After 10 years,
TMS is coming back.

Read-only polling with a model-specific register map

Use a configuration profile for each verified controller. The addresses and scaling below are deliberately fictional to prevent accidental use on live refrigeration equipment. The serial settings shown are illustrative, not Danfoss defaults; confirm baud rate, parity and stop bits from the exact controller documentation.

from datetime import datetime, timezone
from pymodbus.client import ModbusSerialClient

# EXAMPLE ONLY: replace with the official register map
PROFILE = {
    "model": "verified-controller-model",
    "unit_id": 1,
    "room_temp": {
        "address": 100,  # FICTIONAL, NOT a vendor address
        "scale": 0.1,
        "signed": True,
    },
}

def decode_word(raw, signed=False):
    if signed and raw >= 0x8000:
        return raw - 0x10000
    return raw

client = ModbusSerialClient(
    port="/dev/ttyUSB0",
    baudrate=9600, parity="N", stopbits=1,
    bytesize=8, timeout=2,
)

try:
    if not client.connect():
        raise ConnectionError("RS-485 adapter unavailable")

    reg = PROFILE["room_temp"]
    reply = client.read_holding_registers(
        address=reg["address"], count=1,
        device_id=PROFILE["unit_id"],
    )
    if reply.isError():
        raise RuntimeError(f"Modbus error: {reply}")

    raw = decode_word(reply.registers[0], reg["signed"])
    payload = {
        "controller": PROFILE["model"],
        "temperature_c": raw * reg["scale"],
        "timestamp": datetime.now(timezone.utc).isoformat(),
        "quality": "sample_read_only",  # Not yet validated against a real device
    }
    print(payload)
finally:
    client.close()

Publish verified readings to AWS IoT Core

The gateway uses its own provisioned device certificate and private key to authenticate to AWS IoT Core. MQTT payloads include device identity, measurement time and quality status.

# pip install paho-mqtt
import json
import os
import ssl
import paho.mqtt.client as mqtt

ENDPOINT = os.environ["AWS_IOT_ENDPOINT"]
THING_ID = os.environ["TMS_THING_ID"]
TOPIC = f"tms/{THING_ID}/telemetry"

# Paths to securely provisioned device credentials
CA = "/etc/tms/certs/AmazonRootCA1.pem"
CERT = "/etc/tms/certs/device.pem.crt"
KEY = "/etc/tms/certs/private.pem.key"

client = mqtt.Client(
    callback_api_version=mqtt.CallbackAPIVersion.VERSION2,
    client_id=THING_ID,
    protocol=mqtt.MQTTv311,
)
client.tls_set(
    ca_certs=CA,
    certfile=CERT,
    keyfile=KEY,
    cert_reqs=ssl.CERT_REQUIRED,
    tls_version=ssl.PROTOCOL_TLS_CLIENT,
)

telemetry = {
    "device_id": THING_ID,
    "temperature_c": 2.4,
    "quality": "sample_read_only",  # Not yet validated against a real device
    "source": "modbus_rtu",
}

client.connect(ENDPOINT, port=8883, keepalive=60)
client.loop_start()
try:
    result = client.publish(
        TOPIC, json.dumps(telemetry), qos=1
    )
    result.wait_for_publish(timeout=10)
    if not result.is_published():
        raise TimeoutError("MQTT publish not confirmed")
finally:
    client.disconnect()
    client.loop_stop()

Controller profiles make integrations maintainable

Each controller integration should ship with a versioned, verified profile rather than hard-coded assumptions shared across manufacturers.

{
  "vendor": "EXAMPLE_ONLY",
  "model": "VERIFY_EXACT_MODEL",
  "protocol": "modbus_rtu",
  "serial": {
    "baudrate": 9600,
    "parity": "N",
    "stopbits": 1,
    "slave_id": 1
  },
  "registers": {
    "room_temperature": {
      "address": 100,
      "function": "holding",
      "signed": true,
      "scale": 0.1,
      "unit": "celsius"
    }
  },
  "read_only": true,
  "verified_against_manual": false
}

How remote setpoint requests would work

App → authenticated API → policy validation → signed/authorised cloud command → gateway → controller. The gateway checks the device model, approved parameter, permitted range, freshness and command expiry before any write.

• Default to read-only integrations.
• Require role-based access and audit logs for every requested change.
• Verify controller readback after a write; show failure if unconfirmed.
• Rate-limit and expire commands; reject requests when communications are stale.
• Never bypass compressor protection, defrost logic or safety interlocks.