Feature: Add offset option for scaling measurement values

config/devices.toml

@@ -18,6 +18,7 @@ signed=true
 multiplier=1
 divisor=1
 decimalshiftright=0
+offset=-20 # will be added to the value after the multiplier/divisor and decimalshiftright have been applied, negative offset gets subtracted
 input=false # true = Input Register false = Holding Register
 name="Test_Int16"
 #see https://thin-edge.github.io/thin-edge.io/html/architecture/thin-edge-json.html
@@ -33,6 +34,7 @@ signed=false
 multiplier=1
 divisor=1
 decimalshiftright=0
+#offset=0
 input=false
 datatype="float"
 name="Test_Float32"

tedge_modbus/operations/c8y_coils.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 """Cumulocity IoT c8y_Coils operation handler"""
+
 from .context import Context
 
 

tedge_modbus/operations/c8y_modbus_configuration.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 """Cumulocity ModbusConfiguration operation handler"""
+
 import json
 import logging
 import toml

tedge_modbus/operations/c8y_modbus_device.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 """Cumulocity Modbus device operation handler"""
+
 import logging
 from dataclasses import dataclass
 import json

tedge_modbus/operations/c8y_registers.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 """Cumulocity IoT c8y_Registers operation handler"""
+
 from .context import Context
 
 

tedge_modbus/operations/c8y_serial_configuration.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 """Cumulocity SerialConfiguration operation handler"""
+
 import json
 import logging
 import toml

tedge_modbus/reader/mapper.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 """Modbus mapper"""
+
 import json
 import struct
 import sys
@@ -136,7 +137,7 @@ def map_register(
                 * (register_def.get("multiplier") or 1)
                 * (10 ** (register_def.get("decimalshiftright") or 0))
                 / (register_def.get("divisor") or 1)
-            )
+            ) + (register_def.get("offset") or 0)
 
             on_change = register_def.get("on_change", False)
 

tedge_modbus/reader/reader.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 """Modbus reader"""
+
 import argparse
 import json
 import logging
@@ -20,7 +21,6 @@
 from .mapper import MappedMessage, ModbusMapper
 from ..operations import set_coil, set_register
 
-
 DEFAULT_FILE_DIR = "/etc/tedge/plugins/modbus"
 BASE_CONFIG_NAME = "modbus.toml"
 DEVICES_CONFIG_NAME = "devices.toml"

tests/unit/test_mapper.py

@@ -340,3 +340,86 @@ def test_event_mapping(self):
         self.assertEqual(len(messages2), 1)
         event_data2 = json.loads(messages2[0].data)
         self.assertEqual(event_data2["text"], "This event tests the event mapping")
+
+    def test_value_scaling_combined(self):
+        register_def = {
+            "number": 100,
+            "startbit": 0,
+            "nobits": 16,
+            "multiplier": 3,
+            "divisor": 4,
+            "decimalshiftright": 1,
+            "offset": -20,
+            "signed": False,
+            "measurementmapping": {"templatestring": '{"temp": %%}'},
+        }
+
+        messages, _ = self.mapper.map_register(
+            read_register=[20], register_def=register_def
+        )
+        data = json.loads(messages[0].data)
+        self.assertAlmostEqual(data["temp"], 130.0)
+
+    def test_value_scaling_multiplier(self):
+        register_def = {
+            "number": 100,
+            "startbit": 0,
+            "nobits": 16,
+            "multiplier": 3,
+            "signed": False,
+            "measurementmapping": {"templatestring": '{"temp": %%}'},
+        }
+
+        messages, _ = self.mapper.map_register(
+            read_register=[20], register_def=register_def
+        )
+        data = json.loads(messages[0].data)
+        self.assertAlmostEqual(data["temp"], 60.0)
+
+    def test_value_scaling_divisor(self):
+        register_def = {
+            "number": 100,
+            "startbit": 0,
+            "nobits": 16,
+            "divisor": 4,
+            "signed": False,
+            "measurementmapping": {"templatestring": '{"temp": %%}'},
+        }
+
+        messages, _ = self.mapper.map_register(
+            read_register=[20], register_def=register_def
+        )
+        data = json.loads(messages[0].data)
+        self.assertAlmostEqual(data["temp"], 5.0)
+
+    def test_value_scaling_decimalshiftright(self):
+        register_def = {
+            "number": 100,
+            "startbit": 0,
+            "nobits": 16,
+            "decimalshiftright": 2,
+            "signed": False,
+            "measurementmapping": {"templatestring": '{"temp": %%}'},
+        }
+
+        messages, _ = self.mapper.map_register(
+            read_register=[20], register_def=register_def
+        )
+        data = json.loads(messages[0].data)
+        self.assertAlmostEqual(data["temp"], 2000.0)
+
+    def test_value_scaling_offset(self):
+        register_def = {
+            "number": 100,
+            "startbit": 0,
+            "nobits": 16,
+            "offset": 10,
+            "signed": False,
+            "measurementmapping": {"templatestring": '{"temp": %%}'},
+        }
+
+        messages, _ = self.mapper.map_register(
+            read_register=[50], register_def=register_def
+        )
+        data = json.loads(messages[0].data)
+        self.assertAlmostEqual(data["temp"], 60.0)