From 22db14bb4cda186d4588cf167cfde24cd39d8c51 Mon Sep 17 00:00:00 2001
From: andig <andi@evcc.io>
Date: Sun, 15 Sep 2024 16:18:27 +0200
Subject: [PATCH] Modbus: always assume RTU for serial devices (#16134)

---
 meter/mbmd.go              |  5 +++--
 util/modbus/modbus.go      |  2 +-
 util/modbus/modbus_test.go | 18 ++++++++++++++++++
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/meter/mbmd.go b/meter/mbmd.go
index 29876ea5e..a0497ebc4 100644
--- a/meter/mbmd.go
+++ b/meter/mbmd.go
@@ -53,8 +53,9 @@ func NewModbusMbmdFromConfig(other map[string]interface{}) (api.Meter, error) {
 
 	// assume RTU if not set and this is a known RS485 meter model
 	if cc.RTU == nil {
-		b := modbus.IsRS485(cc.Model)
-		cc.RTU = &b
+		if rtu := modbus.IsRS485(cc.Model); rtu {
+			cc.RTU = &rtu
+		}
 	}
 
 	modbus.Lock()
diff --git a/util/modbus/modbus.go b/util/modbus/modbus.go
index 2448418e9..3514db37d 100644
--- a/util/modbus/modbus.go
+++ b/util/modbus/modbus.go
@@ -47,7 +47,7 @@ func (s Settings) Protocol() Protocol {
 	switch {
 	case s.UDP:
 		return Udp
-	case s.RTU != nil && *s.RTU:
+	case s.Device != "" || s.RTU != nil && *s.RTU:
 		return Rtu
 	default:
 		return Tcp
diff --git a/util/modbus/modbus_test.go b/util/modbus/modbus_test.go
index 70a18082e..4ee4b0434 100644
--- a/util/modbus/modbus_test.go
+++ b/util/modbus/modbus_test.go
@@ -3,6 +3,7 @@ package modbus
 import (
 	"testing"
 
+	"github.com/samber/lo"
 	"github.com/stretchr/testify/require"
 )
 
@@ -23,3 +24,20 @@ func TestParsePoint(t *testing.T) {
 		require.Equal(t, tc.ops, ops)
 	}
 }
+
+func TestSettingsProtocol(t *testing.T) {
+	tc := []struct {
+		Settings
+		res Protocol
+	}{
+		{Settings{UDP: true}, Udp},
+		{Settings{RTU: lo.ToPtr(true)}, Rtu},
+		{Settings{Device: "foo"}, Rtu},
+		{Settings{URI: "foo"}, Tcp},
+		{Settings{}, Tcp},
+	}
+
+	for _, tc := range tc {
+		require.Equal(t, tc.res, tc.Protocol(), tc)
+	}
+}