LoPy4 change uplink channels by itself?

  • Hi everyone, the problem I am having now is, LoPy4 changes uplink channels by itself.
    Since my gateway only listens to 8 channels, I deleted all the CN470 channels and add 8 channels by doing this:
    for i in range(0, 96):
    lora.add_channel(index=84, frequency=487100000, dr_min=0, dr_max=5)
    lora.add_channel(index=85, frequency=487300000, dr_min=0, dr_max=5)
    lora.add_channel(index=86, frequency=487500000, dr_min=0, dr_max=5)
    lora.add_channel(index=87, frequency=487700000, dr_min=0, dr_max=5)
    lora.add_channel(index=80, frequency=486300000, dr_min=0, dr_max=5)
    lora.add_channel(index=81, frequency=486500000, dr_min=0, dr_max=5)
    lora.add_channel(index=82, frequency=486700000, dr_min=0, dr_max=5)
    lora.add_channel(index=83, frequency=486900000, dr_min=0, dr_max=5)
    It works fine at the beginning. In the figure below you can see its sending uplinks using the 8 channels I added.
    After LoPy4 wakes up from deep sleep, I use lora.nvram_save() and lora.nvram_restore() to restore LoRa's join status. However, LoPy4 will not send uplink using the 8 channels I added at the beginning. Instead, its sending uplinks on random channels in the CN470 frequency band. In the figure below, you can see it is using none of the channels I defined at the beginning.
    In the documentation, it says that the lora.nvram_save can store the LoRaWAN state, but it looks like uplink channels information will not be saved?
    So I disabled the lora.nvram_save and lora.nvram_restore, then I copied the "delete all the channels and add my own channels" code and pasted it to the place where LoPy4 just wakes up from deep sleep. But I had the same issues, which makes no sense.
    Has anyone run into a similar problem?? Really appreciate if someone can give me some suggestions. Thank you!

  • @robert-hh Okay thanks, I will try this firmware, and test lora.remove_channel(i), then add channel AS923-2 freqs (921.4MHz & 921.6MHz ).

  • @Gusti-Made-Arya-Wijaya I added a 1.20.2.r6 version for LoPy4 with the cn470 channel remove fixed to Shared stuff. Maybe that one works.

  • @robert-hh yes, the bug in lora.remove_channel(i) is not fixed yet, I think lora.remove_channel(i) is not work in all regions. Need help to fix it, because in Indonesia using AS923-2

  • @Gusti-Made-Arya-Wijaya There is in the README.MD of the pycom-micropython-sigfox directory, and in the ESP32 port directory. It's tricky to set up the build environment. It has to be a Linux OS.

  • @robert-hh yes, I have tried it and tested my code like on previous page. Is there any guidance to build custom firmware?

  • @Gusti-Made-Arya-Wijaya There was this bug that ora.remove_channel(i) did not work for the CN470 region. I made a PR in Aug 2020 to fix that, but I cannot tell whether that was implemented. I do not see it in the Release/v1.20 branch, which seems to be the most recent one, with the most recent change on Dec 6, 20121. The repository management of Pycom is by black box. With many branches of unclear usage.

  • @Gusti-Made-Arya-Wijaya Didn't you try already the firmware from Shared Stuff and it did not work? In that case, you have to change the source files and build your own firmware.

  • @Gusti-Made-Arya-Wijaya @robert-hh Hello Robert, Should I modify region.c file in ...../pycom-micropython-sigfox/lib/lora/mac/region then re-compile the firmware? or can use this firmware https://github.com/robert-hh/Shared-Stuff.git ?

  • @robert-hh hello, sorry for super late reply, I have tried it, but still can't join using gateway with AS923-2 freq plan, If I replace the gateway with AS923-1 freq plan, my Lopy4 can join. So the freq play from lopy4 is not change

  • @Gusti-Made-Arya-Wijaya Don't you have to call prepare_channels before lora.join()? And do you have a gateway in reach?

  • hello @robert-hh I have uploaded firmware from https://github.com/robert-hh/Shared-Stuff.git and then uploaded script that I posted previously. but my lopy4 still can't join AS923-2 (921.4MHz & 921.6MHz ).

  • @robert-hh Hello, any update on this? I have the same issue, I want to change the uplink/downlink channel from AS923 to AS923-2 (912.4Mhz and 921.6MHz) but Lopy4 still keep default channel. I've modified code from https://github.com/pycom/pycom-libraries/blob/master/examples/lorawan-regional-examples/main_AS923.py , here is my code

    # Copyright (c) 2019, Pycom Limited.
    # This software is licensed under the GNU GPL version 3 or any
    # later version, with permitted additional terms. For more information
    # see the Pycom Licence v1.0 document supplied with this file, or
    # available at https://www.pycom.io/opensource/licensing
        OTAA Node example  as per LoRaWAN AS923 regional specification
        - compatible with the LoPy Nano Gateway and all other LoraWAN gateways
        - tested works with a LoRaServer, shall works on TTN servers
    from network import LoRa
    import socket
    import ubinascii
    import struct
    import time
    LORA_NODE_DR = 4
        utility function to setup the lora channels
    def prepare_channels(lora, channel, data_rate):
        # AS923_FREQUENCIES = [
        #     { "chan": 1, "fq": "923200000" },
        #     { "chan": 2, "fq": "923400000" },
        #     { "chan": 3, "fq": "922200000" },
        #     { "chan": 4, "fq": "922400000" },
        #     { "chan": 5, "fq": "922600000" },
        #     { "chan": 6, "fq": "922800000" },
        #     { "chan": 7, "fq": "923000000" },
        #     { "chan": 8, "fq": "922000000" },
        # ]
        AS923_FREQUENCIES = [
            { "chan": 1, "fq": "922600000" },
            { "chan": 2, "fq": "922400000" },
            { "chan": 3, "fq": "922200000" },
            { "chan": 4, "fq": "922000000" },
            { "chan": 5, "fq": "921800000" },
            { "chan": 6, "fq": "921600000" },
            { "chan": 7, "fq": "921400000" },
            { "chan": 8, "fq": "921200000" },
        if not channel in range(0, 9):
            raise RuntimeError("channels should be in 1-8 for AS923")
        if channel == 0:
            import  uos
            channel = (struct.unpack('B',uos.urandom(1))[0] % 7) + 1
        for i in range(0, 8):
        upstream = (item for item in AS923_FREQUENCIES if item["chan"] == channel).__next__()
        # set default channels frequency
        lora.add_channel(int(upstream.get('chan')), frequency=int(upstream.get('fq')), dr_min=0, dr_max=data_rate)
        return lora
        call back for handling RX packets
    def lora_cb(lora):
        events = lora.events()
        if events & LoRa.RX_PACKET_EVENT:
            if lora_socket is not None:
                frame, port = lora_socket.recvfrom(512) # longuest frame is +-220
                print(port, frame)
        if events & LoRa.TX_PACKET_EVENT:
            print("tx_time_on_air: {} ms @dr {}", lora.stats().tx_time_on_air, lora.stats().sftx)
        Main operations: this is sample code for LoRaWAN on AS923
    lora = LoRa(mode=LoRa.LORAWAN, region=LoRa.AS923, device_class=LoRa.CLASS_C, adr=False, tx_power=20)
    # create an OTA authentication params
    # dev_eui = binascii.unhexlify('0000000000000000')
    # app_key = binascii.unhexlify('a926e5bb85271f2d') # not used leave empty loraserver.io
    # nwk_key = binascii.unhexlify('a926e5bb85271f2da0440f2f4200afe3')
    app_eui = ubinascii.unhexlify('**************')
    app_key = ubinascii.unhexlify('*******************')
    # join a network using OTAA
    # lora.join(activation=LoRa.OTAA, auth=(dev_eui, app_key, nwk_key), timeout=0, dr=2) # AS923 always joins at DR2
    lora.join(activation=LoRa.OTAA, auth=(app_eui, app_key), timeout=0, dr=2) # AS923 always joins at DR2
    prepare_channels(lora, LORA_CHANNEL,  LORA_NODE_DR)
    # wait until the module has joined the network
    print('Over the air network activation ... ', end='')
    while not lora.has_joined():
        print('.', end='')
    # create a LoRa socket
    lora_socket = socket.socket(socket.AF_LORA, socket.SOCK_RAW)
    # set the LoRaWAN data rate
    lora_socket.setsockopt(socket.SOL_LORA, socket.SO_DR, LORA_NODE_DR)
    # msg are confirmed at the FMS level
    lora_socket.setsockopt(socket.SOL_LORA, socket.SO_CONFIRMED, 0)
    # make the socket non blocking y default
    lora.callback(trigger=( LoRa.RX_PACKET_EVENT |
                            LoRa.TX_PACKET_EVENT |
                            LoRa.TX_FAILED_EVENT  ), handler=lora_cb)
    time.sleep(4) # this timer is important and caused me some trouble ...
    for i in range(0, 1000):
        pkt = struct.pack('>H', i)
        print('Sending:', pkt)

  • @sheng That's fine. I will then make a Pull Request for the fix of lora.remove_channel(). Because that did not work before.

  • @robert-hh It Finally Works! But I didn't use the lora.add_channel function, instead, I just remove all the channels I dont need. So its something like this.
    for i in range(0, 79):
    for i in range(88,96):
    Again, thank you so much for your help and patience, I really appreciate it!

  • @sheng You could try to move the join before the channel reconfiguration. AFAIK, the channel udate is part of the join response,

  • @robert-hh I see what you mean, but I am using ChirpStack. I tried the method you provided, but I still have the same problem. After I upload the code to the board, it works fine, it only uses the eight channels I added. But after it went back from deep sleep, it started sending using random frequencies again, which is annoying.
    It seems the lora_add_channel() is not working.

  • @sheng no. You have to remove all channels, like you did initially, because the ttn server can add channels by service messages. And these are the ones you see.
    edit: My code change makes the call to lora.remove_channel() working, which it did not before.

  • @robert-hh Thank you for your help, but I am having the same problem even though I am using the firmware you provided. I didn't make any changes to the firmware. What I did is just flash my board with the firmware you provided, and then run the same code again(but this time, I didn't remove all the channels, I just add 8 channels). Am I doing it right? Or I understand it wrong. Do you mean I don't need to remove any channels? And I can just add the channels I am using with "lora.add_channel" if I am using the firmware you provided.
    Again, thank you so much for your patience and time. Really appreciate it!

  • @sheng Right

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