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new 19dcd452ff5 net/tcp: add kconfig to support retransmission at a fixed
time
19dcd452ff5 is described below
commit 19dcd452ff535c2ce3f9e16002bb9eac3d5254ca
Author: zhanghongyu <[email protected]>
AuthorDate: Mon Aug 4 21:26:55 2025 +0800
net/tcp: add kconfig to support retransmission at a fixed time
the maximum retransmission interval allowed for car projects
cannot exceed 6 seconds, and allows for fixed retransmission intervals.
according to the previous algorithm, the retransmission interval
may be 0.5 * 2 ^ 4 = 8 seconds, which does not meet the requirements.
Signed-off-by: zhanghongyu <[email protected]>
---
net/tcp/Kconfig | 16 +++++++++++++++-
net/tcp/tcp_input.c | 2 ++
net/tcp/tcp_timer.c | 2 ++
3 files changed, 19 insertions(+), 1 deletion(-)
diff --git a/net/tcp/Kconfig b/net/tcp/Kconfig
index 734379daa7b..09c1dda7cd5 100644
--- a/net/tcp/Kconfig
+++ b/net/tcp/Kconfig
@@ -105,7 +105,21 @@ config NET_TCP_RTO
int "RTO of TCP/IP connections"
default 3
---help---
- RTO of TCP/IP connections (all tasks)
+ Default retransmission timeout (RTO) of TCP/IP connections (all
tasks).
+ In units of half seconds. When the same data packet is
retransmitted
+ multiple times due to timeout, the RTO will be doubled. but the
maximum
+ RTO is NET_TCP_RTO * 16. When this packet is ACKed, the RTO
will be
+ reset to this value. This algorithm helps to reduce network
congestion
+ to some extent.
+
+config NET_TCP_FIXED_RTO
+ bool "Use fixed RTO"
+ default n
+ ---help---
+ Use fixed RTO for TCP/IP connections (all tasks), i.e. do not
use
+ the RTO exponentially increasing algorithm. This is useful for
projects
+ that require a fixed RTO value or have restrictions on the
maximum
+ retransmission time.
config NET_TCP_MAXRTX
int "Maximum retransmitted number of TCP/IP data packet"
diff --git a/net/tcp/tcp_input.c b/net/tcp/tcp_input.c
index 07780467135..df74dcb3d26 100644
--- a/net/tcp/tcp_input.c
+++ b/net/tcp/tcp_input.c
@@ -1082,6 +1082,7 @@ found:
}
#endif
+#ifndef CONFIG_NET_TCP_FIXED_RTO
/* Do RTT estimation, unless we have done retransmissions. */
if (conn->nrtx == 0)
@@ -1102,6 +1103,7 @@ found:
conn->sv += m;
conn->rto = (conn->sa >> 3) + conn->sv;
}
+#endif
/* Set the acknowledged flag. */
diff --git a/net/tcp/tcp_timer.c b/net/tcp/tcp_timer.c
index 76715c0471c..5e0fefc1b51 100644
--- a/net/tcp/tcp_timer.c
+++ b/net/tcp/tcp_timer.c
@@ -579,7 +579,9 @@ void tcp_timer(FAR struct net_driver_s *dev, FAR struct
tcp_conn_s *conn)
/* Exponential backoff. */
+#ifndef CONFIG_NET_TCP_FIXED_RTO
conn->rto = TCP_RTO << (conn->nrtx > 4 ? 4: conn->nrtx);
+#endif
tcp_update_retrantimer(conn, conn->rto);
conn->nrtx++;
