contrib example: TCP drainage simulator with two devices

Simulates two Modbus TCP slave servers:

Digital IO (DIO) with 8 discrete inputs and 8 coils. The first two coils each
control a simulated pump. Inputs are not used.

Water level meter (WLM) returning the current water level in the input
register. It increases chronologically and decreases rapidly when one or
two pumps are active.

Author: serpent213

examples/contrib/drainage_sim.py

@@ -0,0 +1,70 @@
+#!/usr/bin/env python3
+
+# Simulates two Modbus TCP slave servers:
+#
+# Port 5020: Digital IO (DIO) with 8 discrete inputs and 8 coils. The first two coils each control
+#            a simulated pump. Inputs are not used.
+#
+# Port 5021: Water level meter (WLM) returning the current water level in the input register. It
+#            increases chronologically and decreases rapidly when one or two pumps are active.
+
+import asyncio
+import logging
+from datetime import datetime
+
+from pymodbus import __version__ as pymodbus_version
+from pymodbus.datastore import ModbusSequentialDataBlock, ModbusSlaveContext, ModbusServerContext
+from pymodbus.device import ModbusDeviceIdentification
+from pymodbus.server import StartAsyncTcpServer
+
+INITIAL_WATER_LEVEL = 300
+WATER_INFLOW = 1
+PUMP_OUTFLOW = 8
+
+logging.basicConfig(level = logging.INFO)
+
+dio_di = ModbusSequentialDataBlock(1, [False] * 8)
+dio_co = ModbusSequentialDataBlock(1, [False] * 8)
+dio_context = ModbusSlaveContext(di = dio_di, co = dio_co)
+wlm_ir = ModbusSequentialDataBlock(1, [INITIAL_WATER_LEVEL])
+wlm_context = ModbusSlaveContext(ir = wlm_ir)
+
+async def update():
+    while True:
+        await asyncio.sleep(1)
+
+        # Update water level based on DIO output values (simulating pumps)
+        water_level = wlm_ir.getValues(1, 1)[0]
+        dio_outputs = dio_co.getValues(1, 2)
+
+        water_level += WATER_INFLOW
+        water_level -= (int(dio_outputs[0]) + int(dio_outputs[1])) * PUMP_OUTFLOW
+        water_level = max(0, min(INITIAL_WATER_LEVEL * 10, water_level))
+        wlm_ir.setValues(1, [water_level])
+
+async def log():
+    while True:
+        await asyncio.sleep(10)
+
+        dio_outputs = dio_co.getValues(1, 8)
+        wlm_level = wlm_ir.getValues(1, 1)[0]
+
+        logging.info(f"{datetime.now()}: WLM water level: {wlm_level}, DIO outputs: {dio_outputs}")
+
+async def run():
+    ctx = ModbusServerContext(slaves = dio_context)
+    dio_server = asyncio.create_task(StartAsyncTcpServer(context = ctx, address = ("0.0.0.0", 5020)))
+    logging.info("Initialising slave server DIO on port 5020")
+
+    ctx = ModbusServerContext(slaves = wlm_context)
+    wlm_server = asyncio.create_task(StartAsyncTcpServer(context = ctx, address = ("0.0.0.0", 5021)))
+    logging.info("Initialising slave server WLM on port 5021")
+
+    update_task = asyncio.create_task(update())
+    logging_task = asyncio.create_task(log())
+
+    logging.info("Init complete")
+    await asyncio.gather(dio_server, wlm_server, update_task, logging_task)
+
+if __name__ == "__main__":
+    asyncio.run(run(), debug=True)