Who-Is Service response : Device Object's Instance number and Address

[rprronad]

Who is allocating the Device Object's Instant number and address to the BACnet device by sending Who-Is service from the client device and also Who can able use(Only client or Both client and server) the Who-Is service in the BACnet network?

[bbartling]

can you give more context to your use case?

if you are setting up inside a building for the first time imitating this command I think its the devices inside the building that responding. The devices BACnet Instance ID and address is configured by the vendor that initially set it up and each device needs to be unique.

I think BAC0 does a who-is or something like that to the nature on an interval so it understands the local environment.

[rprronad]

Thanks @bbartling,

From the below attached file, I came to know that Instance number has been generated for the particular BACnet device, so can you confirm for particular case, if two vendor using this BAC0 library & developed some protocol converters means, at time it will give same Instance ID for vendor device and then it will go offline as you said earlier.

So How can it be identified and resolve the conflict of Instance number ?

[bbartling]

when i make an app like:

bacnet = BAC0.lite()

if i need it to be custom IDs or ports, etc... I make bacnet var with passing in something like this below. I am experimenting with dual NIC card Nano Pi device where the internet connection is one NIC and the other NIC is for the OT LAN that requires a static IP for the buildings BACnet network:

# BACnet NIC setup:
BACNET_INST_ID = 3056672
IP_ADDRESS = "192.168.0.109"
SUBNET_MASK_CIDAR = 24
PORT = "47808"
BBMD = None

bacnet = BAC0.lite(ip=IP_ADDRESS, port=PORT , mask=SUBNET_MASK_CIDAR, deviceId=BACNET_INST_ID, bbmdAddress=BBMD)

you dont need to pass in all those params, if you just need a custom deviceID you can just pass that one in or set the others as None

I typically set my device ID's real high with the assumptions that the people setting up the stuff inside the buildings set devices IDs real low...and it generally works. At least when I was in the field setting up the stuff I would just start at device 1 and increment up by 1 for each embedded device I was setting up in the temperature control system where it was rare if it were the last device was over the value of 100. A 100+ BACnet devices inside a building is more than likely a large building...so the field guys usually make device ID's low and if you go high shooting at the hip your generally good to go

[rprronad]

@bbartling Thanks, Gave me good information.

and now Can you suggest me How to do I/O data mapping table for BACnet to Modbus Protocol converter ? Give some examples as well.

[bbartling]

are building something custom for a specific building or a very generic application that would work in any building?

is your app to be a "server" where people on some external platform write to it like via Modbus where then there would be a BACnet API on the other side to see translated values? OR would it be your just doing something custom on some random building... read Modbus values, then write to the BACnet system for some translated values of the Modbus sensor..

[rprronad]

I'm developing s/w for "very generic application that would work in any building" and that Protocol converter is to translate the Data from Modbus registers into BACnet things.

[bbartling]

So if you wanted to make a gateway for Modbus to BACnet this may get you started. I have only tinkered with Modbus and dont know a whole lot about.

This code below the app reads a modbus sensor value (its a power meter) every 60 seconds and then it also acts as a discoverable BACnet device (server) where then the modbus sensor can be visible to the BACnet network if other devices or control systems request that value from the BACnet server.

I dont honestly know a ton about Modbus and when I was making my app I had to get some help on stackoverflow to making the Modbus client read request work...but that code below did work on a power meter inside a building at one point in time the Modbus registry stuff could be very unique to the device

Good luck : )

import asyncio
from datetime import datetime, timezone, timedelta
import threading
import logging
from BAC0.core.devices.local.models import analog_value
import BAC0

from pymodbus.client import ModbusTcpClient
from pymodbus.constants import Endian
from pymodbus.payload import BinaryPayloadDecoder

# Constants for BACnet NIC setup
IP_ADDRESS = "192.168.0.109"
SUBNET_MASK_CIDAR = 24
PORT = "47820"
BBMD = None
BACNET_INST_ID = 3056672

# Constants for the Modbus meter sensor
MODBUS_METER_ADDRESS = '192.168.0.111'
MODBUS_METER_PORT = 502
MODBUS_INPUT_REG = 17

# BACnetApp class for BACnet setup
class BACnetApp:
    @classmethod
    async def create(cls):
        self = BACnetApp()
        self.bacnet = await asyncio.to_thread(BAC0.lite, ip=IP_ADDRESS, port=PORT, mask=SUBNET_MASK_CIDAR, deviceId=BACNET_INST_ID, bbmdAddress=BBMD)
        self.building_meter = -1.0  # Default power value
        _new_objects = self.create_objects()
        _new_objects.add_objects_to_application(self.bacnet)
        logging.info("BACnet APP Created Success!")
        return self

    # create one discoverable BACnet point on the your 
    # BACnet server app
    def create_objects(self):
        _new_objects = analog_value(
            name="power-level",
            description="Writeable point for electric meter reading",
            presentValue=-1.0, # default data
            is_commandable=False,
        )
        return _new_objects

    async def update_bacnet_api(self, value):
        electric_meter_obj = self.bacnet.this_application.get_object_name("power-level")
        electric_meter_obj.presentValue = value
        print("BACnet API updated to:", electric_meter_obj.presentValue)

    async def keep_baco_alive(self):
        counter = 0
        while True:
            counter += 1
            await asyncio.sleep(0.01)
            if counter == 100:
                counter = 0
                async with self.server_check_lock:
                    await self.update_bacnet_api(self.building_meter)

    async def modbus_meter_reader(self):

        try:
            client = ModbusTcpClient(MODBUS_METER_ADDRESS,
                                     port=MODBUS_METER_PORT)
            
            result = client.read_input_registers(500,2,units=1)
            print(result.registers)
            decoder = BinaryPayloadDecoder.fromRegisters(result.registers, 
                                                         byteorder=Endian.Big)
            data = decoder.decode_32bit_float()
            print("MODBUS electric meter read: ", data)
            self.building_meter = round(data,3)
            client.close()

        except:
            print("ERROR ON MODBUS METER READ")
            client.close()
            self.building_meter = -1.0

        await asyncio.sleep(60)

async def main():
    bacnet_app = await BACnetApp.create()

    tasks = [bacnet_app.keep_baco_alive(), bacnet_app.modbus_meter_reader()]

    bacnet_app.server_check_lock = asyncio.Lock()  # Create a lock for synchronization

    await asyncio.gather(*tasks)

asyncio.run(main())

[bbartling]

I also forgot to note @rprronad if you get some odd errors when updating the BACnet api for the Modbus sensor value i think it can because in BACnet they use very odd data types something like a primitive data type called a Real...

So you may have to do something like this below if you attempt to update the BACnet side with a numeric value and it errors out:

from bacpypes.primitivedata import Real


    async def update_bacnet_api(self, value):
        electric_meter_obj = self.bacnet.this_application.get_object_name("power-level")

        electric_meter_obj.presentValue = Real(value)

[bbartling]

This function looks sort of odd too but I notice that BAC0 dies if its not in a while loop...and if the asnycio sleeps are long like anything up to a second or greater i notice lag on the BACnet server when testing it out on a BACnet scan tool.

    async def keep_baco_alive(self):
        counter = 0
        while True:
            counter += 1
            await asyncio.sleep(0.01)
            if counter == 100:
                counter = 0
                async with self.server_check_lock:
                    await self.update_bacnet_api(self.building_meter)

[rprronad]

I really appreciate your patient explanations and quick responses and Thanks a lot @bbartling for sharing your knowledge and wishes.

[bbartling]

let me know how it goes...it maybe can be done better. Post whatever you make.

The Modbus side is a bit of a mystery so I would be learning from you on what you get working

[rprronad]

Okay sure @bbartling,

& also If you got any updates, just mail me.