     g_inflight_sync_request = false;
+    invalidate_inflight_encode_cache();
   }
   g_batch_tail = (g_batch_tail + 1) % BATCH_QUEUE_DEPTH;
   g_batch_count--;
@@ -872,6 +886,33 @@ static bool send_inflight_batch(uint32_t ts_for_display) {
   if (!g_inflight_active) {
     return false;
   }
+
+  bool cache_match = g_inflight_encoded_valid &&
+      g_inflight_encoded_batch_id == g_inflight_batch_id &&
+      g_inflight_encoded_sync_request == g_inflight_sync_request;
+  if (cache_match) {
+    g_batch_ack_timeout_ms = compute_batch_ack_timeout_ms(g_inflight_encoded_payload_len);
+    uint32_t send_start = millis();
+    bool ok = send_batch_payload(g_inflight_encoded_payload, g_inflight_encoded_payload_len, ts_for_display, g_inflight_batch_id);
+    uint32_t send_ms = millis() - send_start;
+    if (SERIAL_DEBUG_MODE && send_ms > 1000) {
+      serial_debug_printf("tx: resend batch took %lums", static_cast<unsigned long>(send_ms));
+    }
+    if (ok) {
+      g_last_batch_send_ms = millis();
+      if (g_inflight_sync_request) {
+        serial_debug_printf("sync: request tx batch_id=%u", g_inflight_batch_id);
+      } else {
+        serial_debug_printf("tx: resent batch_id=%u len=%u", g_inflight_batch_id, static_cast<unsigned>(g_inflight_encoded_payload_len));
+      }
+    } else if (g_inflight_sync_request) {
+      serial_debug_printf("sync: request tx failed batch_id=%u", g_inflight_batch_id);
+    } else {
+      serial_debug_printf("tx: resend failed batch_id=%u", g_inflight_batch_id);
+    }
+    return ok;
+  }
+
   BatchInput input = {};
   input.sender_id = sender_id_from_short_id(g_short_id);
   input.batch_id = g_inflight_batch_id;
@@ -966,8 +1007,14 @@ static bool send_inflight_batch(uint32_t ts_for_display) {
   uint32_t encode_start = millis();
   if (!encode_batch(input, encoded, sizeof(encoded), &encoded_len)) {
     g_last_tx_build_error = TxBuildError::Encode;
+    invalidate_inflight_encode_cache();
     return false;
   }
+  memcpy(g_inflight_encoded_payload, encoded, encoded_len);
+  g_inflight_encoded_payload_len = encoded_len;
+  g_inflight_encoded_batch_id = g_inflight_batch_id;
+  g_inflight_encoded_sync_request = g_inflight_sync_request;
+  g_inflight_encoded_valid = true;
   uint32_t encode_ms = millis() - encode_start;
   if (SERIAL_DEBUG_MODE) {
     serial_debug_printf("tx: batch_id=%u count=%u mask=%08lX bin_len=%u",
@@ -1025,6 +1072,7 @@ static bool send_meter_batch(uint32_t ts_for_display) {
     g_inflight_count = 0;
     g_inflight_batch_id = 0;
     g_inflight_sync_request = false;
+    invalidate_inflight_encode_cache();
   }
   return ok;
 }
@@ -1057,6 +1105,7 @@ static bool send_sync_request() {
     g_inflight_active = false;
     g_inflight_sync_request = false;
     g_inflight_batch_id = 0;
+    invalidate_inflight_encode_cache();
   }
   return ok;
 }
@@ -1078,6 +1127,7 @@ static void finish_inflight_batch() {
   g_inflight_count = 0;
   g_inflight_batch_id = 0;
   g_inflight_sync_request = false;
+  invalidate_inflight_encode_cache();
   g_batch_id++;
 }
 
@@ -1449,6 +1499,7 @@ static void sender_loop() {
         g_inflight_count = 0;
         g_inflight_batch_id = 0;
         g_inflight_sync_request = false;
+        invalidate_inflight_encode_cache();
       }
       note_fault(g_sender_faults, g_sender_last_error, g_sender_last_error_utc, g_sender_last_error_ms, FaultType::LoraTx);
       display_set_last_error(g_sender_last_error, g_sender_last_error_utc, g_sender_last_error_ms);