From 239918ccc173cb2c2a62f41a40fd893f57faf1d6 Mon Sep 17 00:00:00 2001
From: yuanjm <yuanjianmin@espressif.com>
Date: Wed, 15 Apr 2020 10:26:04 +0800
Subject: [PATCH] tcp: Make retransmission timeout (RTO) configurable

---
 src/core/tcp.c         | 6 ++++--
 src/include/lwip/opt.h | 9 +++++++++
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/src/core/tcp.c b/src/core/tcp.c
index 5b4f4e5e..1abea8e0 100644
--- a/src/core/tcp.c
+++ b/src/core/tcp.c
@@ -1901,8 +1901,10 @@ tcp_alloc(u8_t prio)
     /* As initial send MSS, we use TCP_MSS but limit it to 536.
        The send MSS is updated when an MSS option is received. */
     pcb->mss = INITIAL_MSS;
-    pcb->rto = 3000 / TCP_SLOW_INTERVAL;
-    pcb->sv = 3000 / TCP_SLOW_INTERVAL;
+    /* Set initial TCP's retransmission timeout to 3000 ms by default.
+       This value could be configured in lwipopts */
+    pcb->rto = LWIP_TCP_RTO_TIME / TCP_SLOW_INTERVAL;
+    pcb->sv = LWIP_TCP_RTO_TIME / TCP_SLOW_INTERVAL;
     pcb->rtime = -1;
     pcb->cwnd = 1;
     pcb->tmr = tcp_ticks;
diff --git a/src/include/lwip/opt.h b/src/include/lwip/opt.h
index 9fe0bf04..08c2628a 100644
--- a/src/include/lwip/opt.h
+++ b/src/include/lwip/opt.h
@@ -1337,6 +1337,15 @@
 #define TCP_CALCULATE_EFF_SEND_MSS      1
 #endif
 
+/**
+ * LWIP_TCP_RTO_TIME: Initial TCP retransmission timeout (ms).
+ * This defaults to 3 seconds as traditionally defined in the TCP protocol.
+ * For improving timely recovery on faster networks, this value could
+ * be lowered down to 1 second (RFC 6298)
+ */
+#if !defined LWIP_TCP_RTO_TIME || defined __DOXYGEN__
+#define LWIP_TCP_RTO_TIME               3000
+#endif
 
 /**
  * TCP_SND_BUF: TCP sender buffer space (bytes).