LoRa.ABP Downlink messages no receive

  • I have implemented a LoRa nanogateway with LoPy connected to TTN.
    I have also another LoPy (Node) transmitting data via this gateway.

    Whenever I create a downlink message via TTN I can see it in nanogateway but the message is never arrived at LoPy Node.

  • @jcaron I know that you must perform an uplink in order to have a downlink.

    The strange thing is that the nanogateway makes the LoRa TX but nothing is received.

    Nano Gateway code

    """ LoPy Nano Gateway class """
    from network import WLAN
    from network import LoRa
    from machine import Timer
    from network import Server as tcpserver
    import os
    import binascii
    import machine
    import json
    import time
    import errno
    import _thread
    import socket
    PROTOCOL_VERSION = const(2)
    PUSH_DATA = const(0)
    PUSH_ACK = const(1)
    PULL_DATA = const(2)
    PULL_ACK = const(4)
    PULL_RESP = const(3)
    STAT_PK = {"stat": {"time": "", "lati": 0,
                        "long": 0, "alti": 0,
                        "rxnb": 0, "rxok": 0,
                        "rxfw": 0, "ackr": 100.0,
                        "dwnb": 0, "txnb": 0}}
    RX_PK = {"rxpk": [{"time": "", "tmst": 0,
                       "chan": 0, "rfch": 0,
                       "freq": 868.1, "stat": 1,
                       "modu": "LORA", "datr": "SF7BW125",
                       "codr": "4/5", "rssi": 0,
                       "lsnr": 0, "size": 0,
                       "data": ""}]}
    TX_ACK_PK = {"txpk_ack":{"error":""}}
    class NanoGateway:
        def __init__(self, id, frequency, datarate, ssid, password, server, port, ntp='pool.ntp.org', ntp_period=3600):
            self.id = id
            self.frequency = frequency
            self.datarate = datarate
            self.sf = self._dr_to_sf(datarate)
            self.ssid = ssid
            self.password = password
            self.server = server
            self.port = port
            self.ntp = ntp
            self.ntp_period = ntp_period
            self.rxnb = 0
            self.rxok = 0
            self.rxfw = 0
            self.dwnb = 0
            self.txnb = 0
            self.stat_alarm = None
            self.pull_alarm = None
            self.uplink_alarm = None
            self.udp_lock = _thread.allocate_lock()
            self.lora = None
            self.lora_sock = None
        def start(self):
            # Change WiFi to STA mode and connect
            print("Starting nanogateway")
            self.wlan = WLAN(mode=WLAN.STA)
            # Get a time Sync
            self.rtc = machine.RTC()
            self.rtc.ntp_sync(self.ntp, update_period=self.ntp_period)
            # Get the server IP and create an UDP socket
            self.server_ip = socket.getaddrinfo(self.server, self.port)[0][-1]
            print("Gateway IP:",self.server_ip)
            self.sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
            self.sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
            # Push the first time immediatelly
            # Create the alarms
            self.stat_alarm = Timer.Alarm(handler=lambda t: self._push_data(self._make_stat_packet()), s=60, periodic=True)
            self.pull_alarm = Timer.Alarm(handler=lambda u: self._pull_data(), s=25, periodic=True)
            # Start the UDP receive thread
            _thread.start_new_thread(self._udp_thread, ())
            # Initialize LoRa in LORA mode
            self.lora = LoRa(mode=LoRa.LORA, frequency=self.frequency, bandwidth=LoRa.BW_125KHZ, sf=self.sf,
                             preamble=8, coding_rate=LoRa.CODING_4_5, tx_iq=True)
            # Create a raw LoRa socket
            self.lora_sock = socket.socket(socket.AF_LORA, socket.SOCK_RAW)
            self.lora_tx_done = False
            self.lora.callback(trigger=(LoRa.RX_PACKET_EVENT | LoRa.TX_PACKET_EVENT), handler=self._lora_cb)
        def stop(self):
            # TODO: Check how to stop the NTP sync
            # TODO: Create a cancel method for the alarm
            # TODO: kill the UDP thread
        def _connect_to_wifi(self):
            self.wlan.connect(self.ssid, auth=(None, self.password))
            while not self.wlan.isconnected():
            print("WiFi connected!")
            tserver.init(login=("nemet", "nemet.gr"), timeout=60)
        def _dr_to_sf(self, dr):
            sf = dr[2:4]
            if sf[1] not in '0123456789':
                sf = sf[:1]
            return int(sf)
        def _sf_to_dr(self, sf):
            return self.datarate
        def _make_stat_packet(self):
            now = self.rtc.now()
            STAT_PK["stat"]["time"] = "%d-%02d-%02d %02d:%02d:%02d GMT" % (now[0], now[1], now[2], now[3], now[4], now[5])
            STAT_PK["stat"]["rxnb"] = self.rxnb
            STAT_PK["stat"]["rxok"] = self.rxok
            STAT_PK["stat"]["rxfw"] = self.rxfw
            STAT_PK["stat"]["dwnb"] = self.dwnb
            STAT_PK["stat"]["txnb"] = self.txnb
            return json.dumps(STAT_PK)
        def _make_node_packet(self, rx_data, rx_time, tmst, sf, rssi, snr):
            RX_PK["rxpk"][0]["time"] = "%d-%02d-%02dT%02d:%02d:%02d.%dZ" % (rx_time[0], rx_time[1], rx_time[2], rx_time[3], rx_time[4], rx_time[5], rx_time[6])
            RX_PK["rxpk"][0]["tmst"] = tmst
            RX_PK["rxpk"][0]["datr"] = self._sf_to_dr(sf)
            RX_PK["rxpk"][0]["rssi"] = rssi
            RX_PK["rxpk"][0]["lsnr"] = float(snr)
            RX_PK["rxpk"][0]["data"] = binascii.b2a_base64(rx_data)[:-1]
            RX_PK["rxpk"][0]["size"] = len(rx_data)
            return json.dumps(RX_PK)
        def _push_data(self, data):
            token = os.urandom(2)
            packet = bytes([PROTOCOL_VERSION]) + token + bytes([PUSH_DATA]) + binascii.unhexlify(self.id) + data
            with self.udp_lock:
                    self.sock.sendto(packet, self.server_ip)
                except Exception:
                    print("PUSH exception")
        def _pull_data(self):
            token = os.urandom(2)
            packet = bytes([PROTOCOL_VERSION]) + token + bytes([PULL_DATA]) + binascii.unhexlify(self.id)
            with self.udp_lock:
                    self.sock.sendto(packet, self.server_ip)
                except Exception:
                    print("PULL exception")
        def _ack_pull_rsp(self, token, error):
            TX_ACK_PK["txpk_ack"]["error"] = error
            resp = json.dumps(TX_ACK_PK)
            packet = bytes([PROTOCOL_VERSION]) + token + bytes([PULL_ACK]) + binascii.unhexlify(self.id) + resp
            with self.udp_lock:
                    self.sock.sendto(packet, self.server_ip)
                except Exception:
                    print("PULL RSP ACK exception")
        def _lora_cb(self, lora):
            events = lora.events()
            if events & LoRa.RX_PACKET_EVENT:
                self.rxnb += 1
                self.rxok += 1
                rx_data = self.lora_sock.recv(256)
                stats = lora.stats()
                self._push_data(self._make_node_packet(rx_data, self.rtc.now(), stats.rx_timestamp, stats.sfrx, stats.rssi, stats.snr))
                self.rxfw += 1
            if events & LoRa.TX_PACKET_EVENT:
                self.txnb += 1
                lora.init(mode=LoRa.LORA, frequency=self.frequency, bandwidth=LoRa.BW_125KHZ,
                          sf=self.sf, preamble=8, coding_rate=LoRa.CODING_4_5, tx_iq=True)
        def _send_down_link(self, data, tmst, datarate, frequency):
            self.lora.init(mode=LoRa.LORA, frequency=frequency, bandwidth=LoRa.BW_125KHZ,
                           sf=self._dr_to_sf(datarate), preamble=8, coding_rate=LoRa.CODING_4_5,
            while time.ticks_us() < tmst:
        def _udp_thread(self):
            while True:
                    data, src = self.sock.recvfrom(1024)
                    _token = data[1:3]
                    _type = data[3]
                    if _type == PUSH_ACK:
                        print("Push ack")
                    elif _type == PULL_ACK:
                        print("Pull ack")
                    elif _type == PULL_RESP:
                        self.dwnb += 1
                        ack_error = TX_ERR_NONE
                        tx_pk = json.loads(data[4:])
                        tmst = tx_pk["txpk"]["tmst"]
                        t_us = tmst - time.ticks_us() - 5000
                        if t_us < 0:
                            t_us += 0xFFFFFFFF
                        if t_us < 20000000:
                            self.uplink_alarm = Timer.Alarm(handler=lambda x: self._send_down_link(binascii.a2b_base64(tx_pk["txpk"]["data"]),
                                                                                                   tx_pk["txpk"]["tmst"] - 10, tx_pk["txpk"]["datr"],
                                                                                                   int(tx_pk["txpk"]["freq"] * 1000000)), us=t_us)
                            ack_error = TX_ERR_TOO_LATE
                            print("Downlink timestamp error!, t_us:", t_us)
                        self._ack_pull_rsp(_token, ack_error)
                        print("Pull rsp")
                except socket.timeout:
                    print("Socket Timeout")
                except OSError as e:
                    if e.errno == errno.EAGAIN:
                        #print("UDP recv errno.EAGAIN")
                        print("UDP recv OSError Exception")
                except Exception:
                    print("UDP recv Exception")
                # Wait before trying to receive again

    Node code

    from network import LoRa
    import socket
    import binascii
    import struct
    import time
    import pycom
    # Initialize LoRa in LORAWAN mode.
    lora = LoRa(mode=LoRa.LORAWAN)
    # create an ABP authentication params
    dev_addr = struct.unpack(">l", binascii.unhexlify('260110AD'.replace(' ','')))[0]
    nwk_swkey = binascii.unhexlify('2F8184207979F18CE1F64B6B74B75A99'.replace(' ',''))
    app_swkey = binascii.unhexlify('53A7AA9AFA94FEB1F859F76EF5E0BA4C'.replace(' ',''))
    # join a network using ABP (Activation By Personalization)
    lora.join(activation=LoRa.ABP, auth=(dev_addr, nwk_swkey, app_swkey))
    # remove all the non-default channels
    for i in range(3, 16):
    # set the 3 default channels to the same frequency
    lora.add_channel(0, frequency=868100000, dr_min=0, dr_max=5)
    lora.add_channel(1, frequency=868100000, dr_min=0, dr_max=5)
    lora.add_channel(2, frequency=868100000, dr_min=0, dr_max=5)
    # create a LoRa socket
    s = socket.socket(socket.AF_LORA, socket.SOCK_RAW)
    # set the LoRaWAN data rate
    s.setsockopt(socket.SOL_LORA, socket.SO_DR, 5)
    # make the socket blocking
    i = 1
    while True:
        print("sending:",i,i % 255,"msg:",struct.pack('LB',i,i % 255))
        s.send(struct.pack('LB',i,i % 255))
        for k in range(29):
            rx = s.recv(256)
            if rx:
        i += 1

  • You are aware that downlink messages are send only as a reply to an uplink? So you need to send an uplink to receive a previously queued downlink.

    Also, it would probably help if you shared your code.

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