From fee9c23a1599a48797a2934521fa4d517a76aa0b Mon Sep 17 00:00:00 2001
From: nicoboy <contact@nicolasboyer.fr>
Date: Sun, 21 Jun 2026 16:18:05 +0200
Subject: [PATCH] =?UTF-8?q?Buffer=20UART=20bytes=20before=20UDP=20send=20?=
 =?UTF-8?q?=E2=80=94=20fix=20MAVLink=20frame=20fragmentation?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Accumulate UART bytes and flush to UDP only when buffer is full (512B)
or after 3ms of UART inactivity (end-of-frame gap). Fixes mavp2p
"packet too short" / "invalid magic byte" errors caused by sending
partial MAVLink frames in separate UDP packets.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 src/main.cpp | 39 ++++++++++++++++++++++++---------------
 1 file changed, 24 insertions(+), 15 deletions(-)

diff --git a/src/main.cpp b/src/main.cpp
index 961ed3a..dae6a46 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -40,6 +40,13 @@ uint32_t bytesUartToUdp = 0;
 uint32_t bytesUdpToUart = 0;
 unsigned long lastStatsTime = 0;
 
+// ── Buffer UART → UDP ────────────────────────────────────
+#define UART_BUF_SIZE   512
+#define UART_FLUSH_MS   3
+uint8_t uartBuf[UART_BUF_SIZE];
+int uartBufLen = 0;
+unsigned long uartLastByteTime = 0;
+
 // ── LED non bloquante ─────────────────────────────────────
 void updateLED() {
   unsigned long elapsed = millis() - ledStateStart;
@@ -135,21 +142,23 @@ void loop() {
 
   if (!wifiConnected) return;
 
-  // UART → UDP (H743 → Jetson)
-  if (MavSerial.available()) {
-    uint8_t buf[512];
-    int len = 0;
-    while (MavSerial.available() && len < (int)sizeof(buf)) {
-      buf[len++] = MavSerial.read();
-    }
-    if (len > 0) {
-      udp.beginPacket(TARGET_IP, UDP_PORT);
-      udp.write(buf, len);
-      udp.endPacket();
-      bytesUartToUdp += len;
-      setLedState(LED_ACTIVITY);
-      Serial.printf("[UART->UDP] %d bytes\n", len);
-    }
+  // UART → UDP (H743 → Jetson) — accumulation puis flush
+  while (MavSerial.available() && uartBufLen < UART_BUF_SIZE) {
+    uartBuf[uartBufLen++] = MavSerial.read();
+    uartLastByteTime = millis();
+  }
+
+  bool flushNow = uartBufLen > 0 &&
+    (uartBufLen >= UART_BUF_SIZE || millis() - uartLastByteTime >= UART_FLUSH_MS);
+
+  if (flushNow) {
+    udp.beginPacket(TARGET_IP, UDP_PORT);
+    udp.write(uartBuf, uartBufLen);
+    udp.endPacket();
+    bytesUartToUdp += uartBufLen;
+    setLedState(LED_ACTIVITY);
+    Serial.printf("[UART->UDP] %d bytes\n", uartBufLen);
+    uartBufLen = 0;
   }
 
   // UDP → UART (Jetson → H743)